Sharif Journal of Civil Engineering
https://sjce.journals.sharif.edu/
Sharif Journal of Civil Engineeringendaily1Tue, 19 Mar 2024 00:00:00 +0330Tue, 19 Mar 2024 00:00:00 +0330-
https://sjce.journals.sharif.edu/article_23526.html
-Experimental investigation of the performance of replaceable-rigid connection
https://sjce.journals.sharif.edu/article_23156.html
After the Northridge earthquake, a set of prequalified connections were introduced by international design codes. Thease connections include reduced beam secrion (RBS) moment connection, bolted unstiffended and stiffended extended end-plate moment connection, bolted flange plate (BFP) moment connection, welded unreinforced flange-welded web (WUF-W) moment connection, kaiser bolted bracket (KBB) moment connection, conxtech conxl moment connection, sideplate moment connection, simpson strong tie strong frame moment connection, double tee moment connection, slottedweb (SW) moment connection. After ensuring the seismic performance of this set during earthquakes, concerns surfaced that forming plastic hinges in beam elements would result in either making repairs impossible or incredibly expensive in the event of a moderate or severe earthquake. Hence, a type of replaceable connections was introduced wherein plastic hinges would be placed in pre-determined elements. Their intuitive replaceability feature would make repairs and reutilization of the structure a much easier task. In this study, the experimental investigations of 4 full-scale samples of a replaceable rigid connection under cyclic loading were carried out. The results of the experiments demonstrated that in the proposed connection, the plastic hinge is formed in the fuse element while the beam and the column maintain their elasticity, allowing the connection to be replaced. Also, taking into account the early buckling of the fuse plates installed on the beam flanges, the moment capacity of the connection is decreased by 22 percent compared to the moment capacity of the fuse. According to the results obtained from the backbone diagrams, stiffness of the connection after replacing the fuse plates in P12 and P15 samples has decreased by 8.61% and 6.14%, respectively; this could be due to slight changes on the holes on the beam web and flanges as well as changes in the pre-tensioning forces of the bolts. Investigations have revealed that, the 20% increase in the moment capacity of the fuse (using 15 mm-steel plates instead of 12 mm in the fuse plates of the beam flanges) has increased the cumulative energy dissipation of the connection by 12%.analysis of polymetric -strip reinforced-soil walls adjacent to the rock foundations
https://sjce.journals.sharif.edu/article_23204.html
In some roadway projects, especially in a mountainous region, the mechanically stabilized earth walls must be constructed in front of stable features such as a rockface for a variety of reasons, including the construction of new roadways, widening of urban transportation corridors, and reduction of rockfall risk. There has been limited research into the dynamic performance of the MSE wall adjacent to the rock slope; thus, the seismic behavior of this retaining system is still poorly understood. The most common methods for seismic stability analyses of reinforced-soil retaining walls are based on pseudo-static limit-equilibrium approaches, where seismic coefficients are applied to the potential failure soil mass. In the pseudo-static method, the assignment of an appropriate lateral seismic coefficient (Kh) that would be able to simulate the seismic inertial force induced in the sliding wedge has a considerable effect on the accuracy of the analyses. Since earthquake acceleration is the main cause of the inertial force induced in the failure mass, the seismic acceleration coefficient (Kh) is determined mostly based on the peak ground acceleration at the wall base level. The seismic events are transient in nature, and the earthquake-induced forces vary in intensity during vibrations. However, in the pseudo-static method, the seismic force is applied to the failure soil mass indefinitely. Therefore, the use of peak ground acceleration could lead to over-conservative results. To overcome this limitation, the seismic coefficient is usually expressed as a fraction of the peak ground acceleration for design purposes. The value of this fraction has not been clearly defined for reinforced-earth retaining walls. Most of the proposed methods for calculating the seismic acceleration coefficient are based on theoretical assumptions, and the validation of this important parameter has not been evaluated based on an experimental approach. In this study, initially, the seismic behavior of the polymeric-strip reinforced-earth retaining walls built on the rock foundation is investigated using shaking table tests. Then, the assumptions of the pseudo-static approach are simulated by push-back pressure tests. To apply back pressure to a model wall, a special apparatus was designed and made in the Tarbiat Modares University laboratory. Finally, the horizontal seismic coefficient is estimated by comparing and adjusting the result of the shaking table and push-back pressure tests. The results presented are based on the acceptable seismic performance of the retaining wall and are compared with the previously proposed relations and AASHTO design code.Experimental investigation of the dynamic behavior of slender structures supported on combined pile-raft foundation: towards of performance-based design
https://sjce.journals.sharif.edu/article_23205.html
In this research, the experimental investigation of the inertial interaction of soil-pile raft structure has been conducted for slender structures supported by the combined pile-raft foundation with emphasis on the new concept of design method (performance-based design). Most of the former studies based on this concept have focused on the surface foundation, where the surface foundation's rocking motion acts as a source of energy dissipation to protect the superstructure. Meanwhile, less attention has been paid to the surface foundation combined with piles (Combined pile-raft foundation) as an economic support system for high-rise and heavy structures. Mainly, the focus of optimizing these foundations through parametric analysis has been on variables such as pile arrangement and pile length for vertical static loading. When the heavy structures are subjected to the lateral load caused by the earthquake, the foundation experiences significant inertial moments. Thus, the nonlinear behavior of the foundation is not far from expected. The present research intends to examine the rocking behavior of combined pile-raft foundations as the foundation of slender structures. Evaluating the response of the superstructure and its possible benefit from the nonlinear behavior of the foundation is the principal goal of this research. In this regard, using experimental models, some characteristics of combined pile-raft foundations, such as the arrangement of piles and the relative length of the piles, have been investigated on the response of the superstructure. Three physical models were constructed in the laboratory. Each model contained a single degree of freedom superstructure supported by a floating pile raft foundation in sandy soil. Two characteristics were considered for evaluating pile raft characteristics: pile configuration and pile length ratio. The superstructure was identical in all three physical models. An experimental procedure based on forced vibration tests was presented to assess the dynamic response of the models at different levels of foundation nonlinearity. According to the experimental measurements, the nonlinear behavior of the foundation has a significant role in the response of the superstructure. Dynamic demand reduction as well as drift reduction are the two most important factors that benefit the superstructure from foundation nonlinearity. Accordingly, the dynamic behavior of the models is divided into two individual phases. Also, comparing the results of the models showed that the arrangement of piles and the relative length of the piles in the combined pile-raft foundation have a significant impact on superstructure response.Which parents are able to comment on using autonomous vehicles for their child's school trip? (a case study of Kerman city)
https://sjce.journals.sharif.edu/article_23206.html
Autonomous vehicles are a proper option for children's school trips due to their high potential. Parents are the main decision-makers in choosing their children's school trip mode, and it is essential for policymakers to be aware of their behavior and willingness, especially when technology is not yet available to the public. Previous studies of self-driving cars (SAVs) have focused on the rejection or acceptance of this technology by adult users, while SAVs are an attractive option for students' educational trips. Few studies in this field emphasize the need to do it, but in the current study, unlike previous studies, the factors affecting the behavior of parents who are unable to make a decision in this regard have been investigated using mathematical modeling. The virtual link of the current study questionnaire (in six sections) was uploaded by the school principals in the educational groups of the selected schools with the parents after experimental questioning and correction. Data analysis shows that almost a high percentage of parents (29%) have not been able to give a definite opinion about whether or not their child uses autonomous vehicles. In this article (for the first time), the factors affecting the inability of parents to make decisions are studied. The binary logit model on the May 2021 questionnaire of parents of fourth to ninth-grade students in Kerman schools (1435 cases) has a correct estimation percentage of 77.1 and a good fit coefficient equal to 0.4. The estimated model shows that the behavioral characteristics and accidental history of parents influence their decisions. In the case of Kerman, parents who have a history of fatal accidents in close relatives and who have a high level of concern about the way they drive and the possibility of a high-traffic accident in public transportation have not been able to decide whether to reject or accept this technology.Analysis of blue and grey water footprints of traditional construction with emphasis on different climatic regions of Iran: a comparative study
https://sjce.journals.sharif.edu/article_23160.html
Traditional patterns could be an effective solution for water consumption and pollution-related problems in the construction industry. However, the water footprint of traditional buildings in Iran has not been investigated. Iran has rich experience in constructing traditional buildings. This paper presents a comprehensive analysis of the grey and blue water footprints of the construction of traditional buildings in Iran with emphasis on different climate zones. The results are compared with modern buildings (concrete and steel). High-quality data related to 11 materials factories and 34 traditional buildings (stone, wood, clay, and brick) are presented. Blue and grey water footprints of building materialization are calculated using the water footprint network and life cycle assessment methods. The focus is on the structures of buildings. The grey and blue water footprints of modern structures are 327 times and 1.5 times larger than the grey and blue water footprints of traditional structures, respectively. Steel and cement production are influential parameters in the greywater footprint of modern structures. Employee meals have the greatest impact on the water footprint of traditional structures. The blue water footprint dominates the water footprint of traditional structures, which is 2.26 times larger than the greywater footprint. Stone structures have a blue water footprint of 0.85 m3/m2, which is dominated by the blue water footprint of employees' food (38.82%) at construction sites. They have a smaller blue water footprint than adobe and brick structures (1.41 - 1.42 m3/m2) and are close to the water footprint of wooden structures. The water footprint of brick structures is mainly influenced by the energy used (57.04%) for brick production. On the other hand, the greywater footprint dominates the blue water footprint of modern structures, which is 99.61 times larger than the blue water footprint. Steel structures have a blue water footprint of 1.86 m3/m2 and a greywater footprint of 208 m3/m2, the main pollutant of which is cadmium. Concrete structures have a blue water footprint of 1.60 m3/m2 and a greywater footprint of 137 m3/m2, with mercury as the main pollutant. From the water footprint viewpoint, it is better to use concrete structures than steel structures if both have suitable properties for the conditions they are used in. According to the results, the non-use of traditional buildings leads to an increase in water consumption and pollution.The effect of waste leachate on the dynamic parameters of clay soils
https://sjce.journals.sharif.edu/article_23249.html
Leachate is a hazardous liquid that leads to numerous environmental problems. Soil pollution is one of the most important of these problems caused by poor leachate management facilities and limited land availability. Studies show that soil characteristics change during contamination, and these changes are a function of the type of soil and leachate. Therefore, it is necessary to evaluate the static and dynamic behavior of soils after contamination with leachate. Despite the importance of this issue, studies in this field are limited only to static behavior, and the effect of leachate on the dynamic behavior of soils remains almost unknown. Hence, an experimental effort has been made in this study to evaluate the effect of waste leachate sampled from the Alborz landfill on the dynamic parameters of three different clays under different overburden pressures (6.29, 18.88, and 31.47 kPa). For this purpose, the amount and type of heavy metals in the leachate were first determined using an inductively coupled plasma (ICP) spectrometer. Then, cylindrical soil samples were prepared in three different leachate contents (0%, 6%, and 12.5%) and subjected to a simple dynamic shear test. Moreover, the samples were photographed using an SEM microscope to investigate the effect of leachate on the soil texture. Based on the hysteresis loops obtained from simple shear tests and, subsequently, amounts of shear modulus (G) and damping ratio (D) calculated from them, it was found that pollution and its increase cause an increase in the shear modulus and a decrease in the damping ratio so that the growth of the shear modulus and the decrease in the damping ratio are affected by the type of soil and are more pronounced in soils with a lower paste range. It was also observed that the greatest effect of leachate on improving the shear modulus of the soil can be seen at lower levels of pollution. The increase in the influence of shear modulus and damping ratio of clay from overburden pressure was identified as one of the effects of soil contamination with leachate, which was more evident in clays with high paste range.Seismic response estimation of mid-rise steel moment frame buildings using a new energy-based methodology
https://sjce.journals.sharif.edu/article_23209.html
Nonlinear Time History Analysis (NTHA) contains a complex and rigorous process for structural seismic evaluation. Nonlinear static (Pushover) analysis can simplify this process. This paper aims to develop an energy-based seismic assessment methodology using pushover analysis. This methodology can estimate the response of mid-rise buildings with much fewer computational operations than NTHA and consider higher mode effects. Other advantages of the proposed procedure include using the capacity curve of Multiple Degrees Of Freedom (MDOF) systems directly instead of the Equivalent Single Degree Of Freedom (ESDOF) and computing the energy demand of the structure based on the mean spectrum corresponding to the desired hazard level instead of the various earthquake record spectrums. The proposed methodology converts the pushover capacity curve to the energy capacity curve for each mode, and the energy demand curve is superimposed on it. The intersection of these two curves is considered the target response. NTHA and Modal Pushover Analysis (MPA) are employed to validate and compare the proposed methodology with other ones. Also, 4, 8, and 9-story steel moment frame buildings are selected, modeled, and analyzed using OpenSEES software. The results show that the proposed methodology can estimate the responses of the building with reasonable accuracy compared to the mean results of the NTHA. Also, the proposed method significantly reduces the error of the responses compared to the MPA. Nevertheless, it can be concluded that the proposed energy-based methodology can be a simple, efficient, and rapid alternative for NTHA.Experimental investigation on cyclic behavior of non-structural masonry walls strengthened with bed joint reinforcement and textile-reinforced
concrete
https://sjce.journals.sharif.edu/article_23207.html
One of the main damages of the nonstructural masonry walls during an earthquake is its instability and collapse on the combination of deformation at the in-plain direction caused by lateral inter-story drift of structures and out-of-plane inertial forces applied to the wall because of earthquake acceleration. In most of the researches, only one of these actions was investigated, or their interactions were not directly investigated.
In this research, a combination of in-plane and out-of-plane loadings was carried out, and the effect of reinforcing on the nonstructural walls by using fiber mesh reinforced mortar and bed joint rebar has been investigated.
