Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
A COMPARISON OF THREE AND TWO DIMENSIONAL ANALYSES OF ROCKFILL DAMS IN NARROW VALLEYS; CASE STUDY: VANYAR DAM
A COMPARISON OF THREE AND TWO DIMENSIONAL ANALYSES OF ROCKFILL DAMS IN NARROW VALLEYS; CASE STUDY: VANYAR DAM
3
11
882
FA
M.
Honarmand
Faculty of Engineering Arak University
M.
Derakhshandi
Dept. of Civil Engineering Science and Research Branch Islamic Azad University
A.H.
Sadeghpour
Faculty of Architecture Kashan University
Journal Article
2012
09
26
A two dimensional analysis on the largest cross-section of earth dams gives accurate results, provided that the dam is located in a U-shape valley. The Vanyar Dam is constructed in a narrow valley. According to the geometry of the valley, there is not a plane strain condition throughout the long side of the dam. In this research, the results of three and two dimensional numerical analyses of the Vanyar dam are compared, in terms of settlement, pore water pressure and total vertical stress. These analyses are carried out by the finite difference method, using FLAC-3D and FLAC-2D software packages. The numerical results obtained for the settlements are verified by comparing them with measured settlement data. The settlements obtained by three and two dimensional analyses in the upper half of the height of the dam are in good agreement. Moreover, it is shown that for the lower half of the height of the dam, the settlements obtained by two dimensional analyses are generally greater than those obtained by three dimensional analyses. In the core axis at cross section C, the maximum settlement of 88.14 cm is recorded at the height of 48 m from the bedrock ($\frac{z}{h}=0.55$), which is about 1\% of the dam height. Furthermore, the settlements obtained by three dimensional numerical analyses are in better agreement with measurement data, compared to two dimensional analyses. It indicates that the results of two dimensional numerical analyses of the earth dams located in the narrow valley are not sufficiently accurate. The total vertical stresses of the three and two dimensional numerical analyses are compared with those recorded by the pressure cells. To prevent damage to the pressure cells, light compaction is performed around the instruments. Therefore, a low stiffness area is formed around the pressure cells. This phenomenon is called local arching, which causes the vertical stresses recorded by pressure cells to be less than those numerically calculated. Moreover, the pore water pressures recorded by the piezometers are consistent with numerical results.
A two dimensional analysis on the largest cross-section of earth dams gives accurate results, provided that the dam is located in a U-shape valley. The Vanyar Dam is constructed in a narrow valley. According to the geometry of the valley, there is not a plane strain condition throughout the long side of the dam. In this research, the results of three and two dimensional numerical analyses of the Vanyar dam are compared, in terms of settlement, pore water pressure and total vertical stress. These analyses are carried out by the finite difference method, using FLAC-3D and FLAC-2D software packages. The numerical results obtained for the settlements are verified by comparing them with measured settlement data. The settlements obtained by three and two dimensional analyses in the upper half of the height of the dam are in good agreement. Moreover, it is shown that for the lower half of the height of the dam, the settlements obtained by two dimensional analyses are generally greater than those obtained by three dimensional analyses. In the core axis at cross section C, the maximum settlement of 88.14 cm is recorded at the height of 48 m from the bedrock ($\frac{z}{h}=0.55$), which is about 1\% of the dam height. Furthermore, the settlements obtained by three dimensional numerical analyses are in better agreement with measurement data, compared to two dimensional analyses. It indicates that the results of two dimensional numerical analyses of the earth dams located in the narrow valley are not sufficiently accurate. The total vertical stresses of the three and two dimensional numerical analyses are compared with those recorded by the pressure cells. To prevent damage to the pressure cells, light compaction is performed around the instruments. Therefore, a low stiffness area is formed around the pressure cells. This phenomenon is called local arching, which causes the vertical stresses recorded by pressure cells to be less than those numerically calculated. Moreover, the pore water pressures recorded by the piezometers are consistent with numerical results.
https://sjce.journals.sharif.edu/article_882_6c3cf77d52820cd0fe646d38bc2145ca.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
A STUDY ON THE STRESS-\\DILATANCY BEHAVIOR OF ANZALI SAND
A STUDY ON THE STRESS-\\DILATANCY BEHAVIOR OF ANZALI SAND
13
20
883
FA
A.
Hajiani Boushehrian
School of Engineering Shiraz Azad University
0000-0003-3612-5641
M.
Veiskarami
Civil and Environmental Engineering Shiraz University
A.
Vosooghi
Civil and Environmental Engineering Shiraz University
M.
Hamidzadeh
Faculty of Engineering University of Guilan
Journal Article
2012
11
04
Since the late 1960s, several constitutive models have been developed for sands describing their stress-strain ehavior. Most of these models were established based on a measure of the plastic work and some yield criteria, among them being the Lade-Duncan model. It was in the mid 1980s when the stress level concept was found to be an appreciable factor controlling the behavior of sands. The stress level is defined as the confining pressure or the vertical stress on a shear plane, which differs from point to point in a granular medium under a system of external loads. Based on this concept, a number of strength - dilatancy models were developed for sands. The shear strength of sand is related to the level of stress and the type of test in which the shear strength parameters are measured. In this research, the geotechnical properties of Anzali Sand (located in Guilan province, northern Iran, on the coastal line of the Caspian Sea) are investigated, in accordance with its strength -dilatancy behavior. As this particular type of sand is abundant in northern Iran, such research appears to be worthwhile, as most seismic geotechnical investigations, as well as other conventional studies, deal with the strength of this sand. For example, the liquefaction potential and the post - liquefied behavior of Anzali Sand are all based on a strength -dilatancy model, the behavior of which was measured by a number of different direct shear tests, as the most popular and available tests for sand. The dilative behavior of Anzali Sand was generalized to capture its relevant properties. Findings indicate that Anzali Sand, at least in the direct shear tests; does not show a very interpretable behavior, possibly due to inherent errors within the direct shear test, although a rather reasonable relationship between the peak and critical state friction angles was found as functions of the stress level and the density index.
