Three Dimensional Dynamic Response Time Analysis For The Continuous Rigid Frame Bridge With Long-Span And High Piers

Because of the strong adaptability of terrain, the maturity of design and construction technology, long-span capability and the reasonable cost, the continuous rigid frame bridge of prestressed concrete is widely adopted and has already become the main bridge type of the prestressed concrete bridge in recent years. With the constant development and application of the long-span and high piers continuous rigid frame bridge in our country, the corresponding issues have been researched and discussed deeply.The dynamic problems of bridge structures have always been cared for by bridge workers. It consists of two aspects: one is free vibration and another is dynamic response of the bridge structure. Firstly, combined with Lizigou long-span railway bridge of the Neikun railway line, its space free-vibration is analyzed with the FEM(finite element method) of solid element in this thesis. The analysis result is very precise. Secondly, solid model and three-dimensional beam element model are built up respectively in the transient-dynamic response time history analysis of Lizigou long-span railway bridge, and then a series of contrast analysis are done under the moving load. On the base of dynamic equation, with the Newmark integral method, taking into account influence of the moving load, velocity and stiffness, the dynamic response of the bridge are discussed under the effect of moving load. The process of the train through the bridge at three different velocities of 90km/h, 120km/h, 160km/h are simulated separately in two different girder material. Middle-span deflection time response graph of five spans and the time history response stress graph of the top and bottom flange in the middle-span section are given.According to the calculation, the following results can be obtained: the free-vibration of the bridge is mainly the longitudinal bend and the calculation frequency is coincident with the measured result; The free-vibration period of four high piers can fit the limiting criterion which is established at the high-pier meeting in 1959; the deflection graph under the moving load is a kind of analogous sine wave, which surround the static-deflection graph with certain frequency; From the time history response stress graph induced by the moving load on the top and bottom flange of the girder section, the time history response stress graph at the top and bottom is approximately symmetry to the time axis and time response stress is a little lagged. From the contrast of the different time history response graph at different speed, it can be noticed that the stress peak value is not evidently influenced by the change of the velocity. Through the calculated results of the two models, both are very consistent. Obviously, the space response of the bridge can be well simulated with the three-dimensional beam element and the complexity of the three-dimensional solid modeling can be avoided and much calculation time can be saved.