Investigation On Static Performanceof Large Rectangular Section Concrete-filled Steel Tube Column With Force Transmission Components

Large rectangular section concrete-filled steel tube column(LRCFT column) has been widely used in complicated super high-rise buildings, and it is very important for the stability of the whole structure. Working together is the basic problem for LRCFT column, which has an important influence on the performance of structure. For the problem of working together of LRCFT column, a new kind of force transmission mechanism has been carried out in this paper, that is force transmission components－distribution beams and inner periphery ribs are arranged at floor node zone to coordinate deformation between steel tube and core concrete, and force steel tube and core concrete to work together. The main contents in this paper are as follows.(1) A new kind of force transmission mechanism was carried out based on the working together performance of LRCFT column, and specific structure and arrangement form of force transmission components were given, meantime mechanical principle of concrete-filled rectangular steel tube(CFRT) column with force transmmssion components was analysed. Under axial compression the working together performance of CFRT columns that consist of force transmission components not being arranged, ring stiffeners being arranged, both ring stiffeners and studs being arranged, and force transmission components being arranged were analysed, which revealed the importance and necessaries for the performance of LRCFT column to arrange force transmission components. The axial compression tests and numerical analysis of CFRT column were analysed, and the test results showed that they were in good agreement by using finite element method(FEM), furthermore verified that bond action was not an accurate way to ensure the performance of LRCFT column, but arranging force transmission components improved the mechanical performance of CFRT column effectively, and ensured working together of LRCFT column fully.(2) Based on mechanical principle for LRCFT column with force transmission components, the theory model of working together that the interaction of distribution beam transfering external load to concrete works as Winkler assumption on elastic foundation beam was carried out. The equations of percentage of load-carrying shared by concrete were established, in which the interaction of distribution beam and concrete was regarded as elastic foundation beam, steel tube provided stiffness, concrete was simplified to elastic foundation, and distribution beam worked as beam. Applying the boundary conditions of CFRT column with distribution beam, the calculation method of percentage of load-carrying shared by concrete can be abtained. Based on mechanical behavior among distribution beam, steel tube and concrete, the stiffnesses solutions of each component of LRCFT column were obtained, which ensured the solution of percentage of load-carrying shared by concrete. By studying mechanical behavior of distribution beam, the design method of distribution beam was determined to guide engineering design. The actual example was analysed, which verified the validity and good practicability of analytical method in this paper.(3) Based on the theory model of working together, the relationships of percentage of load-carrying shared by concrete with stiffnesses of each component of LRCFT column were studied, accordingly the ranges of distribution beam section size were given. Proceedly from governing equations on stiffnesses, coupling between two factors was considered and by using nonlinear regression method, the simplified calculation formulas for each stiffness coefficient were obtained. The error of calculation were discussed, which showed that the simplified calculation formulas were reasonable. Through the simplified calculation formulas the stiffnesses can be calculated quickly, thereby the percentage of load-carrying shared by concrete is given to guide the design of distribution beam.(4) Working together performance of LRCFT column with force transmission components were studied under axial compression, bending and eccentric compression. Based on―Technical specification for structures with concrete-filled rectangular steel tube members‖(CECS159:2004), the design methods of carrying capacity under axial compression, bending and eccentric compression for CFRT column with force transmission components were obtained, and the proposal that design method of carrying capacity under big eccentric compression of specification need to be improved further was proposed and the calculation formula was given. A model of30-stories frame was established and the quantity design of force transmission components was studied. From the standpoints of elastic and plastic design, the working together performance of LRCFT column with force transmission components was studied. It was shown that for CFRT structure, with too much or too little distribution beams the optimal distribution effect can’t be reached, when the quantity is suitable and location is reasonable the performance of CFRT stucture is acceptable.