A parametric study aimed at assessing fatigue performance of bolted connections

Abstract

The fatigue design provisions in the AASHTO-LRFD Bridge Design Specifications (2012) state that steel components with open holes should be classified as Fatigue Category D details, while bolted connections with pretensioned bolts are Category B details. The two-category difference in fatigue performance between holes with and without bolts is based on experimental evidence which showed that compressive stresses imposed by pretensioned bolts in the region around the bolt holes reduce the effective net tensile stresses. Fatigue category classification is based solely on the presence or absence of pretensioned bolts, without consideration to the influence of connection geometry, including bolt spacing and plate thickness. A numerical study was undertaken to determine the fatigue performance of connections with pretensioned bolts and various geometric configurations. Approximately 150 high-resolution finite element models were analyzed using the finite element software Abaqus 6.13-3. Models consisted of single steel plates with unfilled bolt holes and connections with pretensioned bolts. The parameters of the study were bolt diameter, bolt spacing, plate thickness, bolt pattern, edge distance, and ratio of nominal stress to pretensioned bolt load. The effect of these parameters on fatigue initiation life was evaluated by comparing calculated stress fields of bolted and unbolted plates. The change in stress (Δσlocal) between the two configurations was used as a means to estimate the level of improvement in terms of AASHTO fatigue categories. A linear regression analysis was performed to investigate the sensitivity of the change in stress to the parameters of the study. It was found that the plate thickness was the dominant parameter, and that the change in stress decreased with increasing plate thickness. Results from this investigation suggest that there is a size effect associated with the thickness of plate that should be considered in the AASHTO fatigue category classification for bolted connections.