Fatigue cracking in bridges from out-of-plane displacements

Abstract

The interaction of the various components of a bridge structure under normal vehicular loading has sometimes resulted in cracking in unexpected locations in relatively short periods of time. In girder type bridges this cracking has often occurred in the web at short gaps between attachments and the flanges. Although the problem has been more prevalent with welded members, cracking has also occurred in riveted members.This paper examines three cases of fatigue cracking from out-of-plane displacements: one case in which transportation and handling resulted in high cyclic stresses at the ends of transverse web stiffeners; a second case in which the end rotation of transverse floor beams framing into longitudinal girder webs resulted in cracking at the end of the connection plates welded to the girder web; and a third case in which riveted connection plates connecting cantilever brackets to floor beams were found to be susceptible to in-plane bending as a result of relative movement between the girder and the floor system.Field and laboratory studies were beneficial in assessing the mode of behavior and causes of fatigue cracking. The results of these studies were useful in developing ways to avoid such cracking in the future.