Since the late 1960s, several constitutive models have been developed for sands describing their stress-strain ehavior. Most of these models were established based on a measure of the plastic work and some yield criteria, among them being the Lade-Duncan model. It was in the mid 1980s when the stress level concept was found to be an appreciable factor controlling the behavior of sands. The stress level is defined as the confining pressure or the vertical stress on a shear plane, which differs from point to point in a granular medium under a system of external loads. Based on this concept, a number of strength - dilatancy models were developed for sands. The shear strength of sand is related to the level of stress and the type of test in which the shear strength parameters are measured. In this research, the geotechnical properties of Anzali Sand (located in Guilan province, northern Iran, on the coastal line of the Caspian Sea) are investigated, in accordance with its strength -dilatancy behavior. As this particular type of sand is abundant in northern Iran, such research appears to be worthwhile, as most seismic geotechnical investigations, as well as other conventional studies, deal with the strength of this sand. For example, the liquefaction potential and the post - liquefied behavior of Anzali Sand are all based on a strength -dilatancy model, the behavior of which was measured by a number of different direct shear tests, as the most popular and available tests for sand. The dilative behavior of Anzali Sand was generalized to capture its relevant properties. Findings indicate that Anzali Sand, at least in the direct shear tests; does not show a very interpretable behavior, possibly due to inherent errors within the direct shear test, although a rather reasonable relationship between the peak and critical state friction angles was found as functions of the stress level and the density index.
https://sjce.journals.sharif.edu/article_883_210f760a89db30aa72ca258a3483cc7f.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
STRUCTURAL CONTROL WITH ACTIVE TUNED MASS DAMPER BY TYPE 2 FUZZY LOGIC CONTROLLER FOR SEISMIC EXCITATION
STRUCTURAL CONTROL WITH ACTIVE TUNED MASS DAMPER BY TYPE 2 FUZZY LOGIC CONTROLLER FOR SEISMIC EXCITATION
21
32
884
FA
H.
Shariatmadar
Dept. of Civil Engineering Ferdowsi University of Mashhad
0000-0001-5966-3317
S.
Golnargesi
Dept. of Civil Engineering Ferdowsi University of Mashhad
Journal Article
2012
12
17
This study focuses on the application of an interval type 2 fuzzy logic controller in an active tuned mass damper (ATMD) for the purpose of decreasing structural response under different types of earthquake excitation. One of the main shortcomings of type 1 fuzzy logic systems is their inability to consider uncertainty in the fuzzy rule base data. Type 2 fuzzy logic systems have the ability to handle this problem, and also take into account uncertainty in loading and structural behavior. To evaluate the efficiency of the proposed control method (interval type 2 fuzzy logic control method), a realistic eleven story shear building, located in Rasht City, Iran, was used. The active tuned mass damper (ATMD) is placed on the top floor of an eleven story shear building. This building has been analyzed under different time history records, including Hachinohe and El Centro earthquakes as far-field ground motions, and Kobe and Northridge earthquakes as near-field ground motions. The results obtained by the proposed control method were compared with those of the uncontrolled structure, the structure with the tuned mass damper (TMD) and the structure with the active tuned mass damper (ATMD) with a type 1 fuzzy logic controller. Numerical results indicated that the interval type 2 fuzzy logic controller used in the active tuned mass damper (ATMD) is very effective in reducing structural response under the effect of different base excitations. The comparison of time history responses for a type 1 fuzzy logic controller and an interval type 2 fuzzy logic controller also show that the displacement response obtained using an interval type 2 fuzzy logic controller is smaller and smoother than that obtained by a type 1 fuzzy logic controller. In view of the external control force needed to reduce the building response, the magnitude of the control force in the type 2 fuzzy logic controller is little more than that needed for the type 1 fuzzy logic controller with the average being about 8 percent.
This study focuses on the application of an interval type 2 fuzzy logic controller in an active tuned mass damper (ATMD) for the purpose of decreasing structural response under different types of earthquake excitation. One of the main shortcomings of type 1 fuzzy logic systems is their inability to consider uncertainty in the fuzzy rule base data. Type 2 fuzzy logic systems have the ability to handle this problem, and also take into account uncertainty in loading and structural behavior. To evaluate the efficiency of the proposed control method (interval type 2 fuzzy logic control method), a realistic eleven story shear building, located in Rasht City, Iran, was used. The active tuned mass damper (ATMD) is placed on the top floor of an eleven story shear building. This building has been analyzed under different time history records, including Hachinohe and El Centro earthquakes as far-field ground motions, and Kobe and Northridge earthquakes as near-field ground motions. The results obtained by the proposed control method were compared with those of the uncontrolled structure, the structure with the tuned mass damper (TMD) and the structure with the active tuned mass damper (ATMD) with a type 1 fuzzy logic controller. Numerical results indicated that the interval type 2 fuzzy logic controller used in the active tuned mass damper (ATMD) is very effective in reducing structural response under the effect of different base excitations. The comparison of time history responses for a type 1 fuzzy logic controller and an interval type 2 fuzzy logic controller also show that the displacement response obtained using an interval type 2 fuzzy logic controller is smaller and smoother than that obtained by a type 1 fuzzy logic controller. In view of the external control force needed to reduce the building response, the magnitude of the control force in the type 2 fuzzy logic controller is little more than that needed for the type 1 fuzzy logic controller with the average being about 8 percent.
https://sjce.journals.sharif.edu/article_884_170c944978496731ba71f34c25826a34.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
EXPERIMENTAL INVESTIGATION OF THE BEHAVIOR OF LIGHTWEIGHT CONCRETE FOOTING REINFORCED WITH GFRP REBAR
EXPERIMENTAL INVESTIGATION OF THE BEHAVIOR OF LIGHTWEIGHT CONCRETE FOOTING REINFORCED WITH GFRP REBAR
33
40
885
FA
A.
Vatani Oskouei
Dept. of Civil Engineering Shahid Rajaee Teacher Training University
0000-0001-6489-8508
M.
Pirgholi Kivi
Technical and Engineering Complex
Moghadas Ardebili Institute of Higher Education
H.
Araghi
University of Applied Sciences Natural Disaster Research Center
Journal Article
2012
12
16
The subject of pre-fabrication plays an important role in the construction of standard structural members. To this end, it is needed to reduce the weight of these pre-fabricated members for ease of transportation. The application of lightweight concrete (LWC) and Fiber Reinforced Polymer (FRP) bars instead of normal concrete and steel bars inside the foundations is helpful in reducing the weight of pre-fabricated foundations.Application of Glass Fiber Reinforced Polymer (GFRP) bars in construction practices has been developed because of its unique properties, including corrosion resistance, high tensile strength, ease of performance and availability. Furthermore, the GFRP shows different behavior in concrete members, compared with normal steel reinforced bars. This behavior needs more consideration to show accuracy by appropriate testing methods.In this study, four specimens of full scale concrete footing reinforced by GFRP bars on the soil bed have been investigated. One of the specimens is made of normal weight concrete and three others are made of structural lightweight concrete. One of the lightweight footings contains polymer fiber, too. The constructed foundations were placed under compressive force, then the data related to LVDTs and strain gauges was recorded using a data logger; after that, it was analyzed.The results of this study indicate that further study is needed for real application of ACI relations to estimate the ultimate strength of lightweight concrete footings reinforced by GFRP bars. It was also concluded that the concrete mix can affect the maximum bearable load of footing, while adding fiber to concrete mix can be useful in order to control crack width. According to results, strain in normal weight footing bars gets almost 55% of the ultimate strain of the bar, because of the better band between the footing concrete and the GFRP bar. In lightweight concrete footing, the maximum strain gets 27% of the ultimate strain of the bar.
