Welding under service conditions ‐ Influence of different boundary conditions during welding

Steel structures, such as bridges, must be continuously maintained. Due to increasing traffic loads, design and execution shortcomings, many steel bridges are subject to various types of damage, such as cracks. The bridges must be maintained by crack removal and re‐welding the cracks. During this work, the bridge is closed for traffic in order to suppress the crack flank movement during welding. As a result, traffic loads on other routes are higher, which increases further damage on detour routes and subsequently additional welding work and costs on these structures. Therefore, the aim is to provide a method that allows welding work on steel structures under running traffic, respectively under cyclic loads. First, measurements at a representative steel bridge were conducted to derive gap opening parameters of amplitude and frequency for welding tests under cyclic loads. Monitoring cracks shows that the crack behavior is complex and the description of the force redistribution during welding is a challenge. In order to quantify the influence of different boundary conditions during welding on weld quality and fatigue, experimental investigations were carried out under displacement control only and force control only. For both, the weld quality and the fatigue strength was comparable to the standard requirements, so that welding under service conditions is possible under certain aspects.