This paper summarizes results from a comprehensive research program that aims at developing rational guidelines for the design of confinement reinforcement in concrete columns. The first part of the paper briefly introduces an analytical model for confined concrete in tied columns. The model is based on the results of testing 24 square columns with various tie configurations under concentric compression. The second part presents results from square columns tested under cyclic flexure and shear, and constant axial load simulating earthquake loads. The specimens tested included normal-strength concrete (NSC) and high-strength concrete (HSC) columns confined by steel and NSC columns confined by fiber-reinforced polymers (FRP). Performance-based procedures for the design of confinement reinforcement in these columns are proposed in light of the experimental results and analytical models. The design procedures incorporate various ductility parameters that include energy dissipation capacity, ductility factors, and cumulative ductility indices in addition to the type, amount, and configuration of the confinement reinforcement and the level of axial load. The areas in which further research is needed are also discussed.
{"title":"Toward the Performance-Based Design of Confined Concrete","authors":"S. Sheikh, Y. Li","doi":"10.14359/18261","DOIUrl":"https://doi.org/10.14359/18261","url":null,"abstract":"This paper summarizes results from a comprehensive research program that aims at developing rational guidelines for the design of confinement reinforcement in concrete columns. The first part of the paper briefly introduces an analytical model for confined concrete in tied columns. The model is based on the results of testing 24 square columns with various tie configurations under concentric compression. The second part presents results from square columns tested under cyclic flexure and shear, and constant axial load simulating earthquake loads. The specimens tested included normal-strength concrete (NSC) and high-strength concrete (HSC) columns confined by steel and NSC columns confined by fiber-reinforced polymers (FRP). Performance-based procedures for the design of confinement reinforcement in these columns are proposed in light of the experimental results and analytical models. The design procedures incorporate various ductility parameters that include energy dissipation capacity, ductility factors, and cumulative ductility indices in addition to the type, amount, and configuration of the confinement reinforcement and the level of axial load. The areas in which further research is needed are also discussed.","PeriodicalId":104265,"journal":{"name":"SP-238: International Symposium on Confined Concrete","volume":"55 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127172286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A two-stage analytical model for evaluating the stress-strain behavior of square concrete columns confined with glass fiber-reinforced polymer (GFRP) is proposed. Fifty-one square columns (divided into seventeen groups) were tested under static axial compression up to failure. The main factors considered in the test are as follows: grades of concrete, bonding shape, amounts of GFRP jackets, and space of fiber strips. The results clearly showed the efficiency of the GFRP jackets in enhancing the ultimate strain and the strength of the columns. The analytical model was calibrated using data from the tests, and good agreement between test and computation results was obtained.
{"title":"Experimental Study on Stress-Strain Relationship of Confined Concrete with GFRP Jackets","authors":"Changdong Zhou, Xi Lu","doi":"10.14359/18272","DOIUrl":"https://doi.org/10.14359/18272","url":null,"abstract":"A two-stage analytical model for evaluating the stress-strain behavior of square concrete columns confined with glass fiber-reinforced polymer (GFRP) is proposed. Fifty-one square columns (divided into seventeen groups) were tested under static axial compression up to failure. The main factors considered in the test are as follows: grades of concrete, bonding shape, amounts of GFRP jackets, and space of fiber strips. The results clearly showed the efficiency of the GFRP jackets in enhancing the ultimate strain and the strength of the columns. The analytical model was calibrated using data from the tests, and good agreement between test and computation results was obtained.","PeriodicalId":104265,"journal":{"name":"SP-238: International Symposium on Confined Concrete","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127304400","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recent worldwide applications of fiber reinforced polymers (FRP) wraps and tubes for existing and new structural members have continued to emphasize the significance of confined concrete. This study presents an overview of the related finite element (FE) studies for, but not limited to, the FRP-confined concrete applications of commercial FE programs such as ABAQUS and ANSYS. The capabilities, limitations, and remarks of the concrete models available in the programs are addressed. When the built-in options cannot be satisfied, several recommendations are also given for the user-defined concrete material models. The needs for future research and developments are also indicated.
