Mechanical Performance of Mega Steel Frame-Prestressed Composite Bracing Structure

The mega structure has been widely studied and applied due to the clear force transferring way, good structural integrity and flexible layout of diverse building functions. Based on the structure of mega truss or mega frame, the research and application of the mega structure with many kinds of bracing structures become a hot topic in recent years. Mega steel frame-prestressed composite bracing structure with a rigid-flexible composite bracing system composed of rigid Λ-shape steel brace and inverted Λ-shape flexible cable is a new kind of mega structure and this composite bracing system is set up in the mega steel frame. By establishing the three-dimensional finite element model and considering the material and geometric nonlinearity, the structural performance under static load in whole process was analyzed and the energy dissipation as well as failure mode under earthquake is also investigated for this new system in this paper. The results indicate that the lateral deformation is mainly decided by horizontal load and the corresponding curve of lateral displacement has the characteristic of flexure mode as a whole, whereas the deflection of mega beam is mainly governed by vertical load and pretension of cables. The internal force equilibrium of composite brace is decided by vertical load and the degree of force unbalance is about 15% when the fluctuation of vertical load is 20%, but the change of anti-symmetric horizontal load has no effect on the internal force equilibrium. The composite braces not only help the mega beam to bear the vertical load but also greatly enhance the lateral stiffness of main structure and so the lateral stiffness of whole system is relatively uniform. Due to the TMD effects of substructure and additional dampers, the seismic energy is mainly dissipated by dampers and substructure and then the main structure is able to maintain elastic. The desired failure mode of MFPCBS under lateral loads is as follows: the web members of mega beam appear to yield at first, and then the braces between mega column limbs, Λ-shape rigid bracing truss, floor beams between mega column limbs and mega column limbs in order.