Pseudo-Static Test And Seismic Performance Of Stilted RC Frame Structure With Brace At Bottom

The difference in height of embedded ends in the bottom columns of stilted reinforced concrete（RC）frame structure will cause the uneven distribution of the bottom stiffness,which leads to the embedded distribution of the shear force.Setting brace is one of the effective measures to improve the uneven distribution of stiffness.At present,there are few researches on the control of the bottom stiffness in stilted structure,which are mostly limited to the finite element analysis and lack of corresponding experimental verification.The seismic performance of stilted RC frame structure with bottom braced is studied by means of experiment and numerical simulation.Based on the above research background,following work has been conducted: 1)The design principle of the bottom brace of RC stilted frame structure based on reducing the stiffness non-uniformity is determined.25 numerical simulation models with 4 kinds of bottom brace layout are built,in which the brace stiffness ratio k of the bottom story is increased from 2 to 10.According to the results of elastic response spectrum analysis,the most suitable arrangement of brace and stiffness ratio are proposed as the test prototype;2)Based on the load-displacement control loading mode,a 1/3 scaled pseudo-static test of three-story two-span stilted RC frame substructure was conducted,whose bottom is enhanced by reverse V braces and a tension beam.The failure mechanism and seismic performance of the specimen are studied by comparing with the RC frame structure without brace;3)The correctness of finite element analysis model is verified by comparing the finite element analysis results with the experimental results.Numerical models with different kinds of bottom brace layout and different brace stiffness ratios are built.The static elasto-plastic method is used to analyze the elasto-plastic seismic response characteristics of the structures,and the optimal brace arrangement and brace stiffness ratio k are given.The main conclusions are as follows:（1）The result of quasi-static test shows that: compared with the structure without braces,the damage of the short column of the stilted RC frame structure with tension beam and reverse V braces is significantly reduced,and the damage is concentrated on the beam ends of the second floor and the top of the middle column of the third floor.The failure mechanism of the specimens is "beam column mixed hinge mode",and the hysteretic energy dissipation and deformation performance are better.（2）Combining the results of response spectrum and static elastic-plastic analysis,the tensile beam and reverse V braces significantly change the failure mode of the stilted RC frame structure.There is no plastic hinge at the column end of the stilted layer,so the failure mechanism is more reasonable.At the same time,it has better ductility and deformation ability under large earthquake,which shows it is a more reasonable layout form of bottom brace.（3）The results of response spectrum and static elastic-plastic analysis show that when k=3～5,the 7-story and 2-span stilted RC frame structure with tensile beam and reverse V braces has a relatively small shear nonuniformity coefficient σ,and the percentage of short column shear force in total shear foece is very small.Meanwhile,it can greatly reduce the shear force and bending moment of beams and columns at the first floor,and the failure state of stilted short column is obviously improved.Increasing k has little effect on seismic performance.In conclusion,3～5 is a reasonable range for k.