Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
EFFECT OF CONCRETE STRENGTH, FLEXURAL REINFORCEMENT AND INITIAL DAMAGE ON THE DYNAMIC PROPERTIES OF REINFORCED CONCRETE BEAMS
EFFECT OF CONCRETE STRENGTH, FLEXURAL REINFORCEMENT AND INITIAL DAMAGE ON THE DYNAMIC PROPERTIES OF REINFORCED CONCRETE BEAMS
3
12
666
FA
M. R.
Esfahani
Dept. of Civil Engineering Ferdowsi University o&am
0000-0002-2655-2466
S.
Golnargesi
Dept. of Civil Engineering Ferdowsi University o&am
M. M.
Hoseinian
Dept. of Civil Engineering\\ Ferdowsi University o&
Journal Article
2010
05
02
This paper investigates the effect of concrete strength, the amount of flexural reinforcement and initial damage of reinforced concrete beams on the results of modal tests. A total of eight reinforced concrete beam specimens with the dimensions of 150×200×2200 mm were manufactured and tested. The beams were reinforced using steel bars with 6, 8, 12 and 18 mm diameter (a 6 mm bar diameter was used for transverse reinforcement, while other diameters were used as longitudinal reinforcement). In order to investigate the effect of concrete strength on dynamic parameters, two different concrete mixtures were used to produce concrete with compressive strengths of 21MPa and 40MPa (standard cube specimens). Modal tests, involving static and dynamic stages, were carried out in sequence. In the static stage, under the application of static load, damage was induced to the specimen in the form of shear and flexural cracks. A four-point loading system was employed in the static stage by a hydraulic jack. The mid-span deflection of the beam and the applied load were recorded by a displacement transducer (LVDT) and a load-cell, respectively. The load-cell was in direct contact with the hydraulic jack and measured the magnitude of the applied load at every moment. The data from the LVDT and the load-cell were recorded by a data-logger acquisition system. After the end of each static stage, the specimen was unloaded and then dynamic tests were carried out. For the dynamic tests, 23 degrees of freedom (DOF) were defined for the beam. Three specimens were damaged before the tests to study the effect of initial damage on the dynamic properties of beams. In the dynamic tests, the frequency changes and damping ratios of beams were measured at different ages of the specimens.Test results showed that the frequencies of beams decreased with increasing the damage level of the specimens. The increase of tensile reinforcement and concrete strength increased the frequencies of the beams. The intensity of the damage level in each specimen affected its mode shape. The location of damage was determined by the results of mode shape curvatures.
This paper investigates the effect of concrete strength, the amount of flexural reinforcement and initial damage of reinforced concrete beams on the results of modal tests. A total of eight reinforced concrete beam specimens with the dimensions of 150×200×2200 mm were manufactured and tested. The beams were reinforced using steel bars with 6, 8, 12 and 18 mm diameter (a 6 mm bar diameter was used for transverse reinforcement, while other diameters were used as longitudinal reinforcement). In order to investigate the effect of concrete strength on dynamic parameters, two different concrete mixtures were used to produce concrete with compressive strengths of 21MPa and 40MPa (standard cube specimens). Modal tests, involving static and dynamic stages, were carried out in sequence. In the static stage, under the application of static load, damage was induced to the specimen in the form of shear and flexural cracks. A four-point loading system was employed in the static stage by a hydraulic jack. The mid-span deflection of the beam and the applied load were recorded by a displacement transducer (LVDT) and a load-cell, respectively. The load-cell was in direct contact with the hydraulic jack and measured the magnitude of the applied load at every moment. The data from the LVDT and the load-cell were recorded by a data-logger acquisition system. After the end of each static stage, the specimen was unloaded and then dynamic tests were carried out. For the dynamic tests, 23 degrees of freedom (DOF) were defined for the beam. Three specimens were damaged before the tests to study the effect of initial damage on the dynamic properties of beams. In the dynamic tests, the frequency changes and damping ratios of beams were measured at different ages of the specimens.Test results showed that the frequencies of beams decreased with increasing the damage level of the specimens. The increase of tensile reinforcement and concrete strength increased the frequencies of the beams. The intensity of the damage level in each specimen affected its mode shape. The location of damage was determined by the results of mode shape curvatures.
https://sjce.journals.sharif.edu/article_666_fae0b27c451c728867a567e8c1bb4e53.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
ANALYSIS OF ENGINEERING CONSULTING INDUSTRY OF IRAN USING OF MICHAEL PORTERS COMPETITIVE MODEL
ANALYSIS OF ENGINEERING CONSULTING INDUSTRY OF IRAN USING OF MICHAEL PORTERS COMPETITIVE MODEL
13
19
667
FA
Z.
Soltani
Faculty of Engineering Science and Research Bra&zwn
A.
Bakhshiani
Sharif University of Technology
M.
Mofid
Sharif University of Technology
Journal Article
2009
11
30
This study analyzes the industry of engineering consulting services. This industry which encompasses the wide scope of engineering consulting firms in all specialized fields is discussed as one of the sub-branches of construction industry from the profitability perspective. The construction industry is one of the most important industries in the world and especially in Developing countries. Engineering consulting companies are firms that undertake all responsibilities of design stages including studies, researches, providing executive Plans, and supervision of implementations. In this study, the five competitive forces of Michael Porter, the famous strategist and researcher in the field of strategy, is employed as a tool for the analysis. These five forces are the bargaining power of buyers, the bargaining power of suppliers, the threat of new entrants, the threat of substitutes products or services and rivalry among existing competitors. As Porter recommends the required data was gathered through in person interviews with managers of consulting engineering firms and questionnaire. In the next stage, considering the information obtained from the structural analysis of the industry, the period to which the industry is conditioned has been estimated based on the Porters life cycle chart of industries; and accordingly, the appropriate competitive strategy for operating companies is suggested for further profitability in this industry. As the obtained result shows the industry of engineering consulting services is in its maturity stage in Irans current condition and the best competitive strategy recommended by Michael Porter for this industry is efficient marketing and having competitive cost. This study is conducted in order to verify the importance of applying management science instead of the traditional style of management in construction industry
This study analyzes the industry of engineering consulting services. This industry which encompasses the wide scope of engineering consulting firms in all specialized fields is discussed as one of the sub-branches of construction industry from the profitability perspective. The construction industry is one of the most important industries in the world and especially in Developing countries. Engineering consulting companies are firms that undertake all responsibilities of design stages including studies, researches, providing executive Plans, and supervision of implementations. In this study, the five competitive forces of Michael Porter, the famous strategist and researcher in the field of strategy, is employed as a tool for the analysis. These five forces are the bargaining power of buyers, the bargaining power of suppliers, the threat of new entrants, the threat of substitutes products or services and rivalry among existing competitors. As Porter recommends the required data was gathered through in person interviews with managers of consulting engineering firms and questionnaire. In the next stage, considering the information obtained from the structural analysis of the industry, the period to which the industry is conditioned has been estimated based on the Porters life cycle chart of industries; and accordingly, the appropriate competitive strategy for operating companies is suggested for further profitability in this industry. As the obtained result shows the industry of engineering consulting services is in its maturity stage in Irans current condition and the best competitive strategy recommended by Michael Porter for this industry is efficient marketing and having competitive cost. This study is conducted in order to verify the importance of applying management science instead of the traditional style of management in construction industry
https://sjce.journals.sharif.edu/article_667_b5dc4e5d9b495d0196f61d45b26ef33e.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
USE OF THE DELPHI METHOD AND THE DEMATEL TECHNIQUE IN RECOGNIZING AND \r\nORGANIZING THE EFFECTIVE VARIABLES ON BUILDING STRUCTURE QUALITY IN TEHERAN
USE OF THE DELPHI METHOD AND THE DEMATEL TECHNIQUE IN RECOGNIZING AND \r\nORGANIZING THE EFFECTIVE VARIABLES ON BUILDING STRUCTURE QUALITY IN TEHERAN
21
30
668
FA
M.
