In order to study the effectiveness of combined carbon fiber-reinforced polymer （CFRP） sheets and steel jacket in strengthening the seismic performance of corrosion-damaged reinforced concrete （RC） columns, twelve...In order to study the effectiveness of combined carbon fiber-reinforced polymer （CFRP） sheets and steel jacket in strengthening the seismic performance of corrosion-damaged reinforced concrete （RC） columns, twelve reinforced concrete columns are tested under combined lateral cyclic displacement excursions and constant axial load. The variables studied in this program include effects of corrosion degree of the rebars, level of axial load, the amount of CFRP sheets and steel jacket. The results indicate that the combined CFRP and steel jacket retrofitting technique is effective in improving load-carrying, ductility and energy absorption capacity of the columns. Compared with the corrosion-damaged RC column, the lateral load and the ductility factor of many strengthened columns increase more than 90% and 100%, respectively. The formulae for the calculation of the yielding load, the maximum lateral load and the displacement ductility factor of the strengthened columns under combined constant axial load and cyclically increasing lateral loading are developed. The test results are also compared with the results obtained from the proposed formulae. A good agreement between calculated values and experimental results is observed.展开更多
The application of fi ber-reinforced polymer (FRP) composites for the development of high-performance composite structural systems has received signifi cant recent research attention. A composite of FRP–recycled aggr...The application of fi ber-reinforced polymer (FRP) composites for the development of high-performance composite structural systems has received signifi cant recent research attention. A composite of FRP–recycled aggregate concrete (RAC)–steel column (FRSC), consisting of an outer FRP tube, an inner steel tube and annular RAC fi lled between two tubes, is proposed herein to facilitate green disposal of demolished concrete and to improve the ductility of concrete columns for earthquake resistance. To better understand the seismic behavior of FRSCs, quasi-static tests of large-scale basalt FRSCs with shear connectors were conducted. The infl uence of the recycled coarse aggregate (RCA) replacement percentage, shear connectors and axial loading method on the lateral load and deformation capacity, energy dissipation and cumulative damage were analyzed to evaluate the seismic behavior of FRSCs. The test results show that FRSCs have good seismic behavior, which was evidenced by high lateral loads, excellent ductility and energy dissipation capacity, indicating RAC is applicable in FRSCs. Shear connectors can signifi cantly postpone the steel buckling and increase the lateral loads of FRSCs, but weaken the deformation capacity and energy dissipation performance.展开更多
The seismic performance of steel reinforced ultra-high-strength concrete columns(SRSHC) with various shear-span ratios(λ) were studied through a series of experiments.The concrete compressive cube strength value of e...The seismic performance of steel reinforced ultra-high-strength concrete columns(SRSHC) with various shear-span ratios(λ) were studied through a series of experiments.The concrete compressive cube strength value of experimental specimens ranged from 92.9 MPa to 108.1 MPa.The main experimental variables affecting seismic performance of specimens were axial load ratio and stirrup reinforcement ratio.The columns(λ=2.75) subjected to low cyclic reversed lateral loads failed mainly in the flexural-shear mode failure and columns(λ≤2.0) subjected to low cyclic reversed lateral loads failed mainly in the shear mode failure.Shear force-displacement hysteretic curves and skeleton curves were drawn.Coefficient of the specimen displacement ductility was calculated.Experimental results indicate that ductility decreases with axial pressure ratio increasing,and increases with stirrup reinforcement ratio increasing.Limit values of axial pressure ratio and minimum stirrup reinforcement ratio of columns are proposed to satisfy definite ductility requirement.The suggested values provide a reference for engineering application and for the amendment of the current Chinese design code of steel reinforced concrete composite structures.展开更多
The bearing capacity of FRP confined concrete-filled steel tubular （FRP-CFST） columns under axial compression was investigated. This new type of composite column is a concrete-filled steel tube （CFST） confined wit...The bearing capacity of FRP confined concrete-filled steel tubular （FRP-CFST） columns under axial compression was investigated. This new type of composite column is a concrete-filled steel tube （CFST） confined with fiber-reinforced polymer （FRP） wraps. Totally 11 short column specimens were tested to failure under axial compression. The influences of the type and quantity of FRP, the thickness of steel tube and the concrete strength were studied. It was found that the bearing capacity of short FRP-CFST column was much higher than that of comparable CFST column. Furthermore, the formulas for calculating the bearing capacity of the FRP-CFST columns are proposed. The analytical calculated results agree well with the experimental results.展开更多
