Optimal Design Of Beam String Structure

As a new type pre-stress structure, beam string structure has been widely used in large-span structure such as gymnasium, convention & exhibition center and so on. Optimal design for beam string structure can economize steel, reduce cost and improve load bearing of structure. It can not only develop the theory of beam string structure, but also direct the engineering practice. In this paper, such optimal design problems as the sections size, cable load ,the shape of cable, sag of beam string structure are discussed. All these are meaningful in beam string structure's engineering application. In aspect of section size optimization of beam string structure, the paper establishes the math model considering constraint conditions which satisfy the demands of stress, strain and local stability specified by Code for Design of Steel Structure, then the paper presents the corresponding solve method. In this solve method ,two variables( pre-stress and section size) included in the founded model are separated. First, the pre-stress load is determined, then the section size is selected through fully press method. To satisfy the strain constraint condition, we can adjust the pre-stress load or the section size. It's demonstrated that the method is simple and effective. The method is the basis of cable shape and sag optimization. In the section size optimization considering the cable shape, the relevant math model is founded. The model includes three kinds of variables, i.e., the pre-stress load,section size and location of node. In the solve method, variables are divided into two optimal spaces. The pre-stress load and section size compose the first optimal space,they are solved through variable separate method. Location of node belongs to the second optimal space, it is determined by evolutionary method of node. In the section size optimization considering the sag of beam string structure, the sensitivity calculating formulation is firstly derived, then the math model is set up and the solve method is presented. Numerical examples show that using this method can realize optimal choice of structure sag.