Shokouh Abdi
School of Civil Engineering\r\nIran Unviersity of Sc&
M.
Zahedi
School of Civil Engineering\r\nIran Unviersity of Sc&
A.
Makouei
School of Industrial Engineering\r\nIran Unviers&zwnj
Journal Article
2010
02
10
There does not seem to be a serious lack of technical and lawful documents, technical knowledge, quantity and quality of engineers and experts, the existence of responsible organizations, and suitable construction materials, etc., in the country. However, in a major city such as Tehran, the quality of building construction related to structural resistance against earthquake loadings should be promoted. Why? Regarding managerial aspects, improving this situation implies a strategic plan. In this regard, recognition of the present and real situation and considering effective elements in the lack of construction quality is an important step related to the quality management process of building constructions. The subject of the present research is surveying those elements which have an effect on the lack of construction quality in Tehran for personal buildings up to five stories, including field studies and the surveying of some expert opinions. The methodologies of getting expert judgments and organizing gathered data are on the basis of the DELPHI method and the DEMATEL technique, respectively, which are known methods in the Group Multiple Attribute Decision Making managerial field. In this paper, after explaining a totality of survey necessities, the used managerial techniques will be illustrated briefly. Then, the process of the Delphi method in the recognition and categorizing of effective variables on building structure quality will be investigated. Then, the interaction of elements (directly and indirectly) using the DEMATEL technique is illustrated, step by step. The element rankings, due to different mathematical indexes, are presented next. These rankings are the supplementary results of applying the DEMATEL technique. In the conclusion of this technique, the mathematical indexes, in alignment with managerial points of view, are iscussed and, finally, applicable managerial results are shown.
There does not seem to be a serious lack of technical and lawful documents, technical knowledge, quantity and quality of engineers and experts, the existence of responsible organizations, and suitable construction materials, etc., in the country. However, in a major city such as Tehran, the quality of building construction related to structural resistance against earthquake loadings should be promoted. Why? Regarding managerial aspects, improving this situation implies a strategic plan. In this regard, recognition of the present and real situation and considering effective elements in the lack of construction quality is an important step related to the quality management process of building constructions. The subject of the present research is surveying those elements which have an effect on the lack of construction quality in Tehran for personal buildings up to five stories, including field studies and the surveying of some expert opinions. The methodologies of getting expert judgments and organizing gathered data are on the basis of the DELPHI method and the DEMATEL technique, respectively, which are known methods in the Group Multiple Attribute Decision Making managerial field. In this paper, after explaining a totality of survey necessities, the used managerial techniques will be illustrated briefly. Then, the process of the Delphi method in the recognition and categorizing of effective variables on building structure quality will be investigated. Then, the interaction of elements (directly and indirectly) using the DEMATEL technique is illustrated, step by step. The element rankings, due to different mathematical indexes, are presented next. These rankings are the supplementary results of applying the DEMATEL technique. In the conclusion of this technique, the mathematical indexes, in alignment with managerial points of view, are iscussed and, finally, applicable managerial results are shown.
https://sjce.journals.sharif.edu/article_668_192fc044e74dffea144f9ac5dc9f3395.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
INVESTIGATION OF LATERAL RESISTANCE OF SINGLE VERTICAL PILE LOCATED NEAR SLOPE REINFORCED BY RANDOMLY DISTRIBUTED CARPET SHREDS
INVESTIGATION OF LATERAL RESISTANCE OF SINGLE VERTICAL PILE LOCATED NEAR SLOPE REINFORCED BY RANDOMLY DISTRIBUTED CARPET SHREDS
31
38
669
FA
S.M.A.
Zomorodian
Dept. of Water Engineering\r\nShiraz University
M.
Dehghan
Dept. of Civil Engineering \r\nEstahba Branch, Islami
Journal Article
2010
03
08
The behaviour of pile foundations located near slopes is different from their behaviour while they are located at ground level, as piles may not only induce failure in the slope (especially at shallow depths), but, also, the lateral bearing capacity of the piles themselves may decrease to a great extent owing to the nearby slope. Several numerical and experimental studies on laterally loaded single piles installed in sites near to the crests of slopes have been performed. Traditional soil reinforcing techniques involve the use of continuous geosynthetic inclusions oriented in a preferred direction to enhance the strength and stability of soil. Soils reinforced with randomly distributed inclusions have attracted considerable interest over past years. In this type of reinforcement, soil is mixed randomly with discrete small inclusions, such as tyre shreds, fibres, filaments and small meshes, until it becomes like a homogeneous material. However, the effect of soil reinforcement by randomly distributed waste carpet on the overall behaviour of laterally loaded vertical piles installed near stabilized slopes has not yet been investigated. In this paper, the influence of reinforcing a sandy slope with carpet shreds on the lateral resistance of a single vertical pile near a slope was studied, using a randomly distributed method. An experimental testing programme was undertaken using small-scale model tests, with the goal of evaluating the lateral resistance of a single pile located near a reinforced sandy slope. A broad series of conditions, including unreinforced cases, was tested by varying parameters such as: carpet shred content (i.e. ratio of the weight of the shreds to weight of dry sand), aspect ratios of carpet shreds (ratio of length to width), pile distance from the slope crest, relative density of sand, angle of the slope, embedded length, skin friction and the cross-section of the pile. The carpet shred content and aspect ratio were found to influence the lateral resistance of a single pile located near the reinforcing sandy slope. The optimum carpet shred contents and aspect ratios of the carpet shred were 1.5 and 3, respectively, and with these values, a good improvement in the lateral resistance of piles was reached.
The behaviour of pile foundations located near slopes is different from their behaviour while they are located at ground level, as piles may not only induce failure in the slope (especially at shallow depths), but, also, the lateral bearing capacity of the piles themselves may decrease to a great extent owing to the nearby slope. Several numerical and experimental studies on laterally loaded single piles installed in sites near to the crests of slopes have been performed. Traditional soil reinforcing techniques involve the use of continuous geosynthetic inclusions oriented in a preferred direction to enhance the strength and stability of soil. Soils reinforced with randomly distributed inclusions have attracted considerable interest over past years. In this type of reinforcement, soil is mixed randomly with discrete small inclusions, such as tyre shreds, fibres, filaments and small meshes, until it becomes like a homogeneous material. However, the effect of soil reinforcement by randomly distributed waste carpet on the overall behaviour of laterally loaded vertical piles installed near stabilized slopes has not yet been investigated. In this paper, the influence of reinforcing a sandy slope with carpet shreds on the lateral resistance of a single vertical pile near a slope was studied, using a randomly distributed method. An experimental testing programme was undertaken using small-scale model tests, with the goal of evaluating the lateral resistance of a single pile located near a reinforced sandy slope. A broad series of conditions, including unreinforced cases, was tested by varying parameters such as: carpet shred content (i.e. ratio of the weight of the shreds to weight of dry sand), aspect ratios of carpet shreds (ratio of length to width), pile distance from the slope crest, relative density of sand, angle of the slope, embedded length, skin friction and the cross-section of the pile. The carpet shred content and aspect ratio were found to influence the lateral resistance of a single pile located near the reinforcing sandy slope. The optimum carpet shred contents and aspect ratios of the carpet shred were 1.5 and 3, respectively, and with these values, a good improvement in the lateral resistance of piles was reached.
https://sjce.journals.sharif.edu/article_669_5c04925674920eb58467fb52ce4ef728.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
SEISMIC ANALYSIS OF ANCHOR SHEET PILE WITH A GRANULAR SOIL USING PSEUDO-STATIC APPROACH
SEISMIC ANALYSIS OF ANCHOR SHEET PILE WITH A GRANULAR SOIL USING PSEUDO-STATIC APPROACH
39
46
670
FA
M.H.
