Analysis of Technological Cracks in Welded Joints of Railway Bridges

Abstract

Whilst verifying the quality of welded joints in railway bridges in Poland, it was found that many of them contained cracks of technological, fracture and fatigue origin. This problem is associated with early welded bridge structures, in which many technological imperfections were discovered. General data for x‐ray testing on approximately 200 bridges in service are given. The tests were carried out over the period 1967–1990. The number of joints tested was 15 875 and the number of cracks discovered in the joints was 437 in the 34 bridges tested. Repeated tests on the joints containing cracks in time intervals of 5–8 years neither demonstrated further growth in the cracks nor the formation of new cracks. All the cracks discovered were formed during welding operations where there was no service loading. An analysis of the stress levels necessary for the development of crack growth was carried out via fatigue laboratory tests on three butt splice models which were similar to the joints in the bridges tested. Concurrently, the probable stress level near to the cracks was determined analytically. The calculated and measured stresses under service loadings did not exceed empirically assessed weld endurance limits for these joints and confirmed no crack growth. Hot cracks and other welding imperfections in welded joints in structures are permissible if there is neither growth in service nor resistance or rigidity loss of the structure.