The subject of pre-fabrication plays an important role in the construction of standard structural members. To this end, it is needed to reduce the weight of these pre-fabricated members for ease of transportation. The application of lightweight concrete (LWC) and Fiber Reinforced Polymer (FRP) bars instead of normal concrete and steel bars inside the foundations is helpful in reducing the weight of pre-fabricated foundations.Application of Glass Fiber Reinforced Polymer (GFRP) bars in construction practices has been developed because of its unique properties, including corrosion resistance, high tensile strength, ease of performance and availability. Furthermore, the GFRP shows different behavior in concrete members, compared with normal steel reinforced bars. This behavior needs more consideration to show accuracy by appropriate testing methods.In this study, four specimens of full scale concrete footing reinforced by GFRP bars on the soil bed have been investigated. One of the specimens is made of normal weight concrete and three others are made of structural lightweight concrete. One of the lightweight footings contains polymer fiber, too. The constructed foundations were placed under compressive force, then the data related to LVDTs and strain gauges was recorded using a data logger; after that, it was analyzed.The results of this study indicate that further study is needed for real application of ACI relations to estimate the ultimate strength of lightweight concrete footings reinforced by GFRP bars. It was also concluded that the concrete mix can affect the maximum bearable load of footing, while adding fiber to concrete mix can be useful in order to control crack width. According to results, strain in normal weight footing bars gets almost 55% of the ultimate strain of the bar, because of the better band between the footing concrete and the GFRP bar. In lightweight concrete footing, the maximum strain gets 27% of the ultimate strain of the bar.
https://sjce.journals.sharif.edu/article_885_0efe32849d230d7f53049ddc4a4b0c60.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
EXPERIMENTAL STUDY ON STRENGTHENING OF RC CONNECTIONS WITH FRP SHEETS BY EMBEDDING SURFACE GROOVES
EXPERIMENTAL STUDY ON STRENGTHENING OF RC CONNECTIONS WITH FRP SHEETS BY EMBEDDING SURFACE GROOVES
41
50
896
FA
A.
Reza Sattari
Dept. of Civil Engineering Semnan University
M.
Kazem Sharbatdar
Dept. of Civil Engineering Semnan University
0000-0001-6106-1235
A.
Dalvand
Dept. of Civil Engineering Semnan University
Journal Article
2012
12
31
In this research, an experimental study on the strengthening of RC connections using FRP sheets has been undertaken. The innovation of this research is in using narrow grooves for concrete surface preparation in the joint panel zone and the ductile zone of the beam, in order to increase adherence between FRP sheets and the concrete surface, and in preventing their debonding. For this purpose, four RC connections were made and tested under constant axial load and increasing cyclic loading. The first connection, as the standard reference specimen, had closed tie spacing in the ductile regions of the beam, column and panel zone. The second connection, as a weak reference specimen, did not have these conditions in all regions. Two other connections, which had properties like the weak reference specimen, were strengthened using two different strengthening patterns with FRP sheets. In the first strengthened connection, an ordinary surface preparation method was performed for installing FRP sheets, and the surface grooving method was used for the second strengthened connection. According to the results, without regarding the closed tie spacing in the weak specimen, ultimate load and ductility were decreased by 25\% and 17\%, respectively, compared to the standard specimen. Shear failure and concrete crushing were prevented in the ductile regions of the beam and panel zone in both strengthened connections. Also, it was observed that in the strengthened connection with a grooving pattern, early debonding of FRP sheets was prevented, and sheets reached their ultimate tensile strength. This specimen had desirable ductility and bearing capacity, similar to the standard specimen. In the final stages of loading in the strengthened specimen with an ordinary surface preparation method, the maximum strain of the U-shaped sheets reached 0.49\%; close to the recommended amount by the design code for the allowed strain of FRP sheets equal to 0.4\%, although half the ultimate rupture strain of sheets. Also, some regions in the borders of the sheets were debonded and by increasing strains, progressive debonding was seen in these regions. But, in the strengthened specimen with the surface grooving method, even no slight debonding was observed, and the maximum strain of sheets was 0.97\%; close to the ultimate rupture strain amount and twice that of the design code amount.
In this research, an experimental study on the strengthening of RC connections using FRP sheets has been undertaken. The innovation of this research is in using narrow grooves for concrete surface preparation in the joint panel zone and the ductile zone of the beam, in order to increase adherence between FRP sheets and the concrete surface, and in preventing their debonding. For this purpose, four RC connections were made and tested under constant axial load and increasing cyclic loading. The first connection, as the standard reference specimen, had closed tie spacing in the ductile regions of the beam, column and panel zone. The second connection, as a weak reference specimen, did not have these conditions in all regions. Two other connections, which had properties like the weak reference specimen, were strengthened using two different strengthening patterns with FRP sheets. In the first strengthened connection, an ordinary surface preparation method was performed for installing FRP sheets, and the surface grooving method was used for the second strengthened connection. According to the results, without regarding the closed tie spacing in the weak specimen, ultimate load and ductility were decreased by 25\% and 17\%, respectively, compared to the standard specimen. Shear failure and concrete crushing were prevented in the ductile regions of the beam and panel zone in both strengthened connections. Also, it was observed that in the strengthened connection with a grooving pattern, early debonding of FRP sheets was prevented, and sheets reached their ultimate tensile strength. This specimen had desirable ductility and bearing capacity, similar to the standard specimen. In the final stages of loading in the strengthened specimen with an ordinary surface preparation method, the maximum strain of the U-shaped sheets reached 0.49\%; close to the recommended amount by the design code for the allowed strain of FRP sheets equal to 0.4\%, although half the ultimate rupture strain of sheets. Also, some regions in the borders of the sheets were debonded and by increasing strains, progressive debonding was seen in these regions. But, in the strengthened specimen with the surface grooving method, even no slight debonding was observed, and the maximum strain of sheets was 0.97\%; close to the ultimate rupture strain amount and twice that of the design code amount.
https://sjce.journals.sharif.edu/article_896_061412e4a03c02f9902576ec55ebbe77.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
COST-BENEFIT ANALYSIS OF CONSTRUCTION AND REHABILITATION OF STEEL BRACED FRAMES WITH INFILL PANELS USING SEISMIC DAMAGE FRAGILITY CURVES
COST-BENEFIT ANALYSIS OF CONSTRUCTION AND REHABILITATION OF STEEL BRACED FRAMES WITH INFILL PANELS USING SEISMIC DAMAGE FRAGILITY CURVES
51
59
888
FA
M.
Ahmadi Pazoki
Dept. of Civil Engineering Tarbiat Modares University
H.
Shakib
Dept. of Civil Engineering Tarbiat Modares University
P.