Jahangir
Dept. of Civil Engineering K.N. Toosi University of
S.N.
Moghaddas Tafreshi
Dept. of Civil Engineering K.N. Toosi University of Te&zw
0000-0002-7149-6686
Journal Article
2009
05
07
Sheet piles have been commonly used in the construction industry since early in the last century. They are used in a wide variety of both temporary and permanent building applications, including retaining walls, slope stabilization, seepage control barriers, sea walls, dock and harbor works, permanent foundations and ground reclamation work. Since the understanding and knowledge of designing under static and dynamic loads (i.e., earthquake) need to be increased, this paper presents the seismic analysis of an anchor free earth support sheet pile in granular soil by developing the static Coulomb method in the framework of the pseudo-static method. Parametric studies quantify the effects of the soil internal angle of friction ($\phi$) and the horizontal and vertical seismic coefficients ($k_h$ and $k_v$) on the active and net passive pressure distribution on the sheet pile, the maximum bending moment and depth of penetration of the sheet pile and, also, the tension force in the anchor. The results indicate that an increase in the soil internal angle of friction and the horizontal seismic coefficient can significantly influence the performance of the sheet pile. The effect of an increase in horizontal seismic coefficient on the parameters above is more effective for the low values of soil internal angle of friction ($\varphi > 30^\circ$) than for high values of soil internal angle of friction ($\varphi > 35^\circ$) Likewise, the effect of vertical seismic coefficient on the performance of the sheet pile is not significant, particularly for low values of horizontal seismic acceleration. On the other hand, the vertical seismic coefficient on the behavior of the sheet pile is more remarkable for the high value of horizontal seismic coefficient ($k_h \geq 0.2$) and poor quality backfill ($\varphi < 30^\circ$) Overall, in practice, the use of incompetent backfill material ($\varphi < 30^\circ$) and also a strong earthquake ($k_h \geq 0.2$) is infrequent. Consequently, considering the undesirable effects of the vertical seismic coefficient in combination with the horizontal seismic coefficient may possibly be ignored.
Sheet piles have been commonly used in the construction industry since early in the last century. They are used in a wide variety of both temporary and permanent building applications, including retaining walls, slope stabilization, seepage control barriers, sea walls, dock and harbor works, permanent foundations and ground reclamation work. Since the understanding and knowledge of designing under static and dynamic loads (i.e., earthquake) need to be increased, this paper presents the seismic analysis of an anchor free earth support sheet pile in granular soil by developing the static Coulomb method in the framework of the pseudo-static method. Parametric studies quantify the effects of the soil internal angle of friction ($\phi$) and the horizontal and vertical seismic coefficients ($k_h$ and $k_v$) on the active and net passive pressure distribution on the sheet pile, the maximum bending moment and depth of penetration of the sheet pile and, also, the tension force in the anchor. The results indicate that an increase in the soil internal angle of friction and the horizontal seismic coefficient can significantly influence the performance of the sheet pile. The effect of an increase in horizontal seismic coefficient on the parameters above is more effective for the low values of soil internal angle of friction ($\varphi > 30^\circ$) than for high values of soil internal angle of friction ($\varphi > 35^\circ$) Likewise, the effect of vertical seismic coefficient on the performance of the sheet pile is not significant, particularly for low values of horizontal seismic acceleration. On the other hand, the vertical seismic coefficient on the behavior of the sheet pile is more remarkable for the high value of horizontal seismic coefficient ($k_h \geq 0.2$) and poor quality backfill ($\varphi < 30^\circ$) Overall, in practice, the use of incompetent backfill material ($\varphi < 30^\circ$) and also a strong earthquake ($k_h \geq 0.2$) is infrequent. Consequently, considering the undesirable effects of the vertical seismic coefficient in combination with the horizontal seismic coefficient may possibly be ignored.
https://sjce.journals.sharif.edu/article_670_17c276c8e723eb46aef576537e9d56d0.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
THE EFFECT OF LATERAL LOADING PATTERNS ON SEISMIC MODIFICATION FACTORS OF MOMENT-RESISTANT FRAMES WITH MEDIUM DUCTILITY
THE EFFECT OF LATERAL LOADING PATTERNS ON SEISMIC MODIFICATION FACTORS OF MOMENT-RESISTANT FRAMES WITH MEDIUM DUCTILITY
47
57
671
FA
J.
Vaseghi Amiri
School of Civil Engineering Noshirvani Univer
G.R.
Abdollahzade
School of Civil Engineering\r\nNoshirvani Univer&zwnj
M.R.
Banihashemi
School of Civil Engineering \r\nNoshirvani Univer&zwn
Journal Article
2010
04
04
Many seismic codes permit a reduction in design loads, taking advantage of the fact that the structures possess significant reserve strength (overstrength) and the capacity to dissipate energy (ductility). Overstrength and ductility are incorporated in the structural design through a force reduction factor or a response modification factor. The factor represents the ratio of the forces that would develop under the specified ground motion if the structure were to behave elastically to the prescribed design forces at the strength limit state. Such a design concept is based on the assumption that well-detailed structures can develop lateral strength in excess of their design strength and sustain large nonlinear deformation without collapse. The role of the force reduction factor is essential in designing the earthquake load-resisting elements. In documents such as ATC-19 and ATC-34 [1], the behavior factor was calculated as the product of three factors: overstrength factor, ductility factor, and redundancy factor. Many researchers have studied parameter influence on the seismic modification factors of different systems. Since the loading pattern can affect the structure of the hinges of the formed plastic, it can also influence the seismic responses of the structure, such as the behavior factor. In this research, the effect of lateral loading patterns on overstrength, ductility, and the seismic modification factors of moment-resistant frames with medium ductility, is investigated by nonlinear static analysis (pushover) and nonlinear dynamic analysis. Also, the effects of any other parameters influencing the value of the R factor, such as type of consumer sector, are considered, i.e; Iranian (IPE, IPB), American (W)), number of bays and height. The results show that the value variations of nonlinear dynamic analysis generally matched well with those obtained from the pushover analysis. Also, the results show that the value of ductility and the R factor obtained from the frames made for the American sector was more than the Iranian sectors under the same condition. Finally, according to the analysis results, the modified rectangular and the rectangular-triangular loading patterns make the highest R factor for American sectors and Iranian sectors, respectively.
