Multiaxial fatigue strength of structural bolts under combined cyclic axial and shear demands

Abstract

High-strength bolts are used extensively in structures and are regarded as the better option for connections subjected to fatigue when compared to welds and rivets. Studies have shown the superior resistance of highstrength bolts to fatigue and conclude that it should not be an issue when a bolt is properly pre-tensioned. Nevertheless, a recent application of properly pre-tensioned bolts subjected to shear stress reversals shows extensive fatigue cracking and total severing of up to 50% of the bolts in the connections. Sufficient evidence based on experimental testing and field observations exist to suggest the possibility of fully pre-tensioned bolts coming loose due to shear stress reversals. The problem of transverse vibrational loosening of bolts has been extensively researched, as well as the issue of bolt fatigue. Only recently have they been considered together although no studies of this interaction have been conducted on highstrength bolts. Certain mechanisms mark the onset of bolt loosening and fatigue when bolts are subjected to cyclic shear or shear combined with tension. In this study, causes of bolt loosening and fatigue failure of bolted connections are explored. Specifically, the study pertains to structural bolts that are subjected to cyclic loads in multiple directions with shear reversals, which are typical of miter gate-to-pintle socket connections.

Assembling bolted joints under water: influence of a surrounding medium on bolt preload and slip factor

“…Self-loosening of bolts was investigated intensively over the course of the last decades and describes the phenomenon of loss of bolt preload because of vibrating or cyclically loaded fasteners. Especially dynamic transverse loads (shear loads) are supporting the effect [40][41][42][43]. When referred to, self-loosening of bolts on offshore structures is ascribed to insufficient bolt preload caused by low accuracy of the tightening method or inadequate lubrication [11], [44].…”