Research on Interface Sliding Behavior and Seismic Performance of Stirrup-Confined Concrete Filled Circular Steel Tubular Columns Under High Axial Compression Ratio

Normal concrete filled steel tube columns (CFST) exhibit poor potency under high axial compression ratio in seismic action. In contrast to other inner constraint measures of CFST, the transverse stirrups effectively prompt the constraint confinement efficiency and seismic performance of CFST columns under high axial compression ratio. Based on the test and the research of circular and square CFST columns’ seismic performance under high axial compression ratio, the three-dimension solid finite element model was established and the test results were verified, The mechanical properties parameter analysis of stirrup-confined circular CFST columns under monotonic loading and hysteretic loading was carried out. The influence of stirrups on the interface sliding behaviour, stress level and seismic performance was probed. The research results elucidate: 1) The interface sliding behaviour exists between steel tube and concrete under compression-bending loading, which leads to the inconsistent changes in the neutral axis height of steel tube and concrete during the loading progress. Under the hysteretic loading, the tensile area of concrete lessens conspicuously and the difference between the neutral axis of concrete and steel tube augments, resulting in greater interface sliding. Finally, the full section of concrete is compressed while the steel tube resists bending. 2) When the steel tube consumption remains unchanged, the difference between the neutral axis of concrete and steel tube reduces after the stirrups were set to the end of the columns. The diminishing of the interface sliding gives rise 10% of the bending stiffness. The stirrups directly constrain the concrete and resist the buckling of the steel tube, which increased the tensile stress level of the steel tube and the compression stress level of the concrete and the stress level is more uniform. The tensile area of steel tube increases while the compressive area of concrete decreases, which leads to the 20%-50% increase of the ultimate capacity. 3) Stirrups effectively improve the seismic performance of the CFST columns under hysteretic loading. When the steel consumption of CFST column remains unchanged, the stiffness of high axial compression ratio CFST columns remains unchanged. The bearing capacity increases by 10%-20%, and the energy dissipation of the CFST columns is increases by 2 times. The energy dissipation of the concrete increases by 1 time due to the confinement effect of the steel tube and the stirrups. The compression region height of the CFST column is reduced, which leads to the greater rotational capacity of the member. The plastic energy dissipation of the steel tube can be effectively elicited by a factor of 3.