Lack of Fit in High Strength Bolted Connections

Abstract

The significance of lack of fit in structural steelwork for buildings is studied. Lack of fit is caused by rolling or fabrication tolerances, welding distortions, etc. When imperfect fit occurs between elements, supposedly transferring load, site disputes often arise over the necessity for remedial action. Imperfect contact is of particular significance in friction‐type bolted connections when there may be visible separation between the faying surfaces. The paper reviews the effect of imperfect contact on the development and maintenance of the bolt preload, the required contact area size and disposition, the coefficient of slip, joint slip resistance and ultimate strength of the connection. It is concluded that lack of fit is detrimental for some slip resistant and fatigue resistant joints but otherwise is not structurally significant, especially where the bolts act primarily as high tensile fasteners. To clarify this distinction, the use of friction‐type bolts in general is reviewed. Test results pertaining to lack of fit in flush end‐plate connections are presented.