Mohammadi
Economic Engineering Group Tarbiat Modares University
Journal Article
2013
01
26
Damage from earthquake reconstruction is mainly due to the poor performance of structures under seismic loads. Structural costs include constructional costs, plus all costs related to damage from earthquake reconstruction, maintenance and the management of the structure. The cost of construction for various structures is quite different at different performance levels. A question may arise that if the primary constructional cost is less, will the plan be economical or not? In the case of a positive answer, engineers tend to select the lower performance level. In this paper, a comprehensive comparison has been conducted between the primary cost of construction and econstruction, due to the damage from credible earthquakes, during the useful life of the structure, at various levels of performance. The analysis and design of the structures have been conducted in Perform (3D) package. A structural design criterion was developed to support the proper functioning of the building and reducing earthquake damage. Furthermore, infill panels can increase the stiffness and strength of structures. So, they should be considered in the phase of building design. In this study, steel braced frames with infill panels, with three and six stories, are considered. The frames have three spans, in which X braces have been used in the middle span for all stories. Incremental dynamic analysis (IDA) was carried out, and the performance levels were determined from the IDA curves. Then, fragility curves were obtained for the braced steel frames with infill panels, which show the probability of exceedance from the performance level that the structure had been designed for. To investigate the effect of infill panels on the probabilistic behavior of structures, the fragility curves were obtained for the braced steel frames without infill panels. After that, performance levels were assessed using the cost benefit analysis method. Results show that selection of a higher performance level has more economic justification; and the immediate occupancy (IO) is the most economical performance level for these types of structure. Finally, sensitivity analyses on the results of the cost benefit analysis show that changes in the useful life of structures and minimum absorption rate have no significant sensitivity.
Damage from earthquake reconstruction is mainly due to the poor performance of structures under seismic loads. Structural costs include constructional costs, plus all costs related to damage from earthquake reconstruction, maintenance and the management of the structure. The cost of construction for various structures is quite different at different performance levels. A question may arise that if the primary constructional cost is less, will the plan be economical or not? In the case of a positive answer, engineers tend to select the lower performance level. In this paper, a comprehensive comparison has been conducted between the primary cost of construction and econstruction, due to the damage from credible earthquakes, during the useful life of the structure, at various levels of performance. The analysis and design of the structures have been conducted in Perform (3D) package. A structural design criterion was developed to support the proper functioning of the building and reducing earthquake damage. Furthermore, infill panels can increase the stiffness and strength of structures. So, they should be considered in the phase of building design. In this study, steel braced frames with infill panels, with three and six stories, are considered. The frames have three spans, in which X braces have been used in the middle span for all stories. Incremental dynamic analysis (IDA) was carried out, and the performance levels were determined from the IDA curves. Then, fragility curves were obtained for the braced steel frames with infill panels, which show the probability of exceedance from the performance level that the structure had been designed for. To investigate the effect of infill panels on the probabilistic behavior of structures, the fragility curves were obtained for the braced steel frames without infill panels. After that, performance levels were assessed using the cost benefit analysis method. Results show that selection of a higher performance level has more economic justification; and the immediate occupancy (IO) is the most economical performance level for these types of structure. Finally, sensitivity analyses on the results of the cost benefit analysis show that changes in the useful life of structures and minimum absorption rate have no significant sensitivity.
https://sjce.journals.sharif.edu/article_888_0a113ef6b61820daa5611c870ed8d5ee.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
EVALUATION OF THE EFFECTS OF GEOTECHNICAL PARAMETERS ON THE HYDRO-MECHANICAL BEHAVIOR OF ROCK MASS IN CONCRETE DAM SITES WITH 3D FULLY COUPLED NONLINEAR ANALYSIS
EVALUATION OF THE EFFECTS OF GEOTECHNICAL PARAMETERS ON THE HYDRO-MECHANICAL BEHAVIOR OF ROCK MASS IN CONCRETE DAM SITES WITH 3D FULLY COUPLED NONLINEAR ANALYSIS
61
73
887
FA
A. R.
Naeini
Civil and Environmental Engineering Tarbiat Modares University
M.
Taghi Ahmadi
Civil and Environmental Engineering Tarbiat Modares University
Journal Article
2013
01
01
Dam foundations, as the most unknown media part of a dam-foundation-reservoir system, play important roles in system stability, due to the hydro-mechanical behavior of rock mass, especially after the first impounding. In this research, an equivalent continuum model with fully coupled stress-seepage behavior is developed for the rock foundation. First, the mathematical model and the governing equations of the coupled fields are introduced and then the finite element formulation is derived via Galerkins method. In order to describe the material nonlinearity, anisotropy, effective discontinuities, and alteration of permeability, due to either the closure or opening of rock mass joint systems, a multi-laminate material constitution rule is employed.The role of discontinuities could be paramount in rock mass behaviour. Therefore, effective and consistent modelling of these under normal and shear stresses is proposed. In most three-dimensional analysis programs, Mohr-Coulomb criterion is employed for rock mass modelling, and only a few two-dimensional analysis programs, such as UDEC, enjoy more realistic models of rock mass behaviour, such as that of Barton-Bandis. In this research, the Barton-Bandis constitutive law is developed and implemented for joint modelling in three-dimensional finite element analysis using an equivalent continuum approach. The solution algorithm is based on elasto-viscoplastic analysis with a non-associated flow rule, considering mobilized joint roughness, and explicit time integration.Hydraulic conductivity is based on cubic law, using more recent relationships between mechanical and hydraulic apertures for computing the hydraulic conductivity tensor.The performance of the developed model is examined by an existing hydromechanic test case. The methodology is applied to the case of a gravity dam with its surrounding rock. A sensitivity analysis of the foundation behavior is carried out, due to the variations of geometric parameters such as the number of joint sets, dip and dip direction angles, and scale effects, etc.It is concluded that in some cases, the inclusion of hydro-mechanical interaction effects could increase shear stress several-fold, and, thus, its negligence could lead to obviously non-conservative assessment of foundation behavior.
Dam foundations, as the most unknown media part of a dam-foundation-reservoir system, play important roles in system stability, due to the hydro-mechanical behavior of rock mass, especially after the first impounding. In this research, an equivalent continuum model with fully coupled stress-seepage behavior is developed for the rock foundation. First, the mathematical model and the governing equations of the coupled fields are introduced and then the finite element formulation is derived via Galerkins method. In order to describe the material nonlinearity, anisotropy, effective discontinuities, and alteration of permeability, due to either the closure or opening of rock mass joint systems, a multi-laminate material constitution rule is employed.The role of discontinuities could be paramount in rock mass behaviour. Therefore, effective and consistent modelling of these under normal and shear stresses is proposed. In most three-dimensional analysis programs, Mohr-Coulomb criterion is employed for rock mass modelling, and only a few two-dimensional analysis programs, such as UDEC, enjoy more realistic models of rock mass behaviour, such as that of Barton-Bandis. In this research, the Barton-Bandis constitutive law is developed and implemented for joint modelling in three-dimensional finite element analysis using an equivalent continuum approach. The solution algorithm is based on elasto-viscoplastic analysis with a non-associated flow rule, considering mobilized joint roughness, and explicit time integration.Hydraulic conductivity is based on cubic law, using more recent relationships between mechanical and hydraulic apertures for computing the hydraulic conductivity tensor.The performance of the developed model is examined by an existing hydromechanic test case. The methodology is applied to the case of a gravity dam with its surrounding rock. A sensitivity analysis of the foundation behavior is carried out, due to the variations of geometric parameters such as the number of joint sets, dip and dip direction angles, and scale effects, etc.It is concluded that in some cases, the inclusion of hydro-mechanical interaction effects could increase shear stress several-fold, and, thus, its negligence could lead to obviously non-conservative assessment of foundation behavior.
https://sjce.journals.sharif.edu/article_887_7ce3284b743aefde80ffd9aec500e085.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
DETERMINATION OF APPROPRIATE SAMPLING AREA TO IDENTIFY ROAD POLLUTANTS
DETERMINATION OF APPROPRIATE SAMPLING AREA TO IDENTIFY ROAD POLLUTANTS
75
81
890
FA
N.