{"title":"Finite Element Study of Confined Concrete","authors":"Wai-Fah Chen, Yi-ming Lan","doi":"10.14359/18274","DOIUrl":"https://doi.org/10.14359/18274","url":null,"abstract":"Recent worldwide applications of fiber reinforced polymers (FRP) wraps and tubes for existing and new structural members have continued to emphasize the significance of confined concrete. This study presents an overview of the related finite element (FE) studies for, but not limited to, the FRP-confined concrete applications of commercial FE programs such as ABAQUS and ANSYS. The capabilities, limitations, and remarks of the concrete models available in the programs are addressed. When the built-in options cannot be satisfied, several recommendations are also given for the user-defined concrete material models. The needs for future research and developments are also indicated.","PeriodicalId":104265,"journal":{"name":"SP-238: International Symposium on Confined Concrete","volume":"80 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121093013","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
It has been widely known that concrete filled steel tubular (CFT) columns have much higher strength and deformation capacities than common reinforced concrete (RC) columns because of beneficent interactive confinement effect between the filled concrete and the steel tube. The confinement effect by steel tube furthermore contributes to improving ductility of high-strength concrete, and enables application of the CFT columns in high-rise buildings located on seismic regions. This paper describes the axial and the flexural behaviors of CFT columns with circular and square sections based on many experimental researches conducted in Japan. The emphasis of this paper will be placed on the stress-strain curve models for concrete in CFT columns, which play the fundamental role in assessing both of the axial and the flexural behaviors of the CFT columns.
{"title":"Confined Concrete in Concrete-Filled Steel Tubular Columns","authors":"K. Sakino","doi":"10.14359/18277","DOIUrl":"https://doi.org/10.14359/18277","url":null,"abstract":"It has been widely known that concrete filled steel tubular (CFT) columns have much higher strength and deformation capacities than common reinforced concrete (RC) columns because of beneficent interactive confinement effect between the filled concrete and the steel tube. The confinement effect by steel tube furthermore contributes to improving ductility of high-strength concrete, and enables application of the CFT columns in high-rise buildings located on seismic regions. This paper describes the axial and the flexural behaviors of CFT columns with circular and square sections based on many experimental researches conducted in Japan. The emphasis of this paper will be placed on the stress-strain curve models for concrete in CFT columns, which play the fundamental role in assessing both of the axial and the flexural behaviors of the CFT columns.","PeriodicalId":104265,"journal":{"name":"SP-238: International Symposium on Confined Concrete","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132662780","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Accuracy of various stress-strain relationship models for concrete confined by lateral steel reinforcement in prediction of the moment-curvature response of a section under various loading patterns was investigated. Fiber model was implemented in a computer program developed for flexural analysis of reinforced concrete columns. Both monotonic and hysteretic analysis were performed. Each confined concrete model was used in the analysis for several loading cases on a circular, and a loading case on a rectangular section, keeping all other parameters fixed. Results were compared to each other and also validated against experimental data from six large-scale reinforced concrete circular columns and a rectangular section tested under the analyzed loading cases. In general, analysis underestimated the moment and overestimated the curvature capacities under a high level of axial load regardless of the model used, and there was a better agreement between analysis and test for low level or no axial load. Results from various models were close to each other, though different from test results, for cases with a constant or proportionally variable axial load. For a monotonic curvature with non-proportionally variable axial load, predictions by some recent models had a better agreement with experimental data. Evidently the level of axial load, and in turn the depth of compression zone, is related to the degree of confinement-utilization, and affects the confined concrete behavior. This is rarely addressed by the models.
{"title":"Analytical Performance of Reinforced Concrete Columns using Various Confinement Models","authors":"A. Esmaeily, Karen Lucio","doi":"10.14359/18266","DOIUrl":"https://doi.org/10.14359/18266","url":null,"abstract":"Accuracy of various stress-strain relationship models for concrete confined by lateral steel reinforcement in prediction of the moment-curvature response of a section under various loading patterns was investigated. Fiber model was implemented in a computer program developed for flexural analysis of reinforced concrete columns. Both monotonic and hysteretic analysis were performed. Each confined concrete model was used in the analysis for several loading cases on a circular, and a loading case on a rectangular section, keeping all other parameters fixed. Results were compared to each other and also validated against experimental data from six large-scale reinforced concrete circular columns and a rectangular section tested under the analyzed loading cases. In general, analysis underestimated the moment and overestimated the curvature capacities under a high level of axial load regardless of the model used, and there was a better agreement between analysis and test for low level or no axial load. Results from various models were close to each other, though different from test results, for cases with a constant or proportionally variable axial load. For a monotonic curvature with non-proportionally variable axial load, predictions by some recent models had a better agreement with experimental data. Evidently the level of axial load, and in turn the depth of compression zone, is related to the degree of confinement-utilization, and affects the confined concrete behavior. This is rarely addressed by the models.","PeriodicalId":104265,"journal":{"name":"SP-238: International Symposium on Confined Concrete","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132295248","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this study, FRP jacketed short reinforced concrete columns with low concrete strength and inadequate transverse reinforcement were tested under uniaxial compression. The diameter of the longitudinal bars and spacing of the transverse bars were designed to allow buckling of longitudinal bars. The effects of the jacket thickness, pre-damage, cross-section shape and the usage of FRP jackets - either continuous or as straps like hoops or spirals - were investigated. The test results showed that external confinement of these type of columns was very effective in terms of deformability and strength enhancement. The buckling of the longitudinal bars was delayed significantly by the FRP jackets. The pre-damage did not have an adverse effect on the performance of the jacketed members. It was also observed that for equivalent amount of FRP, continuous jackets and straps provided similar performances. The compressive strengths and the corresponding axial deformations of the columns were also predicted by the empirical equations proposed by the authors before. It was seen that these predictions were in reasonable agreement with experimental results.
