| Composite-sectioned high strength concrete filled steel tubular (CSCFT) column is a new novel type of column, which consists of a circular steel tube embedded at the core area of the high strength concrete filled square steel tube column. The CSCFT column effectively combines the external square steel tube, internal circular steel tube and high strength concrete. It is suitable for the low portion story columns of earthquake resistant high-rise buildings and for the columns that are exerted to significantly large gravity loads. Till now experimental study on the seismic behavior of the CSCFT column has not been performed yet. In this dissertation, quasi-static tests and numerical simulation are carried out to investigate the seismic behavior of the CSCFT column. The main works and outcomes are as follows:(1) Quasi-static tests on twelve specimens were conducted to study and to reveal the seismic behavior and cumulative damage performance of the CSCFT column, including the failure mode, load-carrying capacity, deformation capacity, energy dissipation capacity, stiffness degradation, as well as the influence of cumulative damage on the seismic behavior of CSCFT columns. The test results indicated that the hysteretic behavior of the CSCFT column was stable and the CSCFT column had excellent seismic behavior, but cumulative damage made the specimens much more severe damage.(2) Quasi-static tests on five CSCFT column specimens and three high strength concrete filled square steel tube (CFST) column specimens were conducted to study the seismic behavior of the earthquake-resilient CSCFT column. The test results indicated that at the drift ratio of1/100, buckling of the square steel tube did not occur for the CFST column specimen and the CSCFT column specimens, which the square steel tube had the width-to-thickness ratio of24.7. It means that if the frame-core tube structure reaches its elastic-plastic drift ratio under the severe earthquakes, the CFCST columns could be used continually without any repair work.(3) By using the fiber model-based OpesnSEES program, the calculated lateral force-displacement hysteretic curves of the CSCFT column specimens had a good agreement with the test curves. Parameter analysis of the hysteretic behavior of the CSCFT columns indicated that:increasing the axial force ratio led to a decrease of the deformation capacity, reducing the width-to-thickness ratio of square steel tube led to an increase of the deformation capacity, increasing the diameter to width ratio led to an increase of load-carrying capacity, increasing the yield strength of steel tubes led to an increase of load-carrying capacity and the deformation capacity. Based on the test and numerical analysis results, the sectional parameter values of the CSCFT columns were proposed.(4) The determination methods for the moment and the rotation angle corresponding to the characteristic points of the moment-rotation angle skeleton curve of the CSCFT column were proposed. The peak moment can be determined by superposition method. Two methods for determining the rotation angle were developed. One method is to use the measured moment-curvature curves of the CSCFT column specimens and a simplified curvature-rotation angle relationship, or to use the calculating formula of the rotation angle obtained from the numerical simulated moment-curvature curves. Another method is to use the calculating formula of the rotation angle obtained from the measured moment-rotation angle curves of the CSCFT column specimens. Determining of the performance points on the moment-rotation angle curve of the CSCFT column was proposed. |