Mokhtarani
Faculty of Civil & Environmental Engineering
Tarbiat Modares University
F.
Zahed
Transportation Research Institute Mimistry of Road and Urban Development
Journal Article
2013
01
01
The purpose of this study is to practically determine an appropriate sampling area for identification of pollution from the exploitation of roads in Iran. To fulfill this objective, after field study, the classification of roads, based on environmental priorities, was carried out. Then, monitoring and assessing the environmental impact resulting from the exploitation of the roads was undertaken. To achieve this, four roads under different climate conditions were selected and various parameters of water, soil and air were evaluated, according to the corresponding traffic load, in two separate periods of time. Based on examination, the values of most investigated parameters, except soil parameters, were below the standard limits. Although there is no rational and meaningful relation between traffic load and the obtained values in soil samples, more attention should be paid to the source of some basic pollutants, such as total petroleum hydrocarbon, ands nickel and vanadium, which, in some cases, violate standards. Asphalt, tires, and vehicle fuel are the main sources of nickel, vanadium and TPH in road transportation. Even though concentration of these contaminants in the water and air samples of the road margin was insignificant, in his tudy, hemaximumconcentration of 14 mg/kg of TPH in soil was observed. Nickel concentration in the three cases was even higher than standard levels, and concentration of 90 mg/kg of soil, which is about twice the standard level, has been recorded for this contaminant. The maximum concentration of 162 mg/kg of vanadium, which is nearly three times the standard level, was also measured in the soil. High concentrations of soil pollutants, in comparison to other environments such as water and air, can be related to its ability to retain contaminants. Therefore, in order to assess the impact of emissions from the exploitation of roads on the physical environment, the soil bed is a better location in comparison with the air and water resources of rim roads.
The purpose of this study is to practically determine an appropriate sampling area for identification of pollution from the exploitation of roads in Iran. To fulfill this objective, after field study, the classification of roads, based on environmental priorities, was carried out. Then, monitoring and assessing the environmental impact resulting from the exploitation of the roads was undertaken. To achieve this, four roads under different climate conditions were selected and various parameters of water, soil and air were evaluated, according to the corresponding traffic load, in two separate periods of time. Based on examination, the values of most investigated parameters, except soil parameters, were below the standard limits. Although there is no rational and meaningful relation between traffic load and the obtained values in soil samples, more attention should be paid to the source of some basic pollutants, such as total petroleum hydrocarbon, ands nickel and vanadium, which, in some cases, violate standards. Asphalt, tires, and vehicle fuel are the main sources of nickel, vanadium and TPH in road transportation. Even though concentration of these contaminants in the water and air samples of the road margin was insignificant, in his tudy, hemaximumconcentration of 14 mg/kg of TPH in soil was observed. Nickel concentration in the three cases was even higher than standard levels, and concentration of 90 mg/kg of soil, which is about twice the standard level, has been recorded for this contaminant. The maximum concentration of 162 mg/kg of vanadium, which is nearly three times the standard level, was also measured in the soil. High concentrations of soil pollutants, in comparison to other environments such as water and air, can be related to its ability to retain contaminants. Therefore, in order to assess the impact of emissions from the exploitation of roads on the physical environment, the soil bed is a better location in comparison with the air and water resources of rim roads.
https://sjce.journals.sharif.edu/article_890_024d7f84fff11dd7e8d9c510137a2381.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
RELIABILITY INDEX EVALUATION OF MRF STEEL STRUCTURES DESIGNED ACCORDING TO IRANIAN CODE
RELIABILITY INDEX EVALUATION OF MRF STEEL STRUCTURES DESIGNED ACCORDING TO IRANIAN CODE
83
90
891
FA
A.
Yazdani
Dept. of Civil Engineering University of Kurdistan
P.
Zargar
Dept. of Civil Engineering University of Kurdistan
Journal Article
2013
01
06
Reliability theory, which itself is a part of general probabilistic concepts, plays a basic role in the design provisions of structures. In limit state or performance-based design, the structural reliability theory plays an essential role in setting the design criteria, as well as demonstrating the target reliability level appropriate to each society. Structural reliability is necessary for having a model that makes it possible to perform rational calculations in the presence of uncertainties in the various parameters encountered in loading parameters and those of structures such as material property, geometric dimensions and the nonlinear dynamic analysis procedure. Although several procedures for structural reliability evaluation, treating non-linear displacement responses, have been proposed, they require complex procedures that may not be used in the practical design process. In the present study, a ductility-based procedure is proposed to maintain both accuracy and simplicity, based on non-linear dynamic response analysis. The use of results of the nonlinear dynamic analysis for a few records to establish the seismic demand curve could be considered the computationally intensive part of the incremental dynamic analysis (IDA). The IDA is an emerging structural analysis method that offers thorough seismic demand and limit-state capacity prediction capability by using a series of nonlinear dynamic analyses under a suite of multiply scaled ground motion records. We used probabilistic tools, by applying the total probability theorem, in order to derive the hazard values for the ductility-based response. This study presents an analytical foundation for probability-based formats for seismic design and assessment of structures. In this study, a reliability assessment of six steel moment resisting frames (MRF), designed according to Iranian codes, is carried out. The reliability indices of these designed steel MRF structures are to be estimated using the present procedure, the ductility-based procedure.
