The performance of different nonlinear modelling strategies to simulate the response of RC columns subjected to axial load combined with cyclic biaxial horizontal loading is compared. The models studied are classified...The performance of different nonlinear modelling strategies to simulate the response of RC columns subjected to axial load combined with cyclic biaxial horizontal loading is compared. The models studied are classified into two categories according to the nonlinearity distribution assumed in the elements： lumped-plasticity and distributed inelasticity. For this study, results of tests on 24 columns subjected to cyclic uniaxial and biaxial lateral displacements were numerically reproduced. The analyses show that the global envelope response is satisfactorily represented with the three modelling strategies, but significant differences were found in the strength degradation for higher drift demands and energy dissipation.展开更多
In order to evaluate the seismic behavior of confined RC column-composite beam joints, five interior joints were tested under low cyclic reversed load. The weakening extent of flanges, the number of studs, and whether...In order to evaluate the seismic behavior of confined RC column-composite beam joints, five interior joints were tested under low cyclic reversed load. The weakening extent of flanges, the number of studs, and whether to reinforce weakened flanges were used as parameters in designing these five joints. Failure characteristics, hysteretic curves, skeleton curves, ductility, energy dissipation, strength degradation, and stiffness degradation were analyzed. The test results revealed that the steel beam flanges in the joints were equivalent to the tie rod. Weakened flanges resulted in poor seismic behavior; however, the seismic behavior could be improved by increasing studs and reinforcing weakened flanges. The joint steel plate hoops, equivalent to stirrups, did not yield when the maximum load was reached, but yielded when the failure load was reached for the joints with shear failure. Increasing stud-type joints and reinforcing flange-type joints ensured good seismic behavior and met project requirements. Based on the experimental results, the failure mechanism of the joints was discussed, and the shear capacity equations of the joints was presented.展开更多
Reinforced concrete(RC) columns are widely used as supporting structures for high-piled wharfs.The study of damage model of a RC column due to underwater explosion is a critical issue to assess the wharfs antiknock se...Reinforced concrete(RC) columns are widely used as supporting structures for high-piled wharfs.The study of damage model of a RC column due to underwater explosion is a critical issue to assess the wharfs antiknock security.In this study,the dynamic response and damage model of circular RC columns subjected to underwater explosions were investigated by means of scaled-down experiment models.Experiments were carried out in a 10.0 m diameter tank with the water depth of 2.25 m,under different explosive quantities(0.025 kg-1.6 kg),stand-off distances(0.0 m-7.0 m),and detonation depths(0.25 m-2.0 m).The shock wave load and dynamic response of experiment models were measured by configuring sensors of pressure,acceleration,strain,and displacement.Then,the load distribution characteristics,time history of test data,and damage models related to present conditions were obtained and discussed.Three damage models,including bending failure,bending-shear failure and punching failure,were identified.In addition,the experie nce model of shock wave loads on the surface of a RC column was proposed for engineering application.展开更多
Reinforced concrete(RC)columns are often subjected to off-central explosion due to the uncertainty of blast locations.However,few studies have focused on the dynamic response of RC columns under offcentral explosions....Reinforced concrete(RC)columns are often subjected to off-central explosion due to the uncertainty of blast locations.However,few studies have focused on the dynamic response of RC columns under offcentral explosions.A field blast experiment was conducted under close-in explosion with varying detonation offset distances(0 m,0.5 m,and 1 m),the overpressure load and dynamic responses of the full-scale RC columns were measured.Compared with the centrally detonated condition,a relative offset distance of 1.67 decreases the maximum and residual deflections of the RC column by 16.8%and 21.4%,respectively,while increasing the maximum and residual support rotations by 24.7%and 17.8%.Based on the experimental results,a theoretical model was proposed that considers the detonation location and charge mass,boundary conditions,axial compression ratio and material properties.The theoretical model exhibited good agreement with the experimental results,with prediction errors below 10%for both maximum and residual deflection.The effects of parameters were analyzed,and it indicated that an increase in offset distance results in decreased maximum and residual deflections but an increased support angle,thereby exacerbating damage.Higher axial load ratio,span-depth ratio,and longitudinal reinforcement ratio reduce both deflections and support angle.Additionally,a rapid method to predict the maximum and residual deflection of RC columns under off-central blast loading was also proposed based on the Generalized Regression Neural Network(GRNN).Eleven features which related to the RC column properties and the blast characteristics were used in the training process of GRNN,and accurate predictions were achieved with prediction errors within 20%.This study fills the gap in predicting the dynamic response of RC columns under off-central explosion,providing valuable references for blast-resistant design.展开更多
