The authors have been carrying out a series of research for the prevention of hot cracks produced by welding on the steel structures in service condition from a mechanical point of view. The opening displacement of root gap, Δδ, which can be easily measured before welding, has been already proposed as the practical mechanical measure for deciding the initiation of the hot cracks.
In this study, based on Δδ, a way which judges the advisability of welding under the pulsating loads is concretely shown with taking the bridge in service condtion an instance. Therefore, first, the various displacement, vibration and acceleration are measured at the weld joints of the bridge in the service condition. So, the wave of vibtation of Δδ in service condition is clarified and its amplitude and the number of oscillations are known. On the other hand, as one of powerful approach to prevention of hot cracks based on Δδ, it is considered that the critical value, Δδcr which is mechanical property of the welding electrode for the hot cracks, is made as big as possible. From this point of view, the new welding electrode was tried to be developed. As the results of weld cracking test, Δδcr, of the newly developed welding electrode could be made three or four times as big as that of commonly used welding electrodes. From this fact, the welding under the pulsating loads should be easy. In these considerations, a way based on Δδ which judges the advisability of welding under the pulsating loads is shown. Then, applying the judging method to the repair work on the bridges in service condition, its validity is concretely shown.