Retrofitting of pre-damaged welds using the spot-heating technique

Welded steel bridges are prone to fatigue cracking due to increased axle loads of heavy-duty traffic and extended operation times. There are multiple weld toe treatments like grinding, TIG dressing and mechanical impact treatment that can prolong the fatigue life of pre-damaged welds as long as no macroscopic cracks have initiated at the weld toe. However, these methods usually require expensive gear, require skilled operators, are time consuming or the quality control proves to be difficult. Spot-heating is a simple and cheap method for fatigue improvement that has already been investigated in the 50s and 60s, but the application has not been implemented widespread in practice in recent years. The University of Applied Sciences in Munich performed fatigue tests on pre-damaged and subsequently spot-heated specimens that showed a good efficacy of the technique making it a promising approach for retrofitting. In this paper the common post-weld treatment methods and their effectiveness on pre-damaged welded structures as well as the previous results of the experimental investigations using the spot-heating technique are presented.