The behavior of reinforced concrete(RC)square columns strengthened with self-compacting concrete(SCC)-filled steel tubes under cyclic loading was experimentally investigated.Tests were carried out on eleven reinforced...The behavior of reinforced concrete(RC)square columns strengthened with self-compacting concrete(SCC)-filled steel tubes under cyclic loading was experimentally investigated.Tests were carried out on eleven reinforced columns and one unreinforced column.The parameters studied for the strengthened columns included axial compression ratio,reinforcement rate,defect rate,strength of SCC,and the section form of a reinforced steel tube.The results show that the steel tube SCC reinforcement method can effectively strengthen RC columns,exert the restraint effect of steel tube,and delay the development of internal concrete cracks.The method can also significantly improve the bearing capacity of RC columns.Regarding ductility,the improvement of the reinforced column is obvious,the deformation resistance of the specimen is enhanced,and the degradation of stiffness and strength is relatively slow,indicating that it has good seismic performance.展开更多
Numerical analysis is carried out to study the sectional properties of the fiber-reinforced polymer（FRP）-confined reinforced concrete（RC）circular columns. The axial load ratio, the FRP confinement ratio and the lo...Numerical analysis is carried out to study the sectional properties of the fiber-reinforced polymer（FRP）-confined reinforced concrete（RC）circular columns. The axial load ratio, the FRP confinement ratio and the longitudinal reinforcement characteristic value are the three main parameters that can influence the neutral axis depth when concrete compression strain reaches an ultimate value. The formula for computing the central angle θ, corresponding to the compression zone, is established according to the data regression of the numerical analysis results. The numerical analysis results demonstrate that the concrete stress enhancement from transverse confinement and strain hardening of the longitudinal reinforcement can cause a much greater flexural strength than that defined by the design code. Based on the analytical studies and the test results of 36 large scale columns, the formula to calculate the flexural strength when columns fail under seismic loading is proposed, and the calculated results agree well with the test results. Finally, parametric studies are conducted on a typical column with different axial load ratios, longitudinal reinforcement characteristic value and FRP confinement ratios. Analysis of the results shows that the calculated flexural strength can be increased by 50% compared to that of unconfined columns defined by the code.展开更多
In order to improve the load capacity, seismic performance and performance-cost ratio of the columns, the concrete at the base of reinforced concrete （RC） columns is substituted with engineered cementitious composit...In order to improve the load capacity, seismic performance and performance-cost ratio of the columns, the concrete at the base of reinforced concrete （RC） columns is substituted with engineered cementitious composites （ECC） to form ECC/RC composite columns. Based on the existing material properties, the mechanical behaviors of the ECC columns, ECC/RC composite columns and RC columns were numerically studied under combined vertical and horizontal loading with the software of ATENA. Then, the failure mechanism of ECC columns and ECC/RC composite columns were comprehensively studied and compared with that of the RC columns. Then, the effects of the height of the ECC, the axial compression ratio, and the transverse reinforcement ratio on the mechanical behaviors of the composite or the ECC column are studied. The calculation results show that the ultimate load capacity, ductility and crack resistance of the ECC or ECC/RC composite columns are superior to those of the RC columns. The ECC/RC composite column with a height of the ECC layer of 1.2h （ h is the height of the cross section） can achieve similar mechanical properties of a full ECC column. With high shear strength, ECC can undertake the shear force and significantly reduce the amount of stirrups, avoiding construction issues and promoting its engineering application.展开更多