To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete （SRUHSC） columns and steel reinforced concrete （SRC） beams, six interior frame joint specimens...To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete （SRUHSC） columns and steel reinforced concrete （SRC） beams, six interior frame joint specimens were designed and tested under low cyclically lateral load. The effects of the axial load ratio and volumetric stirrup ratio were studied on the characteristics of the frame joint performance including crack pattern, failure mode, ductility, energy dissipation capacity, strength degradation and rigidity degradation. It was found that all joint specimens behaved in a ductile manner with flexural-shear failure in the joint core region while plastic hinges appeared at the beam ends. The ductility and energy absorption capacity of joints increased as the axial load ratio decreased and the volumetric stirIup ratio increased. The displacement ductility coefficient and equivalent damping coefficient of the joints fell between the corresponding coefficients of the steel reinforced concrete （SRC） frame joint and RC frame joint. The axial load ratio and volumetric stirrup ratio have less influence on the strength degradation and more influence on the stiffness degradation. The stiffness of the joint degrades more significantly for a low volumetric stirrup ratio and high axial load ratio. The characteristics obtained from the SRUHSC composite frame joint specimens with better seismic performance may be a useful reference in future engineering applications.展开更多
A beam-column joint of precast and partial steel reinforced concrete( PPSRC) is proposed for precast reinforced concrete frames. The PPSRC consists of partial steel and reinforced concrete. The partial steel is locate...A beam-column joint of precast and partial steel reinforced concrete( PPSRC) is proposed for precast reinforced concrete frames. The PPSRC consists of partial steel and reinforced concrete. The partial steel is located in the core joint region and the connections between concrete members. This paper presents an experimental study of a series of PPSRC specimens. These specimens are tested under low cyclic loading.Experimental results demonstrate that the bearing capacity of the PPSRC specimens is 3 times that of the ordinary reinforced concrete( RC) beam-column joints. The strength and stiffness degradation rates are slower compared with that of the RC beam-column joints. In addition,the strength of the core joint region and the connections is higher than other parts of the PPSRC specimens. Beam failure occurs firstly for the PPSRC specimens,followed by column failure and connections failure. The failure of the core joint region occurs finally.Test results show that the seismic performance of the PPSRC is better than that of the ordinary RC beam-column joints.展开更多
Steel tubed-reinforced-concrete(TRC) columns have been gradually used in the construction of high-rise buildings recently because of their high axial load-carrying capacities and excellent seismic behavior. Existing s...Steel tubed-reinforced-concrete(TRC) columns have been gradually used in the construction of high-rise buildings recently because of their high axial load-carrying capacities and excellent seismic behavior. Existing studies about their seismic behavior were focused on columns with relatively thick tubes, i.e., diameter-to-thickness/width-to-thickness(D/t) ratios were below 100,while little is known about thin-walled TRC columns, especially for square TRC columns. Considering the infilled concrete of square TRC columns is non-uniformly and non-effectively confined, accordingly, stiffened square TRC columns are usually adopted in practice. Thus, two thin-walled circular TRC columns(D/t=120) and two stiffened square ones with diagonal stiffeners in plastic hinge regions(D/t=106) were tested under a constant axial compression combined with cyclic lateral loading.Both the circular and stiffened square TRC columns had the same cross sectional area, tube thickness, reinforcing bar ratio and column height. Flexural failure occurred for all the four specimens. Test results showed the strengths of the stiffened square TRC columns were a little higher in comparison to their circular counterparts; the ductility and energy dissipation capacities were excellent for both the stiffened and circular TRC columns, indicating very good confinement was gained from the yielded steel tubes of the plastic hinge regions at the peak loads. And shear stresses(35–90 MPa) in the sheared plates showed their moderate contribution of carrying lateral loads. Finally, cross sectional capacity analysis results demonstrated the method for TRC columns is acceptable for the stiffened square TRC columns.展开更多
Statically push-out tests of 20 steel reinforced concrete short columns （SRCSC） with stud connectors on the surface of shape steel after fire and two SRCSC under ambient temperature were carried out, in order to stu...Statically push-out tests of 20 steel reinforced concrete short columns （SRCSC） with stud connectors on the surface of shape steel after fire and two SRCSC under ambient temperature were carried out, in order to study the failure mode, load-slip relationship and the interfacial shear transfer of SRC members after fire. Experimental results show that the typical failure modes and load-slip curves of SRCSC after fire are almost the same as the case under ambient temperature. The interfacial shear transfer of SRCSC declines exponentially not only with the increase of the peak temperature the specimen experienced but also with the increase of the peak temperature duration. The interfacial shear transfer of the specimens with studs arranged at the steel web is much higher than those with studs arranged at the steel flange. Empirical formulas of SRCSC interfacial shear transfer after fire are proposed, and the calculated results generally agree well with the experimental results.展开更多
