Plastic Design of Eccentrically Loaded Fasteners

Bolts, rivets, and other fasteners in structural connections are often used in single or multiple shear. If the force incident upon a group of such fasteners is eccentric, the fastener group is subjected to a moment in addition to the force. The capacity of the group to transmit force is in general reduced if a moment must be transmitted at the same time. For each group of fasteners and for each direction of force a relationship exists between the values of the force F and of the moment M that may be applied simultaneously. This relationship may be termed interaction, and is usually expressed in formulas, curves or tables. In many published tables the eccentricity E, rather than the moment M, is used, but by means of the relationship M = FE these tables can be easily converted to the type which gives M versus F. A knowledge of the interaction is indispensable for the design or checking of a group of fasteners under an eccentric load. A fastener group is sometimes loaded by a pure force F0, without any moment. The capacity of a group for pure force F0 is simply the sum of the capacities of the individual fasteners. A group may also be subjected to a pure moment M0, unaccompanied by force; an example is furnished by the bolts in a flanged connection transmitting power in a rotating shaft. The capacity of a group for pure moment M0 is the sum of the contributions of the individual fasteners; this individual contribution is the force exerted by the fastener times the distance to the center of rotation.