The effects of length and location of the steel corrosion on the structural behavior and load capacity of reinforced concrete (RC) columns have been investigated. Results of the accelerated corrosion process and eccen...The effects of length and location of the steel corrosion on the structural behavior and load capacity of reinforced concrete (RC) columns have been investigated. Results of the accelerated corrosion process and eccentric load test are presented in detail. Effects of the location of the partial length, the corrosion level within partial length and the asymmetrical deterioration of the concrete section on the mechanical behavior and load capacity of corroded RC columns are discussed. It is found that the mechanical behavior and load carrying capacity of corroded RC columns are simultaneously affected by the above mentioned factors. For the corroded RC columns with large eccentricity, a higher corrosion level in the tensile corroded length and a greater asymmetrical deterioration of the concrete section can result in less ductile behavior and larger load reduction of the column; while for the corroded RC columns with small eccentricity, the less ductile behavior and the larger load reduction of the column may result from the higher corrosion level in the compressive corroded length and the greater asymmetrical deterioration of the concrete展开更多
To improve the seismic performance of columns, engineered cementitious composite （ECC） is introduced to partially substitute concrete at the base of the columns to form ECC,/reinforced concrete （ RC） composite col...To improve the seismic performance of columns, engineered cementitious composite （ECC） is introduced to partially substitute concrete at the base of the columns to form ECC,/reinforced concrete （ RC） composite columns. The mechanical behaviors of the ECC/RC composite columns are numerically studied under low-cyclic loading with the finite element analysis softwareof MSC. MARC. It is found that the ECC/RC composite columns can significantly enhance the load capacity, the ductility ad energy dissipation of columns. Then, the effects of the height of the ECC, the axial compression ratio and the longitudinal reinforcement ratio on the seismic behaviors of the composite columns are parametrically studied. The results show that the ECC/RC composite column with a height of the ECC layer of 0. Sh（h is the height to the cross-section） can achieve similar seismic performance of a full ECC column. The peak load of the composite column increases significantly while the ductility decreases with the increase of the axial compression ratio. Increasing the longitudinal reinforcement ratio within a certain range can improve the ductility and energy dissipation capacity and almost has no effect on load capacity. The aalysis results ae instructive and valuable for reference in designing ECC structures.展开更多
Additional hysteretic experiments for corroded rectangular reinforced concrete(RC)columns with an axial load ratio of 0.27 were implemented.A quasi-static cyclic lateral loading with constant axial force was subjected...Additional hysteretic experiments for corroded rectangular reinforced concrete(RC)columns with an axial load ratio of 0.27 were implemented.A quasi-static cyclic lateral loading with constant axial force was subjected to tests.Herein,a modified ductility factor model for corroded RC column is developed on the basis of the previous work and additional experiments.The model involves the influence of both the corrosion ratio of longitudinal rebar and the axial load ratio.A four-linear envelope curve model concerning lateral load and displacement is proposed in a combination of determination rules of the peak point and the failure strength point.The hysteretic model of corroded RC columns is developed by considering both degraded unloading stiffness and reloading stiffness on the history peak point.The hysteretic model can predict the residual life of corroded RC columns under seismic loading.展开更多
Reinforced concrete （RC） columns lacking adequately detailed transverse reinforcement do not possess the necessary ductility to dissipate seismic energy during a major earthquake without severe strength degradation....Reinforced concrete （RC） columns lacking adequately detailed transverse reinforcement do not possess the necessary ductility to dissipate seismic energy during a major earthquake without severe strength degradation. In this paper, a new retrofit method, which utilized fiber-reinforced plastics （FRP） confinement mechanism and anchorage of embedded bars, was developed aiming to retrofit non-ductile large RC rectangular columns to prevent the damage of the plastic hinges. Carbon FRP （CFRP） sheets and glass FRP （GFRP） bars were used in this test, and five scaled RC columns were tested to examine the function of this new method for improving the ductility of columns. Responses of columns were examined before and after being retrofitted. Test results indicate that this new composite method can be very effective to improve the anti-seismic behavior of non-ductile RC columns compared with normal CFRP sheets retrofitted column.展开更多