For this purpose, three wall specimens with scale of 1 to 1 were made of Leca blocks. Walls were subjected to a combination of in-plane cyclic loading and out-of-plane loading. The results showed that nonstructural walls, without reinforcement, failed under out-of-plain force in low in-plain drift, and the test process was stopped. On the other hand, strengthening the nonstructural wall with fiber mesh reinforced concrete caused an increase of 15% and 54% in the drift ratio related to the reduction of the wall resistance and the maximum in-plane force compared to the nonstructural wall, which was strengthened with bed joint reinforcement.Recognize adaptive ecologies and their applications in architectural structures
https://sjce.journals.sharif.edu/article_23211.html
The understanding of architecture as an ecology of interactive systems moves past limitations and restricted tendencies toward spatial environments that are adaptive, perceptual, and behavioral. In this framework, the environment seeks to build interaction scenarios to activate relationships between components. In this case, architecture moves away from well-known models that always lead to disciplined responses and toward understanding adaptive ecologies that include active particles for communication and exploration. The current research investigated and discussed the design of a system that can replace the current methods of planning the construction of infrastructure units in the future. The result is the simulation of a cellular self-assembly system that can produce and rebuild its structure when needed. Therefore, there is a revolution in construction and a complete revision of architectural standards and construction planning, disremembering demolitions and laborious construction costs. This study aims to explore the function of quorum sensing, a mechanism of intra-species communication that serves as the central regulatory system in the formation and concurrent response to environmental changes. The algorithmic design features of the system's constituent units were also examined. During the assembly process, extracellular matrices act as the milieu in which individual cells interact with one another and the desired environment as constructed building blocks. This allows for parallel assembly and error correction at a general level, both automatically, and has significant implications for the field. The proposed model uses a two-level control system (micro-macro) to ensure that the interactions among the components, on the one hand, and between the components and their environment, on the other hand, are in line with the objectives of the plan and the balance of the whole system. This two-level approach primarily follows a bottom-up process at the scale of the interaction of its constituent particles and subsequently utilizes a top-down process during the overall regulation of the system through the extracellular matrix. Ultimately, the simulation results obtained using Grasshopper3d software were shown in three scales: small (chair), medium (shelter), and large. This approach has been demonstrated to be effective in previous research and offers a promising framework for further investigation in this field. This research can take essential steps in developing simulator machines to build a construction self-assembly system based on sequential configurations and numbers.Reliability evaluation of stochastic subspace identification and frequency domain decomposition methods in estimating modal parameters of a structure excited by the earthquake
https://sjce.journals.sharif.edu/article_23210.html
One of the most common methods of identifying modal parameters in the field of operational modal testing is the method of identifying sub-random space and frequency domain analysis. Unfortunately, the scope of these methods' application is limited to static signals with a long pick-up time, and if the above conditions are violated, the results will be erroneous; This is in the context that the above two conditions are not met regarding the earthquake signal, and so far the reliability of these methods and their error rate in the face of this group of signals have not been studied. In this regard, in this study, the performance of these methods in earthquake conditions (both conditions are violated) is studied.
For this purpose, an numerical model of two two-dimensional frames with different heights (five and ten floors) is created and stimulated by using 20 earthquake records in the near and far fields. Using the obtained results and comparing them with the results of the numerical model, the error values for the modal parameters are obtained; Also, with the statistical study of the errors in the estimation of the frequency of the structure, the probability distribution function of the error and an estimate of the distance of the error are suggested .The results of the study showed that (a) the method of identifying random subspace has a better performance than the method of frequency domain analysis; (B) The random subspace detection method is not able to detect the first modes and is proposed to identify higher modes; (C) the efficiency of the frequency domain decomposition method decreases with increasing structural height; (D) By optimizing and locating the sensors, the performance of the frequency domain analysis method is dramatically improved. However, in the random subspace detection method, the detectability increases with the number of sensors.Numerical Study of the Liquefiable Sand–Pile Behavior Under the Effect of Near-field Ground Motions
https://sjce.journals.sharif.edu/article_23208.html
Three-dimensional analyses are conducted to study the effects of ground motion and the presence of velocity pulse on the pile responses in liquefiable soils. Liquefaction of soils is an important issue in geotechnical engineering. Soil liquefaction occurs when saturated or partially saturated soil substantially loses strength and stiffness in response to applied stress, such as shaking during an earthquake or other sudden changes in stress conditions. The forward directivity effect, which includes a large velocity pulse at the beginning of the velocity time history of the ground motion and contains most of the seismic energy from the rupture, is the most damaging phenomenon observed in near-field ground motions. To investigate the effect of near-field ground motions on the seismic response of a soil-pile system, a three-dimensional model consisting of the two-layered soil and the pile is constructed. Modeling is conducted by using the FLAC 3D software. The P2PSand model is applied for the modeling of sandy soil. P2PSand model refers to a Practical TWO-surface Plastic SAND constitutive model for general 3D geotechnical earthquake engineering applications aimed at capturing essential soil dynamic characteristics. The model is a modified extension of the fabric-dilatancy-related sand plasticity DM04 model developed by Dafalias and Manzari. The Dafalias-Manzari two-surface model (DM04) is a critical-state compatible and state parameter-related plasticity model developed in the framework of Bounding Surface theory, which has been widely implemented and studied. Dynamic analyses are conducted for the soil-pile system under the excitations of four selected ground-motion suites that were recorded on the rock. The results show that near-field velocity pulses have a considerable effect on the behavior of the system and cause sudden large displacement demands on the piles and soil. The pulse in the record of near-field ground motion has caused the pore water pressure coefficient (Ru) to increase and liquefaction in the upper soil layer.Numerical Study of the Liquefiable Sand–Pile Behavior Under the Effect of Near-field Ground Motions
https://sjce.journals.sharif.edu/article_23212.html
Three-dimensional analyses are conducted to study the effects of ground motion and the presence of velocity pulse on the pile responses in liquefiable soils. Liquefaction of soils is an important issue in geotechnical engineering. Soil liquefaction occurs when saturated or partially saturated soil substantially loses strength and stiffness in response to applied stress, such as shaking during an earthquake or other sudden changes in stress conditions. The forward directivity effect, which includes a large velocity pulse at the beginning of the velocity time history of the ground motion and contains most of the seismic energy from the rupture, is the most damaging phenomenon observed in near-field ground motions. To investigate the effect of near-field ground motions on the seismic response of a soil-pile system, a three-dimensional model consisting of the two-layered soil and the pile is constructed. Modeling is conducted by using the FLAC 3D software. The P2PSand model is applied for the modeling of sandy soil. P2PSand model refers to a Practical TWO-surface Plastic SAND constitutive model for general 3D geotechnical earthquake engineering applications aimed at capturing essential soil dynamic characteristics. The model is a modified extension of the fabric-dilatancy-related sand plasticity DM04 model developed by Dafalias and Manzari. The Dafalias-Manzari two-surface model (DM04) is a critical-state compatible and state parameter-related plasticity model developed in the framework of Bounding Surface theory, which has been widely implemented and studied. Dynamic analyses are conducted for the soil-pile system under the excitations of four selected ground-motion suites that were recorded on the rock. The results show that near-field velocity pulses have a considerable effect on the behavior of the system and cause sudden large displacement demands on the piles and soil. The pulse in the record of near-field ground motion has caused the pore water pressure coefficient (Ru) to increase and liquefaction in the upper soil layer.List of Articles and Journal Info
https://sjce.journals.sharif.edu/article_23528.html
-ABSTRACT OF PAPERS IN ENGLISH
https://sjce.journals.sharif.edu/article_23527.html
-Optimizing the geometry of hunchbacked block-type gravity quay walls using non-linear dynamic analyses and supervised machine learning technique
https://sjce.journals.sharif.edu/article_23246.html
In the present study, the seismic behavior of hunchbacked block-type gravity quay walls rested on non-liquefiable dense seabed soil layer is investigated and the optimal geometries for these wall types are proposed by performing non-linear time history dynamic analyses using Lagrangian explicit finite difference method. For this purpose, first, a reference numerical model of the hunchbacked quay wall is developed and its seismic response is validated against the well-documented physical model tests. Then, the optimal hunch angles corresponding to the minimum horizontal displacement and zero rotation of the hunchbacked quay wall are estimated through the sensitivity analyses on the hunch angle of the wall, the friction angle of the backfill, and the ratio of hunch height to wall height. Subsequently, the statistical relationships are presented to predict the optimal hunch angle of the walls using the multiple non-linear regression based on the supervised machine learning technique. The results of non-linear dynamic analyses show that the deformation pattern, the movement mechanism, and consequently the seismic response of the hunchbacked quay wall change considerably with the variation of the hunch angle of the wall. In this regard, the rotation angle of the wall towards the seaside due to seismic loading decreases, and the deformation pattern and the movement mechanism of the hunchbacked quay wall alter from overturning towards the seaside to overturning towards the landside with an increase of the hunch angle. For all considered values of the ratio of hunch height to wall height and the backfill friction angle, increasing the hunch angle in the range of 25 to 35 degrees leads to a significant decrease in wall deformation. While increasing the hunch angle in the range of 35 to 50 degrees has less influence on reducing the wall deformation. For hunch angle values greater than 50 degrees, increasing the hunch angle has the opposite effect on improving the seismic performance of the hunchbacked quay wall and its seismic-induced deformations increase. Additionally, in the ratio of hunch height to wall height equal to 0.7, the optimal hunch angles corresponding to the zero wall rotation and the maximum reduction in the horizontal displacement of the wall decrease from 42.7 to 9. 23 degrees and from 53 to 34.5 degrees, respectively, with an increase of the friction angle of the backfill soil from 15 to 45 degrees.The effect of fiber length and composition on the compressive and flexural strength of concrete
https://sjce.journals.sharif.edu/article_23247.html
The use of fibers is often aimed at increasing the ductility and load-bearing capacity of the desired concrete, and controlling the spread of cracks by adding fibers to the concrete causes this. The fibers improve the behavior of the concrete after the first crack due to the bridging property on the micro-cracks. In this paper, 15 concrete mixing designs in the form of 90 cubic specimens with dimensions (15 * 15 * 15) cm for compressive strength test and 42 specimens with dimensions (15 * 15 * 60) cm for flexural strength test have been made. 3 mixing designs were made as a reference with 3 water to cement ratios (0.24, 0.29, 0.34) without fibers and with fibers with 3 different lengths of polypropylene fibers with lengths of (6, 12, 18) mm, respectively. A mixing scheme with 40 mm long hook metal fibers and another mixing scheme with a combination of 40 mm hooked metal fibers and 12 mm polypropylene fibers were investigated. The highest 28-day compressive strength was related to the samples with composite fibers with a resistance of 76.16 MPa, which was 16.3% higher than the reference sample. Concrete specimens with metal fibers with a flexural strength of 16.1 MPa have the highest strength among all concrete mixing designs in this study and show a 60% increase in flexural strength compared to the specimen without fibers. In the concrete samples tested with polypropylene fibers, after the compressive strength test, with the increase in the length of the polypropylene fibers, the workability and compressive strength of the concrete decreased, but the plasticity of the concrete samples increased. After the flexural strength test, the flexural strength and ductility of the concrete samples increased with the increase in the length of the polypropylene fibers, but it led to a decrease in the workability of the concrete.Evaluation of the effect of recycled fibers on the strength of sand stabilized with cement against freeze-thaw cycles
https://sjce.journals.sharif.edu/article_23248.html
In this research, the effect of soil stabilization with cement at the same time as its reinforcement with fibers has been studied on the shear strength of sandy soil exposed to freeze-thaw cycles. In order to achieve this goal, laboratory studies were carried out with the help of unconfined compressive strength tests (UCS tests) on different compounds obtained from mixing cement, fibers and sandy soil. More than 336 cylindrical laboratory models with dimensions including 3.6cm in diameter and 8cm in length have been made. Various modes have been observed during the failure of the samples, including shear, tensile, plastic yielding and composite failure modes. The fibers used in the present research are waste products of tire factories known as DTY. Percentages of 2, 4, and 6 for cement and 0, 0.5, and 1 for fibers with lengths of 0.5, 1, and 1.5 cm were used relative to the weight of dry sandy soil in making the samples. Uniaxial cylindrical samples were tested for unconfined compressive strength after 7 and 28 days curing time and under 0, 1, 2 and 3 freeze-thaw cycles. The results show that the act of stabilizing the soil with cement along with reinforcing it to a certain amount of fibers improves the uniaxial compressive strength before and after freezing and thawing cycles. This amount depends on the percentage of cement and the curing period. Also, adding cement in a certain curing time increases the unconfined compressive strength before and after applying the cycle, increases stiffness, reduces the ductility and toughness of the sample, and brittle failure when breaking occurs in the soil. Also, the addition of fibers to some extent improves the weaknesses caused by soil stabilization, such as reducing the failure axial strain, decreasing the residual strength and the toughness of the materials in the conditions before and after freezing and thawing.Investigation of the effect of far-field ground motion records on the seismic response of mid-rise hybrid concrete-steel buildings
https://sjce.journals.sharif.edu/article_23255.html
Hybrid concrete-steel buildings in height are usually referred to as buildings that have two lower and upper parts of concrete and steel materials, respectively. Due to the change in mass, stiffness, and damping in the vertical direction, these buildings have complex seismic behavior. Therefore, in this study, the seismic behavior of hybrid concrete-steel buildings at mid-rise height against far-field ground motions was considered. Initially, different models in groups of 7 and 13 stories were designed by considering different ratios of the number of concrete to steel floors. The connection of the upper steel section to the lower concrete section was considered a pin joint in nonlinear modeling in Opensees software due to its implementation. Then incremental dynamic analysis was performed on all models using 22 different far-field records. Also, the maximum structural response diagram at the threshold of complete damage level was obtained according to the outputs of incremental dynamic analysis in different stories under all records along with their average. Fragility curves were extracted at four damage states based on the HAZUS technical report. The results showed that there was a critical area at the junction of the steel frame with the concrete in which the structural response value underwent a sudden change and made this area inclined to much damage, which in the groups of 7 and 13 stories reached 65.2% and 98%, respectively. Finally, the median collapse capacity was obtained from fragility curves for hybrid buildings at different heights. As the number of concrete floors increased, the median collapse capacity of the model increased, which indicated the better seismic performance of the hybrid concrete-steel building. Among the investigated models, the lowest level of fragility was when the ratio of the number of concrete floors to the total floors of the Hybrid concrete-steel building was almost equal to 0.6.Seismic Evaluation of Self-Centering Thin Steel Plate Shear Walls, Subjected to Seismic Sequences