Reliability theory, which itself is a part of general probabilistic concepts, plays a basic role in the design provisions of structures. In limit state or performance-based design, the structural reliability theory plays an essential role in setting the design criteria, as well as demonstrating the target reliability level appropriate to each society. Structural reliability is necessary for having a model that makes it possible to perform rational calculations in the presence of uncertainties in the various parameters encountered in loading parameters and those of structures such as material property, geometric dimensions and the nonlinear dynamic analysis procedure. Although several procedures for structural reliability evaluation, treating non-linear displacement responses, have been proposed, they require complex procedures that may not be used in the practical design process. In the present study, a ductility-based procedure is proposed to maintain both accuracy and simplicity, based on non-linear dynamic response analysis. The use of results of the nonlinear dynamic analysis for a few records to establish the seismic demand curve could be considered the computationally intensive part of the incremental dynamic analysis (IDA). The IDA is an emerging structural analysis method that offers thorough seismic demand and limit-state capacity prediction capability by using a series of nonlinear dynamic analyses under a suite of multiply scaled ground motion records. We used probabilistic tools, by applying the total probability theorem, in order to derive the hazard values for the ductility-based response. This study presents an analytical foundation for probability-based formats for seismic design and assessment of structures. In this study, a reliability assessment of six steel moment resisting frames (MRF), designed according to Iranian codes, is carried out. The reliability indices of these designed steel MRF structures are to be estimated using the present procedure, the ductility-based procedure.
https://sjce.journals.sharif.edu/article_891_cfbce4c1d7c425baf21d6b6f2babe6be.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
ASSESSMENT OF THE SAFETY MARGIN IN THE SEISMIC DESIGN OF FOUNDATIONS BASED ON ASCE 41-06 STANDARD
ASSESSMENT OF THE SAFETY MARGIN IN THE SEISMIC DESIGN OF FOUNDATIONS BASED ON ASCE 41-06 STANDARD
91
100
892
FA
A.
Azarbakht
Dept. of Civil Engineering Arak University
A.
Analooei
Dept. of Civil Engineering Arak University
Journal Article
2013
01
30
The seismic linear demand of structures is usually reduced by employing a force-reduction factor in most force-based seismic regulations. This approach is simple enough to be widely used by designers. However, calibration of the employed force-reduction factor has a high level of importance, since it is supposed that this factor can transfer the structural linear response to the structural nonlinear response. Current force reduction factors in the ASCE 41-06 standard, which is the latest regulation for seismic rehabilitation programs, results in conservative designs in the case of foundations when compared to design regulations, e.g., IBC 2000. This conservation source comes from the fact that the force reduction factor is limited between one and two in the case of force-controlled members.The aim of the current paper is to evaluate the influence of SFSI effects on the force-reduction factor, based on the ASCE 41-06 standard, focusing on force-controlled members. For this purpose, the beam on the nonlinear inkler oundation approach is used, which is a simple and efficient method. First, a collection of 3, 6, 10 and 15 story concrete moment-resisting frames, founded on soft, medium and hard soil, are designed and analysed for the case of fixed-base and flexible-base assumptions. Eight ground motion records were chosen in order to estimate the median response of the considered frames for a pre-defined seismic scenario. A comparison has been made between the results of the nonlinear response history analysis of each frame, under flexible and fixed base conditions, with the response based on the equivalent linear static approach. The results show that the equivalent linear static approach load ombinations, in the case of foundations, can lead to conservative designs. Finally, by adjusting linear to nonlinear results, a set of new force-reduction factors has been proposed in order to deal with this problem.
The seismic linear demand of structures is usually reduced by employing a force-reduction factor in most force-based seismic regulations. This approach is simple enough to be widely used by designers. However, calibration of the employed force-reduction factor has a high level of importance, since it is supposed that this factor can transfer the structural linear response to the structural nonlinear response. Current force reduction factors in the ASCE 41-06 standard, which is the latest regulation for seismic rehabilitation programs, results in conservative designs in the case of foundations when compared to design regulations, e.g., IBC 2000. This conservation source comes from the fact that the force reduction factor is limited between one and two in the case of force-controlled members.The aim of the current paper is to evaluate the influence of SFSI effects on the force-reduction factor, based on the ASCE 41-06 standard, focusing on force-controlled members. For this purpose, the beam on the nonlinear inkler oundation approach is used, which is a simple and efficient method. First, a collection of 3, 6, 10 and 15 story concrete moment-resisting frames, founded on soft, medium and hard soil, are designed and analysed for the case of fixed-base and flexible-base assumptions. Eight ground motion records were chosen in order to estimate the median response of the considered frames for a pre-defined seismic scenario. A comparison has been made between the results of the nonlinear response history analysis of each frame, under flexible and fixed base conditions, with the response based on the equivalent linear static approach. The results show that the equivalent linear static approach load ombinations, in the case of foundations, can lead to conservative designs. Finally, by adjusting linear to nonlinear results, a set of new force-reduction factors has been proposed in order to deal with this problem.
https://sjce.journals.sharif.edu/article_892_c2aee86157b4a40b78132f1e71a9e6f1.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
PREDICTION OF WORKFORCE PRODUCTIVITY AND INVESTIGATION OF ITS IMPACT ON PROJECT PERFORMANCE
PREDICTION OF WORKFORCE PRODUCTIVITY AND INVESTIGATION OF ITS IMPACT ON PROJECT PERFORMANCE
101
110
893
FA
F.
Nasirzadeh
Dept. of Civil EngineeringTehran PNU
P.
Nojedehi
School of Engineering Islamic Azad University, Science and Research
Journal Article
2013
02
06
Workforce productivity is affected by various factors that have complex interactions with each other. In this research, the various factors affecting workforce productivity are identified through a literature review and by conducting interviews with different experts involved in the construction projects. The effects of these factors on workforce productivity is modeled using cause and effect feedback loops, considering the complex relationships existing between these factors, and a qualitative model of the workforce productivity is built. The proposed model consists of five sub-systems, including the project execution sector, project duration and cost sector, project quality sector and workforce productivity sector.Having the qualitative model of labor productivity, the relationships existing between different factors are determined. These relationships could be simply determined for some of the factors. here he elationships could not be simply determined, extrapolation or expert judgment is used. The required data are gathered for a housing project executed in Iran. Finally, the quantitative model of the workforce productivity is built.Using the developed model, direct and indirect effects of different factors on workforce productivity can be simulated. Asensitivity analysis is then conducted to show how the labor productivity is affected by different factors. Moreover, the effects of workforce productivity on project performance are evaluated, in terms of project cost and project duration. It is also shown how project quality is affected by different influencing factors, quantitatively.Finally, using the developed model, the main causes of a decrease in workforce productivity could be identified. herefore,workforce productivity, as well as project performance, could be enhanced by implementation of appropriate solutions.
Workforce productivity is affected by various factors that have complex interactions with each other. In this research, the various factors affecting workforce productivity are identified through a literature review and by conducting interviews with different experts involved in the construction projects. The effects of these factors on workforce productivity is modeled using cause and effect feedback loops, considering the complex relationships existing between these factors, and a qualitative model of the workforce productivity is built. The proposed model consists of five sub-systems, including the project execution sector, project duration and cost sector, project quality sector and workforce productivity sector.Having the qualitative model of labor productivity, the relationships existing between different factors are determined. These relationships could be simply determined for some of the factors. here he elationships could not be simply determined, extrapolation or expert judgment is used. The required data are gathered for a housing project executed in Iran. Finally, the quantitative model of the workforce productivity is built.Using the developed model, direct and indirect effects of different factors on workforce productivity can be simulated. Asensitivity analysis is then conducted to show how the labor productivity is affected by different factors. Moreover, the effects of workforce productivity on project performance are evaluated, in terms of project cost and project duration. It is also shown how project quality is affected by different influencing factors, quantitatively.Finally, using the developed model, the main causes of a decrease in workforce productivity could be identified. herefore,workforce productivity, as well as project performance, could be enhanced by implementation of appropriate solutions.
https://sjce.journals.sharif.edu/article_893_d56b9fc4b0f1be8871f5e1c40c0067e7.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
DAMAGE DETECTION IN STRUCTURES BY WAVELET ANALYSIS USING MODAL ANALYSIS DATA
DAMAGE DETECTION IN STRUCTURES BY WAVELET ANALYSIS USING MODAL ANALYSIS DATA
111
121
894
FA
Y.
