Fracture behaviour and design of steel tensile connections with staggered bolt arrangements

This paper presents an experimental, numerical, and reliability study on the fracture behaviour of bolted steel tensile connections with various bolt arrangements. A total of 36 full-scale specimens were tested under tension until fracture. The main test parameters included the geometric pattern of the connections and the connection details such as pitch, gauge, edge distance and material. The test results show that the predictions of the ultimate capacity based on the s2/4g rule can be conservative, which may be mainly due to the ‘reinforcement’ effect of the biaxial stress state that exists between the bolt holes. However, for the specimens fabricated using higher strength steel with lower ductility, the conservatism is reduced substantially. Moreover, the test efficiency, which is defined as the ratio of the test ultimate capacity over the theoretical capacity of the gross section, was also examined. A higher test efficiency can be found when the hole spacing/edge distance is decreased/increased, although substantial increase in the edge distance can be ineffective. In addition, less ductile steel can lead to lower test efficiency. Furthermore, a numerical study was undertaken, where good agreements were observed between the numerical and the test results. With available test data, reliability analysis was finally performed to re-examine the rationale behind the resistance factors used in the current design codes.