https://sjce.journals.sharif.edu/article_23286.html
Despite the knowledge of steel shear wall for many years, not much attention was paid to it. steel shear wall has received attention and is expanding rapidly. Steel shear walls without stiffeners and with stiffeners have been used in America in recent years. This system is 50% cheaper compared to the bending frame. After the events of September 11, a number of scientists were thinking of creating resistant and impervious structures against explosive and seismic loads economically by combining this system and the concrete shear wall system. Steel shear walls are easier to implement. Also, the accuracy of doing the work is at the level of normal executions, and by observing it, the reliability coefficient is many times higher than other types of systems. The execution speed of steel shear walls is high, and because of this, the execution costs are reduced. Also, the efficiency of the shear wall system is more and more suitable than all the advantages of centralized bracing systems such as X and V shape and off-center steel bracing system. The resistance against the overturning anchor caused by the lateral loads and the horizontal load of the floor is the most important task of the steel shear wall. The constituent members of the steel shear wall system include a steel plate wall, two boundary columns and a floor horizontal beam. Also, the horizontal beams of the floor are used as transverse stiffeners in the sheet beam. The goal of centralizing the steel shear wall system is that the beams and columns remain in the elastic range. In this article, five, ten, and twenty-story buildings with steel shear walls were designed using the strip equivalent brace method in ETABS, then seven acceleration maps far from the fault were selected and scaled and modeled in ABAQUS software. The five-class model was compared with the non-centralized model. According to the results of the push-over analysis of the five-story steel shear wall model, the beams and columns remained in the elastic range in the self-centering model, and according to the hysteresis obtained from the push-over analysis of the steel shear wall, they have more energy consumption. The results showed that the drift and maximum drift and maximum displacement and the ratio of the maximum acceleration value of the roof to the acceleration of the selected records in the self-centering steel shear wall have increased compared to the non self-centering ones.Investigating the mechanical behavior of concrete containing recycled concrete and rubber materials as a foundation isolator
https://sjce.journals.sharif.edu/article_23287.html
Considering the seismic conditions of Iran and the many damages that occur as a result, it is necessary to change the current performance of structural design to achieve better performance in the seismic system. On the other hand, environmental concerns have prompted civil engineers to identify appropriate methods of reusing construction waste. The purpose of this research is to investigate the behavior of concrete made with recycled materials as a wide foundation, which has the role of seismic isolation for low or medium height buildings. In this research, the effect of crumb rubber and recycled concrete aggregate on concrete was examined in a laboratory. The design basis of its resistance is 30 MPa. The first mixture, as a control mixture, does not contain rubber granules, Forta fibers and recycled concrete aggregate. In the other three mixtures the difference in the amount of recycled concrete aggregate is 40%, 50% and 60% instead of coarse aggregate, also the percentage of rubber granules is constant and about 15% of the total volume, and the amount of Forta fibers is about 0.5% of the total volume. Compressive strength, Flexural strength and Shear strength tests were performed on the 4 mentioned mixtures at the age of 28 days in a laboratory. The results of the compressive strength test showed that the addition of recycled concrete aggregate, rubber granules and Forta fibers has significantly reduced the compressive strength value. The results of the flexural strength test indicated that the additives cause a noticeable reduction in the flexural strength and this reduction intensifies with the change of recycled concrete aggregate percentage. The results of the shear strength test represented a considerable increase with the increase in the percentage of recycled concrete aggregate. Based on the test results, it is concluded that this type of composition material can be used as a foundation isolator, which showed a favorable shear behavior.Splitting tensile strength of cement-stabilized and face mask fiber-reinforced sand
https://sjce.journals.sharif.edu/article_23288.html
The tendency towards reinforcement of cement-treated sands with inclusion of fibers has increased in recent years. This is due to the fact that fibers reduce the brittle behavior and improve the mechanical properties of the sandy soil samples. Since 2019, because of the epidemic of coronavirus, the use of disposable face masks has become increasingly popular among the public to the extent that their burial, reproduction and reuse have become one of the major environmental problems. Therefore, in this research, an attempt has been made to reuse the mask fibers in the application of cement-reinforced sands. In this regard, samples with 2, 4, 6 and 8% cement contents, reinforced with different amounts of fibers (0, 0.25, 0.5 and 0.75%) in different relative densities (35%, 50%, and 70% sand) were prepared. After seven days of curing, the stabilized/reinforced specimens were subjected to a comprehensive series of Brazilian tensile splitting tests. Based on the results of these experiments, the synergetic influence of cement and mask fiber additives as well as the contribution of relative densities on the tensile strength parameters The results showed that the addition of cement percentage and increasing relative density have a significant effect on improving the tensile strength index of cement sands. The percentage of mask fibers 0.25% is the optimal amount of added fibers (the maximum tensile strength in this percentage of fibers). The key parameter (the ratio of porosity to cement content) definition and several empirical relations for estimating the tensile strength of reinforced and reinforced samples with very good accuracy are presented and the optimal percentages of mask fibers are suggested. Finally, it was observed that the use of fibers, especially in a cemented mixture, has highly positive effects on the tensile behavior of the samples by correcting the failure properties. Using disposable mask fibers instead of conventional fibers can substantially reduce disposal costs and environmental pollutions.Fragility curves production for steel structures by seismic improvement of the high-dimensional model representation method
https://sjce.journals.sharif.edu/article_23298.html
Fragility curves are utilized to evaluate the probability of exceeding the damage index for structures exposed to seismic hazards. The Monte Carlo simulation method, which involves generating random numbers, is computationally expensive for calculating fragility curves. To address this issue, several methods have been proposed to produce fragility curves at a reduced computational cost. This study presents a method that enhances the seismic representation of high-dimensional models to generate accurate fragility curves for steel structures while significantly decreasing computational costs. This method selects uncertain variable values based on the results of initial incremental dynamic analyses. The fragility curves are divided into three zones, and an equation is proposed to estimate mean damage values associated with the boundaries of these zones. Additionally, polynomial response functions were generated to estimate the fragility curves. The proposed method is applied to generate the fragility curves for three steel structures, one with 4, 9, and 12 stories. Fragility curves are generated for four damage levels: non-structural damage (DS1), structural retrofitting required (DS2), intensive structural damage (DS3), and collapse (DS4). The resulting fragility curves are compared with those generated by the Monte Carlo simulation method and other existing methods. The comparison demonstrates that the proposed method achieves fragility curves with a significant decrease in computational costs compared to the Monte Carlo method, while also exhibiting higher accuracy than other methods. The maximum error of the proposed method is approximately 20%, whereas Cornell's and the conventional HDMR methods exhibit errors of up to 80% and 60%, respectively. The errors of other methods increase significantly for fragility curves associated with high damage levels and 9 and 12 story steel structures, where nonlinear structural behavior is pronounced. In contrast, the increase in error is not significant in the proposed method. The findings of this study can be utilized to assess the seismic impact of various stochastic factors, such as random eccentricity or loading-related parameters, on the vulnerability of steel structures.Experimental investigation on the seismic behavior of helical-soil nailed walls
https://sjce.journals.sharif.edu/article_23299.html
Helical nails are a new type of reinforcement elements that have been widely used during the last decade. This has caused that despite their widespread use, the seismic behavior of geotechnical structures reinforced by them is still unknown. Therefore, it was attempted in the present study to evaluate the effects of some structural parameters on the dynamic performance of helical soil-nailed walls (HSNWs) using shaking table tests. For this purpose, eight reduced-scale wall models were constructed with different inclinations, lengths, and arrangements of helical nails and then subjected to input excitations with different durations. The response of each model to base excitation was determined in the form of fundamental frequency, acceleration amplification, facing displacement, and failure mechanism. The results showed that although a uniform increase in the nail length along the wall height significantly improved the seismic performance of the HSNWs, this improvement could also be achieved to some extent by increasing the length of the nails locally in the lower and upper halves of the walls reinforced by horizontal and inclined nails, respectively. The use of inclined nails instead of horizontal ones was an efficient solution to reduce the lateral displacement, the acceleration amplification, and changes in the frequency content. The effectiveness of this solution reduced with the use of shorter nails in the upper half of the wall and eventually minimized by reducing the length of the nails across the wall height. The nails located in the lower half of the wall were identified as having the greatest effect on the seismic performance of HSNWs when horizontal nails were used. The opposite occurred when inclined nails were used. A parabolic failure surface with a specific inflection point was observed to be the potential failure surface of the HSNW. The dimensions of the potential failure surface increased with an increase in the length and inclination of nails. Also, a combination of overturning and base sliding was identified as the predominant deformation mode in HSNWs, although the base sliding mode faded with an increase in the nail inclination.Determination of structural properties using structural modal properties and optimization algorithms: Genetic Algorithm, Particle Swarm Optimization and Teaching–learning-based Optimization
https://sjce.journals.sharif.edu/article_23319.html
This paper investigates the accuracy and convergence rate of different metaheuristic algorithms in determining the stiffness of structural elements using structural modal parameters and defining a suitable objective function. To achieve this purpose, three different structures, including a three-story one-dimensional frame, a six-story one-dimensional frame and a two-dimensional truss, were investigated. The metaheuristic algorithms, employed in this study, were Genetic Algorithm, Particle Swarm Optimization, and Teaching–learning-based Optimization. The objective function utilized in this study consists of two terms; the first part involves the squared difference between the first frequency of the structure obtained from the responses of the investigated structure and the first frequency obtained from the hypothetical stiffness matrix in each generation of algorithms. The second part measures the norm of the difference between the first mode shape of the structure obtained from the responses of the investigated structure and the first mode shape obtained from the hypothetical stiffness matrix in each generation of algorithms. By minimizing the objective function, the Genetic Algorithm, Particle Swarm Optimization, and Teaching–learning-based Optimization determined the element stiffness of the three-story, six-story and truss structures, thus demonstrating the high efficiency of metaheuristic algorithms in resolving unknown parameters of structures. The average run time for the Genetic Algorithm was 3.38 seconds, 4.47 seconds, and 15.73 seconds for the three respective problems. For Particle Swarm Optimization, the times were 3.76 seconds, 6.47 seconds, and 16.76 seconds. The Teaching–learning-based Optimization achieved times of 1.92 seconds, 4.51 seconds, and 12.76 seconds. The Teaching–learning-based Optimization exhibited the highest convergence rate and the lowest error compared to the Genetic Algorithm and Particle Swarm Optimization. For example, in the two-dimensional truss, the values of the objective function in the last iteration of the Genetic Algorithm, Particle Swarm Optimization, and Teaching–learning-based Optimization were 0.012, 6×10-4 and 4×10-4, respectively. The Particle Swarm Optimization demonstrated an acceptable convergence rate and error compared to the Genetic algorithm. The Genetic Algorithm, however, displayed a significant error rate in determining the stiffness of structural elements compared to the other two algorithms.Investigating the static and cyclic undrained behavior of the tire-sand mixture
https://sjce.journals.sharif.edu/article_23320.html
In recent years, the mixture of sand and rubber particles has been used in various fields of civil engineering, such as the stability of roofs, retaining walls, and drainage materials in landfills, due to its durability, cost-effectiveness and solving environmental problems. The purpose of this study is to investigate the effect of tire crumb on the shear strength and dilation in a static state and the liquefaction resistance in a dynamic state. In this regard, in this research, a static and dynamic undrained triaxial test was performed on a mixture of Babolsar sand and tire crumb (size between 1 and 8 mm) under constant confining pressure. The effect of parameters such as the amount of different tire crumbs (0, 5, 10, 20 and 30% by weight) and different relative densities on the static and dynamic behavior of the mixture of sand and rubber crumb and the created pore water pressure was investigated. In the static (consolidated-undrained) triaxial test, the relative densities of the sand–tire mixtures were 45, 60 and 80 percent. The tests were carried out on the specimens at 100 kPa cell pressure. Also, the specimen was loaded under a strain rate of 0.30% per minute, for all the tests until the axial strain reached 20%. In cyclic triaxial tests, the relative density of the sand–tire mixtures was 45 percent and the confining pressure of 100 kPa was used in the experiments. The sinusoidal waveform was applied to the specimen with a frequency of 0.5 Hz. To accuracy evaluation, the behavior of the sand-tire mixture, corrections such as membrane penetration corrections, membrane force and cross-sectional area were applied. The results showed that adding tire crumb to sand reduces the shear strength and dilation of sand. Also, the ratio of the mean diameter of tire particles to the mean diameter of sand particles affects the behavior of shear resistance and dilation of the sand-tire mixture. As the ratio of the mean diameter of tire particles to the mean diameter of sand particles increases, the shear strength and dilation of the sand-tire mixture increases. Also, increasing the amount of tire crumb in sand reduces the excess pore water pressure and as a result reduces liquefaction potential in cyclic loading. This behavior can be attributed to the compressible nature due to the low elastic modulus of the tire crumb.Investigation of mechanical behavior of Aluminum foam under uniaxial tests using Voronoi tessellation method
https://sjce.journals.sharif.edu/article_23323.html
Aluminum foams are among the materials that have many applications in the construction of various building elements, including sandwich panels. This category of materials has unique features due to low density, the presence of small holes, sound insulation, thermal insulation, and corrosion resistance. In this paper, the Voronoi tessellation method is proposed to simulate the porous configuration of aluminum foams, which has the high capability to generate the porous structure with different densities. It is demonstrated that the Voronoi tessellation method can generate porous structures with different densities, hole sizes and wall thicknesses stably. Moreover, the Voronoi tessellation method has a high speed and can be used to construct different sizes of aluminum foams. Comparison of the configurations obtained from the Voronoi tessellation method and experimental tests demonstrates the capability and competence of this method in generating the porous structure of the aluminum foam. In order to numerically investigate the mechanical behavior, the uniaxial tension test is applied to the aluminum nanofoams through the molecular dynamics (MD) method. The MD analysis is performed in the LAMMPS open-access software using the embedded-atom model (EAM) interatomic potential. The periodic boundary condition is imposed in all the boundaries of the atomistic model to satisfy the essential condition of the representative volume element (RVE) based on the homogenization theory. After minimization and relaxation of RVE, the uniaxial tension test is applied in an increment manner to reduce the strain rate effect. The evolution of the stress-strain curve along with the stress contours are presented for the aluminum nanofoam during the uniaxial tension test. Young’s modulus of nanofoam obtained by numerical analysis is compared to that of experimental data to confirm the accuracy of the computational modeling. Moreover, the results emphasize the high dependence of the mechanical behavior of aluminum nanofoams on the density and porosity.Investigation on the behavior of two-tiered MSE walls as bridge abutments