Many seismic codes permit a reduction in design loads, taking advantage of the fact that the structures possess significant reserve strength (overstrength) and the capacity to dissipate energy (ductility). Overstrength and ductility are incorporated in the structural design through a force reduction factor or a response modification factor. The factor represents the ratio of the forces that would develop under the specified ground motion if the structure were to behave elastically to the prescribed design forces at the strength limit state. Such a design concept is based on the assumption that well-detailed structures can develop lateral strength in excess of their design strength and sustain large nonlinear deformation without collapse. The role of the force reduction factor is essential in designing the earthquake load-resisting elements. In documents such as ATC-19 and ATC-34 [1], the behavior factor was calculated as the product of three factors: overstrength factor, ductility factor, and redundancy factor. Many researchers have studied parameter influence on the seismic modification factors of different systems. Since the loading pattern can affect the structure of the hinges of the formed plastic, it can also influence the seismic responses of the structure, such as the behavior factor. In this research, the effect of lateral loading patterns on overstrength, ductility, and the seismic modification factors of moment-resistant frames with medium ductility, is investigated by nonlinear static analysis (pushover) and nonlinear dynamic analysis. Also, the effects of any other parameters influencing the value of the R factor, such as type of consumer sector, are considered, i.e; Iranian (IPE, IPB), American (W)), number of bays and height. The results show that the value variations of nonlinear dynamic analysis generally matched well with those obtained from the pushover analysis. Also, the results show that the value of ductility and the R factor obtained from the frames made for the American sector was more than the Iranian sectors under the same condition. Finally, according to the analysis results, the modified rectangular and the rectangular-triangular loading patterns make the highest R factor for American sectors and Iranian sectors, respectively.
https://sjce.journals.sharif.edu/article_671_5dd9db5e033da9c6fb5ba83c7a7ebea9.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
A STUDY OF CORROSION EFFECTS OF REINFORCEMENTS ON THE CAPACITY OF BRIDGE PIERS VIA THE NONLINEAR FINITE ELEMENT METHOD
A STUDY OF CORROSION EFFECTS OF REINFORCEMENTS ON THE CAPACITY OF BRIDGE PIERS VIA THE NONLINEAR FINITE ELEMENT METHOD
59
68
672
FA
M.A. Shayanfar
Shayanfar
Center of Excellence for Fundamental Studies in S&z
M.
Ghanooni Bagha
Center of Excellence for Fundamental Studies in S&z
Journal Article
2010
04
07
The piers of many bridges in our country, which were constructed long ago, have been exposed to corrosive factors throughout the years and, in many cases, these factors have caused destructive effects. Creating a new 3D analytical model that can consider the effects of the corrosion of reinforcement on concrete columns and using the proper model for nonlinear finite element analysis is the main objective of this research. As corrosion basically causes a reduction in the strength of materials and consequently decreases the capacity of the bridge piers, consideration of their real behavior is of great importance. There are also some other factors which affect the nonlinear behavior of reinforced concrete structures, such as the stress-strain relation of concrete in compression, cracks in concrete, the crushing of concrete, aggregate interlock and dowel action. In addition, the corrosion of reinforcements is one of the crucial causes in affecting the nonlinear behavior of concrete structures, by which the loading capacity and ductility of concrete structures are reduced. Therefore, this factor is also considered using two main approaches, which are: reduction in the area of reinforcements and the bonding of concrete to the reinforcements, which are utilized in the tension stiffening model and in the variation of steel properties. In this study, the aforementioned causes are introduced with credited well-known relations and they are used in the presented model. It is also worthy to note that in this study, three rectangular columns are modeled in a new finite element program, using an advanced composite element, named; the Solid Shell Element, in two different cases. In one case, the corrosion effects of reinforcements are considered, while, in the other case, the corrosion effects are ignored and the analysis results of the two models are compared to those of laboratory experiments.
The piers of many bridges in our country, which were constructed long ago, have been exposed to corrosive factors throughout the years and, in many cases, these factors have caused destructive effects. Creating a new 3D analytical model that can consider the effects of the corrosion of reinforcement on concrete columns and using the proper model for nonlinear finite element analysis is the main objective of this research. As corrosion basically causes a reduction in the strength of materials and consequently decreases the capacity of the bridge piers, consideration of their real behavior is of great importance. There are also some other factors which affect the nonlinear behavior of reinforced concrete structures, such as the stress-strain relation of concrete in compression, cracks in concrete, the crushing of concrete, aggregate interlock and dowel action. In addition, the corrosion of reinforcements is one of the crucial causes in affecting the nonlinear behavior of concrete structures, by which the loading capacity and ductility of concrete structures are reduced. Therefore, this factor is also considered using two main approaches, which are: reduction in the area of reinforcements and the bonding of concrete to the reinforcements, which are utilized in the tension stiffening model and in the variation of steel properties. In this study, the aforementioned causes are introduced with credited well-known relations and they are used in the presented model. It is also worthy to note that in this study, three rectangular columns are modeled in a new finite element program, using an advanced composite element, named; the Solid Shell Element, in two different cases. In one case, the corrosion effects of reinforcements are considered, while, in the other case, the corrosion effects are ignored and the analysis results of the two models are compared to those of laboratory experiments.
https://sjce.journals.sharif.edu/article_672_2dea61eed4bceec564a00115c4d21334.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
ASSESSMENT AND COMPARISON OF DAMAGE LOCALIZATION INDICES IN THREE DIMENSIONAL \r\nREINFORCED CONCRETE FRAMES
ASSESSMENT AND COMPARISON OF DAMAGE LOCALIZATION INDICES IN THREE DIMENSIONAL \r\nREINFORCED CONCRETE FRAMES
69
77
673
FA
R.
Abbasnia
School of Civil Engineering\r\nIran University of Sc&
GH.
Sadri
School of Civil Engineering\r\nIran University of Sc&
Journal Article
2010
04
28
Damage detection and assessment in structures have increasingly received the attention of researchers, due to their role in economical aspects and emergency management after earthquakes. The majority of studies on various methods of damage detection rely on the measured vibration response parameters of structures, as a result of their applicability to large and complex structures. While most research has concentrated on one or two dimensional structures, there are few studies available in the literature on three dimensional structures. The purpose of this study is to apply methods based on modal parameters to three dimensional reinforced concrete frames. To achieve this objective, numerical results are generated for a 3D one story frame with five different scenarios of damage. The application of vibration methods, especially mode shape curvature, and methods based on modal strain energy in damage localization, are also investigated. To implement these methods requires only a small number of mode shapes identified from both damaged and baseline structures. The mode shapes are divided according to their degrees of freedom in order to improve the accuracy of the mode shape curvature indicator method. In addition, the accuracy of the modal sensitivity method has been investigated for two behavioral modes (axial and flexural) of structures. Furthermore, the stiffness matrix has been decomposed to its components (axial and transversal terms) in methods based on modal strain energy. It should be noted that the accuracy of the results is related to damage location. On the other hand, various kinds of indices used in this study have noticeable differences in elements, which are in the proximity of the primary damage location. The results reveal that the mode shape curvature change of rotational degrees of freedom and modal strain energy change associated with the axial term of the stiffness matrix have an acceptable accuracy in damage localization. In addition, it can be concluded that localization of damage at the base of columns via indices applied in this study is more accurate compared to other locations.
Damage detection and assessment in structures have increasingly received the attention of researchers, due to their role in economical aspects and emergency management after earthquakes. The majority of studies on various methods of damage detection rely on the measured vibration response parameters of structures, as a result of their applicability to large and complex structures. While most research has concentrated on one or two dimensional structures, there are few studies available in the literature on three dimensional structures. The purpose of this study is to apply methods based on modal parameters to three dimensional reinforced concrete frames. To achieve this objective, numerical results are generated for a 3D one story frame with five different scenarios of damage. The application of vibration methods, especially mode shape curvature, and methods based on modal strain energy in damage localization, are also investigated. To implement these methods requires only a small number of mode shapes identified from both damaged and baseline structures. The mode shapes are divided according to their degrees of freedom in order to improve the accuracy of the mode shape curvature indicator method. In addition, the accuracy of the modal sensitivity method has been investigated for two behavioral modes (axial and flexural) of structures. Furthermore, the stiffness matrix has been decomposed to its components (axial and transversal terms) in methods based on modal strain energy. It should be noted that the accuracy of the results is related to damage location. On the other hand, various kinds of indices used in this study have noticeable differences in elements, which are in the proximity of the primary damage location. The results reveal that the mode shape curvature change of rotational degrees of freedom and modal strain energy change associated with the axial term of the stiffness matrix have an acceptable accuracy in damage localization. In addition, it can be concluded that localization of damage at the base of columns via indices applied in this study is more accurate compared to other locations.
https://sjce.journals.sharif.edu/article_673_9f396fe44e7c05c16873b05ec425cbad.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
GENERATION OF ARTIFICIAL EARTHQUAKE ACCELEROGRAMS USING WAVELET AND NEURAL NETWORKS
GENERATION OF ARTIFICIAL EARTHQUAKE ACCELEROGRAMS USING WAVELET AND NEURAL NETWORKS
79
88
674
FA
K.
