Seismic Behavior Of Composite Frame System Consisting Of SRNSC Beams And SRUHSC Columns

Steel reinforced ultra-high strength concrete(SRUHSC)composite structures have the excellent seismic behavior and bearing capacity which can meet the requirements of high strength and low consumption on the modern buildings.Based on the National Natural Science Fund Project(No.51178078):Study on Ductility-Based Seismic Behavior and Key Design Technique of Steel Reinforced Ultra-high Strength Concrete Frame System,this paper is devoted to study the seismic behavior of SRUHSC frame system.The detailed contents and conclusions of this thesis are shown as follows:(1)In order to investigate the seismic behavior of steel reinforced ultra-high strength concrete(SRUHSC)frame,a specimen of two-bay and three-story SRUHSC frame was designed and constructed.A series of quasi-static experiments on the SRUHSC frame structure were carried out by using MTS loading system.The seismic behavior of the specimen,including the failure pattern,concrete element cracks,loading-displacement hysteretic curves,lateral load carrying capacity,displacement ductility,energy dissipation,strength and stiffness degradation,etc,were investigated under low reversed cycle lateral loading.The test results indicated that the beam hinge failure mechanism was achieved.SRUHSC frame can have rich and stable hysteretic load-displacement curves even if subjected to large axial load with an axial load ratio high up to 0.38.The top and story ductility coefficients of SRUHSC frame ranged from 4.32?6.06.The strength and stiffness degenerated gradually,which showed that the specimen had excellent seismic behavior with sufficient ductility and high energy dissipation capacity.More importantly,they can be used asdesign reference for practical engineering applications.(2)To investigate the seismic behavior of the SRUHSC column-steel reinforced normal-strength concrete(SRNSC)beam composite frame,two one-fourth scale two-span,three-story frame specimens were designed and constructed.Low reversed cyclic loading tests were conducted on two frame specimens.The failure process and modes were described,meanwhile the hysteretic curves,skeleton curves,bearing capacity,displacement ductility,energy dissipation capacity,stiffness and strength degradation were compared and analyzed.The research results showed that the failure patterns of SRUHSC frame was similar to that of the SRNSC frame.When the designed axial-load ratio was 0.75,the beam hinge failure mechanism was achieved for the two frames,and the hysteretic curves were plump.Moreover,the displacement ductility coefficients of two frames were all more than 3.0,which indicated that the specimens had excellent seismic behavior with sufficient ductility.However,in terms of bearing capacity,displacement ductility,energy disspation capacity,strength and stiffness degeneration,etc.,SRUHSC column-SRNSC beam composite frame was totally better than that of the SRNSC frame which indicates that encasing structural steel and high-strength stirrups into the ultra-high strength concrete is a the good way for alleviating the problem of brittleness and improving structural carrying capacity by significantly making use of the compressive high strength property and enhancing the structural ductility.Therefore,the seismic performance of the SRUHSC column-SRNSC beam composite frame structure system is better than that of the SRNSC frame.(3)Given that the current hysteretic model have rarely been used for SRUHSC frame system,a new hysteretic model for SRUHSC frame considering cyclic deterioration effect was proposed based on the qusai-static test data,meanwhile the corresponding MATLAB program was written and applied to simulate the hysteretic behavior,equivalent viscous damping ratio,power ratio index as well as energy dissipation ratio.Results showed that the calculated results from the presented restoring force model agreed well with the experimental ones.The applicability and accuracy of the proposed model was thus verified.Additionally,the proposed restoring model can describe the seismic performance of SRUHSC frame under cyclic load.This research can provide reliable basis for the nonlinear seismic analysis of the SRUHSC frame structure.(4)Based on the previous experimental study,nonlinear finite element models were used to analyze the mechanical properties of the structure using ABAQUS.The P-? skeleton curves,stiffness degradation and subsequence of plastic hinges were investigated.The finite element analysis results agreed well with the experiments.With the proposed model,an extensive parametric study was carried out to investigate the behavior of SRUHSC frame.The axial-load ratio,concrete strength,volume stirrup ratio,structural steel ratio,yield strength of steel,linear stiffness ratio of beam to column were all considered as analysis parameters.The results indicated that with the increment of the concrete strength,yield strength of steel,and linear stiffness ratio of beam to column,the horizontal load-bearing capacity and the elastic stiffness of the structure were improved,but there was no significant effect on the ductility.With the increment of the volume stirrup ratio and structural steel ratio,the horizontal load-bearing capacity and the ductility of the structure were both improved.However,with the increment of the axial-load ratio,there was no obvious change in the elastic stiffness of the structure,but the horizontal load bearing capacity and the ductility of the structure decreased obviously.