Since most current seismic capacity evaluations of reinforced concrete （RC） frame structures are implemented by either static pushover analysis （PA） or dynamic time history analysis, with diverse settings of the p...Since most current seismic capacity evaluations of reinforced concrete （RC） frame structures are implemented by either static pushover analysis （PA） or dynamic time history analysis, with diverse settings of the plastic hinges （PHs） on such main structural components as columns, beams and walls, the complex behavior of shear failure at beam-column joints （BCJs） during major earthquakes is commonly neglected. This study proposes new nonlinear PA procedures that consider shear failure at BCJs and seek to assess the actual damage to RC structures. Based on the specifications of FEMA-356, a simplified joint model composed of two nonlinear cross struts placed diagonally over the location of the plastic hinge is established, allowing a sophisticated PA to be performed. To verify the validity of this method, the analytical results for the capacity curves and the failure mechanism derived from three different full-size RC frames are compared with the experimental measurements. By considering shear failure at BCJs, the proposed nonlinear analytical procedures can be used to estimate the structural behavior of RC frames, including seismic capacity and the progressive failure sequence of joints, in a precise and effective manner.展开更多
The behavior of slender columns under the effect of eccentric loading has always taken the attention of researchers. When investigating the strengthening of reinforced concrete columns, mainly short and circular colum...The behavior of slender columns under the effect of eccentric loading has always taken the attention of researchers. When investigating the strengthening of reinforced concrete columns, mainly short and circular columns are the targeted elements. This is why the data about slender columns with rectangular sections is limited and infrequent specially when loaded eccentrically. This paper aims to increase the available experimental data in this specific area. The experimental program consisted of twenty seven specimens. The specimens were divided into three groups; one control group and two groups strengthened using two strengthening schemes. Scheme 1 implied the use of near surface mounted （NSM） longitudinal steel bars, while in scheme 2, NSM longitudinal steel bars partially wrapped with one ply of carbon fibers reinforced polymers （CFRP） sheets was used. The test specimen had an overall length of 2000 mm and a 100 x 200 mm rectangular cross section. In addition to the strengthening schemes, the test parameters included three ratios for the internal longitudinal steel bars ＂μ＂ 1%, 1.57% and 2.26%. The parameters were extended to cover three stirrups＇ volumetric ratio ＂ρv＂ 0.73%, 0.49% and 0.37%. The specimens were tested under the effect of eccentric loading with eccentricity-to-section height e/h equals 0.25. The research revealed that the strength gain in specimens strengthened with scheme 2 was higher than with scheme 1. Analytical modeling of the stress strain relation of the strengthened RC columns considering the effect of strengthening scheme, internal reinforcement ratio μ, and stirrups＇ volumetric ratio ＂ρv＂ was proposed. Verification was made using available experimental data. The proposed model showed a reasonable agreement with the experimental results.展开更多
基金Financial support provided by "FCT - Fundao para a Ciência e Tecnologia,"Portugal,through the research project PTDC/ECM/102221/2008
文摘The performance of different nonlinear modelling strategies to simulate the response of RC columns subjected to axial load combined with cyclic biaxial horizontal loading is compared. The models studied are classified into two categories according to the nonlinearity distribution assumed in the elements： lumped-plasticity and distributed inelasticity. For this study, results of tests on 24 columns subjected to cyclic uniaxial and biaxial lateral displacements were numerically reproduced. The analyses show that the global envelope response is satisfactorily represented with the three modelling strategies, but significant differences were found in the strength degradation for higher drift demands and energy dissipation.
基金Supported by the National Natural Science Foundation of China(No.51209094)
文摘In order to evaluate the seismic behavior of confined RC column-composite beam joints, five interior joints were tested under low cyclic reversed load. The weakening extent of flanges, the number of studs, and whether to reinforce weakened flanges were used as parameters in designing these five joints. Failure characteristics, hysteretic curves, skeleton curves, ductility, energy dissipation, strength degradation, and stiffness degradation were analyzed. The test results revealed that the steel beam flanges in the joints were equivalent to the tie rod. Weakened flanges resulted in poor seismic behavior; however, the seismic behavior could be improved by increasing studs and reinforcing weakened flanges. The joint steel plate hoops, equivalent to stirrups, did not yield when the maximum load was reached, but yielded when the failure load was reached for the joints with shear failure. Increasing stud-type joints and reinforcing flange-type joints ensured good seismic behavior and met project requirements. Based on the experimental results, the failure mechanism of the joints was discussed, and the shear capacity equations of the joints was presented.
