Load Distribution in Multiple-Bolt Tension Joints

An analytical and experimental investigation is presented, and a simplified analytical method is derived that closely predicts experimental results. The analysis is applied to butt-type timber tension joints under loading in the elastic range. A program of tests was designed to study the distribution of load among the bolts and the effect of the joint properties on the distribution for comparison with theoretical results. Joints containing six or more bolts in a row are found to have a highly uneven distribution of bolt loads, and the two end bolts together usually carry over 50% of the load. The addition of more than six bolts in a row does not substantially increase the elastic strength of the joint. Small misalinement of bolt holes may cause large shifts in bolt loads. The most even distribution of bolt loads occurs in a butt joint in which the extensional stiffness of the main member is equal to that of both splice plates. Some slight redistribution of load from the more heavily loaded end bolts to the less heavily loaded interior bolts takes place when bolt bearing is the mode of failure.