An Experimental Investigation into the Effect of Clearance and Torque on Load Sharing in a Bolted Joint

The shear load experienced by each bolt in a multi-fastener bolted butt joint is a percentage of the total load applied to the joint. Joint failure can be premature when one fastener is subjected to a disproportional amount of the total load. Conversely, the ultimate load the joint can endure may be increased if the distribution of loads can be equalized by some means. In this investigation, two and four fastener butt joints were studied. An instrumented bolt was constructed that could measure the bending stresses in the bolt associated with the bearing load. That data was converted into force by using a factor determined by calibration of the bolt. Two approaches were employed in an attempt to manipulate the amount of the total load each bolt would experience. The bolt-hole clearance was adjusted strategically in an effort to force additional load to a bolt that had previously carried a smaller portion of the total. This data was verified by use of a finite element model. The second approach was to apply clamping force to certain areas of the joint via bolt torque to shift a portion of the total load within the joint. The study showed clearly that the distribution of bolt shear loads could be predicted and manipulated to the advantage of the entire butt joint.