Multi-axial fatigue strength of structural bolts in slip-critical connections under combined cyclic axial and shear demands
Date
2018
Authors
Rodriguez Lopez, Santiago, author
Mahmoud, Hussam, advisor
Atadero, Rebecca, committee member
Riveros, Guillermo, committee member
Senior, Bolivar, committee member
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Abstract
High-Strength bolts are used extensively in structures and are regarded as the better option for connections subjected to fatigue as compared to welds and rivets. Studies have shown the superior resistance 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 done on high-strength 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. Especially the study pertains to structural bolts that are subjected to cyclic loads in multiple directions with shear reversals, which are typical of mitre gate to pintle socket connections. Certain mechanisms mark the onset of bolt loosening and fatigue when bolts are subjected to cyclic shear or shear combined with tension. The actual mechanisms and limits at which this occurs are explored in the literature and experimentally and recommendations are provided.
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Subject
high strength bolts
multiaxial fatigue
slip-critical
mitre gate
connection reliability
pintle bolts