Optimual Seismic Design Of Structures Based On Collapse Capacity

The seismic effects are regarded as lateral intertia forces along height based on structural elastic modes in traditional seismic design methods, these force-based design approachs could not effectively control the inelasticity displacement of structure during earthquakes. Therefore many optimum seismic design methods were proposed, but none of them was directly based on structural collapse capacity. In this paper, reinforced concrete frame structure was studied, and an optimum seismic design method was proposed to get more uniform collapse capacity on every story. In this approach, an iterative optimization procedure has been adopted to shift inefficient material from strong stories to weak stories until a state of relatively uniform collapse capacity is achieved, and the total material of structure is unchanged. Then, the ground motion parameters and the structural parameters which affect the structural optimized strength distribution pattern and lateral loading pattern were studied. Specific research contents include:(1) The relationship between the structural collapse capacity and ductility ratio was studied, and the concept of collapse ductility was proposed. A method which based on collapse ductility to modify the structural properties was put forward to get more uniform collapse capacity on every story. The coefficient of intensity distribution and lateral force distribution were defined. The optimal structure has higher collapse capacity and the collapse capacity on every story is more uniform.(2) The influences of ground motion features on the structural optimized strength distribution pattern and lateral loading pattern were comprehensively discussed, it showed that the influence of earthquake magnitude, the fault distance and ground motion duration on the structural optimized strength distribution pattern and lateral loading pattern is negligible. It also found that the structural optimized strength distribution pattern and lateral loading pattern of class E ground and near-field records set are obviously different.(3) The influences of various structural properties on structural optimized strength distribution pattern and lateral loading pattern were assessed. The result showed that the total floors of the structure, foundamental period and ductility ratio have great influence on the structural optimized strength distribution pattern and lateral loading pattern. The influence of structural damping ratio, post-yielding stiffness and post-capping stiffness is negligible.(4) Equations of structural optimized base shear coefficients and lateral loading distribution coefficients which apply to the practical engineering were given by regression analysis. And the collapse capacity of the structures which designed by bottom shear method and the optimized method proposed in this paper respectively were compared by collapse fragility analysis, and found that the structure designed by the optimized method has higher collapse capacity than which based on bottom shear method.