Long-extension Concrete Bridge Vibration Underactions Of Earthquake And Road Vehicle

With the development of economy and society, the long-extension bridges of which totallengths are beyond several or tens of kilometers have been built in order to meet therequirements including the smoothness and the stability of the road and the environmentalprotection pressure. And the ratio of the concrete bridges to the road traffic line increasesgreatly. On one hand, different supports of the long-extension bridge may suffer fromvariational seismic ground motions. Yet the spatial variability of ground motion study islagging behind. On the other hand, the possiblity that a road vehicle is driven on a bridgewhen earthquakes occur is higher and higher, which shows that road vehicle-bridge coupledsystem subjected to seismic excitation should be in-depth study. However, no valuableinformation on this subject is available. On the basis of the summary and general study of thepredecessor’s research experiences in China and abroad, the paper deals with the vibration oflong-extension concrete bridge under the actions of earthquake and road vehicle, in which thespatial variation of seismic ground motion and the bridge vibration under the simultaneousaction of earthquake and road vehicle are considered.The main contents and research results are as follows:1. The mechanism of spatial variability of seismic ground motion is discussed. Anoperable scheme for the seismic wave simulation is presented. According to the spectraltheory, the unconditional simulation method is used to generate seismic acceleration timehistories of bridge supports where site characteristics and coherent model are known. Theconditional simulation method based on multivariate linear prediction theory is used wherethe seismic acceleration time history of one support and coherent model are provided. Themethods to eliminate error of earthquake wave and their applicabilities are discussed.2. Dynamic response of a simply-supported beam subjected to two-point seismicexcitation is studied using the analytic method and the numerical solution, which results showthat the phase component of seismic wave plays an important role.3. Some mistakes are popular in the computation methods of the bridge seismic analysis.The applicabilities of accurate solution method, large mass method and large stiffness methodin bridge aseisimatic analysis are discussed. The numberical results show that different input pattern of seismic has great impact to convergence speed and solving precision. Input patternof seismic acceleration in accurate solution method is only suitable for linear analysis, andinput pattern of seismic displacement applies to nonlinear analysis. Compare with largestiffness method, the solving precision of large mass method is higher.4. A continuous rigid frame bridge is taken as a case study. The time history of realearthquake record is taken as a reference. The conditional simulation method is used togenerate seismic acceleration time histories of bridge supports. The errors in time historiesare eliminated using residual value method of zero final displacement. Large mass method isused to solve the equilibrium equations of motion bridge structure. The numberical resultsshow that the influence of loss of earthquake wave coherence on bridge dynamic responsecan not be neglected and only full consideration of spatial variability can obtain safer results.5. The dynamic interaction model of road vehicle-bridge coupled system subjected toseismic ground motion is established, which consists of road vehicle subsystem and bridgesubsystem. Both of them are established with finite element method. The rigid componentassumption is introduced to the road vehicle subsystem, the mode superposition method isapplied to the bridge subsystem to reduce the degrees-of-freedom, and the dynamicinteraction between two subsystems is expressed with wheel road relation. The numbericalsolution flow is introduced, in which some key schemes are presented. And a calculationsoftware named DIARVB is prepared.6. A freight car running over a3-span continuous rigid frame bridge subject toearthquakes is taken as a case study to verify the applicability. The results show that dynamicof bridge subsystem is completely controlled by seismic excitation. The seismic excitationtransferred by bridge subsystem may amplify the vibration of road vehicle, which mayendanger the running safety of vehicle. The vehicle speed plays an important role in dynamicresponse of vehicle subsystem. And the spectral characteristic of earthquake wave influencesdynamic response of coupled system.