Study On Seismic Behavior Of Cross-Shaped Concretefilled Steel Tubular Columns

Special-shaped concrete-filled steel tube(CFST)structure,as a new type of structure,not only has excellent mechanical properties,but also can be flexibly applied in the building because of its various sections that can save space and make room more beautiful.In civil engineering,the seismic performance of the structure is a crucial index to appraise the excellence of this structure.However,earthquake,which lead frequent and drastically displacement of structure,makes the accumulation of damage in structure which can finally destroy it.The horizontal bearing capacity and ductility of the structure will directly affect the performance of the structure in the earthquake.At present,the research on the seismic behavior of special-shaped CFST is deficient.Therefore,this paper intends to study the seismic behavior of cross-shaped concretefilled steel tube(C-CFST)under low-cyclic loading.Two smart aggregates(SAs)are used to detect the damage of concrete with stress wave analysis method.The main research contents and conclusions in this paper are as follows:(1)Three factors which called length-width ratio,width-thickness ratio of section and axial compression ratio are considered to make nine C-CFST which are taken by low-cyclic loading.The failure modes and hysteretic curves of C-CFSST under lowcyclic loading are obtained in this experiment.The skeleton curve,ductility,strength degradation,stiffness degradation and energy dissipation capacity of each C-CFST are obtained based on the analysis of the hysteretic curve.The deformation of each specimen occurs 3-6cm above the stiffener,nine specimens all have plump hysteretic curves,and the ductility and energy consumption capacity are great.In this experiment,the ultimate bearing capacity of the specimens are increase with the increase of lengthwidth ratio or the decrease of width-thickness ratio.The high axial compression ratio not only affects the ultimate bearing capacity,but also lead the variety of failure mode.(2)Nine C-CFST model are established based on ABAQUS finite element software.The accuracy of the finite element model was proved by comparing the difference of analysis results and experiments results in the failure mode,hysteretic curves,and ultimate bearing capacity.(3)In this paper,two SAs are embedded in concrete to monitor the damage of the concrete by using stress wave method.The relationship between the wavelet packet energy and the damage level of concrete is established.The results show that,the wavelet packet energy decreases with the increase of the load level which means the increase of damage level of concrete.In the three cycles of the same loading level,the variety of specimens' wavelet packet energy is not obvious which means the change of damage level is not distinct.The test results can clearly find that under the same loading level,the value of wavelet packet energy which collected in the negative loading is far higher than the value which collected in the positive loading because the SAs is embedded in the negative loading side.This fully proves the effectiveness of SAs in structural damage monitoring.