On the bearing strength of bolts in clearance holes

In the design of a bolted connection between carbon steel elements, the bearing strength of bolts in clearance holes is determined using codes of practice. The complexity of the formula for calculating the strength varies; the formulae in BS 5950 and the American AISC code are relatively simple but the one in EC3 is more complicated. A number of aspects concerned with the design procedure in EC3 could be improved; these are identified and discussed with reference both to the requirements of BS 5950 and theory. Initially, using simple theoretical arguments, small alterations are suggested for the minimum values specified in EC3 for some of the parameters involved in the calculation; these make the design procedure and the formula for calculating the bearing strength both logical and simple. A refined theoretical approach is then applied and it is found that, surprisingly, failure may occur due to shearing of the plates alone and bearing may not be involved in it at all. Strictly, these comments only apply to carbon steel elements. However, they could apply to elements in other ductile materials (e.g. stainless steels). The findings are applied to experimental results for both carbon steel and stainless steel specimens and it is shown that they provide good estimates of both the failure loads and failure modes of test specimens. Two possible design approaches are suggested.

► The bearing strength of bolted connections is analysed using simple theory.
► The theory predicts both the failure mode and the strength accurately.
► Two simple design procedures are proposed.
► Procedures apply to structural steels but could apply to other ductile materials.