https://sjce.journals.sharif.edu/article_23345.html
Mechanically stabilized earth (MSE) walls are commonly used as bridge abutments to support bridge deck loads. In this type of abutments, the use of a tiered configuration can play a prominent role in reducing induced horizontal stress, reducing lateral deformation, and consequently, improving the performance of bridge abutments. Despite the importance of this issue, the influence of various factors on the performance of tiered MSE abutments under deck loads is not yet fully understood. Therefore, by simulating a bridge deck on a tiered MSE abutment in the form of a strip footing, the effects of the reinforcement type, the connetion type of deck to abutment, and the deck location were investigated. For this purpose, three two-tiered mechanically stabilized earth walls (T-TMSEWs) were constructed using three different reinforcements and then loaded with strip footings at three different distances from the wall creast. By preventing and allowing the footings to tilt, the influence of the degree of footing freedom was also examined as the third variable. Particle image velocimetry showed that the use of a two-tiered configuration in MSE abutments and a decrease in the soil–reinforcement interaction and stiffness changed the slip surface geometry and prevented the development of deep slip surfaces in the lower tier. It was found that although the decrease in reinforcement stiffness and its interaction with soil decreased the bearing capacity of the strip footings on two-tiered MSE abutments, they also reduced the lateral pressure induced in T-TMSEWs by strip footing. Also, allowing the footing to tilt was found to be an effective solution for minimizing the deformation of the backfill surface and the induced lateral pressure. Moreover, comparison of the results with analytical methods showed that the construction of MSE abutments in a two-tiered configuration reduced the lateral pressure in the upper tier. This became more noticeable with a decrease in the soil–reinforcement interaction and reinforcement tensile stiffness and an increase in the distance from the footing to the wall crest.Measuring the volume of water penetration into concrete and compressive strength under acute conditions without breakage the sample using new tests
https://sjce.journals.sharif.edu/article_23346.html
To directly measure the strength and permeability of concrete, a core should be separated from the concrete and then tested in the laboratory with destructive methods. For example, to measure the permeability of concrete by existing standards, concrete must be broken and divided into half. Also, acute conditions such as temperature cycles that concrete faces in summer can have negative effects on concrete characteristics. Therefore, in this research, using innovative tests, in addition to investigating the effect of temperature cycles (40, 80, 120 and 160 cycles) on the permeability and surface resistance of concrete at different ages, measuring the depth of water penetration and resistance Concrete is compressed without breaking it. According to the results, by using the calibration charts and the equations obtained from the methods of cylindrical chamber and friction transfer, it is possible to obtain the depth of water penetration and the compressive strength of concrete without the need to break the concrete and with a correlation coefficient of over 96%. It was also observed that the cycles of temperature changes have negative effects on the durability and surface resistance of concrete in such a way that the number of 40, 80, 120 and 160 cycles of temperature changes increases the permeability of concrete by 4.1, 8.7, and 7 12.5 and 16.5 have been equaled. Also, the acute conditions of temperature changes have negative effects on the surface resistance of concrete in such a way that the surface layer resistance of concrete has decreased by more than 44% under 160 cycles of temperature changes. Considering that the surface layer of concrete has a direct relationship with the penetration of harmful substances into the concrete, it was observed that with the increase in the strength of the surface layer of concrete, the volume of water penetration into concrete has decreased. By increasing the resistance of the surface layer by 15%, the volume of water infiltration into the concrete has decreased by about 140%.Static analysis of the stress-gradient nanobeam by analytical and Nystrom numerical method
https://sjce.journals.sharif.edu/article_23347.html
This paper deals with the static analysis of the Euler-Bernoulli nanobeam based on the Eringen’s nonlocal theory. This theory is used for the nanoscale structures such as nanobeams which claims that the stress tensor is associated with the strain tensor by a linear integral transformation. The kernel function of the transformation contains an attenuation function. Several candidates have been proposed for the attenuation function. In this paper, the exponential attenuation function is utilized and the corresponding integral equation is solved directly. To do so, two different methods of the Nystrom numerical method and analytical method are employed, respectively. The Nystrom numerical method is one of the numerical solutions that is extensively utilized to solve different integral equations. This method builds up a linear system of equations that is conveniently solved by the computational programs. Next, the function of the answer is predicted and then examined by the analytical method. In fact, the analytical method is determination of the unknown constants in order to justify the integral equation by inserting the mentioned probable answer in the integral equation and putting both side equivalent to each other. At last, the displacement and curvature function of the nanobeam is determined according to the answer of the integral equation so that the mentioned integral equation converts to an equivalent differential equation that is newly proposed. On the other hand, the resultant displacement function is a closed form function which contains some constants that should be found by utilizing the boundary conditions of the nanobeam. For the sake of verification, the offered function is employed to determine the dimensionless displacement of a specified point of the beam and compare it with the results given in the previously proposed papers. Additionally, the mentioned function is employed to analyze several nanobeams with new boundary conditions and load functions. Then, the displacement function is plotted. Lastly, a contradiction is also determined based on the displacement graphs in the pervious section.Evaluation of Temperature Variation Effects on the Swelling Characteristics of Fine-graded Soils improvement with Sodium Alginate in Constant Volume condition
https://sjce.journals.sharif.edu/article_23359.html
In some regions with hot and dry climate conditions, the temperature varies greatly between day and night. Therefore, the materials used in construction projects are exposed to a large number of thermal cycles on a daily basis. In this research, the application of sodium alginate polymer as an eco-friendly additive for soil stabilization and improvement of its geotechnical characteristics is studied. The study involves conducting geotechnical tests on both control and stabilized soil samples (with and without sodium alginate polymer) such as standard compaction test, swelling tests, and measuring Atterberg limits, while specimens were subjected to the same temperature variations as those recorded in the Khuzestan province, in the southwest of Iran. In fact, this study aims to investigate the effect of temperature ranges on the changes in swelling potential of high plasticity clayey soils stabilized with sodium alginate polymer. Consolidation tests were carried out on compacted clay samples - containing different concentrations of sodium alginate polymer with treatment durations of 1 and 14 days - in accordance with the method C of ASTM standard. The temperature range considered in this research was 23 to 45℃ due to the simulation of the temperature in Khuzestan province in the spring and autumn seasons. Observations indicated an increase in the swelling potential up to 13% in a sigmoidal manner with the repetition of temperature ranges and the stabilization of swelling changes, or so-called aging of swelling, which occurs with the repetition of temperature fluctuations. Additionally, the samples were analyzed using X-ray Diffraction XRD and X-ray Fluorescence (XRF) techniques to investigate the changes in their compositions. These methods revealed the formation of palygorskite mineral in specimens. This mineral intensifies the soil's swelling potential and is considered one of the contributing factors to the observed increase in swelling in the stabilized soil samples containing sodium alginate polymer.Numerical study on semi-supported steel composite shear wall at the edges under near and far-fault loading
https://sjce.journals.sharif.edu/article_23360.html
The shear wall is one of the most important systems to resist lateral loads in the building. In addition to controlling the lateral displacement of the structure and dealing with the lateral force, this system significantly increases the stiffness of the structure.The purpose of this article is to investigate the nonlinear behavior of semi-supported steel composite shear wall at the edges under monotonic and cyclic loading near and far-fault. In this article, after verification, firstly, the semi-supported steel shear wall is modeled and analyzed in ETABS software to select the boundary members and select the critical opening, then the base model of the semi-supported steel shear wall is converted to a semi-supported composite shear wall and in Finally, it is modeled and checked in ABAQUS software. Among the investigated variables are reducing the thickness of the concrete coating on both sides of the steel plate of the wall, the results showed that the addition of concrete to the SSSW model (converting the model to SSCSW) increases the initial in-plane hardness by 350% and results in the domain of the built models showed that Also, when concrete was added to the SSSW model, the ductility increased by 150% in two states near and far from the fault. And comparing the ultimate strength (peak of the cyclic diagram) also showed that regardless of the type of cyclic loading pattern, the calculated value for SSCSW is 28% higher than SSSW. using concrete coating on one side of the steel plate of the wall and increasing the thickness of the steel plate of the wall.In steel shear wall, to avoid nonlinearization of boundary elements, capacity-based design is performed, which results in a significant increase in the amount of steel used in boundary elements. To reduce the boundary element steel, a semi-supported steel shear wall (SSSW) has been proposed and its efficiency has been proven in previous studies.In addition, it seemed that the use of concrete coating on steel plate could improve the strength and ductility of the SSSW system. For this purpose, an 8-storey building equipped with SSSW was first designed and its most critical opening was converted to a composite model (SSCSW) and its finite element model was produced.This model was presented against near and far fault cycle loading analysis and cyclic curve, capacity, dissipation energy, This model was presented against near and far fault cycle loading analysis and cyclic curve.capacity, dissipation energy,Investigation of numerical models for predicting cavitation phenomenon in venturis using ANSYS FLUENT software
https://sjce.journals.sharif.edu/article_23361.html
In today's world, cavitation is one of the most important phenomena in fluid mechanics. A phenomenon in which very small bubbles are created during the flow as the flow moves and the pressure in some areas reaches the under pressure of the saturated vapor, and when these bubbles move and reach areas with higher pressure, they burst and create energetic microjets, which cause a lot of vibration and noise when these microjets hit the walls. It also causes destructive effects such as structural erosion of ships propellers, pump blades and dam overflow, and it also causes a decrease in efficiency and malfunction of hydraulic devices. Today, the phenomenon of cavitation in various fields, including marine industries, such as the construction of submarines and underwater projectiles, all kinds of valves and pumps, and some external flows, such as the overflow of hydropower plants and the overflow of dams, is considered. This phenomenon has attracted the attention of many scientists over time. These scientists have often looked for ways to eliminate or minimize the destructive effects caused by this phenomenon. Therefore, it is very important to find a better understanding about cavitation and the mechanism of its occurrence. In this research, it has been tried to study and compare different cavitation models in different geometries, and also, in one sample, the results of the numerical model have been compared with the results of the laboratory model. In general, in the computer analysis and comparison of the convergence speed of the Schooner and Zwart models, it was observed that the convergence speed of the Schnerrand model is higher than the convergence speed of the Zwart model. The speed obtained in the throat under the same conditions shows a constant value in all models, which shows that the speed is independent of both Schnerrand and Zwart models.Probabilistic models for prediction of the yield stress of rebars and compressive strength of concrete based on Bayesian linear regression
https://sjce.journals.sharif.edu/article_23362.html
This paper proposes probabilistic models for predicting the yield stress of reinforcing steel bars and the compressive strength of concrete used in Iran’s construction industry. The importance of this research stems from recognition that the strength of construction materials is one of the main parameters in performance-based design, in calibration of load and resistance factor design (LRFD) provisions, and in risk and resilience analysis of civil infrastructure. Moreover, due to the common practice of on-site casting of the concrete and a large number of rolling mill companies producing reinforcing steel bars, there is a considerable amount of uncertainty in the compressive strength of concrete and the yield stress of steel bars. In this paper, first an extensive database is compiled from concrete and steel laboratory tests. One key field of data for developing the concrete strength model is the nominal design strength of concrete, which was unavailable for a notable portion of the collected data. The database was augmented to account for the missing data using classification algorithms of k-nearest neighbors (KNN) and RBF-Kernel based on machine learning. Next, a probabilistic model is developed using Bayesian linear regression using the Rtx software to predict the compressive strength of concrete as a function of its nominal strength, curing duration, and the quality grade of the concrete manufacturer. The models are Subsequently are diagnosed for the quality of prediction, heteroskedasticity, and normality of the errors to ensure they are statically sound and well represent the underlying data. Next, a model reduction procedure is implemented to discard the inconclusive predictors from the model and to eliminate high correlations among the model parameters to achieve the final model form. Finally, the yield stress of reinforcing steel of Grades A-III and A-IV are modeled using Bayesian random variables whose distribution parameters are also random are inferred from the collected data. Bayesian inference enables the quantification of epistemic uncertainties in the model parameters and hence, makes it possible to update the model using Bayesian updating as new data emerge.Scenario creation of Shared Autonomous Vehicles Penetration Rate, a Quantitative Environmental Analysis
https://sjce.journals.sharif.edu/article_23394.html
In 2022, the air pollution levels in Iranian cities increased by an average of 35% compared to 2019, which is concerning considering the growing transportation needs due to population growth. However, alternative travel methods with better environmental performance can help reduce the role of transportation in creating pollution.
One potential solution is the use of shared autonomous vehicles, which have the potential to significantly reduce greenhouse gas emissions. However, estimating the exact effects of this travel method on climate change can be challenging due to various factors that come into play.
To address this issue, a study was conducted using the SUMO software and random travel demand to quantitatively analysis the environmental impact of shared autonomous vehicles in a specific section of Tehran city. The analysis considered different scenarios related to the penetration rate, fleet size, and sharing policies.
Simulation-based approaches were employed to assess the environmental impact, with a particular focus on greenhouse gas emissions. The results of the study indicated that simultaneous service to two users, compared to other sharing scenarios, can reduce greenhouse gas emissions by up to 10%. This suggests that efficient sharing policies can have a positive impact on the environment.
Moreover, the study found that In scenarios where both autonomous car-sharing and private car modes exist, increasing the fleet size of shared autonomous vehicles can lead to increased congestion, resulting in higher pollutant emissions. Additionally, the penetration rate of these vehicles is crucial, as a penetration rate of 100% tends to result in almost zero greenhouse gas emissions. Regarding the impact of the fleet size of shared autonomous vehicles on fuel consumption, it can be said that increasing the fleet size in scenarios where both modes exist would lead to an increase in fossil fuel consumption and a decrease in electric fuel consumption.
