Mechanical Behavior Of Steel-tube-Confined Concrete-filled Steel Tubular Stubs Under Axial Compression

This application proposed an innovative steel-tube-confined concrete-filled steel tubes(STC-CFST),which is composed of concrete-filled-steel-tube,outer steel tube and intermediate sandwich material.The outer steel tube and the intermediate sandwich material do not bear the loading directly,but provide high efficiency horizontal confinement to the concrete core passively.Preliminary analysis shows that the STC-CFST columns have the advantage of high bearing capacity,good ductility,excellent fire-resistant behavior,which can be used for the repair and strengthening of the CFST when its function of use changes.As an innovative structural member,there is no investigations on STC-CFST columns.This dissertation intends to provide the experimental and numerical analysis on the mechanical behavior of STCCFST columns under axial compression.The main works are listed as follows:10 STC-CFST and 6 CFST columns were designed and tested under axial compressive loading.The failure modes,axial load-vertical deformation relations,the development of horizontal deformation were obtained.Based on the comparison of the test results between STC-CFST and CFST columns,the improvement on the behavior of CFST from the outer steel tube has been analyzed.The stress states of inner steel tube and outer steel tube,and their interaction have also been achieved according to the tested vertical and horizontal strain gauge readings.Finite element program ABAQUS was employed to develop the model to simulate the behavior of STC-CFST columns under axial compression,and the reliability of finite element analysis has been verified by test results.Based on the established finite element model,the working mechanism of STCCFST column under axial compression was analyzed.This analysis include the development of deformation,the stress distribution and the inter action between the inner steel tube,outer steel tube and core concrete of STC-CFST columns.Based on the proposed finite element analysis mode,extensive parametric studies were then carried out to numerically investigate the behavior of STC-CFST under axial compression.Study parameters include the inner steel ratio,the outer steel ratio,the total steel ratio,the distribution of inner steel and outer steel,the compressive strength of concrete and the yield strength of steel.