Research On Dynamic Stability Of Rigid Frame Bridge With High-piers Under Earthquake

Recently Rigid-Frame Bridges have been built for only twenty years in our country and they have been used as the preferred bridge type in coplicated terrain mountain areas. They play important role as lifeline engineering in certain cases such as earthquake relief and so on. Therefore study on their seismic performance needs to be carried out, especially on their dynamic stability under earthquake action. Dynamic stability of a rigid-frame bridge has been investigated in this dissertation, and the seismic performance of the bridge is evaluated. The research of seismic response of rigid-frame bridge with high piers is of great significance to the seismic design and evaluation of other similar bridges.In this dissertaion, the studies on the dynamic stability of rigid-frame bridge with high piers are performed. The research content includes:the theory and example analysis of the elastic dynamic stability; the nonliear simulation method of bridge piers; the material parameters of reinforcement and concrete; the nonlinear dynamic stability of high pier and full bridge. The specific contents are as follows,1) Based on the massive domestic and international literature of the seismic response, static stability resarch and dynamic stability of rigid-frame bridges, summarizes the two key points of the research on the dynamic stability of rigid-frame bridge:what is the suitable and practical dynamic criteria and how to solve the dynamic stability of the bridge. The criteria based on Liapunov's motion stability theory and numerical simulation method are put forward to solve the dynamic stability of comples structures under earthquake. And the key point of the numerical simulation of rigid frame bridge is how to deal with the nonlinearity of the structure.2) In order to determine the reinforcement and concrete matrrial parameters which are suitable for this bridge, the strain corresponding to five damage states is investigated, which can also be used to evaluate the performance levels of the bridge under earthquake. The five damage states of the bridge piers subjected to seismic action are:members yielding, concrete cover crushing, concrete cover spalling, bar buckling, structure limit state respectively.3) Due to the challenging nature of accurately modeling the material nonlinearity of both steel reinforcement and concrete, conducting nonlinear static and dynamic analysis of the rigid frame bridge with high pier remains as a significant difficulty. The fiber model is choosed to model the nonlinearity of the rigid-frame bridge which is the most precise and latest method. The section code is developed and the nonlinear static analysis is done to the piers.4) The nonlinear IDA is done to the full bridge and piers based on the fiber model under earthquake action. The whole process of the structure from initial exitation, nonlinear vibrating to instabe failure is simulated. During the analysis B-R criteria is used to judge the critical load of the bridge. The dynamic performance and instablility mechanism of the bridge are researched.