Overall, this study highlights the potential environmental benefits of shared autonomous vehicles in reducing greenhouse gas emissions. By implementing efficient sharing policies, increasing fleet size and density, and aiming for high penetration rates, we can strive towards a greener and more sustainable transportation system.Numerical solution for one-dimensional pure-convection problems using the high-order Taylor-Galerkin meshless method
https://sjce.journals.sharif.edu/article_23395.html
The present study proposes a novel approach for solving one-dimensional pure convection problems, utilizing a high-order Taylor Galerkin element-free method. The standard Galerkin method has limitations in solving such problems due to the predominance of convective terms over diffusion terms, leading to unstable and fluctuating analysis results over time. To address this issue, high-order stabilizing terms can be added to the standard Galerkin method. However, due to the limitations in the derivability of the standard Galerkin shape function, it is not possible to incorporate high-order terms in the equation. In this context, the proposed high-order Taylor Galerkin element-free method enables the inclusion of stabilizing terms with high-order derivatives in the equations, utilizing the moving least-squares (MLS) shape function and exponential weight function, which exhibit the continuity of all their derivatives. This approach provides a promising solution for addressing the limitations of the finite element method and achieving more accurate and stable analysis results for one-dimensional pure convection problems. The accuracy of the numerical simulation was evaluated using two one-dimensional pure convection benchmark problems: the Gaussian wave motion problem and the classical water hammer problem, both analyzed up to the fourth-order. The results of the numerical simulations demonstrated that increasing the number of stabilizing terms led to improved accuracy and decreased fluctuations. Therefore, it can be concluded that the stability terms up to the fourth-order in the equations display acceptable accuracy for these two problems. This development has significant implications for the analysis of fluid mechanics and other related phenomena. By enabling a more comprehensive analysis of fluid dynamics, researchers can investigate complex fluid dynamics with greater precision and detail, yielding valuable insights into a wide range of physical processes. In conclusion, the proposed high-order Taylor Galerkin element-free method is a noteworthy advancement in numerical analysis, overcoming the limitations of the standard Galerkin method and demonstrating superior accuracy and stability in the solution of pure convection problems. This approach provides an efficient and accurate method for numerical analysis and has the potential to be extended to other areas of research, including computational fluid dynamics, heat transfer, and structural mechanics.Assessment of unsaturated behavior of Gorgan loessial soil under anisotropic triaxial compression in medium suctions range
https://sjce.journals.sharif.edu/article_23396.html
Collapsible soils, such as loess, are classified as problematic soils and are usually stable in unsaturated conditions in the nature. However, when they are exposed to a moisture increase especially under an applied load, they undergo a sudden decrease in volume or collapse. Various aspects of the behavior of unsaturated collapsible soils including volume change, soil-water retention, and shear strength have been extensively investigated so far. However, few studies have been carried out on the effect of initial shear stress on the hydromechanical behavior of unsaturated collapsible soils. The aim of this study is to investigate the effect of initial shear stress on the hydromechanical behavior of Gorgan loessial soil under anisotropic triaxial consolidation in medium suctions range using a fully automated unsaturated triaxial device. In this study, a set of stress-controlled triaxial tests were performed on reconstituted specimens of Gorgan loessial soil implementing “suction decrease under constant mean net stress” hydromechanical stress path. The tests were conducted in medium-range suctions under different initial shear stresses. Strain-controlled triaxial shear tests were also conducted at the end of anisotropic consolidation, to evaluate the shear behavior of the tested specimens. Results taken from the wetting stage indicate that the volume reduction of the specimens increases with an increase in initial shear stress under constant mean net stress. The results obtained from shear tests on specimens with constant matric suction and mean net stress in the wetting stage show that the greater the initial shear stress, the lower the shear strength of the specimen. Also, according to the independent stress variables approach, the shear resistance parameters including c´, ϕ´, and ϕb have been obtained 4.7 kPa, 32.9º, and 13.6º respectively. In addition, regression lines through the steady-state data points, used to define the CSL of the reconstituted specimens, had an M-value of 1.19.Analytical and experimental study on two-tiered MSE walls
https://sjce.journals.sharif.edu/article_23397.html
A pseudo-static coefficient is required for pseudo-static analysis of mechanically stabilized earth (MSE) walls, but there are no clear criteria for its selection. The current study assessed the horizontal pseudo-static coefficient (kh) for MSE walls by considering the effects of a tiered configuration and reinforcement type. For this purpose, by selecting two reinforcement types (steel strip and geogrid), six two-tiered MSE walls with three different offset distances and two integrated MSE walls (without tier) were prepared and then were shaken using shaking table tests to determine the geometry of the slip surfaces and the force distribution along the reinforcements at the failure stage. The physical models then were simulated using the limit-equilibrium horizontal slice method to estimate the value of kh required to establish slip surfaces and reinforcement forces similar to those observed in shaking table tests. Because the equivalent pseudo-static coefficients obtained were the corresponding to failure stage, they were considered as the upper bound values. The analytical models used a new formulation of the horizontal slice method (HSM) based on the slip surfaces observed in the shaking table tests. This formulation made it possible to determine the distribution of kh along the wall height as a function of the reinforcement type, offset distance, and PGA. It was found that, as the offset distance increased, the pseudo-static coefficient required for the upper and lower halves of the tiered wall models increased and decreased, respectively. This was observed in both types of reinforcement, but was more prominent in walls reinforced with metal strips. Moreover, the distribution of kh along the wall height showed that a lower pseudo-static coefficient was required for the upper layers of the integrated walls, but the reverse was true when using a tiered configuration. This change in the trend of the kh distribution, which was due to the increase in the dimensions of wedge failure in the lower half and a decrease in dimensions in the upper half of the wall required a larger coefficient in the upper layers of the tiered walls.Assessing long-term (3-year) mechanical properties of recycled aggregate concrete containing zeolite and silica fume
https://sjce.journals.sharif.edu/article_23425.html
Using recycled concrete aggregate as a sustainable solution has been the subject of much research in recent years. The use of recycled aggregate has led to a reduction in the quality of concrete in various studies. A promising approach to enhance the concrete properties of recycled aggregate concrete involves the use of pozzolans as supplementary cementitious materials. In this study, cement was replaced by silica fume in 8% of the specimens, while in other specimens, cement was replaced by zeolite in 15%. Natural aggregate was substituted with recycled concrete aggregate in varying proportions of 30%, 50%, and 100%. Subsequently, various mechanical and durability tests were conducted to evaluate the properties of each specimen. Compressive and tensile tests were carried out to assess the mechanical properties of the specimens. The tests revealed that specimens containing recycled aggregate exhibited inferior properties compared to natural aggregate concrete. Over the long term (3 years), the specimens containing recycled aggregate also displayed lower compressive strength. Specimens containing silica fume demonstrated higher compressive strength in the short term when used with natural aggregate concrete, but showed similar performance over the 3-year period. In specimens containing recycled aggregate, silica fume had a more pronounced effect, leading to higher compressive strength in the short term but similar or reduced strength over the 3-year period. A similar trend to that observed in compressive strength was found in splitting tensile strength. As the percentage of recycled aggregate replacement increased, tensile strength decreased. The use of silica fume increased splitting tensile strength, even over the 3-year period. On the other hand, using zeolite did not result in a significant change, and specimens exhibited similar or reduced compressive strength over the 3-year period. In general, it can be inferred that the use of supplementary cementitious materials can enhance mechanical properties in the short term. However, durability tests, including water penetration depth and water absorption percentage, demonstrated almost the opposite trend. This suggests that the use of supplementary cementitious materials generally has a negative impact on concrete properties in the long term.Numerical modeling of land subsidence induced by groundwater extraction considering unsaturated effects and using element-free Galerkin (EFG) method
https://sjce.journals.sharif.edu/article_23426.html
This study aims to provide a coupled flow-deformation (hydromechanical) model for simulating land subsidence associated with groundwater extraction in aquifers. For this simulation, we have adopted the element-free Galerkin (EFG) method and considered the unsaturated effects in the aquifers based on the aquifer's hydrologic and geotechnical characteristics. This model gives us a better understanding of the aquifer's geological characteristics, enabling us to forecast changes in the hydraulic head and land subsidence.
To ensure the credibility of our model and validate the code, we modeled unsaturated hydromechanical benchmark problems. Then, using the EFG method as a numerical tool, we modeled an isotropic aquifer to investigate the effects of groundwater pumping on land subsidence and hydraulic changes in the aquifer. To ascertain the reliability of the modeling, we compared EFG results with finite element method (FEM) models. The comparison results were satisfying, and the land subsidence and hydraulic head profiles demonstrate that the EFG method is capable of land subsidence simulation caused by water pumping. Furthermore, our findings highlight the nonlinear correlation between groundwater extraction and the subsequent decrease in hydraulic head and land subsidence augmentation. Finally, we performed a parametric study to better understand the effect of various characteristics of aquifers and observe the effect of the aquifer's parameters, such as hydraulic conductivity, elastic modulus, and Poisson's ratio. We investigated the effect of each parameter on land subsidence increase and hydraulic head decline. The results show that elastic modulus and Poisson's ratio have the most significant effect on land subsidence. Although hydraulic conductivity controls the hydraulic decrement and land subsidence increase time, it slightly affects the final hydraulic head and land subsidence at the steady-state stage. These results highlight the importance of in-situ measurement of elastic modulus and Poisson's ratio parameters with acceptable accuracy for groundwater extraction projects, as these parameters play a significant role in the feasibility studies.Modification of soil modeling and using it in the fish-bone model
https://sjce.journals.sharif.edu/article_23427.html
The basic design of any structure requires sufficient and detailed modeling of each structural element. It must be taken into consideration that the modeling of each member of the structure and performing nonlinear dynamic analysis due to the presence of multiple degrees of freedom, is time consuming. Therefore, a wide range of structures cannot be evaluated. To resolve this issue, researchers have recommended using simplified equivalent models to study a wide range of structures, provided that the equivalent ones significantly reflect the behavior of the original structure. One of these models is the fishbone model, which is used for modeling moment resisting steel structures and it also has a suitable accuracy. Additionally, the presence of soil can significantly change the response of the structure. This is despite the fact that accurately modeling of the soil will lead to an increase in degrees of freedom. In this study, the aim is to examine the seismic performance of soil-structure systems and to evaluate the accuracy of the models presented in seismic codes, and after modification, provide a simplified model for placement under the fishbone frame. In this regard, first by modeling a number of foundations on distributed Winkler springs considering nonlinear behavior for the soil, the moment-rotation capacity curve of the foundations were drawn, and then the aforementioned graphs were simplified into bilinear curve through an algorithm. The bilinear models which are presented, has a greater stiffness and strength compared to the model presented by the seismic code. Two equation were suggested for determining the coefficients of the bilinear model by regression. In the next step, instead of modeling vertical distributed springs beneath foundation, a rotational spring with modified bilinear behavior was placed under the fishbone model. The analysis of the seismic response of soil-structure systems under earthquake records shows that using the modified model instead of the model presented in the seismic code leads to responses with appropriate accuracy. In addition, by using the modified model, the time required for the time history analysis is noticeably reduced, which is important in research studies.Application of intelligence models based on soft computing in investigating the discharge coefficient of the sluice gate under free-flow condition and symmetrical sill with the help of KNN, ANN, GEP and SVM models
https://sjce.journals.sharif.edu/article_23428.html
The use of sills with the gates leads to a reduction in the height of the gate. The sills affecting the flow, change its quantities, especially the discharge coefficient. In the present research, the amount of discharge coefficient of the sluice gate is examined for the first presented theoretical relationship in a non-suppressed sill state; to measure its performance using soft computing methods. For the models, 70% of the data were used for the training phase and the rest for the testing phase. The results of statistical indicators showed that in all SVM, KNN, GEP, and ANN models, the model with all input parameters was recognized as the superior model. In the SVM model, the results of various kernels showed that the Radial Basis Function kernel has better results in predicting the discharge coefficient compared to the Polynomial, Linear, and Sigmoid kernels. The results of the correlation coefficient (R), Root Mean Square Error (RMSE), mean percentage Relative Error (MRE%), and Kling Gupta Efficiency (KGE) in the test stage for the SVM model were 0.96, 0.018, 0.90, and 1.92%, respectively. The results of the neighbor coefficient (K) showed that in the K equal 2, the RMSE and MRE had a lower value and were close to the experimental results. In addition, in the KNN model, among distance criteria measures (Manhattan, Euclidean, Euclidean Squared, and Chebychev), the Manhattan criteria has a higher accuracy in predicting the discharge coefficient than the other ones. For this model, the results were 0.97, 0.016, 0.96, and 1.70%, respectively in the testing phase. In addition, the results for the GEP model were 0.98, 0.019, 0.85, and 2.28%, respectively. In the present research, the ANN method is more accurate compared to SVM, GEP, and KNN models; so that, for the ANN model, the KGE was in the very good range.Determination of surface potential of kaolinite for selection of optimal enhancement pattern for removal of heavy metal contaminant in electrokinetics remediation
https://sjce.journals.sharif.edu/article_23429.html
Buffering capacity measurement is one of the common methods to evaluate the contaminant retention by soil or the selection of enhancement method for contaminant removal. However, due to the limitations of this experiment the quantitative use of the results of this experiment involves noticeable errors. The main objective of this paper is to present theoretical and practical insights of zeta potential theory to optimize removal of heavy metal contaminants from clayey soils. To achieve this objective series of zeta potential experiments, buffering capacity measurement, SEM photograph, XRD experiments and batch equilibrium tests were performed on kaolinite, decarbonated kaolinite and washed kaolinite samples. The experiments were performed to align the direction of electro-osmosis flow with the ion migration phenomenon. Based on the results of this paper, with determination of variation of surface potential of clay at different geo-environmental conditions, the curve of zeta potential can be divided to three zones which are called retention, stable and desorption sections. As the carbonate content of sample increases the length of stable section in zeta potential curve increases which shows the resistance of soil to contaminant removal. Based on these three different areas, with selection of optimum enhancement pattern, one can align the direction of electro-osmosis flow with the ion migration phenomenon. Consequently, more uniform removal of heavy metals and an increase in efficiency of electrokinetics method will be achieved. Furthermore, according to the results of this paper as the concentration of heavy metal increases, due to the reduction of double layer thickness the zeta potential reduces which might cause a change in electro-osmosis direction at relatively high heavy metal concentration. Finally, it is shown that the use of fundamental aspect of surface potential of clays with the concept of different retention phases of contaminant in soil is an applicable and theoretical method for optimized contaminant removal from clayey soils.Assessment of Momentum Balance Method in the Determination of Shear Stress in Compound Meandering Channels
https://sjce.journals.sharif.edu/article_23430.html
Shear stress is one of the most important effective factors in the flow dynamics of open channels. The hydraulics of sediment transport in channels is affected by how and the amount of this factor. Considering the three-dimensional and complex nature of the flow in meandering compound channels, based on the effective role of secondary flows and momentum transfer, especially in curves, calculating this parameter by the methods provided for straight channels is challenging. The Momentum balance method, which is introduced as one of the shear stress determination methods in straight channels, can be used to determine the shear stress in meander channels. In this research, using the 3-D flow velocity components data, measured by ADV, the distribution of shear stress in the flow path in a meandering compound channel was investigated. In a physical model, including a rectangular concrete channel, a meander main channel, and two flood plains, the transverse distribution of streamwise velocity is investigated. Then, the transverse distribution of the shear stress in five sections along the flow is calculated using the momentum balance method, and the results have been compared using the logarithmic distribution method of velocity and Reynolds shear stress in these sections. Also, the amount of shear stress in the four depths of the main channel is illustrated. Since the determination of maximum shear stress areas can be effective in flow and sediment studies and issues related to river maintenance, such as bed erosion, especially in arches, the maximum values of relative shear stress in MBM, RSM, and LLM methods were determined as 5.43 and 7.24 in the fourth section and 6.05 in the first section, respectively. The minimum amounts of shear stress observed in section 5 in both RSM and MBM methods. According to the reviewed results, the MBM method can be introduced as a practical method for evaluating shear stress values in meandering Rivers.Health monitoring of structural elements using CT-Xray
https://sjce.journals.sharif.edu/article_23431.html
Structural health monitoring is becoming more reliable as technology advances. There are many structures which are in use throughout cities and environments that requires constant attention due to fatigue of corrosion and environmental effects such as floods, earthquakes, or strong winds. This means that by advent of new damage detection technique, authorities can make sure that these vital structural elements such as road signs or traffic lights and so on are safe.
The important key to these techniques is that they must be simple and relatively inexpensive.
Therefore an attempt was done to use techniques in medical practice and adapt those to structural members.
