Seismic Response Analysis Of Long-span Rigid-frame Bridge And The Shaking Table Model Test

There are some characters about the seismic in the process of propagation, such as wave passage effect, incoherence effect, site-response effect and attenuation affect etc. It has been verified that ground motion is obviously amplified along the ridge. Therefore, the topographic effect on seismic response of large-span bridge under complex landform must be considered. Due to the complex geometric character, the dynamic responses of the curved bridge are different from that of the straight one. Simulating the non-stationary spatial correlative time histories of multi-point ground motion, studying the seismic responses of the curved bridge under multi-point excitations, and simulating earthquake shaking table test for such large-scale spatial structures could provide a guideline to structural performance evaluating and a seismic design reference for curved bridge theoretically and experimentally. The main contents are as following.1. Generation of the multi-point earthquake ground motions considering the topographic effect.The seismic ground motions of two neighboring mountains and the free surface between them are calculated under the P and SV seismic waves with several different incident angles. The incoming waves are chosen from three actual earthquake records with different spectrum characteristics. The ground motion responses reflect a combined influence of ridge scattering effect and traveling-wave effect.2. Seismic responses of large-span rigid-frame bridge under multiple-point excitations and complex topographic conditions.The results derived from the first analysis stage were then used as the inputs in the second analysis stage. Taking a four-span rigid-frame straight bridge of 440m as an example, which was assumed to be built between two neighboring asymmetric mountains, the seismic responses of the bridge are numerically simulated, and the results were compared against those when only the wave passage effect is taken into account. A conclusion is given that the irregular topography will have significant effect on the wave propagation, which cannot be ignored in the seismic design. The conclusion provides an important theoretical reference for the engineering application and for improving the seismic safety of the continuous rigid-framed bridges.3. Simulation of non-stationary artificial ground motion and analysis of seismic response of curved bridge under multi-support earthquake excitations.The phase difference spectrum was introduced to consider the non-stationary properties of frequency contents, the statistic model of the coherence function was used to consider the coherence character, and the apparent wave velocity varying with the frequency of earthquake wave was adopted rather than an arbitrary one, the non-stationary random field considering the temporal-spatial variation was simulated. This random field was then used as the multi-point excitation of a five span continuous rigid-frame curved bridge in horizontal and vertical directions respectively. The pier-top displacement and the pier-bottom internal force of the bridge were calculated, and then the results were compared with those considering uniform and traveling-wave excitation. The influences of incoherency effect and the wave passage effect on the seismic responses of the bridge were discussed.4. Shaking table test on large-scale curved bridge model under multi-point excitation.The curved bridge is a five span structure of 68m+120mx3+68m total length. The curvature radius is R=620m. Based on similar theory, the whole model was made. The horizontal shaking table test of the model bridge by the multiple vibration table array system, located in Beijing University of Technology, was carried out. The acceleration, displacement and strain of the structure under the horizontal earthquake are gained. These test dates were then compared with the theoretical results. The results can provide test data and basis to evaluate the seismic performance of such curved bridge and can be a reference for seismic analysis of similar structure in future.