To research the axial compression behavior of steel reinforced recycled concrete(SRRC)short columns confined by carbon fiber reinforced plastics(CFRP)strips,nine scaled specimens of SRRC short columns were fabricated ...To research the axial compression behavior of steel reinforced recycled concrete(SRRC)short columns confined by carbon fiber reinforced plastics(CFRP)strips,nine scaled specimens of SRRC short columns were fabricated and tested under axial compression loading.Subsequently,the failure process and failure modes were observed,and load-displacement curves as well as the strain of various materials were analyzed.The effects on the substitution percentage of recycled coarse aggregate(RCA),width of CFRP strips,spacing of CFRP strips and strength of recycled aggregate concrete(RAC)on the axial compression properties of columns were also analyzed in the experimental investigation.Furthermore,the finite element model of columns which can consider the adverse influence of RCA and the constraint effect of CFRP strips was founded by ABAQUS software and the nonlinear parameter analysis of columns was also implemented in this study.The results show that the first to reach the yield state was the profile steel in the columns,then the longitudinal rebars and stirrups yielded successively,and finally RAC was crushed as well as the CFRP strips was also broken.The replacement rate of RCA has little effect on the columns,and with the substitution rate of RCA from 0 to 100%,the bearing capacity of columns decreased by only 4.8%.Increasing the CFRP strips width or decreasing the CFRP strips spacing could enhance the axial bearing capacity of columns,the maximum increase was 10.5%or 11.4%,and the ductility of columns was significantly enhanced.Obviously,CFRP strips are conducive to enhance the axial bearing capacity and deformation capacity of columns.On this basis,considering the restraint effect of CFRP strips and the adverse effects of RCA,the revised formulas for calculating the axial bearing capacity of SRRC short columns confined by CFRP strips were proposed.展开更多
基金The Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China (NoIRT0518)
文摘In order to study the effectiveness of combined carbon fiber-reinforced polymer （CFRP） sheets and steel jacket in strengthening the seismic performance of corrosion-damaged reinforced concrete （RC） columns, twelve reinforced concrete columns are tested under combined lateral cyclic displacement excursions and constant axial load. The variables studied in this program include effects of corrosion degree of the rebars, level of axial load, the amount of CFRP sheets and steel jacket. The results indicate that the combined CFRP and steel jacket retrofitting technique is effective in improving load-carrying, ductility and energy absorption capacity of the columns. Compared with the corrosion-damaged RC column, the lateral load and the ductility factor of many strengthened columns increase more than 90% and 100%, respectively. The formulae for the calculation of the yielding load, the maximum lateral load and the displacement ductility factor of the strengthened columns under combined constant axial load and cyclically increasing lateral loading are developed. The test results are also compared with the results obtained from the proposed formulae. A good agreement between calculated values and experimental results is observed.
基金National Natural Science Foundation of China under Grant No.11472084Science and Technology Project of Guangdong Province under Grant No.2017B020238006+1 种基金Science and Technology Planning Project of Guangzhou City under Grant No.201704030057Fundamental Research Funds for the Central Universities under Grant No.21619327
文摘The application of fi ber-reinforced polymer (FRP) composites for the development of high-performance composite structural systems has received signifi cant recent research attention. A composite of FRP–recycled aggregate concrete (RAC)–steel column (FRSC), consisting of an outer FRP tube, an inner steel tube and annular RAC fi lled between two tubes, is proposed herein to facilitate green disposal of demolished concrete and to improve the ductility of concrete columns for earthquake resistance. To better understand the seismic behavior of FRSCs, quasi-static tests of large-scale basalt FRSCs with shear connectors were conducted. The infl uence of the recycled coarse aggregate (RCA) replacement percentage, shear connectors and axial loading method on the lateral load and deformation capacity, energy dissipation and cumulative damage were analyzed to evaluate the seismic behavior of FRSCs. The test results show that FRSCs have good seismic behavior, which was evidenced by high lateral loads, excellent ductility and energy dissipation capacity, indicating RAC is applicable in FRSCs. Shear connectors can signifi cantly postpone the steel buckling and increase the lateral loads of FRSCs, but weaken the deformation capacity and energy dissipation performance.