In this article, the effectiveness of X-ray computed tomography in the inspection of urban structures and building structures is discussed. X-ray tomography is a non-destructive method based on X-ray absorption, which is widely used in the medical field. By using this method, it is possible to study and examine the internal structure of old structures in order to fix defects and maintain the safety of residents, as well as to maintain them as best as possible. For example, urban structures such as electric poles, traffic signs, which cause financial losses or even lives due to natural hazards or wear and tear every year. One of the features of this method is its high accuracy and speed in checking the member. Considering the capabilities of this method, in this research, using a baggage inspection device at the MehrAbad airport, a number of concrete and wooden samples were examined to identify defects such as cracks, holes, or knots in wooden samples. The results of the investigation are directly related to the power of the device and the duration of radiation to the sample. According to the results, defects such as cracks in concrete or knots in wood can be observed.Experimental study on damage detection of a truss bridge under moving load using artificial neural network and empirical wavelet transform
https://sjce.journals.sharif.edu/article_23432.html
Civil structures are always considered one of the most valuable properties of each country. Many factors can lead to local damages in different parts of structures during their operational life. These damages are reflected in the vibration responses of structures. This research aims to detect the existence and determine the location of damage in a truss bridge under moving load using an artificial neural network and experimental wavelet transform. For this purpose, a two-dimensional truss bridge was built in the laboratory to investigate this research's objectives. Earlier experimental studies in damage detection were subjected to excitations such as impact loads and electrodynamic shakers. Since the appearance of damage effects in the vibration responses of the structure mainly depends on the applied location of the impact load, a moving load that crosses the entire length of the bridge can be used as input excitation to detect the presence and location of damages for which there is no available data. After measuring the vibration responses of the bridge, 17 time-domain features were extracted from the raw signals, which were used to detect the presence of damage. Although feature extraction is applied to raw signals, signal processing stage was not eliminated for damage localization. By processing the response signals of healthy and damaged state of the bridge using experimental wavelet transform, these signals were decomposed into different modes and 5 non-parametric damage-sensitive features such as Shannon and Tsallis entropies, Root Mean Square (RMS), Shape Factor and kurtosis which are all based on statistical parameters in addition to energy, were extracted. Finally, these damage-sensitive features were presented as input to the neural network whereas the state of the bridge (healthy or damaged) was considered as its targets. The obtained results showed that the proposed method is able to effectively detect the presence and the location of the damage in the truss bridge.Protection of buried pipe using soil bag
https://sjce.journals.sharif.edu/article_23435.html
Today, the use of geosynthetics to reinforce the soil mass on the pipes is being developed under static and repetitive loads. In the meantime, soil bags are considered as a suitable option for dealing with floods and other geotechnical applications such as road beds, slope stability, and retaining walls. In this paper, the investigation of the buried pipe’s behavior in the unreinforced trench and reinforced trench with soil bag is considered. Therefore, a series of tests were conducted on the unreinforced and reinforced trench (reinforced by one soil bag, two soil bags in columnar arrangement with and without spacing, and three soil bags in two layers of stepped arrangement) containing a pipe with a diameter of 160 mm under static load. The results of the tests show the effect of the soil bag layer on reducing the bed settlement by enclosing the soil inside and preventing the lateral movement of the soil mass above the pipe. Also, the bag, by distributing the stress on a wider surface and significantly reducing it in depth, reduces the transfer stress to the pipe crown and as a result, reduces the deformation of the pipe. Increasing the buried depth of the soil bag results in a reduction in deformation and pressure on the pipe crown and an increase in soil surface settlement. The columnar arrangement of two layers of soil bags with spacing provides better performance in improving pipe behavior compared to those without spacing. Moreover, the use of two layers of soil bag with a stepped arrangement leads to a reduction in surface settlement, pressure on the pipe, and pipe deformation compared to two layers of soil bag with a column arrangement. However, considering the lack of significant difference between the behavior of the stepped and column arrangements (with or without spacing), the use of a column system is recommended, as it saves 33% of the soil bag.Investigating the effect of driven length and diameter of monopile on seismic performance of offshore wind turbines through Physical Modeling
https://sjce.journals.sharif.edu/article_23451.html
Global warming and its following environmental problems have led to increased attention to the use of renewable energy sources in most countries around the world, and wind energy has emerged as a significant contributor. The use of wind energy, through offshore wind turbines, is one of the clean energy harvesting methods that initially began in Europe. Offshore wind turbines, due to their larger size and higher wind speeds, have gained popularity worldwide, including seismic areas such as the United States and Southeast Asia, especially China. These turbines are located in marine environments and are subject to cyclic loads caused by wind, waves, and ocean currents. Monopiles, cylindrical hollow piles with diameters ranging from 2 to 8 meters and lengths of approximately 60 meters, are widely used for the installation of offshore wind turbines. The design regulations for these turbines often overlook influential factors such as soil-structure interaction and refer to seismic design guidelines for onshore turbines. In this research, the seismic performance of monopiles has been investigated by conducting six experiments using a shaking table in a 1g condition. The effects of driven length and monopile diameter were analyzed, along with the impact of the installation medium being either saturated or dry. Various parameters, including ground motion acceleration, displacement, and induced excess pore water pressure, were scrutinized in this study. The results indicate that the saturated environment weakens their seismic performance, therefore, the seismic design considerations for monopiles, based on the existing guidelines for dry structures, are inadequate. Furthermore, increasing the monopile diameter by 57% causes a 24% increase in the acceleration of the superstructure, a 40% increase in the cumulative displacement and a 30% decrease in the average maximum displacement of the cycles during loading. It was also observed that by increasing or decreasing the driven length about 15% compared to the driven length of the base monopile, the acceleration value of the superstructure increases by more than 20% and the cumulative displacement value decreases by about 60%. And the average maximum displacement of the cycles decreases by 30% with an increase of 33% in the driven length.A new strong ground motion model for predicting Peak Ground Acceleration (PGA), pseudo-acceleration spectra and displacement spectra in Iran
https://sjce.journals.sharif.edu/article_23452.html
Due to the inelasticity of the ground and geometric expansion, seismic waves are reduced by moving away from the center of wave propagation, which is called the attenuation of seismic waves. Therefore, the ground motions that occur at the site of the structures are different from the ground motions that are emitted from the source. The upcoming study investigates the attenuation of seismic waves in the geographical area of Iran based on the accelerogram data of Iran.
In this study, a new ground motion model (GMM) for Iran is developed to estimate peak ground acceleration (PGA), pseudo-acceleration spectral values (PSA) in 2, 5, and 10 percent damping, and displacement spectral values (Sd) at 21 oscillator periods ranging from 0.04 s to 4 s. The displacement spectra considered in this research are the displacement spectra with constant resistance-to-weight ratio, which includes both types of elastic and inelastic displacement. Also, the considered resistance-to-weight ratios include five ratios from 0.05 to 0.3. The database of this study includes 659 records of 115 shallow crustal mainshocks that occurred in Iran from 1976 to 2022 with a magnitude range of 5≤Mw≤7.4 and an epicentral distance range of 0 to 200 km. Random-effect coefficients were defined in the mixed-effect regression model for regional differences among the five regions of the Iranian plateau, and no statistical differences were detected among these regions. The effects of nonlinear response of the site soil are taken into account in the developed GMM using the VS30 parameter (average shear wave velocity in the upper 30 meters of the soil profile). The residuals of the proposed GMM are decomposed into three between-event, site-to-site and event-site-corrected components, and their distributions are examined against the predictor variables. The distribution of residuals obtained showed no significant bias for the developed GMM. The output of this research is a GMM for Iran, which can be used to estimate the spectrum of pseudo-elastic acceleration and the spectrum of elastic and inelastic displacement.The investigation of the combined effect of nano-silica, steel, and polypropylene microfibers on the mechanical characteristics, permeability, and chloride attack resistance of cement composite
https://sjce.journals.sharif.edu/article_23453.html
The objective of this study was to investigate the combined impact of nano-silica, steel microfibers, and polypropylene microfibers on the mechanical properties, permeability, and resistance to chloride attack of cement composite. To achieve this goal, a 2% weight ratio of nano-silica was used as a cement substitute, while 1.0% steel and 0.2% polypropylene microfibers, respectively, by volume of the binders were separately and simultaneously employed as additives in the cement composite. Experimental analyses, including compressive, flexural, and tensile strength tests, were conducted to evaluate the mechanical properties. Additionally, the ultrasonic pulse velocity (UPV) and sorptivity tests were employed to assess permeability, and the durability against chloride attack was examined using the Rapid Chloride Migration Test (RCMT). The results demonstrate that the simultaneous incorporation of nano-silica, steel microfibers, and polypropylene microfibers in the cement composite mixture resulted in a significant enhancement in compressive strength, flexural strength, flexural toughness, and tensile strength by 59.3%, 32.3%, 67.2%, and 25.9%, respectively, compared to the control sample after a curing period of 90 days. Moreover, significant decreases were observed in terms of the initial and secondary water absorption rates. Furthermore, the penetration depth of chloride ions was notably reduced from 33.6 mm (in the control composite) to 14.2 mm (in the composite containing the combined effects of nano-silica, steel microfibers, and polypropylene microfibers) after 90 days. The enhancement of mechanical properties, permeability, and durability against chloride attack in cement composite can be attributed to the synergistic mechanisms promoted by the utilization of nano-silica, steel microfibers, and polypropylene microfibers. The filling effect, nucleation sites, and pozzolanic activity of silica nanoparticles significantly contribute to the reduction of porosity and refinement of the cementitious matrix's microstructure. Simultaneously, the inclusion of steel microfibers and polypropylene microfibers reinforces the cement matrix and effectively controls existing microcracks, thereby impeding the propagation of macrocracks and brittle failure in the cement composite. Furthermore, the bridging effect of steel and polypropylene fibers aids in the control of cracks caused by plastic shrinkage during the early stages and secondary or thermal cracks, thereby further improving the properties of cement composite.an investigation on the effective parameters of loose sands liquefaction using improved hypercube sampling method
https://sjce.journals.sharif.edu/article_23473.html
The occurrence of liquefaction phenomenon in saturated loose sandy soils under seismic loads causes the soil particles to tend to decrease in volume. So that if drainage is not possible, the pore water pressure inside the soil increases and in constant stress conditions, the effective stress between particles approaches zero. In this case, the soil particles have no shear resistance and liquefaction occurs. Liquefaction is one of the important issues of concern in seismic geotechnical engineering, which involves many uncertainties in soil and earthquake parameters. The most common method to evaluate the potential of liquefaction is deterministic method which cannot consider the pertinent uncertainties. Soil properties are uncertain due to various sources of variability of soil deposit formation. Currently there is less reliable procedure to account for all pertinent uncertainties in predicting the occurrence of soil liquefaction phenomena when subjected to strong ground motion. In this research, liquefaction reliability analysis was performed by considering the soil and earthquake loading uncertainties using the latest modifications provided by Idris and Boulanger (2014) for the simplified method and using the using improved hypercube sampling (IHS) method. Comparing the results of IHS method with Monte Carlo simulation showed that the proposed method is reliable for liquefaction analysis. The analyses have been performed on well-documented historical cases. The Monte Carlo method has been accepted as the benchmark method in most studies based on liquefaction reliability analysis. Comparison of the Monte Carlo (MC) method and IHS results indicate that the IHS method is more accurate, reliable, and capable over MC for analyzing the reliability of liquefaction and can be used as a benchmark approach in future studies. The results show that the proposed approach is a favorable and useful tool for the reliability analysis of liquefaction potential estimations. Sensitivity analysis based on the coefficient of variation on a wide range of liquefaction and non-liquefaction case histories illustrate that the variability of soil parameters and earthquake loading can have an important effect on the probability of liquefaction. It is worthy to note that different parameters may have the most effect on the probability of liquefaction depending on soil conditions.Numerical Modeling of Swash Zone Morphological Processes in Coarse-Grained Beaches with XBeach Open-Source Model
https://sjce.journals.sharif.edu/article_23474.html
The swash zone and its processes are very important in a beach system due to their significant effects on beach hydrodynamics, morphodynamics and ecosystems, including beach flows, aquifers, and sediment transport. It is important to develop efficient numerical models to evaluate hydrodynamic-morphodynamic processes, particularly in the swash zone. XBeach is a numerical model for beach simulations. In this regard, evaluating the performance of the XBeach model based on the SB and NH modules, comparing the results of morphological process simulations, and sensitivity analysis of the results under different coastal conditions have been considered as research gaps in this field. Based on this, this research is dedicated to modeling three different laboratory models from Masselink, 2012 Zanden,2016 and Demirbilek, 2007 with varying hydrodynamic-morphodynamic conditions to evaluate the performance of the XBeach model in simulating morphological processes of coarse-grained beaches with the presence of bed porosity effects in the form of infiltration/exfiltration. In the numerical modeling process, after calibrating and sensitivity testing the models, the results are extracted and compared with laboratory models. The results of this research indicate that the XBeach model has an acceptable performance in modeling hydrodynamic and morphodynamic processes in the Swash region, and simulation with the NH module performs better compared to the SB module (with a reduction in modeling error of over 5% in various models). Additionally, the results show that phase errors during water infiltration/percolation into the aquifer in XBeach lead to the expansion of numerical modeling errors in calculating changes in the seabed profile and aquifer water level. Despite substantial advances, XBeach remains yet to be further developed since it is inefficient in modeling interactions between the aquifer level and seawater. Those studies should aime to cope with XBeach phase errors in the aquifer (seawater-aquifer interaction) estimations leading to an inaccurate simulation of hydrodynamic-morphodynamic processes in the swash zone.Three-stage automatic operational modal analysis using mathematical mode elimination by density-based clustering method
https://sjce.journals.sharif.edu/article_23475.html
Estimating the modal parameters of a structure is essential for a variety of applications, including health monitoring, damage detection, design verification, and model updating. Modal parameters are the natural frequencies, mode shapes, and damping ratios of a structure. They can be used to understand the dynamic behavior of the structure and to identify any changes that may occur over time. Operational modal analysis (OMA) is a technique that uses the response of a structure to environmental loads to estimate modal parameters. OMA is a non-destructive testing method that can be used on structures in their operating environment. This makes it a valuable tool for health monitoring and damage detection of buildings, bridges, wind turbines, and stadiums. One of the challenges of OMA is that its methods rely on the user's judgment to separate physical modes from spurious modes and to distinguish between real modes of the structure. Spurious modes are not caused by the actual structure, but by noise or other environmental factors. Real modes are caused by the structure itself. In recent years, there has been extensive research on automating OMA methods for modal parameter estimation. Most of these studies have attempted to minimize the need for user intervention in modal parameter calculation by using machine learning techniques. Machine learning techniques can be used to automatically identify physical modes and to distinguish between real modes of the structure. This research uses the Stochastic Subspace Identification (SSI) method for OMA. The DBSCAN clustering method is used to separate physical modes from spurious modes. Finally, the hierarchical clustering method is used to distinguish between real modes of the structure. The proposed algorithm was implemented on a 5-degree-of-freedom structure and a real bridge. The results show that the proposed method has a higher power to separate physical modes from spurious modes than previous methods.A numerical assessment of the horizontal seismic coefficient for soil-nailed walls
