Prying action in an elastic T-stub tensile connection

Abstract

We investigate a bolted T-stub joint in tensile loading as an elastic receding contact problem. In this configuration two flat flanges are fastened together by bolt tension and are subjected to central tension loading, possibly cyclic. Due to the bending flexibility of the flanges, large “prying” contact forces arise which can cause the bolt forces to exceed the applied load. Hence such joints may be prone to failure especially under repeated loading. This elastic analysis is suitable to determine the onset of plastic yield and to investigate fatigue failure.In many design procedures the analysis of a T-stub joint is based on the assumption of lift-off of the entire flange except its outer edges. We treat the T-stub joint as a compliant receding contact problem where the flexural deformation of the components induces variable-location prying forces. We show that the traditional approach can significantly underestimate the prying forces in cases where the prying forces act nearer to the bolt. Our analysis also demonstrates that, in cases in which the predicted lift-off distance is greater than the distance to the flange edge, the use of a longer flange would be protective of the bolt. We present results for the elastic T-stub bolt force based on two beam theories, as well as a sampling of results using three-dimensional finite element elasticity analysis. We also propose a formula for flange thickness that suppresses prying, and interpret our results via the Goodman fatigue criterion to define the required steel-bolt ultimate strength under cyclic loading.