Fatigue testing and analysis of I-girders with trapezoidal corrugated webs

Composite box girders with corrugated steel webs excel conventional concrete box girders in multiple ways in bridge industry, such as deadweight reduction, construction speed and quality. However, girders with trapezoidal corrugated webs are susceptible to fatigue under inevitable repeated heavy traffic loads. This paper conducted a large-scale fatigue test of an inclined I-girder with corrugated web under four-point bending, given the scant fatigue test data for this kind of girder and the inadequate validation of relevant fatigue detail category (FAT). Test results show that the critical crack initiated in combined bending-shear region, though multi-cracks initiated at weld toe of the web-to-flange welded detail in constant moment region. The test girder failed almost simultaneously as the critical crack propagated through the flange plate thickness and extended to one side of the flange plate edge. The other two less critical cracks in the constant moment region approximate to be fatal in the final stage of crack propagation. The fatigue failure criterion of the test girder, therefore, is conservatively recommended as the worst case of two conditions, namely the critical crack reaches 1.6 times of flange plate thickness in length or propagates through flange plate thickness. The parametric finite element analysis (FEA) was also conducted to investigate the influence of the corrugation parameters on the stress conditions at fatigue sensitive spot. The FEA results indicate that the shear force prompted the transfer of the location of critical crack from the constant moment region to the combined bending-shear region, and shortened the fatigue life of test girder by 11.3%. In general, the evaluation results indicate that FAT of the web-to-flange welded detail under four-point bending can be recommended as FAT 90 for nominal stress approach, FAT 120 for structural hot spot stress approach and FAT 225 for effective notch stress approach.