https://sjce.journals.sharif.edu/article_23498.html
It is the objective of the present study to present a methodology for determining the horizontal seismic coefficient for soil-nailed walls based on numerical non-linear dynamic analysis. As a first step, two verification tests were simulated in order to validate the numerical modeling methodology and assumptions both in static and dynamic modes. The static validation phase involved simulating the soil-nailed wall in the Clouterre project and comparing numerical and measured profiles of horizontal displacement after excavation. The dynamic validation phase included a shaking table test on a soil-nailed wall, followed by a comparison of numerical and experimental profiles of the horizontal displacement of the wall at the end of the seismic loading. Afterwards, an in-depth explanation of the numerical modeling methodology used to calculate the seismic coefficient for soil-nailed walls was provided. Thereafter, an extensive parametric study was conducted to examine the effects of various factors on the horizontal seismic coefficient, including the wall height, soil relative density, soil cohesion, earthquake frequency content, ground surface acceleration, and altering the soil nailing design. In the parametric study, three earthquake acceleration records were used: Kocaeli, Avaj and Chi-Chi. The results of the parametric study showed that the ratio of the maximum horizontal seismic coefficient to the maximum ground surface acceleration (khmax/PGA) decreased on average with the increase in the wall height, the predominant frequency of earthquake motion and the maximum ground surface acceleration. Furthermore, the results indicated that the khmax/PGA ratio increased with an increase in soil relative density. Moreover, the ratio increased slightly as soil cohesion increased. Additionally, it was found that modifying the soil nailing design by increasing the diameter, reducing the horizontal spacing, and increasing the length of nails did not significantly alter the khmax/PGA ratio. The calculated horizontal seismic coefficients (khdesign) resulted from the parametric study ranged from 0.18 to 0.46 of the maximum ground acceleration (PGA), which is less than the commonly used range of 0.33 to 0.5 PGA.Experimental Investigation of the Behavior of Column Base Connections with Concentrically-Welded Anchor Rods Using Digital Image Correlation Method
https://sjce.journals.sharif.edu/article_23502.html
Base plate connections are one of the most important connections in steel structures. Besides the moment capacity of the connection, the rotational stiffness is an equally critical property that is frequently used in design. Because of the low rotational stiffness of the column base-plate, column base-plate connections do not have enough rigidity to create perfect plastic hinges. Therefore, concentrically-welded anchor rods were used under the column base plate to transfer loads properly. In this paper, four different weld types were used to connect the anchor rods to the bottom of the base plate. In this new connection, the eccentricity between anchor rods and the steel column is removed to improve the strength and stiffness of the base plate connections. The aim of this paper is to design four different weld types according to the specifications of welding standards. Five laboratory samples with different anchor rod strengths were tested to evaluate strength and ductility of each weld type under tensile loading. Anchor rods were the weakest member in transferring tensile load in each sample and expected to fail at the end of the test. Digital Image Correlation (DIC) method was used to provide force-displacement diagram and full field strain information of each laboratory sample. DIC is a non-contact and non-destructive technique in which digital images of the point of interest (POI) of a test specimen are captured continuously using a high-resolution camera all through the test. Fortunately, experimental results were similar to DIC results. Brittle failure was observed in the samples with high strength anchor rods at the softened heat affected zone (HAZ) in the anchor rods. As a result, all the anchor rods in each laboratory sample fractured at a tensile strength higher than yield strength of the anchor rod. Therefore, to prevent the failure of anchor rods in softened HAZ area, it is recommended to design the anchor rods of the column base connections to remain elastic under cyclic loads. It was also concluded that the fillet weld had a better performance in terms of executive and economy compared to the other welds.Influence of Beam Height-Column Width Ratio on Seismic Behavior of RC Moment Resisting Frames
https://sjce.journals.sharif.edu/article_23511.html
Most reputable international design codes have included provisions for achieving ductile behavior and avoiding brittle and hazardous behavior in reinforced concrete frames. These provisions aim to achieve the concept of weak beam-strong column, where plastic hinges during earthquake occur first in the beams. Analysis of frequent and repetitive failures in strong earthquakes in recent decades of reinforced concrete structures shows that the strong beam-weak column failure mode typically leads to severe damage in these structures. The frequent occurrence of this failure mode can be attributed to two main factors. Firstly, stiffer beams are often used against more flexible columns due to the absence of seismic provisions that limit the relation between beam height and column width finlay results in column severe damage on column and finally collapse of them. Secondly, the effect of the cast-in-situ slab in increasing the negative flexural strength of the beam is often underestimated or ignored, leading to the flexural strength of the columns being less than that of the beams. To assess the impact of the ratio of beam height to column width on the seismic performance of MRFs, a series of computational models were created and analyzed in a parametric study. Prior to that, the FEA performance was validated by comparing its results with experimental data. The findings emphasize the urgent need for a new seismic provision that limits the beam height to column width ratio to a maximum of 1.25. Also, it is indicated that, the values of effective slab width obtained from the provisions of ACI and EC8 are not sufficient to ensure the implementation of the weak beam-strong column design methodology and findings demonstrate that the value of effective slab width is minimally impacted by the beam height when the ratio of longitudinal beam height to column width (h_lb⁄C) is less than 1.5.Determining the location and optimal number of building lifts in high-rise construction projects using a linear integer mathematical model
https://sjce.journals.sharif.edu/article_23516.html
Vertical transportation technology is essential for constructing tall and medium-rise buildings. Although lifts are a functional component of buildings, their vital nature depends on the continuous and uninterrupted use of lifts in each tall building. Therefore, the use of lifts for vertical transportation of materials and human resources has gained greater importance. Extensive research has been conducted on reducing lift travel time between floors, optimizing lift systems design, optimizing lift movement paths and determining the sequence of floor travel, managing lift energy consumption, and floor zoning. However, the optimization of lift installation locations and quantities has not been examined so far. The use of lifts in construction projects incurs multiple costs, including rental or purchase costs, energy consumption during vertical transportation of materials, and operator salaries. One of the main solutions to reduce these costs is to minimize the duration of lift usage, which, by delivering the required materials on time, can also reduce the project's execution time. The installation costs of lifts may also vary at different candidate points due to factors such as weight and dimensional capacity, electricity consumption, the number of visits for monthly or annual maintenance and repair, and lift operator salaries. Additionally, some candidate points may have advantages over other points in terms of the amount of horizontal movement of materials in building floors. These distinctive features present challenges in selecting the optimal installation point. In this article, an integer linear programming model has been proposed to determine the optimal number and location of lift installations. The number of lifts used can affect the number of project working days, and as a result, the optimization is performed simultaneously for the number of working days and the number of lifts. The goal of this optimization model is to minimize the duration of lift usage and the associated costs. Additionally, using this model, the number of project working days is obtained with a balanced distribution of lift activities. To evaluate the effectiveness of the proposed model, it was tested on a case study. The case study involved a 20-story building located in the city of Mashhad, which requires determining the number and location of lifts during the workshop preparation phase. The use of this model can lead to cost reduction and a decrease in the number of project working days.Soil Improvement of Clayey Sand Using Nanoparticle
https://sjce.journals.sharif.edu/article_23525.html
The field of nanotechnology encompasses all technologies that operate on a nanoscale, typically ranging from 1 to 100 nanometers. Nano-particles are the most commonly used materials in this technology. Given the provided definition of nanotechnology, there is a growing interest in exploring its applications in the field of geotechnical engineering. Recently, numerous researchers have directed their efforts toward discovering these applications. This strong interest stems from the unique properties of these particles and their potential to enhance the mechanical and structural characteristics of soil. This article explores the impact of different percentages of calcium oxide and aluminum oxide nanoparticles on the compressive strength of clayey sandy soil with a constant clay content. To achieve this, clayey sandy soil comprising 80% sand and 20% clay, after being treated with varying percentages (0.05%, 0.1%, and 0.2% by dry soil weight) of nanoparticles, including aluminum oxide and calcium oxide, in three different curing times of 7, 14 and 28 days was tested for unconfined compressive strength. The results indicate that samples containing 0.05%, 0.1%, and 0.2% aluminum oxide nanoparticles after 28 days of curing experienced a 24.92%, 46.78%, and 43.28% increase in strength, respectively, compared to the control sample. Similarly, the increase in strength for samples with calcium oxide nanoparticles was 18.73%, 40.43%, and 36.72%, respectively. According to the findings, the curing time did not have a significant effect on strength improvement, and the optimum percentage for both types of nanoparticles was determined to be 0.1%. Further analysis of stress-strain curves revealed that samples with aluminum oxide nanoparticles exhibited a more brittle behavior compared to those with calcium oxide nanoparticles. Subsequently, for microstructural investigations, the samples were analyzed using Field Emission Scanning Electron Microscopy (FESEM). The microstructural examinations demonstrated better compactness among the treated samples, indicating improved microstructural characteristics in the nanoparticle-amended soils.Evaluation of the widely-used equations of Hydraulic Loss Calculation and Calibration of the Hazen-Williams Equation in Drip Irrigation Laterals
https://sjce.journals.sharif.edu/article_23556.html
In designing of drip irrigation systems, Hazen-William’s equation is usually used to determine the hydraulic head loss. The mentioned equation is suggested for pipes with diameters greater than 75 mm and flow rates above 2.3 l/s. However, for trickle irrigation lateral pipes with diameters from 16 to 32 mm are generally used. In this case, the calculated hydraulic head loss is lower than the actual hydraulic head loss, and subsequently, the hydraulic pressure at the desired point will be lower than the required value; In other words, the output flow from the droppers will be reduced and the uniformity of water distribution will be less than the expected amount. Herein, using laboratory models and the use of polyethylene pipes with a diameter of 16, 20, 25 and 32 mm, the amount of hydraulic loss was measured for different flow rates and according to the permissible velocity limits. Hydraulic pressures were measured using data Logger, one record for each second, and the discharge was adjusted volumetrically. To control the discharge and the hydraulic pressure, a by-pass pipe was installed on the physical model. The amount of hydraulic head loss was measured for different flow rates in the permissible flow velocity range (1-2 m/s). Then, by analyzing the recorded data, a new relationship was obtained that calculates the amount of hydraulic head loss in 16 to 32 mm pipes as a function of flow rate and pipe diameter. The Hazen-Williams equation was compared with the results of Moody, Churchill and Colebrook methods, as well as the actual measured values. According to the results, the largest error between the measured and the calculated head loss was for the Colebrook & White equation for the 25 mm pipe and the smallest error was for the same equation for the 32 mm pipe. The obtained relationship is recommended for polyethylene pipes with diameter of 16 to 32 mm and with Reynolds number above 2000 with high confidence. One of the advantages of the obtained relationship is its independence from the Hazen-Williams roughness coefficient and its remarkable accuracy.Experimental study of seismic behavior and modification of the failure region of mechanical bar splices
https://sjce.journals.sharif.edu/article_23557.html
The problem of overcrowding at the junction of the rebars is very significant, particularly for seismic details. Due to bar length limits, splicing of reinforcing bars is unavoidable in reinforced concrete (RC) structures and may alter the overall behavior of structures under static and dynamic stresses. Mechanical couplers can thus offer an appealing solution that eliminates the disadvantages of traditional reinforcement splicing. In the mechanical splice method, couplers are rigid components that are used to join reinforcement bars together. According to existing research, the failure mechanism of a thread splice under tensile and cyclic loads has not been sufficiently investigated. In addition, the use of the thread splice needs further investigation in the plastic hinge areas of ductile members in seismic areas. In this study, two types of patches are introduced by modifying the method of making a threaded splice and combining it with rotary friction welding. The goal is to modify the coupler's failure area with a threaded bar and use it in the plastic hinge areas of ductile members in seismic areas. The splice area in the suggested method is large. Two techniques are used to increase the splice area: cold rolling and rotating friction welding. In total, 96 samples were tested (three repeated samples of each type). Threaded couplers (TC), oversize-threaded couplers (OTC), rotary friction welding splices with threaded couplers (RFWTC), and non-spliced (NS) reference specimens were tested with and without concrete in uniaxial tensile and cyclic tests. Evaluations were conducted on the sensitivity to bar diameter, bar strength, ductility, energy absorption, and failure mode performance. The RFWTC and OTC exhibited superior performance in terms of strength, ductility, energy absorption, and failure mode, making them appropriate for use in high seismic zones. The TC is also suitable for use in zones with low to medium seismic activity. Furthermore, the anticipated model is enough for estimating the threaded couplers' ultimate tensile strength.Investigating the effect of accelerating/decelerating motion of a moving mass
on the out-of-plane dynamics of horizontally curved beams
https://sjce.journals.sharif.edu/article_23563.html
Horizontally curved beams (HCBs) not only are capable to meet some architectural and aesthetic requirements, but can also offer structural advantages in many engineering applications. Due to inherent complexities existing in the treatment of the problems dealing with dynamic actions on HCBs, the dynamic behavior of such salient elements is not essentially well understood. Therefore, in order to address the identified gap concerning the motion type effects of a moving mass on the dynamics of HCBs, the current study deals with assessing how the accelerating/decelerating conditions do contribute to the out-of-plane response of HCBs under the excitation of a moving mass. In this regard, the governing dynamic equations are developed by taking care of the centripetal force, Coriolis acceleration, and inertial actions of the moving mass. Employing the method of separation of variables, and exercising sinusoidal modal functions, the discretized system of differential equations in the matrix form are distilled and solved through application of standard numerical procedures. Spectral responses in terms of the out-of-plane displacement and bending moment are then obtained for various influential parameters. The veracity of the results is also validated against the available data addressed in the technical literature. Through a comprehensive parametric study, the effect of the key parameters, including the central subtended angle and length of the HCB, as well as the mass, initial velocity, and increasing/decreasing acceleration of the moving mass is evaluated on the out-of-plane displacement and bending moment of the supporting HCB. The results of this study suggest that in the accelerating mode, the out-of-plane displacement and bending moment spectra are magnified up to 18.11 and 27.53 percent in comparison with the spectral values corresponding to the constant-velocity mode. On the other hand, in the decelerating condition, the out-of-plane displacement and bending moment spectra are respectively alleviated up to 41.59 and 42.05 percent.Evaluation of the efficiency of metaheuristic algorithms in optimal design of pile wall retaining systems
