Study On Aseismic Performance Of Continuous Girder Bridges Isolated By Lead-Rubber Bearings (LRBs)

With the rapid development of bridge engineering in recent years, the safety problem of the seismic resistance of bridge at highly seismic region is growing concern. Taking several isolation design subjects of continuous bridge with lead rubber bearings(LRB) for examples, this thesis conducts a primary studies on the application of lead rubber bearings on bridges, And the major content is as follows:Firstly, a large number of nonlinear time-history analysis of seismically isolated continuous girder bridges with lead rubber bearings (LRB) were conducted using the ANSYS software. During these analysis, different parameters such as seismic site, intensity, the mechanical parameters of LRB and bridges structure themselves are considered respectively to discuss their influence on the isolation efficiency, and some significant conclusions have been obtained.Secondly, considering the spatial variability effects of ground motions, seismic responses analysis of a long-span continuous girder bridge with lead-rubber-bearings(LRB) is conducted in this thesis. The power spectral density function of ground acceleration can be described as filtered white noises applied to each support point. The spatial variability effects of earthquake ground motions, including the incoherence, the wave-passage and the local site-response effects is taken into account. the equation of motion of LRB structures to multiple excitations is derived, while the stochastic equivalent linearization method is used to linearize the equation of motion. Furthermore, a seismically isolated bridge with LRB is calculated in seven cases, such as uniform excitation and multiple excitations. Mean values of the maximum quasi-static, dynamic and the total response in these cases are obtained and compared.Finally, Proper orthogonal decomposition(POD)-based spectral representation method, is a renewed method for the simulation of stochastic fields. The stochastic model of the spatial varying earthquake ground motions is described in detail. By introducing a pre-decomposition of the spectral matrix of the seismic ground motion into the method, the simplified formula for the simulation of the ground motions is obtained here. And an application of the formula on a long-span seismically isolated continuous girder bridge is taken as a numerical example. Then, the time-domain analysis of this continuous bridge under uniform excitation and multiple excitations is carried out. Meanwhile, the time domain response and the frequency domain response of the isolated bridge is illustrated and compared, and some useful results are obtained.