Foladghadam
Dept. of Civil Engineering Shahid Chamran University of Ahwaz
H.R.
Ghafouri
Dept. of Civil Engineering Shahid Chamran University of Ahwaz
Journal Article
2013
01
26
Over the past few decades, the methods of damage detection in civil and mechanical structures have drawn much attention from various fields in structural health monitoring (SHM) systems. Structural health monitoring (SHM) is related to damage monitoring, with operational loads playing a significant role in terms of fatigue life and damage accumulation prognostics. Many different techniques, like acoustic emission, ultrasonic, acousto-ultrasonic, guided ultrasonic waves or Lamb waves, are nowadays investigated in terms of efficient and user-friendly damage identification systems. This paper proposes a new approach for damage detection in structures with minor damage in the early growth stages. Wavelet analysis, a relatively new mathematical tool, has been used increasingly in recent years. This rather new method has been applied to various fields including civil, mechanical and erospaceengineering. Damage detection in early stages is very crucial in engineering structures. Almost all proposed methods, so far, rely merely on comparison of the structural behavior of the present structure with that of the original intact structure. However, this method is not always applicable, as either the behavior of the original structure is not available, in most cases, or the impact of damage is too negligible in the early stages to be identified. The newly introduced method of Wavelet Analysis has overcome these problems, as it does not require data of the intact structure. The method utilizes experimental mode shapes obtained from data acquisition systems. Then, with a mathematical transformation, the discontinuities of the mode shapes, which are normally very negligible, are highlighted and, therefore, easily identified. Throughout the present study, the applicability of the method for three types of structure, including a simple beam, a frame and a suspended cable bridge, is verified. The obtained results show the great potential of the method in discernment of damage location with great accuracy.
Over the past few decades, the methods of damage detection in civil and mechanical structures have drawn much attention from various fields in structural health monitoring (SHM) systems. Structural health monitoring (SHM) is related to damage monitoring, with operational loads playing a significant role in terms of fatigue life and damage accumulation prognostics. Many different techniques, like acoustic emission, ultrasonic, acousto-ultrasonic, guided ultrasonic waves or Lamb waves, are nowadays investigated in terms of efficient and user-friendly damage identification systems. This paper proposes a new approach for damage detection in structures with minor damage in the early growth stages. Wavelet analysis, a relatively new mathematical tool, has been used increasingly in recent years. This rather new method has been applied to various fields including civil, mechanical and erospaceengineering. Damage detection in early stages is very crucial in engineering structures. Almost all proposed methods, so far, rely merely on comparison of the structural behavior of the present structure with that of the original intact structure. However, this method is not always applicable, as either the behavior of the original structure is not available, in most cases, or the impact of damage is too negligible in the early stages to be identified. The newly introduced method of Wavelet Analysis has overcome these problems, as it does not require data of the intact structure. The method utilizes experimental mode shapes obtained from data acquisition systems. Then, with a mathematical transformation, the discontinuities of the mode shapes, which are normally very negligible, are highlighted and, therefore, easily identified. Throughout the present study, the applicability of the method for three types of structure, including a simple beam, a frame and a suspended cable bridge, is verified. The obtained results show the great potential of the method in discernment of damage location with great accuracy.
https://sjce.journals.sharif.edu/article_894_4b0250793549726d5c1ea3906726ebfe.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
INCREMENTAL INELASTIC DYNAMIC ANALYSIS OF A BUCKLING-RESTRAINED BRACED FRAMES IN ECCENTRIC CONFIGURATION SUBJECTED TO NEAR FAULT EARTHQUAKES RECORDS
INCREMENTAL INELASTIC DYNAMIC ANALYSIS OF A BUCKLING-RESTRAINED BRACED FRAMES IN ECCENTRIC CONFIGURATION SUBJECTED TO NEAR FAULT EARTHQUAKES RECORDS
123
131
889
FA
H.
Shakib
Dept. of Civil Engineering Tarbiat Modares University
R.
Safi
Dept. of Civil Engineering Tarbiat Modares University
Journal Article
2012
10
31
Near-fault earthquakes have different properties compared to far-fault earthquakes because of forward-directivity, long-period pulses and fling-step motion. Near-fault ground motion can cause extensive structural damage compared to far-fault ground motion. The concentration of energy at short intervals and in pulses of near-fault ground motion causes impulsive movement. Application of systems with high ductility and energy absorption subjected to near-fault earthquakes is inevitable. In the buckling-restrained braced frames, yielding of steel core, either in tension or compression, helps to absorb the high magnitude of energy. The usual configuration of these systems is concentric. Application of ductile beam splices and buckling-restrained braces in eccentric configurations makes it possible to use the architectural benefits of eccentrically braced frames and also the design benefits of buckling-restrained braced frames. In this bracing system, brace elements provide the lateral stiffness of steel frames and are designed to undergo large inelastic axial deformations. Link beams should remain elastic, while transferring ultimate brace forces into the columns. In addition to the properties of the eccentric buckling-restrained frames, such as appropriate dynamic performance and ductility ratio, the system has the capability to be easily repaired after an earthquake because the structural damage is concentrated in the braces and not in the link beam. Evaluation and comparison of the dynamic performance of these eccentrically braced frames and buckling-restrained braced frames subject to near-fault and far-fault ground motion is the aim of this thesis. To reach the objective, incremental inelastic dynamic analyses of 2D frames with different heights and length of span are performed, and parameters, such as average maximum inter story drift, input energy and limit states, from the incremental dynamic analysis curves for both bracing systems are compared. Results indicate that eccentric buckling restrained braced frames for high seismic regions and subject to near-fault ground motion have better dynamic performance compared to eccentrically braced frames.