基金funded by the National Natural Science Foundation of China(Grant Nos.51578543)。
文摘Reinforced concrete(RC) columns are widely used as supporting structures for high-piled wharfs.The study of damage model of a RC column due to underwater explosion is a critical issue to assess the wharfs antiknock security.In this study,the dynamic response and damage model of circular RC columns subjected to underwater explosions were investigated by means of scaled-down experiment models.Experiments were carried out in a 10.0 m diameter tank with the water depth of 2.25 m,under different explosive quantities(0.025 kg-1.6 kg),stand-off distances(0.0 m-7.0 m),and detonation depths(0.25 m-2.0 m).The shock wave load and dynamic response of experiment models were measured by configuring sensors of pressure,acceleration,strain,and displacement.Then,the load distribution characteristics,time history of test data,and damage models related to present conditions were obtained and discussed.Three damage models,including bending failure,bending-shear failure and punching failure,were identified.In addition,the experie nce model of shock wave loads on the surface of a RC column was proposed for engineering application.
基金financially supported by the National Natural Science Foundation of China(Grants No.12472399)。
文摘Reinforced concrete(RC)columns are often subjected to off-central explosion due to the uncertainty of blast locations.However,few studies have focused on the dynamic response of RC columns under offcentral explosions.A field blast experiment was conducted under close-in explosion with varying detonation offset distances(0 m,0.5 m,and 1 m),the overpressure load and dynamic responses of the full-scale RC columns were measured.Compared with the centrally detonated condition,a relative offset distance of 1.67 decreases the maximum and residual deflections of the RC column by 16.8%and 21.4%,respectively,while increasing the maximum and residual support rotations by 24.7%and 17.8%.Based on the experimental results,a theoretical model was proposed that considers the detonation location and charge mass,boundary conditions,axial compression ratio and material properties.The theoretical model exhibited good agreement with the experimental results,with prediction errors below 10%for both maximum and residual deflection.The effects of parameters were analyzed,and it indicated that an increase in offset distance results in decreased maximum and residual deflections but an increased support angle,thereby exacerbating damage.Higher axial load ratio,span-depth ratio,and longitudinal reinforcement ratio reduce both deflections and support angle.Additionally,a rapid method to predict the maximum and residual deflection of RC columns under off-central blast loading was also proposed based on the Generalized Regression Neural Network(GRNN).Eleven features which related to the RC column properties and the blast characteristics were used in the training process of GRNN,and accurate predictions were achieved with prediction errors within 20%.This study fills the gap in predicting the dynamic response of RC columns under off-central explosion,providing valuable references for blast-resistant design.
基金Natural Science Foundation of Sichuan Province under Grant Nos.2022NSFSC0319 and 2022NSFSC0095the Science and Technology Research Projects of Mianyang,China under Grant No.15S-02-3。
文摘The behavior of reinforced concrete(RC)square columns strengthened with self-compacting concrete(SCC)-filled steel tubes under cyclic loading was experimentally investigated.Tests were carried out on eleven reinforced columns and one unreinforced column.The parameters studied for the strengthened columns included axial compression ratio,reinforcement rate,defect rate,strength of SCC,and the section form of a reinforced steel tube.The results show that the steel tube SCC reinforcement method can effectively strengthen RC columns,exert the restraint effect of steel tube,and delay the development of internal concrete cracks.The method can also significantly improve the bearing capacity of RC columns.Regarding ductility,the improvement of the reinforced column is obvious,the deformation resistance of the specimen is enhanced,and the degradation of stiffness and strength is relatively slow,indicating that it has good seismic performance.
基金The National Basic Research Program of China (973 Program)(No.2007CB714200)the National Natural Science Foundationof China (No.50608015,50908102)
文摘Numerical analysis is carried out to study the sectional properties of the fiber-reinforced polymer（FRP）-confined reinforced concrete（RC）circular columns. The axial load ratio, the FRP confinement ratio and the longitudinal reinforcement characteristic value are the three main parameters that can influence the neutral axis depth when concrete compression strain reaches an ultimate value. The formula for computing the central angle θ, corresponding to the compression zone, is established according to the data regression of the numerical analysis results. The numerical analysis results demonstrate that the concrete stress enhancement from transverse confinement and strain hardening of the longitudinal reinforcement can cause a much greater flexural strength than that defined by the design code. Based on the analytical studies and the test results of 36 large scale columns, the formula to calculate the flexural strength when columns fail under seismic loading is proposed, and the calculated results agree well with the test results. Finally, parametric studies are conducted on a typical column with different axial load ratios, longitudinal reinforcement characteristic value and FRP confinement ratios. Analysis of the results shows that the calculated flexural strength can be increased by 50% compared to that of unconfined columns defined by the code.
