The Effects of Bolt Pretension, In-Plane Eccentricity, and Friction on the Ductility of Block Shear Connections

Block shear is a complex failure mechanism in bolted and welded steel components such as gusset plates, webs of coped beams, angles and tees. It presumes a combination of tension rupture and shear yield. Multiple variables affect the block shear capacity and ductility of a connection. This study investigates the effects of bolt pretension, connection eccentricity and friction force transfer through a series of destructive experiments followed by refined finite element simulation. Clamping forces create a complex triaxial stress field compounded by the stress concentration at the bolt holes. In-plane load eccentricity with respect to the centerline of the connection causes a change in stress/strain distributions due to the addition of a moment. That alters the magnitude of stress/strain demand on both the tension plane and shear legs. Friction between the connected plates also acts as a means of load transfer between the connected parts; however, little is known about its contribution to the ultimate capacity of the connection. Five full scale connections were tested to compare two levels of bolt tension under two level of eccentricity. In addition, one test was performed including a layer of Teflon between the plates to isolate the effect of friction. Effects of pretensioning, eccentricity, and friction were then analyzed by comparing load-displacement responses and strain data. Bilinear curves provided a means to identify changes in the ductility and total energy absorbed by the connection before failure that gives a comprehensive view of the change in the behavior of the connection. A nonlinear finite element model for the five cases was developed using ABAQUS to verify the results of the experiment. This model will enable a comprehensive study of a variety of connection geometries, material characteristics, loading, etc