{"title":"External Confinement of Low-Strength Brittle Reinforced Concrete Short Columns","authors":"A. Ilki, O. Peker, E. Karamuk, N. Kumbasar","doi":"10.14359/18282","DOIUrl":"https://doi.org/10.14359/18282","url":null,"abstract":"In this study, FRP jacketed short reinforced concrete columns with low concrete strength and inadequate transverse reinforcement were tested under uniaxial compression. The diameter of the longitudinal bars and spacing of the transverse bars were designed to allow buckling of longitudinal bars. The effects of the jacket thickness, pre-damage, cross-section shape and the usage of FRP jackets - either continuous or as straps like hoops or spirals - were investigated. The test results showed that external confinement of these type of columns was very effective in terms of deformability and strength enhancement. The buckling of the longitudinal bars was delayed significantly by the FRP jackets. The pre-damage did not have an adverse effect on the performance of the jacketed members. It was also observed that for equivalent amount of FRP, continuous jackets and straps provided similar performances. The compressive strengths and the corresponding axial deformations of the columns were also predicted by the empirical equations proposed by the authors before. It was seen that these predictions were in reasonable agreement with experimental results.","PeriodicalId":104265,"journal":{"name":"SP-238: International Symposium on Confined Concrete","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129402499","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Theoretically sound empirical models for the axial stress-strain behavior as well as the transverse deformation behavior of concrete with constant confinement under uniaxial compression loading are proposed based on plasticity theory using existing empirical models and test data in the literature. The proposed axial stress-strain model provides strength and ductility increases with increasing confining pressure. The confining pressure is applied in the model as an initial hydrostatic compression loading region. The proposed empirical transverse deformation model uses the plastic strain rate as a function of the axial strain to provide a basis for quantifying the compaction and dilation behavior of confined concrete under uniaxial loading conditions. Concretes with various compressive strengths are considered in combination with confining pressures up to 50% of the unconfined concrete strength. Parameters needed to describe the axial and transverse deformation behaviors are identified and their recommended values are provided.
{"title":"Empirical Models for Confined Concrete under Uniaxial Loading","authors":"Bohwan Oh, R. Sause","doi":"10.14359/18269","DOIUrl":"https://doi.org/10.14359/18269","url":null,"abstract":"Theoretically sound empirical models for the axial stress-strain behavior as well as the transverse deformation behavior of concrete with constant confinement under uniaxial compression loading are proposed based on plasticity theory using existing empirical models and test data in the literature. The proposed axial stress-strain model provides strength and ductility increases with increasing confining pressure. The confining pressure is applied in the model as an initial hydrostatic compression loading region. The proposed empirical transverse deformation model uses the plastic strain rate as a function of the axial strain to provide a basis for quantifying the compaction and dilation behavior of confined concrete under uniaxial loading conditions. Concretes with various compressive strengths are considered in combination with confining pressures up to 50% of the unconfined concrete strength. Parameters needed to describe the axial and transverse deformation behaviors are identified and their recommended values are provided.","PeriodicalId":104265,"journal":{"name":"SP-238: International Symposium on Confined Concrete","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115775730","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A dry column confining method using high-strength steel bars proposed by one of the authors is applied to a total of 24 reinforced concrete (RC) columns. Two series of tests were conducted on these columns. Hoop steel ratio of the columns was 0.1%, typical of RC columns designed before the Japanese Building Code in 1981. These RC columns were laterally reinforced using 19 sets of four high-strength steel bars and L-shaped steel blocks that were attached around the column by tightening the high-strength steel bars. Five specimens were exposed to concentric compression. Uniform bending test was conducted on 9 specimens under constant axial load. High-strength steel bars were pre-tensioned before testing. The amount of pre-tension was controlled by strain in the bars. It was found that the new confining method is effective to increase ductility of the RC columns. Strength of a RC column increases in a proportional manner to the amount of pre-stress in high-strength steel bars. Strength estimation method is proposed. The measured strength varied between 93% to 116% of the calculated strength.