基金The National Natural Science Foundation of China(No.51278118)the Natural Science Foundation of Jiangsu Province(No.BK2012756)the Key Project of Ministry of Education of China(No.113029A)
文摘In order to improve the load capacity, seismic performance and performance-cost ratio of the columns, the concrete at the base of reinforced concrete （RC） columns is substituted with engineered cementitious composites （ECC） to form ECC/RC composite columns. Based on the existing material properties, the mechanical behaviors of the ECC columns, ECC/RC composite columns and RC columns were numerically studied under combined vertical and horizontal loading with the software of ATENA. Then, the failure mechanism of ECC columns and ECC/RC composite columns were comprehensively studied and compared with that of the RC columns. Then, the effects of the height of the ECC, the axial compression ratio, and the transverse reinforcement ratio on the mechanical behaviors of the composite or the ECC column are studied. The calculation results show that the ultimate load capacity, ductility and crack resistance of the ECC or ECC/RC composite columns are superior to those of the RC columns. The ECC/RC composite column with a height of the ECC layer of 1.2h （ h is the height of the cross section） can achieve similar mechanical properties of a full ECC column. With high shear strength, ECC can undertake the shear force and significantly reduce the amount of stirrups, avoiding construction issues and promoting its engineering application.
基金the National Natural Science Foundation of China (No.50508020)
文摘The effects of length and location of the steel corrosion on the structural behavior and load capacity of reinforced concrete (RC) columns have been investigated. Results of the accelerated corrosion process and eccentric load test are presented in detail. Effects of the location of the partial length, the corrosion level within partial length and the asymmetrical deterioration of the concrete section on the mechanical behavior and load capacity of corroded RC columns are discussed. It is found that the mechanical behavior and load carrying capacity of corroded RC columns are simultaneously affected by the above mentioned factors. For the corroded RC columns with large eccentricity, a higher corrosion level in the tensile corroded length and a greater asymmetrical deterioration of the concrete section can result in less ductile behavior and larger load reduction of the column; while for the corroded RC columns with small eccentricity, the less ductile behavior and the larger load reduction of the column may result from the higher corrosion level in the compressive corroded length and the greater asymmetrical deterioration of the concrete
基金The National Natural Science Foundation of China(No.51278118)the Natural Science Foundation of Jiangsu Province(No.BK2012756)+1 种基金the Key Project of Ministry of Education of China(No.113029A)the Third Five-Year Major Scientific and Technological Project of China Metallurgical Group Corporation
文摘To improve the seismic performance of columns, engineered cementitious composite （ECC） is introduced to partially substitute concrete at the base of the columns to form ECC,/reinforced concrete （ RC） composite columns. The mechanical behaviors of the ECC/RC composite columns are numerically studied under low-cyclic loading with the finite element analysis softwareof MSC. MARC. It is found that the ECC/RC composite columns can significantly enhance the load capacity, the ductility ad energy dissipation of columns. Then, the effects of the height of the ECC, the axial compression ratio and the longitudinal reinforcement ratio on the seismic behaviors of the composite columns are parametrically studied. The results show that the ECC/RC composite column with a height of the ECC layer of 0. Sh（h is the height to the cross-section） can achieve similar seismic performance of a full ECC column. The peak load of the composite column increases significantly while the ductility decreases with the increase of the axial compression ratio. Increasing the longitudinal reinforcement ratio within a certain range can improve the ductility and energy dissipation capacity and almost has no effect on load capacity. The aalysis results ae instructive and valuable for reference in designing ECC structures.