Bargi
College of Engineering Unviersity of Tehran
A.
Kave
School of Civil Engineering Iran University of Sc&z
C.
Lucas
College of Engineering\r\nUnviersity of Tehran
H.
Rahami
College of Engineering Unviersity of Tehran
0000-0001-7540-8412
Journal Article
2010
05
02
Due to the lack of earthquake records and limitations on one hand, and the increasing demand on time-history dynamic analysis of structures on the other hand, generation of artificial earthquake accelerograms becomes a more and more important research topic. In such a situation, using artificial accelerograms seems to be the most logical and practical approach. These accelerograms should be constructed in such a manner that includes the seismic characteristics of the region in which a structural design is performed. Because of the random nature of earthquakes, one should generate many records, on which an acceptable analysis can be based. The best accelerogram is one that has compatible characteristics with the desired area. Therefore, it is difficult or may be impossible, in some cases, to choose a proper record for a design area, because the recorded and processed accelerograms of the design location are few. Besides, other location records do not satisfy the geo-seismic characteristics of the desired location. Wavelets are capable of decomposing a time series to different levels, such that each level covers a definite frequency domain. The purpose of the classic wavelet is to provide an alternate way of breaking a signal down into its constituent parts. Low and high frequencies have narrow and wide bands, respectively. Therefore, a signal could be separated into two sub-signals of approximation and detail by using low and high pass filters. In this paper, a combination of artificial neural networks and wavelets are employed for the formation of artificial earthquake accelerograms with a response spectrum similar to that of the target spectrum. Since wavelets permit the decomposition of each signal, it enables use of the parameters to generate many records, where all these follow a single characteristic of the target spectrum. This paper presents a simple and applicable method to generate many artificial records having the given spectrum. Besides, the method applies real records, which are more reliable than other random methods. The feasibility and reliability of the method have been verified with different examples.
Due to the lack of earthquake records and limitations on one hand, and the increasing demand on time-history dynamic analysis of structures on the other hand, generation of artificial earthquake accelerograms becomes a more and more important research topic. In such a situation, using artificial accelerograms seems to be the most logical and practical approach. These accelerograms should be constructed in such a manner that includes the seismic characteristics of the region in which a structural design is performed. Because of the random nature of earthquakes, one should generate many records, on which an acceptable analysis can be based. The best accelerogram is one that has compatible characteristics with the desired area. Therefore, it is difficult or may be impossible, in some cases, to choose a proper record for a design area, because the recorded and processed accelerograms of the design location are few. Besides, other location records do not satisfy the geo-seismic characteristics of the desired location. Wavelets are capable of decomposing a time series to different levels, such that each level covers a definite frequency domain. The purpose of the classic wavelet is to provide an alternate way of breaking a signal down into its constituent parts. Low and high frequencies have narrow and wide bands, respectively. Therefore, a signal could be separated into two sub-signals of approximation and detail by using low and high pass filters. In this paper, a combination of artificial neural networks and wavelets are employed for the formation of artificial earthquake accelerograms with a response spectrum similar to that of the target spectrum. Since wavelets permit the decomposition of each signal, it enables use of the parameters to generate many records, where all these follow a single characteristic of the target spectrum. This paper presents a simple and applicable method to generate many artificial records having the given spectrum. Besides, the method applies real records, which are more reliable than other random methods. The feasibility and reliability of the method have been verified with different examples.
https://sjce.journals.sharif.edu/article_674_0d7de1aca9299fe63f3e0041f02638a3.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
PHYTOREMEDIATION OF STABLE CESIUM FROM SOLUTIONS
PHYTOREMEDIATION OF STABLE CESIUM FROM SOLUTIONS
89
97
675
FA
M.
Borghei
Biochemical & Bioenvironmental Research Cen&zwn
R.
Moogouei
Environmental Planning, Management and Educat
R.
Arjmandi
Dept. of Environmental Management Science and Re&zw
M.
Vosoughi
Dept. of Chemical Petroleum Engineering Sharif U&z
G.
Tajadod
Dept. of Biology North Tehran Branch, Islamic Azad U&zwnj
Journal Article
2010
05
08
Cesium is vastly observed in nuclear wastewaters and is potentially considered a hazardous material, therefore, its removal from nuclear site wastewaters is an important task. Removal of radionuclides and heavy metals by phytoremediation is fast becoming attractive, due to its high efficiency and low cost. Furthermore, native plants, in terms of survival, growth and also reproduction under environmental stresses, have more stability than plants introduced from other environments. For phytoremedition purposes, it is essential to choose metal tolerant and accumulator plant species that are capable of contaminant transport and accumulation in a relatively short treatment time. In this research, the potential of Chenopodium album for phytoremediation of solutions contaminated with cesium was studied. Chenopodium album seeds were germinated in sand, and then one-month-old plantlets were transplanted in plastic trays containing nutrient solutions. Hydroponically grown plants were incubated in different concentrations of cesium chloride, representing 0.47, 1.58, 3.95 mgl$^{-1}$ of cesium ions in the solutions, for a set period. At the end of 14 days, cesium concentrations in the solutions were 0.15$pm$ 0.01, 0.95$pm$ 0.05 and 1.85$pm$ 0.29mgl$^{-1}$respectively, meaning that 68.08$pm$ 2.12%, 39.66$pm$ 3.4% and 52.99$pm$ 7.75% of cesium has been remediated from the contaminated solutions. {it Chenopodium album} plants were found to be efficient in remediating cesium in all concentrations tested. Plant analysis indicated that 396.16$pm$ 6.33,521.4$pm$ 45.65 and 1256.66$pm$ 93.07 mgkg$^{-1}$ of cesium were accumulated in plants after 14 days. Furthermore, the uptake and accumulation increased with increasing metal concentrations in the solutions. At lowest cesium concentration, plant uptake of cesium was found to be higher. For anatomical studies aerial organs of plants, including the stem and leaf, were fixed, handy sections were prepared and colored and, consequently, photographed. Anatomical studies were performed in many parts, including the primary and secondary structure of the control plants, the structure of control leaves and the anatomical structure of aerial organs after treatment with cesium. Microscopic observation of aerial organs indicated that the tissue structures of these organs had not changed. Moreover, increasing cesium concentration in solutions caused a high level of cesium accumulation in shoots, followed by development in xylem organs and crystalline. Cooperating cesium in the crystal structure and its accumulation in vacuoles permit the plant to uptake more radioactive cesium from the environment without any seriously incurred damage to the plant. These changes could be accounted as plant responses to cesium toxicity. It is concluded that hydroponically grown {it Chenopodium album} could be used as a potential candidate plant for phytoremediation of solutions contaminated with cesium. Moreover, the present study offers an effective and highly economical means of controlling radioactive wastewat.
