Research On Three-Dimensionai Modal Pushover Analysis Procedure Of Tall Building Structures

In recent years, the problem of huge economic loss caused by earthquake has been exposed, engineers recognized that traditional seismic criteria for the purpose of life safety cannot satisfy people seismic requirement. In this context,researchers propose the performance-based seismic design theory.Performance-based seismic design theory choose the displacement reaction as evaluation criteria, the traditional design method based on carrying capacity is no longer applicable for engineering, replaced by the displacement-based seismic design method, static pushover analysis is the most widely used procedure. Researchs which have been done on pushover method are limited to planar structures, but actually most of structures have the non-ignorable factor of torsion that can’t be neglected, the spatial structure analysis is very necessary. The static pushover analysis method is extended from planar structures to asymmetric spatial structure, and an energy-based modal pushover analysis method is proposed in asymmetric structure in the paper. Focused on the following aspects of research in the paper:Modal pushover analysis method needs to consider bidirectional lateral force and moment of torsion in spatial structure. Theoretical formula is chose as a starting point, lateral force in accordance with the spatial mode shape is proved to include three-way characteristics of structure in every mode, the impact of three-way loading in spatial structure has been effectively considered.For the two directions of pushover curve in modal analysis of spatial structure, strict theory which has been deduced proves that pushover curve in either direction can represent the performance of the structure in the paper. In order to reflect properties as fully as possible, the pushover curve which has a strong response in primary vibration direction is suggested to be selected for calculation.Considering the phenomenon of reversal of higher-mode pushover curve in modal pushover analysis, direct cause is the choosing of roof displacement as a structural performance evaluation value. The energy-based displacement is chose as the reference value Assessment, and theoretical derivation along with solution method of energy-based displacement is gave from the aspect of structure dynamic theory.A shrink layer asymmetric frame structure is computed as an example with energy-based modal pushover analysis procedure in the paper, and comparison between the structure reactions with reaction of time history analysis proves that the energy-based modal pushover analysis method is feasible in seismic analysis of spatial structure. In addition, comparison among the results with the results of the improved modal pushover analysis method and conventional modal pushover analysis method is analysised, and reaches the conclusion that energy-based modal pushover analysis method has superiority in seismic analysis of spatial structure.