https://sjce.journals.sharif.edu/article_23564.html
The effectiveness of the application of the metaheuristic algorithms in the optimal design of retaining structures is investigated in this paper. For this purpose, an on-going Tabriz metro station project with a deep excavation pit is selected here as a case study. The retaining system of the project consists of secant pile walls supported by a layer of struts. The piles have circular section consisting of reinforced concrete cores covered by steel sleeves and the struts are made of steel rectangular hollow sections. A detailed finite element model is developed in OpenSees platform including all the constructional process in order to perform static analyses. Four different metaheuristic algorithms, namely Genetic, Particle swarm optimization, Bee, and Biogeography-based algorithms are chosen for the optimization problem. The pile external diameter, the steel tube stiffness, the number of longitudinal bars inside the concrete core and their diameters, the center-to-center spaces of the pile elements, the dimensions of structs and their center-to-center spaces, the location of the structs in depth and the buried depth of pile elements are selected as optimization variables. The total cost of the retaining system is considered as an objective function which should be minimized in the design space of the variables. For the optimization purpose, an integration of OpenSees software with MATLAB platform is done to join the modeling space with the mentioned optimization algorithms. The number of iterations for each run is assumed to be 400, which is also considered as a termination criterion. The optimization process is performed 50 times and the best response is reported here. The results demonstrate an excellent performance of Genetic algorithm in obtaining the optimum solution respect to other three considered algorithms. It exhibits a proper standard deviation and convergence rate in producing the optimum response. It is shown that the soil stress is increased in the depth where struts are installed, while they are reduced near the ground level, where the deflection of piles creates the active situation for soil. This is true considering the results of all algorithms. Proceeding the excavation phase increases the soil stress as well as the pile deformation. It can be also obtained that providing a layer of strut seems necessary for reducing pile movements as well as their buried depth.Development of Hybrid Cat Swarming algorithm with genetic operators to solve Vehicle Routing Problem with time window constraint
https://sjce.journals.sharif.edu/article_23565.html
Efficient transportation of goods is crucial for cost reduction, improved delivery time, and enhanced service quality. Advanced logistics systems analyze data to find the most efficient routes. This minimizes fuel consumption and decreases transportation costs. The Vehicle Routing Problem with Time Window Constraints (VRPTW) is a classic optimization problem in the field of operations research and logistics. It is a challenging optimization problem in logistics, classified as NP-hard. Hybrid approaches combine multiple optimization techniques to improve the quality and efficiency of solutions. This paper presents a hybrid cat swarming algorithm that utilizes genetic operators to effectively address the Vehicle Routing Problem with Time Window Constraints problem. The goal is to determine the optimal routes for the vehicles, considering both the vehicle capacity constraints and the time window constraints at each customer location. In this paper the objective function of the algorithm aims to minimize both the total distance traveled and the number of vehicles utilized, ensuring efficient and cost-effective routing. The hybrid cat swarming algorithm proposed in this study offers a novel approach to tackle the challenges posed by the VRPTW problem. By integrating genetic operators such as crossover and mutation, the algorithm enhances performance and improves the quality of solutions. Its primary objective of minimizing total distance and vehicle usage guarantees efficient and economically viable routing strategies. To evaluate the effectiveness of the algorithm, it was tested using a simulated dataset of salmon samples as a benchmark. For samples comprising 50 customers, an improvement of up to 48 to 59 percent in previous response rates has been achieved. For samples comprising 100 customers, optimal global responses, as obtained from previous articles, have been observed in several instances. The proposed algorithm is suitable for transportation and logistics systems with limited customers and leads to cost reduction, improved delivery times, and increased service quality.Lap shear-prestressed bond test to evaluate prestressed FRP concrete joint
https://sjce.journals.sharif.edu/article_23566.html
Abstract:
The use of FRP composites as an effective method for strengthening reinforced concrete structures has been a subject of research due to its numerous benefits. A common failure mode in the application of these composites is the debonding of the FRP sheet from the concrete surface, which can sometimes reduce the capacity of these composites to as low as 10% of their total capacity. As a result, researchers have begun to prestress the FRP sheets and strengthen them with prestressed FRP to optimize the efficiency of these materials. A crucial aspect in the strengthening of a reinforced concrete member with an FRP sheet is the examination of the connection behavior between the FRP sheet and concrete. The significance of this issue has led to dedicated research and experimentation in this field. In this study, a prestress-lab shear test was employed for the first time to investigate the bond behavior of prestressed FRP composites-to-concrete joints. Additionally, the particle image velocimetry (PIV) method was used for result analysis. To verify the effectiveness of this method, eight tests were conducted on prism specimens measuring 150×150×350 mm. The strengthening methods of the specimens involved the use of the external bonded reinforcement (EBR) and external bonded reinforcement on grooves (EBROG) methods. Furthermore, the specimens were prestressed at different levels, including 0%, 20%, and 30% of the ultimate strain of FRP composites. This study examined the specimens in terms of bond strength capacity, failure mode, and stress and strain distribution on the joint surface. The results showed that prestressing increased the bond strength by 70% in the EBR method. Moreover, the bond strength of EBROG specimen with 20% prestressing increased by 123% compared to the control specimen. These findings indicate that prestressing using the EBROG method is a viable technique for enhancing the performance of FRP-to-concrete joints.Derivation and parametric evaluation of frequency response functions of elastic and inelastic structures under pulse-type ground excitations
https://sjce.journals.sharif.edu/article_23567.html
In this paper, the elastic and inelastic responses of yielding single-degree-of-freedom (SDOF) systems with bilinear hysteretic behavior subjected to pulse-type near-fault ground motions are investigated. The evaluated responses are the relative displacement and total acceleration of the structure in the form of frequency response functions. The analytical pulse model proposed by Mavroeidis and Papageorgiou, whose input parameters have clear physical meanings, is used to represent near-fault ground motions. A parametric study with six dimensionless variables is performed to evaluate the frequency response functions of SDOF structures. Out of these six variables, two variables are related to the input pulse excitation, another two variables are related to the properties of the structure, and the last two involve the ratio between the excitation and the structure; they are: the number of pulses, the pulse phase angle (shape), the damping ratio of the structure, the post-yield stiffness ratio of the structure, the excitation- (pulse-) to-structure frequency ratio, and the ratio of the excitation (pulse) amplitude to the yield strength of the structure. The obtained results reveal a notable similarity in the frequency response functions of total acceleration and relative displacement for linear elastic SDOF structures. However, the characteristics of these two responses are completely different when yielding occurs in bilinear SDOF structures. Furthermore, the effect of various parameters of the structure and the input pulse on the structural responses differs depending on the linear or nonlinear behavior of the system. For example, in a linear elastic structure, the maximum frequency responses of displacement and total acceleration always increase with increasing the number of pulses; however, in an elastic-perfectly plastic structure or in a bilinear structure with small post-yield stiffness ratio, the maximum frequency response of total acceleration remains almost constant regardless of the number of input pulses when yielding occurs. For the displacement response, the number of pulses that cause the maximum frequency response is different at different levels of nonlinear behavior.Enhancing the durability and elastic modulus of oil-contaminated soils in wet-dry cycles through stabilization with traditional materials
https://sjce.journals.sharif.edu/article_23568.html
Considering that the infrastructures in different regions experience different weather cycles that can lead to the creation of minor surface cracks to be noticeable, it is necessary to understand the durability behavior of soils. Although previous studies have extensively investigated the Strength behavior of oil-contaminated soil, there is still no accurate understanding of the durability of oil-contaminated soil against wet-dry cycles. To fill these gaps, this research is focused on the durability characteristics of oil-contaminated soils. For this purpose, a series of laboratory tests were conducted to evaluate compaction, durability and microstructural analyses. In that regard, the soil was contaminated with oil in concentrations of 4, 7 and 10% and then stabilized with lime and cement in concentrations of 0, 3, 6 and 9% separately. Initial laboratory experiments, including Atterberg limits and compaction tests, were conducted. Subsequently, durability tests were performed to examine wet-dry cycles in 1, 3, and 6 cycles on oil-contaminated soil samples, as well as those stabilized with cement and lime. The results demonstrated that the highest durability was observed in the sample containing 4% oil and 9% cement in the 6th cycle, showing a 42% increase in resistance compared to a similar sample with the same percentage of oil and cement in the 3rd cycle. Additionally, the elasticity modulus of the oil-contaminated soil sample with 4% oil and stabilized with 6% lime was 2 times that of the 1st cycle in the 3rd cycle and 2.8 times that of the 3rd cycle in the 6th cycle. Microscopic analysis using electron field emission microscopy unveiled that the incorporation of cement and lime as stabilizing agents resulted in a denser and more compact structure of oil-contaminated soil. This comprehensive research endeavor seeks not only to advance the management practices of contaminated soils but also to uphold the conservation of natural resources while offering an alternative solution for the construction of secondary access roads.Intelligent assessment of damage and prediction of seismic damage spectrum under the effect of Near-Fault earthquakes in Iran
https://sjce.journals.sharif.edu/article_23569.html
Predicting seismic damage spectra, capturing both structural and earthquake features, is crucial for design of new buildings and also for resilience evaluation of existing ones. The research objective of this article is to accurately assess and predict the seismic damage spectrum caused by earthquakes in Iran using gene expression programming. Gene expression programming is a method for learning and optimization rooted in genetic principles and molecular biology. For this purpose, a single-degree-of-freedom nonlinear system is considered, along with a collection of earthquake records from Iran, to exact computation of damage spectrum. Subsequently, a mathematical model is developed through the application of gene expression programming and genetic programming algorithms. The Park-Ang damage index is used to computing the level of seismic damage or damage spectra. Both the structural characteristics and seismic properties are significant factors in predicting of the seismic damage spectrum model. Finally, a simplified equation has been suggested for assessing the potential seismic damage spectrum of the structures exposed to ground motions in Iran capturing both structural and earthquake features. This study demonstrates the significant impact of structural and seismic parameters on the seismic damage spectrum, highlighting that an increase in the resistance reduction factor correlates with a rise in damage spectrum across structures of varying vibration periods. The changes in the damage spectrum indicate that as the ductility coefficient increases, the spectral damage decreases. The impact of the damping ratio on SDOF systems in the damage spectrum demonstrates that an increase in the damping ratio leads to an increase in the damage spectrum. The effects of post-yield stiffness ratio in SDOF systems for the damage spectrum showed that a higher stiffness ratio results in the structure exhibiting less damage. The relationship between the Park-Ang index constant and the damage spectrum is such that an increase in the Park-Ang index constant leads to a corresponding rise in the damage spectrum. The influence of soil type on the damage spectrum is comparatively less significant than the impacts of the other parameters discussed.Investigation and numerical study of the behavior of steel plate shear wall with precast concrete frame
https://sjce.journals.sharif.edu/article_23570.html
In this research, 8 numerical models of steel shear wall with galvanized sheets and black sheet in precast concrete frames and steel frames with jointed beam to column connection and bending were investigated by performing static analysis in nonlinear mode under the effect of cyclic load according to ACI-374 loading protocol. In this study, the laboratory sample investigated by Wayne et al. was used to validate the numerical models. In the models with prefabricated concrete frame with joint beam to column connection, 25 x 25 cm concrete cross-section of 3 meters length was used for beams and columns. 6 rebars with a diameter of 22 mm were used for the column and 4 rebars with a diameter of 14 mm were used for the beam. In both beam and column elements, 8 mm diameter and 150 mm distance from each other is used. In order to connect the beam to the column, a corner of 150L was used as a seat under the beams. Also, the thickness of the steel sheets is considered to be 1 mm, which was connected to the boundary elements of the beam and column using a steel strip with a width of 10 cm and a thickness of 1 cm. This steel strip is buried in concrete by means of rebars with a diameter of 20 mm. Also, in order to connect the columns to the rigid floor, the columns were placed in a pot with dimensions of 290 x 290 and thickness of 10 mm. The results of this research showed that by changing the connection of the beam to the column from joint to bending, the parameters of initial stiffness, ultimate strength and energy absorption have increased significantly. In the models with prefabricated concrete frames with joint beam to column connection, the concrete beams and columns remain in elastic state until the end of analysis. Also, the results showed that the average value of the displacement magnification factor in the numerical models has increased by 78% compared to the value suggested in the ASCE publication for special steel shear walls, and in the models with a prefabricated concrete frame with beam-to-joint column connection, the ductility factor is an average Compared to similar models, the connection of the beam to the bending column has increased by 52%.Experimental study of a new metallic damper using hourglass fuse
https://sjce.journals.sharif.edu/article_23571.html
Being one of the world’s most earthquake-prone countries, iran has suffered thousands of live lost in earthquake throughout the past decays. Metallic yielding damper is a specific kind of passive structural control device which has shown effective behavior in past earthquakes. In this paper a new metallic yielding damper made of number of hourglass shape pins (HSP) for enhancing the seismic behavior of building structures is purposed and has been experimen-tally evaluated under monotonic and qusi-static cyclic loading. The speciments were undergo drift levels beyond the expected design ones to identify its complete behavior and all posibale failure modes. The main feature of purposed damper is replaceable hourglass shape pins (HSP) fuse. For this purpose conventional reinforcing steel bars in constructional practice have been shaped by lathe machine in the form of hourglass pins. These hourglass pins dissi-pate energy mostly through flexural and tensile mechanism when subjected to inelastic cyclic deformation and can be replaced easily in case of failure after severe earthquakes. Moreover this damper is economical, easy to install and build with no special fabrication technique. The hysteresis behavior and other important parameters of the damper such as capacity of energy dissipation, effective stiffness and equivalent damping and the effect of how the HSP is connected to its supporting plates (welding or connection by utilizing nuts) on these behav-iors has been studied through laboratory tests. Simplified analytical procedure using plastic analysis and simple rules of mechanics of solids was found to accurately predict the HSP be-havior and found to be consistent with experimental results. The experimental results indicate the bars successfully performed their function as energy absorbers and fuses in all specimens but the way HSP is connected to supporting plates can greatly affects its behavior. In the case of nut connection, a significant amount of pinching was observed in hysteresis loops which is the result of residual displacements between HSP and supporting plates and welding the bars to plates seems to solve this problem, resulting in fat and sustainable hysteresis loop without any significant strength and stiffness degradation and good energy dissipation capacity (with respect to HSP’s low weight) of the purposed damper was reached. Although both types of connections have shown acceptable behavior throughout cyclic loading, but total energy absorption capacity and equivalent viscous damping in welded connection in comparison with nut connection have been improve by 91 and 53 percent respectively.