Cesium is vastly observed in nuclear wastewaters and is potentially considered a hazardous material, therefore, its removal from nuclear site wastewaters is an important task. Removal of radionuclides and heavy metals by phytoremediation is fast becoming attractive, due to its high efficiency and low cost. Furthermore, native plants, in terms of survival, growth and also reproduction under environmental stresses, have more stability than plants introduced from other environments. For phytoremedition purposes, it is essential to choose metal tolerant and accumulator plant species that are capable of contaminant transport and accumulation in a relatively short treatment time. In this research, the potential of Chenopodium album for phytoremediation of solutions contaminated with cesium was studied. Chenopodium album seeds were germinated in sand, and then one-month-old plantlets were transplanted in plastic trays containing nutrient solutions. Hydroponically grown plants were incubated in different concentrations of cesium chloride, representing 0.47, 1.58, 3.95 mgl$^{-1}$ of cesium ions in the solutions, for a set period. At the end of 14 days, cesium concentrations in the solutions were 0.15$pm$ 0.01, 0.95$pm$ 0.05 and 1.85$pm$ 0.29mgl$^{-1}$respectively, meaning that 68.08$pm$ 2.12%, 39.66$pm$ 3.4% and 52.99$pm$ 7.75% of cesium has been remediated from the contaminated solutions. {it Chenopodium album} plants were found to be efficient in remediating cesium in all concentrations tested. Plant analysis indicated that 396.16$pm$ 6.33,521.4$pm$ 45.65 and 1256.66$pm$ 93.07 mgkg$^{-1}$ of cesium were accumulated in plants after 14 days. Furthermore, the uptake and accumulation increased with increasing metal concentrations in the solutions. At lowest cesium concentration, plant uptake of cesium was found to be higher. For anatomical studies aerial organs of plants, including the stem and leaf, were fixed, handy sections were prepared and colored and, consequently, photographed. Anatomical studies were performed in many parts, including the primary and secondary structure of the control plants, the structure of control leaves and the anatomical structure of aerial organs after treatment with cesium. Microscopic observation of aerial organs indicated that the tissue structures of these organs had not changed. Moreover, increasing cesium concentration in solutions caused a high level of cesium accumulation in shoots, followed by development in xylem organs and crystalline. Cooperating cesium in the crystal structure and its accumulation in vacuoles permit the plant to uptake more radioactive cesium from the environment without any seriously incurred damage to the plant. These changes could be accounted as plant responses to cesium toxicity. It is concluded that hydroponically grown {it Chenopodium album} could be used as a potential candidate plant for phytoremediation of solutions contaminated with cesium. Moreover, the present study offers an effective and highly economical means of controlling radioactive wastewat.
https://sjce.journals.sharif.edu/article_675_8fecb20817b3847419bb3de39a609afe.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
PARAMETRIC ANALYSIS OF BURIED STEEL PIPELINES CROSSING ACTIVE FAULTS
PARAMETRIC ANALYSIS OF BURIED STEEL PIPELINES CROSSING ACTIVE FAULTS
99
107
676
FA
V.
Bolvardi
Dept. of Civil Engineering\r\nSharif University of Te
A.
Bakhshi
Dept. of Civil Engineering\r\nSharif University of Te
M.
Tonekabonipour
Dept. of Civil Engineering\r\nSharif University of Te
Journal Article
2010
05
26
Buried pipeline networks are designed to transfer water, gas and oil, and collect wastewater in large industrial cities. The significance of these pipelines as lifeline facilities is more obvious in regions with high risk of earthquake damage. Failure of oil and gas pipelines can cause severe economical and environmental problems. Investigations show that damage to buried pipelines is not attributed to load levels of seismological vibrations. Despite damage to surface structures, large fault movements are the main causes of pipeline damage. Many researchers have studied pipeline behavior against those phenomena with simplified assumptions, in which effects of interactions between soil and pipe are ignored. In this research, the behavior of a pipe under normal and strike-slip fault movements, and contact between them, is simulated using FEM modeling to investigate fault movement effects on pipeline failure and to design an appropriate pipeline. Also, to reach an optimized performance, to design pipelines against seismic load and to offer the relevant equations, several parameters, such as pipe diameter, pipe wall thickness, pipe burial depth, crossing angle between pipe axes and fault, unanchored length of pipe and pipe strength, are considered. These models are made up of three different parts. Two of them are soil blocks, which are divided into similar parts by a fault plane. In order to clarify fault movements during earthquake and their effects on pipes, contact and interaction between the two similar soil parts and a slide based on the maximum shear strength between them are applied. The third part is a steel pipe, which passes through the fault plane inside the soil layers. Soil and pipe are connected to each other by appropriate contact elements, so that the outside surface of the pipe interacts with the inside surface of the soil where the pipe is buried. In each part of the models, elasto-plastic materials are used. Therefore, it is possible to evaluate the roles of mentioned parameters by several analyses. The results from parametric analysis on the effects of those faults on buried steel pipelines show that increasing the angle of the pipe axis and fault line, as well as pipe thickness, and decreasing burial depth diminishes the probability of pipe failure crossing active faults. Changes in pipe diameter also affect the pipe strength slightly. Comparison between results of earlier and current research indicates that they are more conservative.
Buried pipeline networks are designed to transfer water, gas and oil, and collect wastewater in large industrial cities. The significance of these pipelines as lifeline facilities is more obvious in regions with high risk of earthquake damage. Failure of oil and gas pipelines can cause severe economical and environmental problems. Investigations show that damage to buried pipelines is not attributed to load levels of seismological vibrations. Despite damage to surface structures, large fault movements are the main causes of pipeline damage. Many researchers have studied pipeline behavior against those phenomena with simplified assumptions, in which effects of interactions between soil and pipe are ignored. In this research, the behavior of a pipe under normal and strike-slip fault movements, and contact between them, is simulated using FEM modeling to investigate fault movement effects on pipeline failure and to design an appropriate pipeline. Also, to reach an optimized performance, to design pipelines against seismic load and to offer the relevant equations, several parameters, such as pipe diameter, pipe wall thickness, pipe burial depth, crossing angle between pipe axes and fault, unanchored length of pipe and pipe strength, are considered. These models are made up of three different parts. Two of them are soil blocks, which are divided into similar parts by a fault plane. In order to clarify fault movements during earthquake and their effects on pipes, contact and interaction between the two similar soil parts and a slide based on the maximum shear strength between them are applied. The third part is a steel pipe, which passes through the fault plane inside the soil layers. Soil and pipe are connected to each other by appropriate contact elements, so that the outside surface of the pipe interacts with the inside surface of the soil where the pipe is buried. In each part of the models, elasto-plastic materials are used. Therefore, it is possible to evaluate the roles of mentioned parameters by several analyses. The results from parametric analysis on the effects of those faults on buried steel pipelines show that increasing the angle of the pipe axis and fault line, as well as pipe thickness, and decreasing burial depth diminishes the probability of pipe failure crossing active faults. Changes in pipe diameter also affect the pipe strength slightly. Comparison between results of earlier and current research indicates that they are more conservative.
https://sjce.journals.sharif.edu/article_676_dc6a70712a252123c40d2adba6a11d84.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
INVESTIGATION OF ANALYTICAL PROBLEMS OF POST-TENSIONED CONCRETE SLABS USING \r\nFINITE ELEMENT METHOD
INVESTIGATION OF ANALYTICAL PROBLEMS OF POST-TENSIONED CONCRETE SLABS USING \r\nFINITE ELEMENT METHOD
109
118
677
FA
A.R.
Khaloo
Dept. of Civil Engineering\r\nSharif University of Te
M.R.
