Block shear and tear-out in bolted connections as limited by curling

In the literature, the block shear and tear-out phenomena and strengths of cold-formed steel bolted connections have been well understood and thoroughly investigated. However, the strength of these failure modes in the bolted connections between thin and thick plates may be governed by the effect of out of plane curling of the thin plate, and this phenomenon has not been studied in detail yet. It is apparent that the curling not only affects the shear strength but also changes the behaviour of the bolted connections. In particular, the design shear strength of the bolted connections remains unchanged with high ductility even though the end distance between the bolt holes and the free edge is becoming larger. An experimental program on the block shear and tear-out behaviour of bolted connections was performed at the University of Sydney in order to provide a better understanding on the effect of the curling. A total of 48 tests including thicknesses of thin plates (1.0 mm, 1.2 mm and 1.9 mm) and 10 mm thick plates was conducted at the University of Sydney with three configurations of bolted connections in conjunction with two different hole diameters (9 mm and 14 mm) and various end distances as the main variables. Three different failure modes being block shear, tear-out and curling were observed in the tests. In addition, different material properties of the cold-formed sheet steels (i.e., G300, G450, G500 and G550) were also considered in this program to create a large database for the investigation. Consequently, a design equation for block shear and tear-out strength accounting for the curling effect is proposed in this paper. It provides a better correlation with the experimental results than those predicted in the current Australian and New Zealand Standard (AS/NZS 4600) and the North American Specification for cold-formed steel structures (AISI S100). In addition, a calibrated Finite Element Model (FEM) was subsequently developed using the commercial finite element program ABAQUS to verify against the test results. The reliable data set of the FEM models is further utilised to extend the data range in a parametric study and is finally used for the verification procedure of the proposed formula over a wider range of data.