Fatigue performance of a steel truss web-concrete external joint in railway composite continuous girder bridges

This study conducted fatigue tests on two 1:3 steel truss web-concrete external joints to investigate their fatigue performance. The fatigue failure mode of the external joints and the stress distribution of each component were investigated. In addition, a finite element analysis (FEA) model was established, and parametric analysis was carried out to discuss the influence of gusset plate thickness, stiffening plate layout, and gusset plate structural form on fatigue performance. The results show that the fatigue life of the external joints under the design load amplitude is 3.75 million times (187.5 years). Fatigue cracks appear in the junction area between the gusset plate and the end of the stiffening plate, which is a weak fatigue detail of the external joint. The fatigue cracks cause local stress redistribution of the gusset plate. The stress at the junction (GN3) between the gusset plate and the stiffening plate N3 can be reduced by up to 37%, 61%, and 21% by altering the above three factors. Furthermore, the fatigue life of the optimized joint is increased by 1.4 times, indicating that the fatigue performance can be significantly enhanced by improving the stiffening plate layout and the gusset plate structural form.