Javanmardi
Dept. of Civil Engineering\r\nSharif University of Te
Journal Article
2010
05
26
Researchers have always paid great attention to safe and economical design and, therefore, different codes in different areas have been formed. The ACI 318-2011 code insists that two-way post-tensioned slabs shall be classified as class U (without cracking), which means the section must be uncracked in both service and transient conditions (code reference 18.3.3). In addition, two-way post-tensioned slabs must be post-tensioned in both directions for 100% of the load, wich means that one-way behavior for this type of slab is assumed. In this study, two-way post-tensioned slabs with various spans under different loadings have been designed, based on the ACI code. Then, using the Lee-Fenves isotropic damage plasticity model for concrete, the numerical simulation of post-tensioned slabs was performed through the finite element method. The isotropic damage plasticity used a yield criterion that matches the experimental data for both elastic and plastic parts of the stress-strain curves of concrete. The onset and propagation of cracking can be evaluated by simple postprocessing of the finite element plasticity solution. The accuracy of the model was checked by the data provided by previous researchers which indicates simulation was precise. The linear elastic-perfectly plastic stress strain relation was used for steel using the Von-mises yield criterion, while the tendons were simulated by bilinear stress strain curve and Von-mises yield criterion. By using nonlinear finite element software (Abaqus) and the above - mentioned yield criterion, several slabs are studied. Numerical simulation shows that some laws of the ACI code are not satisfied in some cases, including cracked slabs in both service and transient conditions. In addition, over post-tensioning of slabs results in negative deflection and non-economical design. At the end some suggestions for better designs are presented.
Researchers have always paid great attention to safe and economical design and, therefore, different codes in different areas have been formed. The ACI 318-2011 code insists that two-way post-tensioned slabs shall be classified as class U (without cracking), which means the section must be uncracked in both service and transient conditions (code reference 18.3.3). In addition, two-way post-tensioned slabs must be post-tensioned in both directions for 100% of the load, wich means that one-way behavior for this type of slab is assumed. In this study, two-way post-tensioned slabs with various spans under different loadings have been designed, based on the ACI code. Then, using the Lee-Fenves isotropic damage plasticity model for concrete, the numerical simulation of post-tensioned slabs was performed through the finite element method. The isotropic damage plasticity used a yield criterion that matches the experimental data for both elastic and plastic parts of the stress-strain curves of concrete. The onset and propagation of cracking can be evaluated by simple postprocessing of the finite element plasticity solution. The accuracy of the model was checked by the data provided by previous researchers which indicates simulation was precise. The linear elastic-perfectly plastic stress strain relation was used for steel using the Von-mises yield criterion, while the tendons were simulated by bilinear stress strain curve and Von-mises yield criterion. By using nonlinear finite element software (Abaqus) and the above - mentioned yield criterion, several slabs are studied. Numerical simulation shows that some laws of the ACI code are not satisfied in some cases, including cracked slabs in both service and transient conditions. In addition, over post-tensioning of slabs results in negative deflection and non-economical design. At the end some suggestions for better designs are presented.
https://sjce.journals.sharif.edu/article_677_71a3cb155f8dc89bf3d0365288219936.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
DECENTRILIZED H2/LQG CONTROLLER WITH WIRELESS FEEDBACK SYSTEM FOR CABLE STATE \r\nBRIDGE UNDER SEISMIC LOADING
DECENTRILIZED H2/LQG CONTROLLER WITH WIRELESS FEEDBACK SYSTEM FOR CABLE STATE \r\nBRIDGE UNDER SEISMIC LOADING
119
130
678
FA
T.
Taghikhany
Dept. of Civil Engineering\r\nAmirkabir Universit&zwn
A.
Yeganeh Fallah
Dept. of Civil Engineering\r\nAmirkabir Universit&zwn
Journal Article
2010
07
05
One of the main concerns in the application of active and semi-active structural control in large scale structures, as a seismic protection strategy, is the consistency and reliability of real-time data transmission. Coaxial cables, as the primary communication link, provide reliable links for transferring data. However, their installation is time consuming and costly, and it is a tiresome task to change system architecture and reroute wires, especially in large-scale structures. Wireless sensors and communication have the potential to significantly reduce the cost and increase the architecture flexibility of a feedback structural control system. However, replacing coaxial cables with wireless communication channels has drawbacks, such as the coordination of sensing and control nodes, communication range, feedback time delay and potential data loss. Feedback time delay, due to wireless communication, will cause degradation to the performance of a structural control system. A decentralized control strategy is proposed as a remedy to improve the performance of the system due to time delay. In decentralized control strategies, a large control system is divided into distributed sub-systems. Each sub-system has its own controller. These controllers make control decisions through acquiring data from local and neighbouring sensors. On the other hand, in large scale structures, large numbers of degrees of freedom cause numerical difficulties in dynamic analysis and may increase requirements of storages in computation. The reduced-order system solves this problem if it acquires the essential properties of the full-order model, such as passivity and stability. A useful method of the reduced order model is Singular Value Decomposition (SVD). In SVD, the system is transformed to a basis where the states are that are difficult to reach or observe. Then, the reduced model is obtained simply by truncating the states which have this property. This study presents the feasibility of developing a decentralized controller using H2/LQG as a robust-optimum algorithm in a cable-stayed bridge. Due to the large-scale of the structure, the order of the model is reduced using two different reduction methods in finite time and frequency. The controller is developed in centralized and decentralized solutions. The decentralized controller, through developing a gradient-based method, is designed to efficiently solve the system closed-loop H2 optimization problem. The structural responses in centralized and decentralized solutions are compared each other with time delay in data transmission. Results indicate that for large-scale bridges with a time delayed data communication issue, the H2/LQG controller in the decentralized solution gives the maximum reduction of response indices in comparison with other strategies.
One of the main concerns in the application of active and semi-active structural control in large scale structures, as a seismic protection strategy, is the consistency and reliability of real-time data transmission. Coaxial cables, as the primary communication link, provide reliable links for transferring data. However, their installation is time consuming and costly, and it is a tiresome task to change system architecture and reroute wires, especially in large-scale structures. Wireless sensors and communication have the potential to significantly reduce the cost and increase the architecture flexibility of a feedback structural control system. However, replacing coaxial cables with wireless communication channels has drawbacks, such as the coordination of sensing and control nodes, communication range, feedback time delay and potential data loss. Feedback time delay, due to wireless communication, will cause degradation to the performance of a structural control system. A decentralized control strategy is proposed as a remedy to improve the performance of the system due to time delay. In decentralized control strategies, a large control system is divided into distributed sub-systems. Each sub-system has its own controller. These controllers make control decisions through acquiring data from local and neighbouring sensors. On the other hand, in large scale structures, large numbers of degrees of freedom cause numerical difficulties in dynamic analysis and may increase requirements of storages in computation. The reduced-order system solves this problem if it acquires the essential properties of the full-order model, such as passivity and stability. A useful method of the reduced order model is Singular Value Decomposition (SVD). In SVD, the system is transformed to a basis where the states are that are difficult to reach or observe. Then, the reduced model is obtained simply by truncating the states which have this property. This study presents the feasibility of developing a decentralized controller using H2/LQG as a robust-optimum algorithm in a cable-stayed bridge. Due to the large-scale of the structure, the order of the model is reduced using two different reduction methods in finite time and frequency. The controller is developed in centralized and decentralized solutions. The decentralized controller, through developing a gradient-based method, is designed to efficiently solve the system closed-loop H2 optimization problem. The structural responses in centralized and decentralized solutions are compared each other with time delay in data transmission. Results indicate that for large-scale bridges with a time delayed data communication issue, the H2/LQG controller in the decentralized solution gives the maximum reduction of response indices in comparison with other strategies.
https://sjce.journals.sharif.edu/article_678_9fe8593a8a330607d76796b35c64c600.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
ULTIMATE STATE AND DUCTILITY OF PRECAST PRESTRESSED HOLLOW CORE SLABS CONSISTING OF HIGH STRENGTH SELF COMPACTING CONCRETE
ULTIMATE STATE AND DUCTILITY OF PRECAST PRESTRESSED HOLLOW CORE SLABS CONSISTING OF HIGH STRENGTH SELF COMPACTING CONCRETE
131
140
679
FA
A. A.
Maghsoudi
Dept. of Civil Engineering\r\nShahid Bahonar Univer&z
M.