文摘The seismic performance of steel reinforced ultra-high-strength concrete columns(SRSHC) with various shear-span ratios(λ) were studied through a series of experiments.The concrete compressive cube strength value of experimental specimens ranged from 92.9 MPa to 108.1 MPa.The main experimental variables affecting seismic performance of specimens were axial load ratio and stirrup reinforcement ratio.The columns(λ=2.75) subjected to low cyclic reversed lateral loads failed mainly in the flexural-shear mode failure and columns(λ≤2.0) subjected to low cyclic reversed lateral loads failed mainly in the shear mode failure.Shear force-displacement hysteretic curves and skeleton curves were drawn.Coefficient of the specimen displacement ductility was calculated.Experimental results indicate that ductility decreases with axial pressure ratio increasing,and increases with stirrup reinforcement ratio increasing.Limit values of axial pressure ratio and minimum stirrup reinforcement ratio of columns are proposed to satisfy definite ductility requirement.The suggested values provide a reference for engineering application and for the amendment of the current Chinese design code of steel reinforced concrete composite structures.
基金Funded by the National Natural Science Foundation of China (No.50678136)the Hubei Provincial Foundation for Young Outstanding Talents(No. 2004ABB014)
文摘The bearing capacity of FRP confined concrete-filled steel tubular （FRP-CFST） columns under axial compression was investigated. This new type of composite column is a concrete-filled steel tube （CFST） confined with fiber-reinforced polymer （FRP） wraps. Totally 11 short column specimens were tested to failure under axial compression. The influences of the type and quantity of FRP, the thickness of steel tube and the concrete strength were studied. It was found that the bearing capacity of short FRP-CFST column was much higher than that of comparable CFST column. Furthermore, the formulas for calculating the bearing capacity of the FRP-CFST columns are proposed. The analytical calculated results agree well with the experimental results.
基金National Natural Science Foundation of China Under Grant No.50878037
文摘To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete （SRUHSC） columns and steel reinforced concrete （SRC） beams, six interior frame joint specimens were designed and tested under low cyclically lateral load. The effects of the axial load ratio and volumetric stirrup ratio were studied on the characteristics of the frame joint performance including crack pattern, failure mode, ductility, energy dissipation capacity, strength degradation and rigidity degradation. It was found that all joint specimens behaved in a ductile manner with flexural-shear failure in the joint core region while plastic hinges appeared at the beam ends. The ductility and energy absorption capacity of joints increased as the axial load ratio decreased and the volumetric stirIup ratio increased. The displacement ductility coefficient and equivalent damping coefficient of the joints fell between the corresponding coefficients of the steel reinforced concrete （SRC） frame joint and RC frame joint. The axial load ratio and volumetric stirrup ratio have less influence on the strength degradation and more influence on the stiffness degradation. The stiffness of the joint degrades more significantly for a low volumetric stirrup ratio and high axial load ratio. The characteristics obtained from the SRUHSC composite frame joint specimens with better seismic performance may be a useful reference in future engineering applications.
文摘A beam-column joint of precast and partial steel reinforced concrete( PPSRC) is proposed for precast reinforced concrete frames. The PPSRC consists of partial steel and reinforced concrete. The partial steel is located in the core joint region and the connections between concrete members. This paper presents an experimental study of a series of PPSRC specimens. These specimens are tested under low cyclic loading.Experimental results demonstrate that the bearing capacity of the PPSRC specimens is 3 times that of the ordinary reinforced concrete( RC) beam-column joints. The strength and stiffness degradation rates are slower compared with that of the RC beam-column joints. In addition,the strength of the core joint region and the connections is higher than other parts of the PPSRC specimens. Beam failure occurs firstly for the PPSRC specimens,followed by column failure and connections failure. The failure of the core joint region occurs finally.Test results show that the seismic performance of the PPSRC is better than that of the ordinary RC beam-column joints.
