Seismic Behavior Of Novel Concrete Filled Rectangular Corrugated Steel Tubular Columns

Concrete filled steel tubular(CFST)columns have been widely used in high-rise buildings and bridge structures at home and abroad due to their superior seismic performance,high bearing capacity,simple and convenient construction and operation,and good economic benefits.For building structures with low bearing capacity requirements,although reducing the wall thickness of steel pipes will reduce the amount of steel used,under the action of earthquakes,the confinement effect of rectangular steel pipes on concrete is weakened,and the strength of steel can not be fully utilized.In order to take advantage of the high out-of-plane stiffness of corrugated steel plates and improve the confinement efficiency on the core concrete,a novel type of rectangular steel tube welded by two parallel flat plates and two parallel corrugated plates was proposed.For columns with transverse/circumferential/spiral corrugations,the existing research mostly focuses on the static performance of such components,and the research on their seismic performance is lacking.Based on this,the seismic behavior test analysis,finite element analysis and compression-bending bearing capacity analysis of the novel concrete filled rectangular corrugated steel tubular(CFRCST)columns were carried out in this thesis.The main research contents and achievements are as follows:(1)Six specimens of strong axis perpendicular to the flat steel plate and four specimens of weak axis perpendicular to the corrugated plate were designed and completed.The effects of cross-sectional aspect ratios,thickness of flat plates and corrugated plates,reinforcement at the web,loading directions and axial compression ratio were evaluated.The damage processes and failure modes were observed,and the impacts of the test parameters on the hysteretic curves,strength and strength deterioration,stiffness,ductility and energy-dissipation capacities were evaluated.The responses of the transverse,longitudinal and shear strain of flat plates and corrugated plates were also discussed.The test results indicate that all the tested specimens failed with serious buckling at the flat plates corresponding the bottom wave crest of corrugated plates,resulting in the final fracture of welds there.Though the width-to-thickness of the corrugated plates was significantly over the limited value of the design code,the specimen exhibited desirable seismic behavior with full hysteretic curves and ductility factors larger than 3.0.The strength and the energy-dissipation capacities of the specimens were significantly affected by the behavior of the flat plates.The corrugated plates in all specimens,whether as flanges or web plates,bear no axial loads,but mainly contributed to providing transverse confinement to the core concrete.The strongest confinement was found at the wave crest,followed by the middle of the wave,while trough had the weakest confinement contribution.(2)The method to simulate the seismic behavior of the proposed columns based on ABAQUS software was also developed and the FEM models predicted the test results well.In order to obtain the degree of influence of some parameters on the seismic performance of the strong and weak axis specimens,The influence of parameters such as the thickness of the flat steel plate,the form of the corrugated steel plate at the connection with the top of the cap,the compressive strength of the core concrete and the strength of the corrugated steel plate on the seismic performance of the novel columns were further discussed.(3)Based on the relevant specifications of the CFST structure,the difference between the theoretical value and the experimental value of the flexural bearing capacity was compared,and the reason for the difference was analyzed based on the experimental results and the numerical simulation results to modify the calculation formula.In this thesis,the calculation method of the flexural bearing capacity of this novel column was modified mainly based on the flexural bearing capacity formula of CFST members in 《Technical code for concrete filled steel tubular structures》(GB50936-2014).Based on the bearing capacity formula of large eccentric compression members in 《 Code for design of composite structures 》(JGJ138-2016),the calculation method of bearing capacity of this novel columns was revised,and two reduction methods were proposed to correct the bearing capacity of the strong axis specimens.This thesis has 62 figures,12 tables and 95 references.