Seismic Damage Analysis And Seismic Behavior Of L-shaped Concrete-filled Steel Tubular Column

L-shaped concrete-filled steel tubular(L-CFST)column can increase the utilization rate of the indoor space to improve the space layout.It is a new type of structural column in civil engineering.At present,the research on seismic performance of L-CFST column is insufficient.concrete-filled steel tubular(CFST)structure is a structure filled with concrete inside the steel tube,and its bearing capacity is shared by the steel tube and the internal concrete.The damage of the core concrete will greatly impact the bearing capacity of a CFST.Therefore,it is very important to monitor the concrete damage inside the structure.In this paper,the author investigates the seismic behavior of L-CFST columns and develops a new method to monitor the internal concrete damage in the L-CFST column by using embedded piezoceramic smart aggregates(SAs)under low frequency cyclic loading.The main research contents and conclusions in this paper are as follows:(1)Nine L-CFST columns were designed to investigate the seismic behavior of LCFST column,such as the hysteretic behavior,bearing capacity and stiffness.These specimens considering three parameters(slender ratio,axial compression ratio and steel ratio)were tested when applying a cyclic loading on the column.The test results show that the L-CFST has good hysteretic behavior and good energy dissipation capacity.(2)ABAQUS finite element software was used to build 27 models of L-CFST columns.The finite element results are in good agreement with the experimental results.The regression analysis of the test results and the ABAQUS results is carried out to establish the hysteretic model of the L-CFST column,and the author proposed the calculation formulas on the model curve based on the parameters,i.e.load,displacement and stiffness degradation.The results of the hysteretic model of L-CFST columns are in good agreement with the test results and the ABAQUS results,which provides a theoretical basis for the analysis of the non-linear seismic behavior of LCFST columns.(3)The SA enabled active method is used to monitor the concrete damages near the bottom of L-CFST columns,and the wavelet packet analysis is used to establish a damage index.The analyses of the test results of damage detection show that the damage index value of the specimen initially increases linearly with the increase of the loading displacement,and then gradually approaches to 1,and then it will remain basically unchanged.The damage of the concrete inside the specimen increases with the increase of the loading displacement and the increase of cyclic times under the same displacement amplitude will not obviously increase the damage of internal concrete.The monitoring results of smart aggregate can reflect the repeated opening and closing of concrete cracks in the core area during low frequency cyclic loading.The analysis result of the data monitored by the smart aggregate under the lowfrequency cyclic load is basically consistent with the analysis results of the hysteresis curve and the skeleton curve of the specimen.The test results demonstrate that the use of smart aggregate can directly and clearly monitor in real time the damage process of the concrete core,which is no directly visible.It can be concluded that it is feasible to use smart aggregate enabled active sensing to monitor the internal concrete core damage of a concrete filled steel tube structure.