Study On Seismic Performance Of Hollow Prefabricated Reinforced Concrete Pier

To reduce the lifting weight of prefabricated reinforced concrete piers,realize the lightweight design of piers,and promote the application of high-performance materials(high-strength steel bars and UHPC materials,etc)in the piers,so as to further improve the seismic performance of piers,a hollow prefabricated pier with grouted sleeve connection,UHPC grouting material and HTRB600 E high-strength reinforcement was proposed in this thesis.For the seismic performance of the proposed pier,the quasi-static test was carried out and the sensitivity of design parameters of the pier was analyzed using the finite element software.At the same time,the fitting formula for calculating the equivalent plastic hinge length of piers considering multiple parameters was obtained.Based on the plane section assumption and the ideal elastoplastic material assumption,the restoring force model of piers was established.The incremental dynamic analysis IDA was used to establish the seismic vulnerability curves,and the probability of various damage of the pier under earthquakes with different intensities was obtained.The main research contents of this thesis include:The quasi-static test of a hollow prefabricated pier was carried out,which was compared with those of the cast-in-place pier,the conventional prefabricated pier and the prefabricated solid pier with high-strength reinforcement.It was found that the seismic performance of the proposed pier was excellent,the existence of the sleeve made the plastic failure region of the pier be move up.The high-strength longitudinal reinforcement increased the initial stiffness of the pier body,significantly improved the horizontal bending bearing capacity of the pier,accelerated the stiffness degradation of the pier body,and had a negative impact on the overall displacement ductility and the plastic energy dissipation capacity of the pier.The hollow layer was set in the pier body,which slightly enhanced the plastic deformation capacity of the pier,had positive influence on the improvement of its displacement ductility,and had little effect on its energy dissipation capacity and curvature distribution.The finite element model of a hollow prefabricated pier was calibrated by the quasi-static test results,so as to analyze the sensitivity of design parameters of the pier,including axial compression ratio,longitudinal reinforcement strength,slenderness rate and hollow rate.It was found that the decrease of longitudinal reinforcement strength was not conducive to the improvement of resistance capacity to deformation and horizontal bearing capacity of the pier,which accelerated the yield speed of the pier and had a positive influence on the plastic energy dissipation capacity of the pier.The increase of the axial compression ratio of the pier body improved the horizontal flexural bearing capacity of the pier,and accelerated the stiffness degradation of the pier body,which was not conducive to the improvement of the energy dissipation capacity of the pier under the large loading displacement,and had a positive influence on the overall displacement ductility of the pier.The decrease of the slenderness ratio of the pier significantly enhanced the resistance capacity to deformation and horizontal bearing capacity of the pier,and increased the proportion of plastic deformation in the total deformation,thereby improving the displacement ductility and the overall energy dissipation capacity of the pier.The increase of the hollow ratio of the pier body had no apparent effect on the horizontal bearing capacity of the pier,which made the initial stiffness of the pier body be slightly decreased,accelerated the stiffness degradation of the pier body at the later period of loading,and accelerated the growth rate of the overall energy dissipation capacity of the pier.The discontinuity of the overall stiffness distribution of the hollow prefabricated pier was aggravated by the existence of the grouting sleeve,the curvature of the pier body had a significant turning point at the top and bottom sections of the sleeve,making the plastic damage be mainly concentrated on the bottom section of the pier,so that the equivalent plastic hinge length of the pier was significantly smaller than that of the cast-in-place pier.The increase of axial compression ratio was not conducive to the improvement of the overall deformation capacity of the pier,which reduced the rotation angle of the pier bottom section,so that the equivalent plastic hinge length of the pier was decreased.The increase of grouted sleeve length enlarged the length of sleeve stiffness enhancement segment,which made the plastic damage of the pier’s bottom section more concentrated,further reduced the plastic hinge length of the pier.The decrease of longitudinal reinforcement strength increased the curvature of the pier in yield state and ultimate state,which increased of equivalent plastic hinge length.Based on the multiple linear regression,the calculation formula of equivalent plastic hinge of the hollow prefabricated pier was obtained,which considered the longitudinal reinforcement strength,the length of grouted sleeve and the axial compression ratio of the pier.The equivalent plastic hinge length of the pier could be calculated accurately and directly using this formula and according to the longitudinal reinforcement strength,the length of sleeve and the axial compression ratio of the pier.Based on the plane section assumption and the ideal elastic-plastic material assumption,the characteristic point of the trilinear model of the skeleton curve of the hollow prefabricated pier was calculated by analyzing the distribution of the normal stress of the weak section and the curvature distribution of the pier at different stress stages.According to the unloading stiffness equation of the pier under different axial compression ratios and the loading and unloading paths of the pier under reciprocating load,the restoring force model curve of the pier was established.The obtained restoring force model curve of the pier was well fitted with the results of the numerical simulation and the test,which could better and more accurately reflect the seismic performance of the pier under reciprocating load.At the same time,the calculation method of the restoring force model of the pier had great applicability to the establishment of the restoring force model curve of the pier under different working conditions.Based on the incremental dynamic analysis(IDA),the seismic vulnerability of the hollow prefabricated pier had been analyzed.Using the different displacement response of the pier and the peak values of the ground acceleration of earthquakes with different intensity,the IDA curve cluster and the seismic probabilistic demand model were obtained,and then the seismic vulnerability curve of the pier was established.According to the seismic vulnerability curve of the pier,it was found that with the increase of the intensity of earthquakes,the probability of the pier reaching various damage states also was improved significantly,and the slope of seismic vulnerability curves of the pier to the three damage states including: slight damage state,the medium damage state and the severe damage state would be increased first and then decreased.At the same time,there was a difference in the probability of the pier damage under different fortification levels.The exceeding probability of the pier reaching the collapse damage state was enhanced apparently after PGA was greater than 0.5g.