Research On Working Performance Evaluation Methods For Highway Concrete Girder Bridges Based On Dynamic Testing

The total number of highway bridges in china is more than650000which is themost of the world at present. The proportion of concrete girder bridge is about74%.According to statistics, the proportion is42%which age is more than10years in thenational, provincial, prefectural highway and25%which age is more than20years.The diseases concentrated exposure period of the domestic short and medium spanbridge is15~20years and long-span bridge is6~8years. Therefore, there will bemore and more highway bridge appearing the problems about durability and bearingcapacity. Highway construction will gradually focus on maintenance, repair andstrengthening from construction to ensure highway construction career sustainabledevelopment.Accurate assessment of the state of existing bridge is the foundation and basisof maintenance and reinforcement. The detection and maintenance commonlycarried out after the bridges have obvious problem because methods to assess bridgestate at present were time-consuming which would lead to higher cost ofmaintenance and reinforcement. Vehicle impact load is the main load form ofhighway bridge. At present the evaluation of bridge is main focus on technicalcondition and bearing capacity, rarely on dynamic performance which results are notcomprehensive. Bridge dynamic testing has the following advantages: small amountof work, short test time and can reappear the real operation state. Thus, choosingthe concrete girder bridge which has wide distribution to research the dynamicevaluation technique and search the bearing capacity and dynamic performanceevaluation method based on dynamic testing would avoid the disadvantages oftraditional methods and provide a way to rapid、accurate evaluate of the actualworking condition of the bridge.At present, the dynamic load tests assessment system of bridge has not yetmature.This paper focus on how to build a dynamic assessment system of highwayconcrete bridge and study the problem related to testing, analysis and evaluationwhich involved in the system. The main research contents and results are as follows:Firstly, vehicle field tests including moving vehicle and jumping vehilcle wereidentified as the reasonable exciting way in the test of dynamic characteristicsthrough the comparation and analysis of the conventional methods. Thecharacteristics of free vibration response are analyzed and the FFT+FT method wereused to identify the dynamic characteristics based on free vibration responses. Thispaper give the process to test and identify the dynamic characteristics and exampleof engineering application. It would provide foundation for dynamic characteristics evaluation of girder bridge.Secondly, the paper analysed the relation of dynamic and static stiffness ofsimple-supported girder under the influence of elastic support、rotational restraint、axial force and open cracks based on the euler-bernoulli beam. RC rectangular beamload tests were carried out to research the change of the dynamic stiffness、staticstiffnrss and damp ratio. There was finite element analysis of continuous beam tostudy the influence in the dynamic and static stiffness of the joints, axial force andpartial damage. The study above provided theoretical basis for using the staticevaluation index to established the dynamic evaluation index. The regressionanalysis of the measured data collected verified the above analysis conclusion andget the regression formula between dynamic and static stiffness. First order verticalbending frequency testing coefficient to evaluate bridge carrying capacityestablished Using the static deflection testing coefficient range in the specification.Dissipating energy evaluation index and corresponding evaluation grade were putforward to evaluate the speed of dissipating vibration energy using frequency anddamping ratio based on the normal spacing of the moving vehicles in highway.Thirdly, frequency distribution of dynamic response of simple-surpported giderbridge under moving vehicle(simplified as a constant force and harmonic force)were analyzed theoretically. Methods to realize separating the dynamic and staticcomposition in dynamic response by frequency domain low-pass filter were putforword. Frequency distribution of dynamic response of continuous gider bridgeunder moving vehicle were analyzed by FEM. separation methods of separation insimple-surpported gider bridge were extend to continuous gider bridge. There wereintroduction of separation methods application in impact factor calculation、amplitude extraction and bearing capacity quickly evaluation combined with theengineering practice.Then, there were reseach on vehicle-bridge coupling vibration analysismethods to provide means for the following calculation. The dynamic response withstatistical significance of conventional highway girder bridges through the methodof probability distribution. The reasonable limits of vertical acceleration, amplitudeand impact factor were discussed to assess the dynamic performance of girderbridge.Finally, the evaluation contents mainly aimed at the applicability of the bridgewhich includes the bearing capacity and dynamic performance. The comprehensivedynamic evaluation system based on dynamic loading test for the concrete girderbridge was put forward. The paper aslo introduced the flow chart of thecomprehensive evaluation system and examples of engineering application.Based on the above analysis results, the simple and practical methods for girder bridge dynamic characteristics test、estimation and evaluation wrer proposed. Theseparation method of the dynamic deflection was put foword. The reasonable limitsof the dynamic response were got. The work performance evaluation methods basedon dynamic testing for the highway girder bridge were established finally, which canbe used to evaluate the serviceability limit state bearing capacity and dynamicperformance quickly and reasonably.