基金supported by the National Natural Science Foundation of China(Grant Nos.51878097&51438001)Chongqing Research Program of Basic Research and Frontier Technology(Grant Nos.2018CDQYTM0043&106112015CDJXY200001)China Scholarship Council
文摘Steel tubed-reinforced-concrete(TRC) columns have been gradually used in the construction of high-rise buildings recently because of their high axial load-carrying capacities and excellent seismic behavior. Existing studies about their seismic behavior were focused on columns with relatively thick tubes, i.e., diameter-to-thickness/width-to-thickness(D/t) ratios were below 100,while little is known about thin-walled TRC columns, especially for square TRC columns. Considering the infilled concrete of square TRC columns is non-uniformly and non-effectively confined, accordingly, stiffened square TRC columns are usually adopted in practice. Thus, two thin-walled circular TRC columns(D/t=120) and two stiffened square ones with diagonal stiffeners in plastic hinge regions(D/t=106) were tested under a constant axial compression combined with cyclic lateral loading.Both the circular and stiffened square TRC columns had the same cross sectional area, tube thickness, reinforcing bar ratio and column height. Flexural failure occurred for all the four specimens. Test results showed the strengths of the stiffened square TRC columns were a little higher in comparison to their circular counterparts; the ductility and energy dissipation capacities were excellent for both the stiffened and circular TRC columns, indicating very good confinement was gained from the yielded steel tubes of the plastic hinge regions at the peak loads. And shear stresses(35–90 MPa) in the sheared plates showed their moderate contribution of carrying lateral loads. Finally, cross sectional capacity analysis results demonstrated the method for TRC columns is acceptable for the stiffened square TRC columns.
基金Acknowledgements This research is supported by the National Science Foundation of China （Grant Nos. 50908118 and No. 51308307）, Ningbo Science Foundation （No. 2013A610194） and Ningbo Key Scientific Projects （No. XKL11D2079）.
文摘Statically push-out tests of 20 steel reinforced concrete short columns （SRCSC） with stud connectors on the surface of shape steel after fire and two SRCSC under ambient temperature were carried out, in order to study the failure mode, load-slip relationship and the interfacial shear transfer of SRC members after fire. Experimental results show that the typical failure modes and load-slip curves of SRCSC after fire are almost the same as the case under ambient temperature. The interfacial shear transfer of SRCSC declines exponentially not only with the increase of the peak temperature the specimen experienced but also with the increase of the peak temperature duration. The interfacial shear transfer of the specimens with studs arranged at the steel web is much higher than those with studs arranged at the steel flange. Empirical formulas of SRCSC interfacial shear transfer after fire are proposed, and the calculated results generally agree well with the experimental results.
基金The financial support of this work came from the project of National Natural Science Foundation of China(Grant No.51408485)the Natural Science Basic Research Plan in Shaanxi Province of China(Nos.2022JM-258 and 2021JM-332)+1 种基金the Open Fund Project of Qinghai Provincial Key Laboratory of Plateau Green Building and Eco-community(KLKF-2021-001)thanks a lot for the financial support of the above institutions.
文摘To research the axial compression behavior of steel reinforced recycled concrete(SRRC)short columns confined by carbon fiber reinforced plastics(CFRP)strips,nine scaled specimens of SRRC short columns were fabricated and tested under axial compression loading.Subsequently,the failure process and failure modes were observed,and load-displacement curves as well as the strain of various materials were analyzed.The effects on the substitution percentage of recycled coarse aggregate(RCA),width of CFRP strips,spacing of CFRP strips and strength of recycled aggregate concrete(RAC)on the axial compression properties of columns were also analyzed in the experimental investigation.Furthermore,the finite element model of columns which can consider the adverse influence of RCA and the constraint effect of CFRP strips was founded by ABAQUS software and the nonlinear parameter analysis of columns was also implemented in this study.The results show that the first to reach the yield state was the profile steel in the columns,then the longitudinal rebars and stirrups yielded successively,and finally RAC was crushed as well as the CFRP strips was also broken.The replacement rate of RCA has little effect on the columns,and with the substitution rate of RCA from 0 to 100%,the bearing capacity of columns decreased by only 4.8%.Increasing the CFRP strips width or decreasing the CFRP strips spacing could enhance the axial bearing capacity of columns,the maximum increase was 10.5%or 11.4%,and the ductility of columns was significantly enhanced.Obviously,CFRP strips are conducive to enhance the axial bearing capacity and deformation capacity of columns.On this basis,considering the restraint effect of CFRP strips and the adverse effects of RCA,the revised formulas for calculating the axial bearing capacity of SRRC short columns confined by CFRP strips were proposed.
