Performance of Steel Shear Connections under Combined Moment, Shear, and Tension

Beam-to-column connections play a critical role in a structural system's ability to resist widespread collapse by redistributing loads should localized damage occur due to an unanticipated extreme loading event such as a vehicular collision or an accidental explosion. Following the damage of a column in a steel frame designed to carry gravity loads, the strength and ductility demands on adjacent shear connections change substantially from those considered in conventional design. In addition to shear forces, large deflections can lead to the development of significant axial tension through what is known as catenary action. The behavior of steel shear connections under the combined effects of moment, shear, and tension has not been studied extensively and is not generally well-understood. However, this information is essential to assessing and improving the collapse resistance of structures. This paper presents the results of full-scale physical tests designed to investigate the behavior of common steel shear connections under load histories emulating the anticipated effects of the loss of an adjacent column, including large rotations and the development of axial tension. A variety of relative proportions of moment, shear, and tension were used for each type of connection, which included shear tab, single angle and double angle specimens, in order to permit a broad assessment of connection robustness applicable to different building geometries. This study examines the relative performance of these connection types, as well as the effects of connection geometry and combined loading. Observed connection capacities, ductility limits, and failure modes are presented and discussed.