Еffect of the washers on the load-bearing capacity of single-shear bolted connections

Bolted connections are the most common method for joining thin-walled galvanized sheets at the site. For this purpose, small-diameter bolts (M8, M10 or M12) and the corresponding nuts are used. According to the standard BDS EN 1993-1-8, only for single-shear joints with one row of bolts, washers should be provided both under the bolt heads and under the nuts. That is, for two or more rows of bolts, it is not necessary to place washers under the bolt head. In connection with a failure of thin-walled steel silos, a test of single-shear connections with two rows of bolts without washers under the nuts was carried out in the laboratory of the University of Architecture, Civil Engineering and Geodesy (UACEG). Their load-bearing capacity turned out to be lower than the theoretically determined one. The initial explanation is that the lack of flat washers under the bolt heads leads to large rotations, and hence to reducing load-bearing capacity. To test this seemingly logical explanation, the authors conducted a series of laboratory and numerical tests on connections with two rows of bolts. The results show that the presence of washers under the bolt head and under the nut affects the load-bearing capacity of this type of connection.