Fatigue Life of Riveted Railway Bridges

Doktorsavhandling, 1994

This dissertation, which focuses on the fatigue life of riveted steel railway bridges, is based on: - A series of full-scale fatigue tests of nine riveted stringers taken from a railway bridge built in 1896. A review of and comparison with the different full-scale fatigue tests on riveted railway bridge members, which have been conducted in other laboratories over the years, is also given. - A number of field tests on riveted railway bridges. Some 15 bridges have been investigated by the author since 1989. - A theoretical study of the load-carrying capacity of riveted connections. Special emphasis is given to the influence of the clamping force. The phenomenon of fatigue cracking in riveted railway bridges is also accounted for. The structural members and locations where fatigue cracking is likely to occur are especially in foucs. The main finding is that there seems to be a substantial remaining fatigue life of riveted railway bridges still in use today. The full-scale fatigue tests have shown that the common standard fatigue design curve for riveted members and details (virgin specimens) is underestimating the fatigue life. The fatigue damage accumulation of the old bridge stringers, at the start of the laboratory tests, was found to be negligible, i.e. the stresses due to the in-service loading history have in general been low. In situ strain measurements on several riveted railway bridges also show that the stresses seldom, if ever, exceed the fatigue limit for riveted details. Ultrasonic testing, which has shown an absence of fatigue cracks, confirms these conclusions. The fracture toughness is in general low for the steel in old bridges, but there are a number of circumstances that indicates that the ductility is adequate despite this fact. For example low in-service stresses, low strain rates, the absence of fatigue cracks or other major defects, small plate thicknesses and an inherent structural redundancy of built-up riveted bridge members all contribute to a safe behaviour with respect to brittle fracture. Especially the inherent structural redundancy of such members has, during the full-scale fatigue tests, led to the arrest of a propagating fatigue crack when passing from one member part to another.