Continuous Rigid Frame Bridge Seismic Analysis In Applied Research, The Capacity Spectrum Method

Capacity spetrum method is a simplified analysis method based on the push-over analysis method, which is actually to estimate the response of the structure(the response of displacement and acceleration) in the fixed seismic load with the capacity-spectrum and demand-spectrum .the prominent strongpoint of this method is that it not only considers the elasticity and plasticity during the course of calculation but also costs much less time than the non-linearity time-history method.The main contents of this dissertation include:1. the basic principle and procedure of push-over analysis method were studied. The key of push-over analysis method is load pattern and target displacement. for ordinary frame bridges, the lateral load patterns to a single pier model and total bridge modal for push-over analysis at the longitudinal and transverse direction were emphatically discussed. For a single pier, reliable result can be obtained by applying lateral displacement or concentrated force on the top of the pier because the weight at nodes of a single pier model mainly concentrate on the top of the pier. Because the stiffness of super structure is very large, in spite of the variety of pier height, the longitudinal displacements at each node were almost identical, so the load patterns of applying identical displacement on the super structure could be adopted for push-over analysis at the longitudinal direction of a total bridge model. According to the variety of each pier height, reasonable lateral loads concentrated on the top of each pier were chosen for push-over analysis at the transverse direction of the total brodge model.2. the basic principle and procedure of capacity spectrum method were studied. This paper calculates the response of two different bridges with the two method—capacity spectrum method and non-linearity time-history method, and compares the two responses for each bridge. For the ordinary frame bridge, the gap of the two method is small enough to be neglected, while the gap of the two method for the special bridge such as the Luohe Bridge is very large even if considering more modes of vibration and using the improved multi-mode capacity spectrum method which is generally presented for the irregular girder bridge with long natural period. For the bridge of long natural pepiod and big flexibility, the precision of the capacity spectrum method is to be improved.