Linear and Nonlinear Analysis for Large-span Rigid Frame Bridge under the Excitations of Multi-dimensional and Multi-support
|School||Beijing Jiaotong University|
|Course||Bridge and Tunnel Engineering|
|Keywords||large-span rigid frame bridge traveling wave effect seismic responses powerspectral time history analysis plastic hinge|
With the rapid development of bridge engineering, the spans of bridges become larger and larger, and piers become higher and higher, Therefore, systems are often more flexible than ever. Which bring new challenges to seismic design of long span bridges. As a widely used project type, rigid frame bridges are also developing towards large spans and high piers.Currently, seismic design of bridges is all based on uniform excitation method,but ground motion of different pier of large-span bridges are usually not consistent because of influences of traveling wave effect, partially coherent effect and partial site effect. Therefore, study on earthquake responses of large-span bridges under multi-support excitations is of great importance.In this paper, analysis model and principle is summarized firstly, which laid the foundation for the following calculation and analysis. Secondly, as a example, a5-span prestressed concrete rigid frame bridge is analyzed with finite element software-ANSYS using power spectrum method, in which earthquake responses of rigid frame bridge is studied in the condition that traveling wave effect, partially coherent effect and partial site effect is considered both separately and together. Thirdly, multi-dimensional and multi-support artificial seismic waves are generated based on target power spectrum model and target correlation function model, and the rigid frame bridge is analyzed with time history method using the generated artificial seismic waves. Finally, earthquake response of both curved rigid frame bridge and straight rigid frame bridge is studied comparatively. The main conclusions in this paper include the following:1. The influence of partial site effect is obvious,adopting site soil of which characteristic doesn’t vary with spatial location may make rigid frame bridge unfavorable; The influence of partially coherent effect is little; In the condition only seismic wave effect is considered, the moments on the top of piers of rigid frame bridge is usually less compared with results of uniform excitation; The influence of traveling wave effect on the top of piers is relatively large than that at the bottom; After traveling wave effect is taken account, higher modes of rigid frame bridge may be aroused.2. In the condition that traveling wave effect, partially coherent effect and partial site effect is considered comprehensively, the earthquake responses of piers may increase or decrease while the earthquake responses of main girders usually increase compared with the case of uniform seismic excitation. 3.Multi-dimensional and multi-support seismic waves are generated, and multi-dimensional and multi-support time history is implemented after both material nonlinearity and geometric nonlinearity is taken into account, results show that earthquake responses of different direction are coupled with each other in the case of multi-dimensional and multi-support excitations, earthquake responses of rigid frame bridge don’t equal to the simply superimposed results of one-dimensional; Full plastic hinge loops appear on the top of piers in the case of multi-dimensional and multi-support excitations after taking nonlinear property, so ductile design on the top of piers of rigid frame bridges should be paid attention in practical engineering.5. The formula of the most unfavorable input angel of seismic waves of determined response variable of curved rigid frame bridge, under one-dimensional and multi-support excitations and two-dimensional and multi-support excitations, is obtained. According to the formula, exact value of input angel of the one and two-dimensional and multi-support seismic waves, against a determined response variable, can be easily obtained.6. Under three-dimensional and multi-support excitations, transverse moments of piers and main girders of curved rigid frame bridge are usually less than that of straight rigid frame bridge while longitudinal moments of piers and vertical moments of main girders are usually more.