Research On Collapse Of Rigid Frame Bridge With Super High Rise Piers Under Earthquake

In recent years, there are many long span rigid bridges with super high rise piers more than100meters have been built in China. They play important role as lifeline engineering in certain cases such as earthquake relief and so on. Research on these bridges is one of the most important frontiers of bridge engineering. Moreover, several earthquakes have made huge casualties and enormous financial loss in China, in which many bridges collapsed and exaggerated the disaster. Avoiding bridges collapse is an important mission in seismic design and has been paid more attention after the earthquake took place in Wenchuan2008. Based on the popular seismic design method "bridges after small earthquakes could be used continuously; bridges after middle earthquakes could be repaired; bridges after huge earthquakes could be stand as usual" researches on the collapse limiting condition and collapse analysis in bridges have a practical significance to ensure a safe life.Numerical simulation is the main method to analysis the collapse of the complex structure. The first key point is to build an accurate model to analyse the collapse of structure; the second is to set up a precise collapse criterion for the rigid frame bridges with super-long piers based on dynamic response; the third ont is to simulate the effects of the surroundings and other negative factors during the bridge service period.In this dissertation the present research status at home and abroad and the key points of research on callapse of the rigid frame bridge with super high rise piers are introduced in Chapter1. In Chapter2the method of modeling the buckling of longitudinal reinforcement is presented and verified by the pseudo-static tests. The results show that in order to model the degradation in strength and stiffness of RC columns loaded to their failure, the buckling of reinforcements should be taken into account in simulation. In Chapter3the criterion of collapse based vertical displacement of pier top for rigid frame bridge with high piers is proposed and verified by an engineering example. It is demonstrated that the proposed criterion is effective in evaluating the collapse of the structure, and the failure mode of the structure is vertical callapse with several plastic hinge appeared simultaneously in the bridge piers. In Chapter4the effects of deterioration on the callapse ability including spalling of concrete cover, deceasing of steel areas and strength are investigated in depth. It is shown that the deterioration will result in the change of period and collapse capacity of the structure. In Chapter5, the collapse fragility of the bridge under multiple ground motions is investigated. It is illustrated that the deterioration should be taken into account to reflect the real collapse capacity. Finally in Chapter6the full summary and the future research work are given.This study will be a reference for seismic design and earthquake collapse analysis of these rigid frame bridges with super high rise piers.