Torkemanzadeh
Dept. of Civil Engineering\r\nShahid Bahonar Univer&z
M.
Maghsoudi
Dept. of Civil Engineering\r\nShahid Bahonar Univer&z
Journal Article
2010
04
10
The development of self compacting concrete, SCC, is a relatively new type of concrete made with conventional concrete materials and, in some cases, with a viscosity-modifying admixture (VMA). It fills all sections of formwork, encapsulates the reinforcement without any mechanical compaction (vibration) and has reasonable flow-ability, homogeneity, resistance against segregation and mechanical strength. The key point in achieving the self compacting property is providing high flow-ability and deformability, while maintaining a resistance to segregation and sedimentation. This can be achieved by proper balance between constituent materials. Okamura and Ozawa proposed the limiting of the volume of coarse aggregates, along with the use of high amounts of powder, controlling the water-powder ratio by volume and the use of proper super-plasticizers. The lower time and cost of construction, the lower sound pollution and the high homogeneous concrete are some advantages of SCC. In recent years, there have been a number of significant developments in the SCC precast industry. However, very limited reports are available on prestressed SCC elements and, therefore, more research is urgently needed in order to understand the use of SCC in precast prestressed lightweight slabs (hollow core slabs) to formulate design rules. The deficiencies of industrial precast prestressed constructional members, such as the lack or unbounding of concrete cover on prestressing strands, weakness in holding the prestressed jacking forces in precast prestressed end supports in industry, the loss of high amounts of prestressed jacking forces of strands before transferring the forces into the members and etc, are some cases which can cause irreparable damage. It is, therefore, for better investigation of such cases that three precast prestressed hollow core SCC slabs with dimensions of 2m length, 1.2m width and 0.2m height were industrially cast and then experimentally load tested up to failure. Their ultimate state and experimental deflection and curvature ductility are measured and the results are compared theoretically. The results show that production of such industrial products is unsafe and uneconomic.
The development of self compacting concrete, SCC, is a relatively new type of concrete made with conventional concrete materials and, in some cases, with a viscosity-modifying admixture (VMA). It fills all sections of formwork, encapsulates the reinforcement without any mechanical compaction (vibration) and has reasonable flow-ability, homogeneity, resistance against segregation and mechanical strength. The key point in achieving the self compacting property is providing high flow-ability and deformability, while maintaining a resistance to segregation and sedimentation. This can be achieved by proper balance between constituent materials. Okamura and Ozawa proposed the limiting of the volume of coarse aggregates, along with the use of high amounts of powder, controlling the water-powder ratio by volume and the use of proper super-plasticizers. The lower time and cost of construction, the lower sound pollution and the high homogeneous concrete are some advantages of SCC. In recent years, there have been a number of significant developments in the SCC precast industry. However, very limited reports are available on prestressed SCC elements and, therefore, more research is urgently needed in order to understand the use of SCC in precast prestressed lightweight slabs (hollow core slabs) to formulate design rules. The deficiencies of industrial precast prestressed constructional members, such as the lack or unbounding of concrete cover on prestressing strands, weakness in holding the prestressed jacking forces in precast prestressed end supports in industry, the loss of high amounts of prestressed jacking forces of strands before transferring the forces into the members and etc, are some cases which can cause irreparable damage. It is, therefore, for better investigation of such cases that three precast prestressed hollow core SCC slabs with dimensions of 2m length, 1.2m width and 0.2m height were industrially cast and then experimentally load tested up to failure. Their ultimate state and experimental deflection and curvature ductility are measured and the results are compared theoretically. The results show that production of such industrial products is unsafe and uneconomic.
https://sjce.journals.sharif.edu/article_679_ca9c267dad0305d1a6308d2a0cf1c39c.pdf
Sharif University of Technology
Sharif Journal of Civil Engineering
2676-4768
Volume 2-28
3
2012
04
20
DESIGN CHARTS OF STONE COLUMNS FOR STABILIZATION OF RAILWAY EMBANKMENTS \r\nOVERLAID ON SOFT CLAY SUBGRADES
DESIGN CHARTS OF STONE COLUMNS FOR STABILIZATION OF RAILWAY EMBANKMENTS \r\nOVERLAID ON SOFT CLAY SUBGRADES
141
149
680
FA
M.
Esmaeili
School of Railway Engineering\r\nIran University o&zw
M.
Saraei
School of Railway Engineering\r\nIran University o&zw
Journal Article
2010
04
17
An important issue in the design and implementation of railways located on loose beds is to control the stability and settlement of the embankment through stabilization of the beds. Of the very large number of stabilization methods of loose beds, the stone column can be characterized as economically compatible with the nvironment. In this method, loose materials are replaced by stone material with notable shear strength. Stone columns increase the bearing capacity and control settlement of the embankment. Furthermore, it prevents slippage of the soil structure during application of service and earthquake loads. However, not many studies have been conducted on the interaction between surcharge railways and embankments located on stone columns, the mechanism of load transfer from the embankment to the columns and the amount of embankment settlement. This paper is aimed at determining the stability slopes of an embankment at different heights (5m up to15m) using the 2-D finite difference method and Plaxis Software. Then, through considering the bearing mechanism of stone columns, an analytical relation (root minimum square method) between the axial load of the railway, the geometric parameters of the stone column and the strength parameters of the clay bed has been derived. Due to the importance of the settlement control of a railway embankment, a relation has been derived between embankment settlement and mentioned parameters. Moreover, in order to examine the proper arrangement of columns and embankment conditions for different factors of earthquake acceleration, seismic analysis was performed. Also, the results of the pseudo-static analysis of an embankment indicated that by an increase in the horizontal coefficient of an earthquake, Kh, the safety factor decreases. However, all considered embankments relying on the stone column were stable in the horizontal acceleration coefficient within the range of 0.1 to 0.5. Finally, using the derived analytical relations, design graphs of stone columns have been presented on the basis of characteristics of a stone column and bed, and the axial load of the railway.
An important issue in the design and implementation of railways located on loose beds is to control the stability and settlement of the embankment through stabilization of the beds. Of the very large number of stabilization methods of loose beds, the stone column can be characterized as economically compatible with the nvironment. In this method, loose materials are replaced by stone material with notable shear strength. Stone columns increase the bearing capacity and control settlement of the embankment. Furthermore, it prevents slippage of the soil structure during application of service and earthquake loads. However, not many studies have been conducted on the interaction between surcharge railways and embankments located on stone columns, the mechanism of load transfer from the embankment to the columns and the amount of embankment settlement. This paper is aimed at determining the stability slopes of an embankment at different heights (5m up to15m) using the 2-D finite difference method and Plaxis Software. Then, through considering the bearing mechanism of stone columns, an analytical relation (root minimum square method) between the axial load of the railway, the geometric parameters of the stone column and the strength parameters of the clay bed has been derived. Due to the importance of the settlement control of a railway embankment, a relation has been derived between embankment settlement and mentioned parameters. Moreover, in order to examine the proper arrangement of columns and embankment conditions for different factors of earthquake acceleration, seismic analysis was performed. Also, the results of the pseudo-static analysis of an embankment indicated that by an increase in the horizontal coefficient of an earthquake, Kh, the safety factor decreases. However, all considered embankments relying on the stone column were stable in the horizontal acceleration coefficient within the range of 0.1 to 0.5. Finally, using the derived analytical relations, design graphs of stone columns have been presented on the basis of characteristics of a stone column and bed, and the axial load of the railway.
https://sjce.journals.sharif.edu/article_680_fccb3cdc9acc14a6e70a12f74560c026.pdf