基金the Programs for Changjiang Scholars and Innovative Research Team in University of the Ministry of Education of China(No.IRT1067)the National Natural Science Foundation of China(No.51868065)。
文摘Additional hysteretic experiments for corroded rectangular reinforced concrete(RC)columns with an axial load ratio of 0.27 were implemented.A quasi-static cyclic lateral loading with constant axial force was subjected to tests.Herein,a modified ductility factor model for corroded RC column is developed on the basis of the previous work and additional experiments.The model involves the influence of both the corrosion ratio of longitudinal rebar and the axial load ratio.A four-linear envelope curve model concerning lateral load and displacement is proposed in a combination of determination rules of the peak point and the failure strength point.The hysteretic model of corroded RC columns is developed by considering both degraded unloading stiffness and reloading stiffness on the history peak point.The hysteretic model can predict the residual life of corroded RC columns under seismic loading.
基金Project supported by the Science Foundation of Shanghai Municipal Commission of Science and Technology （Grant No.07QA14025）.Acknowledgment The authors thank Dr. WU Yu-fei, the assistant professor of the City University of Hong Kong for providing good suggestion and help during the test. This research was also supported by the grant from the Research Grant Council of the Hong Kong Special Administrative Region （Grant No.Cityu1113/04E）.
文摘Reinforced concrete （RC） columns lacking adequately detailed transverse reinforcement do not possess the necessary ductility to dissipate seismic energy during a major earthquake without severe strength degradation. In this paper, a new retrofit method, which utilized fiber-reinforced plastics （FRP） confinement mechanism and anchorage of embedded bars, was developed aiming to retrofit non-ductile large RC rectangular columns to prevent the damage of the plastic hinges. Carbon FRP （CFRP） sheets and glass FRP （GFRP） bars were used in this test, and five scaled RC columns were tested to examine the function of this new method for improving the ductility of columns. Responses of columns were examined before and after being retrofitted. Test results indicate that this new composite method can be very effective to improve the anti-seismic behavior of non-ductile RC columns compared with normal CFRP sheets retrofitted column.
文摘Since most current seismic capacity evaluations of reinforced concrete （RC） frame structures are implemented by either static pushover analysis （PA） or dynamic time history analysis, with diverse settings of the plastic hinges （PHs） on such main structural components as columns, beams and walls, the complex behavior of shear failure at beam-column joints （BCJs） during major earthquakes is commonly neglected. This study proposes new nonlinear PA procedures that consider shear failure at BCJs and seek to assess the actual damage to RC structures. Based on the specifications of FEMA-356, a simplified joint model composed of two nonlinear cross struts placed diagonally over the location of the plastic hinge is established, allowing a sophisticated PA to be performed. To verify the validity of this method, the analytical results for the capacity curves and the failure mechanism derived from three different full-size RC frames are compared with the experimental measurements. By considering shear failure at BCJs, the proposed nonlinear analytical procedures can be used to estimate the structural behavior of RC frames, including seismic capacity and the progressive failure sequence of joints, in a precise and effective manner.
文摘The behavior of slender columns under the effect of eccentric loading has always taken the attention of researchers. When investigating the strengthening of reinforced concrete columns, mainly short and circular columns are the targeted elements. This is why the data about slender columns with rectangular sections is limited and infrequent specially when loaded eccentrically. This paper aims to increase the available experimental data in this specific area. The experimental program consisted of twenty seven specimens. The specimens were divided into three groups; one control group and two groups strengthened using two strengthening schemes. Scheme 1 implied the use of near surface mounted （NSM） longitudinal steel bars, while in scheme 2, NSM longitudinal steel bars partially wrapped with one ply of carbon fibers reinforced polymers （CFRP） sheets was used. The test specimen had an overall length of 2000 mm and a 100 x 200 mm rectangular cross section. In addition to the strengthening schemes, the test parameters included three ratios for the internal longitudinal steel bars ＂μ＂ 1%, 1.57% and 2.26%. The parameters were extended to cover three stirrups＇ volumetric ratio ＂ρv＂ 0.73%, 0.49% and 0.37%. The specimens were tested under the effect of eccentric loading with eccentricity-to-section height e/h equals 0.25. The research revealed that the strength gain in specimens strengthened with scheme 2 was higher than with scheme 1. Analytical modeling of the stress strain relation of the strengthened RC columns considering the effect of strengthening scheme, internal reinforcement ratio μ, and stirrups＇ volumetric ratio ＂ρv＂ was proposed. Verification was made using available experimental data. The proposed model showed a reasonable agreement with the experimental results.