Near-fault earthquakes have different properties compared to far-fault earthquakes because of forward-directivity, long-period pulses and fling-step motion. Near-fault ground motion can cause extensive structural damage compared to far-fault ground motion. The concentration of energy at short intervals and in pulses of near-fault ground motion causes impulsive movement. Application of systems with high ductility and energy absorption subjected to near-fault earthquakes is inevitable. In the buckling-restrained braced frames, yielding of steel core, either in tension or compression, helps to absorb the high magnitude of energy. The usual configuration of these systems is concentric. Application of ductile beam splices and buckling-restrained braces in eccentric configurations makes it possible to use the architectural benefits of eccentrically braced frames and also the design benefits of buckling-restrained braced frames. In this bracing system, brace elements provide the lateral stiffness of steel frames and are designed to undergo large inelastic axial deformations. Link beams should remain elastic, while transferring ultimate brace forces into the columns. In addition to the properties of the eccentric buckling-restrained frames, such as appropriate dynamic performance and ductility ratio, the system has the capability to be easily repaired after an earthquake because the structural damage is concentrated in the braces and not in the link beam. Evaluation and comparison of the dynamic performance of these eccentrically braced frames and buckling-restrained braced frames subject to near-fault and far-fault ground motion is the aim of this thesis. To reach the objective, incremental inelastic dynamic analyses of 2D frames with different heights and length of span are performed, and parameters, such as average maximum inter story drift, input energy and limit states, from the incremental dynamic analysis curves for both bracing systems are compared. Results indicate that eccentric buckling restrained braced frames for high seismic regions and subject to near-fault ground motion have better dynamic performance compared to eccentrically braced frames.
https://sjce.journals.sharif.edu/article_889_07871915a8107172b3b5dc15a6574ad3.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
31.2
1.2
2015
03
21
INVESTIGATION INTO THE EFFECT OF CARPET FIBER INCLUSION ON THE PORE WATER PRESSURE GENERATION POTENTIAL OF SAND IN A QUICK TANK
INVESTIGATION INTO THE EFFECT OF CARPET FIBER INCLUSION ON THE PORE WATER PRESSURE GENERATION POTENTIAL OF SAND IN A QUICK TANK
133
140
895
FA
R.
Jamshidi Chenari
Faculty of EngineeringUniversity of Guilan
A.
Yousefi Barandagh
Faculty of EngineeringUniversity of Guilan
M.B.
Esfandiari
Faculty of EngineeringUniversity of Guilan
Journal Article
2013
01
06
In this study, the effects of carpet fiber inclusion on pore water pressure development in fine sand are investigated, while dynamic loads are applied. In this regard, quick tank model tests are used. A quick tank comprised of a transparent plastic storage container of sand, a shaker and a water drainage system was employed. Different reinforcement parameters, namely, fiber weight content and fiber aspect ratio varied through physical modeling, in order to study the reinforcement effects. Two different fiber weight contents (0.5 and 1\%) and a wide range of aspect ratios for the slender fiber elements (1, 3, 5, 9) were utilized in order to scrutinize the effect of each factor on the pore water pressure development regime. Dry tamping was employed to mix and prepare the models in a layered structure. Samples were then saturated gradually from the bottom. Harmonic shaking was applied afterwards. Shaking frequency was maintained constant at 2.66 Hz through different models. Furthermore, constant shaking amplitude of 0.34g was chosen in order to guarantee a shaking assumed strong enough to induce excess pore water pressure inside the constructed models. Pore water pressure was recorded at three different levels, at the bottom, middle and top of the models, utilizing three pore pressure transducers connected to a data logger. Records of pore water pressure are then prepared for different models with variable reinforcement parameters, to draw conclusions about their effect on the potential of pore water pressure development in the reinforced models in comparison to the plain sand model. It was noticed that carpet fiber inclusion in fine-grained sand reduces the potential of excess pore water pressure development due to its porous structure. However, this effect is hindered when the level of effective stress rises. It is, therefore, evaluated to be suitable for reinforcement of granular soil in shallow depths. Utilization of such fibers in the reinforcement of backfill material in retaining structures, quay walls and road embankments are also potential applications. Aspect ratio, on the other hand, shows a dual effect on the hydraulic behavior of reinforced sand. On the one hand, increasing the aspect ratio will lead to the formation of larger clusters of porous elements, which, itself, induces a reduction in pore water pressure development potential. On the other hand, larger aspect ratio, while maintaining constant fiber weight fractions, will lead to a decrease in the number of porous elements within the whole mass of the model. This implies that an optimum aspect ratio is to be expected.Systematic reinforcement was also studied in comparison to the plain model. It did not show any significant improvement in pore water pressure reduction potential. Comparison of pore water pressure developed in different random and systematic reinforced models led to the conclusion that laying of the carpet layers horizontally does not allow efficient pore water drainage, as the drainage direction is vertical. A totally different pattern of drainage condition is expected when the distribution is random.
In this study, the effects of carpet fiber inclusion on pore water pressure development in fine sand are investigated, while dynamic loads are applied. In this regard, quick tank model tests are used. A quick tank comprised of a transparent plastic storage container of sand, a shaker and a water drainage system was employed. Different reinforcement parameters, namely, fiber weight content and fiber aspect ratio varied through physical modeling, in order to study the reinforcement effects. Two different fiber weight contents (0.5 and 1\%) and a wide range of aspect ratios for the slender fiber elements (1, 3, 5, 9) were utilized in order to scrutinize the effect of each factor on the pore water pressure development regime. Dry tamping was employed to mix and prepare the models in a layered structure. Samples were then saturated gradually from the bottom. Harmonic shaking was applied afterwards. Shaking frequency was maintained constant at 2.66 Hz through different models. Furthermore, constant shaking amplitude of 0.34g was chosen in order to guarantee a shaking assumed strong enough to induce excess pore water pressure inside the constructed models. Pore water pressure was recorded at three different levels, at the bottom, middle and top of the models, utilizing three pore pressure transducers connected to a data logger. Records of pore water pressure are then prepared for different models with variable reinforcement parameters, to draw conclusions about their effect on the potential of pore water pressure development in the reinforced models in comparison to the plain sand model. It was noticed that carpet fiber inclusion in fine-grained sand reduces the potential of excess pore water pressure development due to its porous structure. However, this effect is hindered when the level of effective stress rises. It is, therefore, evaluated to be suitable for reinforcement of granular soil in shallow depths. Utilization of such fibers in the reinforcement of backfill material in retaining structures, quay walls and road embankments are also potential applications. Aspect ratio, on the other hand, shows a dual effect on the hydraulic behavior of reinforced sand. On the one hand, increasing the aspect ratio will lead to the formation of larger clusters of porous elements, which, itself, induces a reduction in pore water pressure development potential. On the other hand, larger aspect ratio, while maintaining constant fiber weight fractions, will lead to a decrease in the number of porous elements within the whole mass of the model. This implies that an optimum aspect ratio is to be expected.Systematic reinforcement was also studied in comparison to the plain model. It did not show any significant improvement in pore water pressure reduction potential. Comparison of pore water pressure developed in different random and systematic reinforced models led to the conclusion that laying of the carpet layers horizontally does not allow efficient pore water drainage, as the drainage direction is vertical. A totally different pattern of drainage condition is expected when the distribution is random.
https://sjce.journals.sharif.edu/article_895_20aee3a5f4643755a79ee5f6a73050ac.pdf