At present, more than four thousand metal bridge spans are in operation all over the Russian railway network. Through the years of operation, about thirty types of fatigue cracking were identified. The dynamics of the types Т-9 and Т-10 cracks formation has increased significantly in recent years. The formation and growth of fatigue cracking is influenced by such factors as residual welding stress, stress-strain state of the bridge structure, defects, damages, and non-observing the operation and maintenance standards, bridge location and bridge span structure. At present, neither measures nor repair are performed to prevent fatigue cracking not exceeding 20 mm in length. Only when a creak reaches a certain length, the regulatory documents require to drill a hole at a crack mouth in order to prevent its further development. The hole diameter should be equal approximately to the doubled wall thickness. In order to prevent further crack growth and cover the hole, a high-tensile bearing type bolt is fixed into it, creating a volume stress. As a rule, such a repair is not enough to stop the cracking process. The article suggests a number of measures based on induction heating that allows to prevent cracking (including forging reducing gaps between connecting plates and horizontal sheets in a truss), to carry out repair (crack mouth soldering) and reinforcement (fixing metal plates onto a wall with a hole).

Welded metal bridge spans are one of the most wide-spread types of bridge spans, several thousand of them being in operation along motorways and in city areas in Russia. Similar to other welded structures they are prone to fatigue cracking which is usually repaired using metal plates fixed with high-strength bolts. The Siberian Research Institution of Bridges located in Siberian Transport University has developed the structure and technology of welded bridge span reinforcement using round metal plates fixed by induction brazing. To prove the efficiency of the technology a laboratory research and testing of girders reinforced with round metal plates fixed by induction brazing has been conducted. The research shows that after the induction brazing enforcement the bridge structures that have fatigue cracks obtain strength parameters 25 per cent higher compared to those of completely new unreinforced samples without fatigue cracks. The article is part of the dissertation research Usoltseva A.M.

In the production of welded spans of railway bridges since the 70s of the last century, low-alloy structural steels are used. In these constructions in recent years there has been an intensive growth in the formation of fatigue cracks. Currently, the only technology used by Russian Railways for braking fatigue cracks is to drill a hole in the mouth of a crack, followed by setting a high-strength bolt into it and tightening it to a standard force. At the Siberian Research Institute of Bridges (Siberian Research Institute of Bridges SGUPS), innovative technologies have been developed to inhibit the growth of fatigue cracks and strengthen welded spans using soldering and induction heating. Technology has proven effective. It is known that heating a metal to high temperatures can significantly change its structure and characteristics. In the scientific literature there are no data on changes in the strength characteristics of low alloy structural steels as a result of rapid heating. In a laboratory study, an analysis was made of the change in the strength characteristics of low alloy structural steel with rapid induction heating. Studies of structural steel samples showed that quick short-term induction heating of structural steel to the temperature of brazing does not lead to a significant change in its strength characteristics, and brazing and induction heating can be used to strengthen structures with fatigue cracks.