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
Achievements are presented for truss models of RC structures developed in previous years: 1. Two constitutive models, biaxial and triaxial, are based on regular trusses, with bars obeying nonlinear uniaxial σ-ε laws...Achievements are presented for truss models of RC structures developed in previous years: 1. Two constitutive models, biaxial and triaxial, are based on regular trusses, with bars obeying nonlinear uniaxial σ-ε laws of material under simulation;both models have been compared with test results and show a dependence of Poisson ratio on curvature of σ-ε law. 2. A truss finite element has been used in the nonlinear static and dynamic analysis of plane RC frames;it has been compared with test results and describes, in a simple way, the formation of plastic hinges. 3. Thanks to the very simple geometry of a truss, the equilibrium equations can be easily written and the stiffness matrix can be easily updated, both with respect to the deformed truss, within each step of a static incremental loading or within each time step of a dynamic analysis, so that to take into account geometric nonlinearities. So the confinement of a RC column is interpreted as a structural stability effect of concrete. And a significant role of the transverse reinforcement is revealed, that of preventing, by its close spacing and sufficient amount, the buckling of inner longitudinal concrete struts, which would lead to a global instability of the RC column. 4. The proposed truss model is statically indeterminate, so it exhibits some features, which are not met by the “strut-and-tie” model.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
Bonding fiber reinforced polymer （FRP） has been commonly used to improve the seismic behavior of circular reinforced concrete （RC） columns in engineering practice. However, FRP jackets have a significant stress hy...Bonding fiber reinforced polymer （FRP） has been commonly used to improve the seismic behavior of circular reinforced concrete （RC） columns in engineering practice. However, FRP jackets have a significant stress hysteresis effect in this strengthening method, and pre-tensioning the FRP can overcome this problem. This paper presents test results of 25 circular RC columns strengthened with pre-stressed FRP strips under low cyclic loading. The pre-stressing of the FRP strips, types of FRP strips and longitudinal reinforcement, axial load ratio, pre-damage degree and surface treatments of the specimens are considered as the primary factors in the tests. According to the failure modes and hysteresis curves of the specimens, these factors are analyzed to investigate their effect on bearing capacity, ductility, hysteretic behavior, energy dissipation capacity and other important seismic behaviors. The results show that the initial lateral confined stress provided by pre-stressed FRP strips can effectively inhibit the emergence and development of diagonal shear cracks, and change the failure modes of specimens from brittle shear failure to bending or bending-shear failure with better ductility. As a result, the bearing capacity, ductility, energy dissipation capacity and deformation capacity of the strengthened specimens are all significantly improved.展开更多
It is possible for certain building structures to encounter both the seismic load and blast load during their service life.With the development of the economy and the increase of security demand,the need for design of...It is possible for certain building structures to encounter both the seismic load and blast load during their service life.With the development of the economy and the increase of security demand,the need for design of building structures against multi-hazard is becoming more and more obvious.Therefore,the damage analysis of building structures under the combined action of multiple hazards has become a very urgent requirement for disaster prevention and reduction.In this paper,the refined finite element model of reinforced concrete(RC)columns is established by using the explicit dynamic analysis software LS-DYNA.Combined with the Monte Carlo method,the damage law of RC columns under the combined action of random single earthquake or explosion disaster and multi-hazard is studied,and the damage groups are distinguished according to the damage index.Based on the support vector machine(SVM)algorithm,the dividing line between different damage degree groups is determined,and a rapid method for determining the damage degree of RC columns under the combined seismic and blast loads is proposed.Finally,suggestions for the design of RC column against multi-disaster are put forward.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
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
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Achievements are presented for truss models of RC structures developed in previous years: 1. Two constitutive models, biaxial and triaxial, are based on regular trusses, with bars obeying nonlinear uniaxial σ-ε laws of material under simulation;both models have been compared with test results and show a dependence of Poisson ratio on curvature of σ-ε law. 2. A truss finite element has been used in the nonlinear static and dynamic analysis of plane RC frames;it has been compared with test results and describes, in a simple way, the formation of plastic hinges. 3. Thanks to the very simple geometry of a truss, the equilibrium equations can be easily written and the stiffness matrix can be easily updated, both with respect to the deformed truss, within each step of a static incremental loading or within each time step of a dynamic analysis, so that to take into account geometric nonlinearities. So the confinement of a RC column is interpreted as a structural stability effect of concrete. And a significant role of the transverse reinforcement is revealed, that of preventing, by its close spacing and sufficient amount, the buckling of inner longitudinal concrete struts, which would lead to a global instability of the RC column. 4. The proposed truss model is statically indeterminate, so it exhibits some features, which are not met by the “strut-and-tie” model.
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National Natural Science Foundation of China under Grant No.51178029 State Key Laboratory for Disaster Reduction in Civil Engineering at Tongji University under Grant No.SLDRCE08-MB-01
文摘Bonding fiber reinforced polymer （FRP） has been commonly used to improve the seismic behavior of circular reinforced concrete （RC） columns in engineering practice. However, FRP jackets have a significant stress hysteresis effect in this strengthening method, and pre-tensioning the FRP can overcome this problem. This paper presents test results of 25 circular RC columns strengthened with pre-stressed FRP strips under low cyclic loading. The pre-stressing of the FRP strips, types of FRP strips and longitudinal reinforcement, axial load ratio, pre-damage degree and surface treatments of the specimens are considered as the primary factors in the tests. According to the failure modes and hysteresis curves of the specimens, these factors are analyzed to investigate their effect on bearing capacity, ductility, hysteretic behavior, energy dissipation capacity and other important seismic behaviors. The results show that the initial lateral confined stress provided by pre-stressed FRP strips can effectively inhibit the emergence and development of diagonal shear cracks, and change the failure modes of specimens from brittle shear failure to bending or bending-shear failure with better ductility. As a result, the bearing capacity, ductility, energy dissipation capacity and deformation capacity of the strengthened specimens are all significantly improved.
基金supported by the National Natural Science Foundation of China (Grant Nos.51878445,51938011 and 51908405)。
文摘It is possible for certain building structures to encounter both the seismic load and blast load during their service life.With the development of the economy and the increase of security demand,the need for design of building structures against multi-hazard is becoming more and more obvious.Therefore,the damage analysis of building structures under the combined action of multiple hazards has become a very urgent requirement for disaster prevention and reduction.In this paper,the refined finite element model of reinforced concrete(RC)columns is established by using the explicit dynamic analysis software LS-DYNA.Combined with the Monte Carlo method,the damage law of RC columns under the combined action of random single earthquake or explosion disaster and multi-hazard is studied,and the damage groups are distinguished according to the damage index.Based on the support vector machine(SVM)algorithm,the dividing line between different damage degree groups is determined,and a rapid method for determining the damage degree of RC columns under the combined seismic and blast loads is proposed.Finally,suggestions for the design of RC column against multi-disaster are put forward.
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 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.
