Research On Seismic Behavior Of High-speed Railway Bridge Piers Reinforced With High-strength Fine Grained Rebar

Using high-strength rebar in concrete structures can reduce reinforcement ratio,thus benefits environment protection and sustainable development.At present,HRB335 rebar is still widely used in the high-speed railway bridge piers in China,and the application of high-strength rebar needs to be promoted urgently.As the support structure of high-speed railway bridges,the piers must have high seismic performance.The related researches on seismic performance of high-strength rebar reinforced columns in China and abroad are mainly aimed at frame columns of building structures,whose cross section forms,reinforcement ratios,and axial compression ratios are different from those of the high-speed railway bridge piers in China.500 MPa grade fine grained rebar(HRBF500)is a new type high-strength rebar with high ductility and good economical efficiency which is developed independently by China.In this paper,according to the design characteristics of the high-speed railway bridge piers,combining the methods of experimental study,theoretical analysis and numerical simulation,the seismic performance of high-speed railway bridge piers reinforced with HRBF500 rebar is researched,and the main work and achievements are as follows:(1)Five HRBF500 rebar reinforced and one HRB335 rebar reinforced round-ended pier specimens were tested by pseudo-static test method.The results show that the variation rule of seismic performance of the HRBF500 rebar reinforced pier is much the same with that of the one reinforced with HRB335 rebar.Using HRBF500 rebar can improve the load bearing capacity of the pier and significantly reduce the quantity of longitudinal reinforcements.The numerical simulation of the quasi-static specimens was realized based on the OpenSees program platform.Then the effects of parameters including axial compression ratio,concrete strength,stirrup ratio,longitudinal reinforcement strength,reinforcement ratio,width-thickness ratio of cross section,and carbon fiber content of concrete on the seismic performance of the piers were studied.(2)Two HRBF500 rebar reinforced round-ended pier specimens were tested by pseudo-dynamic test method under different seismic waves,and the failure characteristics of high-speed railway bridge piers were investigated.According to the data of the pseudo-dynamic test,the dynamic response and the process of energy absorption,distribution and dissipation of the pier specimens was analyzed.The test results show that the pier specimens exhibit excellent seismic performance,and can satisfy the design requirements for seismic resistance.(3)The general calculation mothed for the characteristic points of the skeleton curve model was proposed based on the moment-curvature analysis of the bottom cross-section and the plastic hinge models,and the restoring force model of the round-ended piers was established.Using the restoring force model established in this paper,the numerical simulation of the quasi-static and pseudo-dynamic specimens was realized based on the OpenSees program platform,and the calculated results agree well with the experiment data.Then the parameter analysis was performed to the prototype piers,and the effects of different seismic waves,longitudinal reinforcement strength and reinforcement ratio on the seismic response of the high-speed railway bridge piers were investigated.(4)Three round-ended bridge pier specimens reinforced with HRBF500 rebar were tested by low-cycle fatigue test method,and the law of cumulative damage development of these specimens under different cyclic displacement amplitude was studied.Since the Park-Ang seismic damage model can not consider the effect of loading history on cumulative damage and dose not satisfy the boundary condition,a modified Park-Ang seismic damage model was established through introducing a factor based on the low-cycle fatigue damage in the energy item and a combination coefficient in the displacement item of the Park-Ang model.The modified Park-Ang seismic damage model was verified by the comparison with the test results in this paper and from Kunnath.(5)The idea of realizing ductile seismic performance of railway piers with low reinforcement ratios by high-strength rebar was proposed,and the mechanism was theoretically analyzed.The idea was verified by a HRBF500 reinforced rectangular pier specimen with a reinforcement ratio of only 0.33%of the whole cross section tested by pseudo-static test method.The calculation formula of minimum reinforcement ratio for ductile seismic performance of rectangular piers was established.A rectangular double column high-speed railway bridge pier specimen reinforced with HRBF500 rebar was laterally tested by pseudo-static test method,and the numerical analysis of the specimen was conducted using the finite element program ABAQUS.The results show that the failure pattern of the rectangular double column high-speed railway bridge pier was bending-shear failure of the tie beam,which was different from that assumed in the design code.