Study On Optimal Design Method For SRC Frame Structures

At present, the experimental researches and many national specifications concerning the steel reinforced concrete (SRC) composite structures always indicate that there are bond-slip behaviors between shaped steel and surrounding concrete. And the bond-slip behaviors have great influence on the load-bearing capacities of SRC structures.Based on the experimental results of bond-slip behaviors between encased steel and concrete and the design requirements for SRC structures, an optimal design scheme of single objective and discrete variables is proposed to design SRC frame structures. In the optimum scheme, the design variables include the layout dimensions of SRC frame structure, structural member sections, the strengths of concrete and steel, the dimensions of steel shapes;the objective function is the cost of the entire materials applied to construct a SRC frame structure;the constraint conditions are main requirements stated in Chinese code for design of SRC structures, which are basic design rules, reasonable calculating theories, indispensable constructions, and some mature requirements and conclusions confirmed by experimental studies on the calculating methods of SRC structures following the bond-slip theory between steel shape and concrete encasement.The outline of the optimal design scheme is as follows: Firstly, the geometric layout of structure, geometric dimensions and cross sectional sizes of structural members as well as material strengths are specified in advance according to the conceptual design and considerable experience drawn from some civil engineering projects. And then, the frame element model of the SRC frame structure is analyzed under all possible loads. The internal forces, including bending moments, axial forces and shear forces, are obtained by finite element method. And the geometric dimensions and cross sectional sizes of structural members can be determined optimally to some extent by conceptual design. Secondly, the SRC frame structure is divided into structural elements of columns and beams. The structural members have initialgeometric sizes and are subject to obtained internal forces and given behavioral and technological constraints. They are analyzed and optimized in partitioned segments in response to the design variables and the cross sectional dimensions are to be optimally chosen further. In the optimization of structural members, the design variables are determined by the SUMT method with discrete design variables. In the early stage, the optimal calculation is done with the method of continuous design variables. With the progress of the iterative computations, the control action of the discreteness of the design variables appeared rapidly until the design variables convergence to the specified discrete value. After the design variables of structural members are corrected, a new structure scheme can be obtained with the new design variables. The steps of the above will be repeated, and the optimal choice of the design variables of structural elements and structure can be obtained. Finally, a number of existing SRC structural projects are checked with the optimal design method of single objective and discrete variables. There is a sharp contrast in the economic effect between optimal design method and the initial design scheme. Moreover, the optimal values of the main design parameters are proposed. All these may contribute to the analysis and design improvement of SRC frame structures and provide a practical method satisfying civil engineering practice and requirements stated in the Codes.