Engineering Applications Of Pseudo Excitation Method And The Parameter Selection

Long span bridges are usually important public facilities and so much attention has been given to evaluating their safety during earthquakes. The current (JTJ004-89) applies only to bridges with 150m or shorter spans, that has not fitted the current requirements. For example, the seismic spatial effects must be taken into account during their design. So a great deal of theoretical research and numerical computations/comparisons must be carried out. In current practice, dynamic analysis for such spatially varying input motions is performed mainly by the time history method, whose chief disadvantage is that the results rely heavily on the selected time histories. The response spectrum method (RSM) adopted as the most important tool by the code is unable to deal with such problems. The random vibration approach is theoretically superior in dealing with such multiple excitation problems, however it has hardly been practically applied due to its computational complexity, in addition to the problems relating to its input and output. The pseudo excitation method (PEM) has brocken its efficiency-bottleneck, and appears to be quite effective in coping with such multiple excitation random analyses. The main research work covers the following aspects:For the seismic response analysis of long-span structures, the response spectrum method, the random vibration method and the time history method are compared. It is found that the spatially varying effects of the ground motions, especially the wave passage effect have great influences on the dynamic responses of long-span bridges. For seismic analysis of multi-degree-of-freedom, multiply supported structures subjected to spatially varying ground motions, the response spectrum method may lead to serious errors, the time history method needs extensive effort, while the proposed pseudo excitation random vibration method has great advantages.Base-isolated building structures are widely accepted in the earthquake engineering due to the effectiveness of vibration reduction. At present, most base-isolated technology uses rubber cushions. Under strong random seismic excitations, rubber cushions will locally enter the nonlinear (elasto-plastic) regions. To compute such problems, conventionally the equivalent linearization scheme combined with the solution of Lyapunov equation is used, which is very inefficient. In the present thesis, the solution of Lyapunov equation is replaced by the use of pseudo excitation method, that remarkably raises the efficiency while the accuracy remains unchanged.