Study On Seismic Performance Of Long-Span Girder Bridges Considering Soil And Struc-Ture Interaction

From earthquake engineering practice, soil and structure interaction has much in-fluence on seismic performance of structure, and it is an important cause of bridgedamages, while damping control is an effective means to reduce the seismic re-sponse of structure. For the above reasons, the seismic performance and dampingcontrol of long-span continuous girder bridges have been studied, which are listed inthe following.(1) Parameter analysis of the seismic response of the continuous girder systemconsidering soil and structure interaction. With the help of FLAC-3D, the wholeanalysis model that includes soil and the bridge has been built using the directmethod. The influence of soil density, Poisson's ratio, the velocity of soil shear wave,the thickness and type of soil and so on is summarized on SSI. According to the re-sults, if the location of the bridge is Class II, III or IV site, and the fortification in-tensity is not less than7, seismic analysis of continuous girder bridges (except forbridges belonging to Class D) should consider SSI.(2) Comparative study of the seismic performance of the three structure systemconsidering soil and structure interaction. With the help of Midas/Civil, the simpli-fied analysis model has been built using the improved Penzien model. And Seismicperformance of three structure systems has been studied from the difference of pierheight, pier type and traveling wave effect. According to the results, in a seismic re-sponse, the pier height and pier type have different influence with different structuresystems. And in a structure system, the pier height and the pier type have differentinfluence with different seismic response. Traveling wave effect has much influenceon the three structure systems: in lognitudinal direction, support displacement oftransition pier will increase, and other seismic response will basically reduce. Intransverse direction, seismic response may increase. So, doing research on the threestructure systems' seismic performance should consider traveling wave effect.(3) Damping control of the seismic response of the continuous girder system con-sidering soil and structure interaction. Viscous damper has good damping effect, butits design and production are difficult and maintenance cost is high. And because ofthese factors, it can't play a role in the process of earthquake. For this reason, thelarge stroke lead damper has been studied in this article. A simplified method ofcalculating the damping force has been proposed on the basis of the finite elementanalysis and test results, in order to facilitate the design of the damper. Like viscous damper, large stroke lead damper can also be placed with the bearingin parallel as a shock absorber used in long-span continuous girder bridges, and thedamping effect is good. With higher performance price ratio, large stroke leaddamper has good prospect in bridge engineering. In damping system,if consideringSSI, support displacement and the main pier deformation will increase, and the in-ternal forces at the bottom of the side pier and the main pier will be reduced. So, thedamping system should consider the influence of SSI, otherwise it is unsafe in thedesign of the bearing, and the amount of the ordinary reinforced bar in the side piermay increase.(4) Exploration of real-time substructure testing with shaking table for long-spancontinuous girder bridges considering soil and structure interaction. With the testingtechniques of real-time substructure testing with shaking table, the shaking table testconsidering SSI can be achieved. According to experimental data, the law in the re-sults of the three structure systems is basically the same with that in the results ofnumerical analysis. But the difference in value is large, and among the seismic re-sponse, the biggest difference is about20%in support displacement and the mainpier deformation. This is mainly related to the way to get interface force, time delay,noise, the control accuracy of shaking table and so on. In other word, when com-mand signal calculated by the numerical substructure drive the array by the controlsystem of shaking table, there is some difference between the table signal and com-mand signal, but this difference is random.(5) Application of neural network in real-time substructure testing with shakingtable. Studying on time-delay compensation is an important aspect in real-time sub-structure testing with shaking table. Time delay will affect the accuracy and the sta-bility of the system, and even cause divergence. In modern control theory, neuralnetwork is the effective way to compensate time delay. So, it can be used to predictthe signal applied to the actuator of the shaking table. According to the simulation,the effect of compensation is significant.