Research On Key Technique Of Fatigue Monitoring For Long-Span Steel Bridge With Fatigue Life Gage

Long-span bridges service under long-term transportation loads, strength degradation of structure materials because of fatigue cumulative damage is key factor of durability. In this decade, fatigue damage monitoring has been exploited and applied to some projects , but the effect of fatigue damage monitoring is not satisfactory, most of them are on the stage of theoretical research all the same, with which damage assessment of long-span bridge is not accuracy. Fatigue life gage is a sensor of cumulative cyclic loading response, which mechanical properties is applicable to fatigue damage monitoring in the extreme. This paper research on key issues of application of fatigue life gage on long-span steel bridge fatigue monitoring.A new prestressed bowshaped structure strain multiplier was designed to solve problem which strain amplitude is much lower than the threshold of fatigue life gage, and this strain multiplier take the advantages of entire structure, lower stiffness, good reliability and convenience to use. Static test and finite element analysis indicate that this strain multiplier have the advantage of good linear response. Fatigue test indicates that strain multiplier have not been damaged for fatigue in the service life of fatigue life gage, fatigue response of fatigue life gage can be derived from the strain amplitude equal to specimen strain multiplied by amplification coefficient of strain multiplier.Based on the speciality of load spectrum of bridge, a new method to infer load spectrum of bridge with two fatigue life gage installed on the same strain multiplier was proposed, substantive progress in the fatigue damage calculation applied to the bridge with fatigue life gage. The test for simulating load spectrum of bridge was done, comparison of the infered load spectrum by means of the electrical resistance changes of two fatigue life gage with the simulated load spectrum showed reasonably good agreement.A example to assess fatigue damage was presented according to the bridge design code of BS5400 so as to show the steps of application and analysis of long-span bridge fatigue damage assessment with fatigue life gage.