{"title":"Compressive and Flexural Behavior of RC Columns Laterally Prestressed by High-strength Steel Bars","authors":"T. Hitaka, K. Sakino, T. Yamakawa, A. Furukawa","doi":"10.14359/18286","DOIUrl":"https://doi.org/10.14359/18286","url":null,"abstract":"A dry column confining method using high-strength steel bars proposed by one of the authors is applied to a total of 24 reinforced concrete (RC) columns. Two series of tests were conducted on these columns. Hoop steel ratio of the columns was 0.1%, typical of RC columns designed before the Japanese Building Code in 1981. These RC columns were laterally reinforced using 19 sets of four high-strength steel bars and L-shaped steel blocks that were attached around the column by tightening the high-strength steel bars. Five specimens were exposed to concentric compression. Uniform bending test was conducted on 9 specimens under constant axial load. High-strength steel bars were pre-tensioned before testing. The amount of pre-tension was controlled by strain in the bars. It was found that the new confining method is effective to increase ductility of the RC columns. Strength of a RC column increases in a proportional manner to the amount of pre-stress in high-strength steel bars. Strength estimation method is proposed. The measured strength varied between 93% to 116% of the calculated strength.","PeriodicalId":104265,"journal":{"name":"SP-238: International Symposium on Confined Concrete","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121268727","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, a continuum damage mechanics (CDM) based constitutive model appropriate for confined concrete is presented. Basically, the tensile and shear damage variables are adopted to describe the degrading of macro-mechanical properties of concrete, and the corresponding damage criteria are established based on elastoplastic damage energy release rates, which can predict the enhancement of strength and ductility of concrete under biaxial compression. To describe the compressive consolidation mechanism under triaxial compressive confinement, the above Drucker-Prager type shear damage criterion is modified to take the third invariant of effective stress into account. The irreversible plastic strains are determined empirically in this paper, though the effective stress space plasticity method is also introduced here. Comparing to experimental tests of concrete under biaxial and triaxial compressive stress states, the predictive results of proposed model show good agreement with test data, which validate the capability of present model for reproducing the nonlinearity of confined concrete.
{"title":"Energy-Based CDM Model for Nonlinear Analysis of Confined Concrete","authors":"Jie Li, Jian‐Ying Wu","doi":"10.14359/18273","DOIUrl":"https://doi.org/10.14359/18273","url":null,"abstract":"In this paper, a continuum damage mechanics (CDM) based constitutive model appropriate for confined concrete is presented. Basically, the tensile and shear damage variables are adopted to describe the degrading of macro-mechanical properties of concrete, and the corresponding damage criteria are established based on elastoplastic damage energy release rates, which can predict the enhancement of strength and ductility of concrete under biaxial compression. To describe the compressive consolidation mechanism under triaxial compressive confinement, the above Drucker-Prager type shear damage criterion is modified to take the third invariant of effective stress into account. The irreversible plastic strains are determined empirically in this paper, though the effective stress space plasticity method is also introduced here. Comparing to experimental tests of concrete under biaxial and triaxial compressive stress states, the predictive results of proposed model show good agreement with test data, which validate the capability of present model for reproducing the nonlinearity of confined concrete.","PeriodicalId":104265,"journal":{"name":"SP-238: International Symposium on Confined Concrete","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126598649","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents an experimental investigation to determine the ultimate strength of concrete under triaxial compression. Concrete of 4 different strength levels were employed and triaxial tests were performed on 100 x 300 mm cylindrical specimens to establish the failure criteria for low, normal and high-strength concrete. The effects of confining pressure and stress path on different grades of concrete were also studied and test results were used to verify the failure criteria proposed by other resources.
{"title":"Failure Criteria of Concrete under Triaxial Compression","authors":"T. Tan, Xin Sun","doi":"10.14359/18275","DOIUrl":"https://doi.org/10.14359/18275","url":null,"abstract":"This paper presents an experimental investigation to determine the ultimate strength of concrete under triaxial compression. Concrete of 4 different strength levels were employed and triaxial tests were performed on 100 x 300 mm cylindrical specimens to establish the failure criteria for low, normal and high-strength concrete. The effects of confining pressure and stress path on different grades of concrete were also studied and test results were used to verify the failure criteria proposed by other resources.","PeriodicalId":104265,"journal":{"name":"SP-238: International Symposium on Confined Concrete","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132371456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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