Dynamic Mechanical Behavior Of Concrete-Filled Steel Tube Composite Column With Stiffening

Concrete-filled steel tube composite column with stiffening is a kind of column which set the stiffening in the traditional steel tube composite column so that the stiffener can break up the concrete to improve the constraint effect of concrete and reformed the mechanical performance of the composite column. At present,scholars at home and abroad from the aspects of theory analysis and experiment validation studied the dynamic properties of the traditional composite concrete filled steel tube column, but less researches on stiffened concrete filled steel tube composite column had been done. Therefore, the series researches on dynamic performance of square concrete filled steel tube composite column with stiffening has been done in this paper. The researches have important significance to structure analysis and engineering application. In this paper,we carried out the following research works:(1) The finite element model of concrete-filled steel tube composite column with stiffening has been established and calculated. The finite results were compared with open test data to verified the accuracy of the calculation model in this paper. Then, it is discussed that the mechanical characteristics and working principle of square concrete filled steel tube composite column with stiffener under low cycle load from the failure pattern,hysteresis curve, skeleton curve to stiffness degradation, ductility and deformation capacity. Research results show that the concrete filled square steel tubes column with stiffener has more good dynamic performance and seismic performance than traditional composite column.(2) This paper discussed the different dynamics performance about strength of materials, steel ratio, axial compression ratio, stiffener size and shape to the composite column. And the results show that the strength of concrete has little influence on the dynamic mechanical properties of square concrete filled steel tube composite column with stiffening while the thickness of the steel tube and its material strength level can significantly affect the dynamic mechanical properties; the greater the steel ratio, the higher ductility coefficient;however the stiffened square concrete filled steel tube composite column with a greater axial compression ratio would have a smaller ductility coefficient as well as the slenderness ratio of the composite column. Besides the effects of axial compression ratio exists a tipping point phenomenon, that is mean the ultimate bearing capacity of the composite column improved before the point value but then suddenly reduced. According to the calculation results, this paper suggested the axial compression ratio point value of the stiffened composite column should not be greater than 0.55; stiffening thickness and width have significantly effects on the dynamic performance of the composite column, also this paper suggested that economic thickness is T - 2 T (T is the thickness of the square steel tube); and the economic width is 0.5 B?0.75 B (B is the width of the square steel tube). The effects of cross shaped stiffener and trilateral shaped stiffener are basically identical.(3) Contrast analysis about the ductility of tube composite column with steel stiffener and FRP stiffener have been done in this paper, the calculation results show that the ductility coefficient of square concrete-filled steel tube column with FRP stiffener is greater than the same condition of steel stiffened steel tube column. Besides the thickness and width of FRP stiffener can significantly improve the dynamic properties of composite column.