Unidirectionally, Laterally Loaded Dowel-Type Fasteners Multiple-Bolt Joints

For many years U.S. design codes modeled the design values of a multiple-bolt joint as the design value of a single-bolt connection multiplied by the number of bolts. The provisions were based on research conducted by Trayer (1932) who observed an equal distribution of load among bolts. This was despite the fact that research conducted as early as in the late 19 century suggested an uneven load distribution among fasteners of metal joints. Today however, it is widely agreed that the strength of a multiple-bolt timber connection loaded statically in one direction is less than n times the capacity of a single-bolt joint, where n stands for the number of bolts. That is, the individual bolts in a multiple-bolt joint do not share the applied load equally, resulting in higher stressed fasteners at certain locations. Individual fasteners fail before other fasteners in the same row are able to carry their maximum load. Hence, for stiff fasteners such as bolts, the total strength of a multiple-bolt joint loaded one-directionally must be smaller than the sum of the capacities of the individual fasteners. To assure safe design, the concept of effective number of fasteners was introduced (Fahlbusch 1949; Lantos 1969; Jorissen 1998).