Behavior of bolt-connected steel plate girder attributable to bolt loosening failure in the lower flange

Abstract

To quantitatively evaluate changes in the structural behavior of a high-strength-bolt-connected steel plate girder attributable to loose bolts in the lower flange, this study conducted tests on bolt loosening in the lower flange using a 12 m steel plate girder connected by high-strength bolts. Its displacement and strain were compared with those of a steel plate girder affected by loosening of a lower flange bolt. In this study, various loosening processes of the lower flange bolt and different load conditions were considered to compare the effects of bolt loosening. The results demonstrated that the displacement of the loaded steel plate girder increased in accordance with the loosening of the high-strength bolts in its lower flange, and that its behavior was affected by both the bolt loosening position and the process of bolt loosening. From the comparison results for the stiffness change in the steel plate girders caused by the loosening of the lower flange bolt, its stiffness decreased by approximately 15%–17% and its measured neutral axis rose by approximately 15.8% depending on the bolt loosening position and bolt loosening process. Thus, it can be surmised that the structural behavior of a bolt-connected steel plate girder is highly affected by the bolt connection of the lower flange due to its considerable structural stiffness change. Although these were conducted under limited experimental conditions, the effect of the lower flange bolt connection on the relative structural stiffness of the plate girder can be considered to induce a stiffness decrease exceeding 15%.