Rotational Ductility of Extended Shear Tab Connections

By AISC Specifications, simple shear connections of beams shall be designed to resist the required shear strength and allow the connected member to accommodate flexible end beam rotation of simple beams. Single plate shear tab connections should be configured so the failure occurs by plate yielding along with bolt group rotation and bolt holes elongation, to avoid weld sudden rupture and bolts failure. The AISC specifications requires an end beam rotation of 0.03 radians with some limiting inelastic deformation in the connection is allowed to accommodate this requirement. Conventional geometry and plate thickness limitations are assigned for shear tab connections to satisfy the ductility requirements. However, in cases where connections cannot satisfy conventional dimensional limitations, extended tab configurations are more general and allow greater geometric variations. Extended shear tab connections in many instances offer practical solutions to the construction process, e.g. by augmenting a clear distance of the support, coping of the supported member is not required any more. Such case includes welding the tab to columns webs. The use of extended tab connections in this case comes to a position of concern when the connection flexibility is not satisfied. Higher rigidity of the connection could result in an unanticipated moment development that the column has not been designed to resist or causes sudden rupture of the bolts or weld. Under other condition for unstiffened tabs welded to column webs (flexible support) substantial distortions of column web could result in yield line mechanism failure. This excess deformation in the column web allows an unlimiting connection rotation around the weld centerline, thus limiting the end beam rotation. To address these concerns a parametric study is performed. Plate thickness, distance between bolt line and weld line, skewed angle, number of bolts and number of bolt columns are the variable parameters considered. The parameters were evaluated in terms of shear strength, corresponding beam end rotation, support web rotation, unanticipated moment and connection failure mechanism. This study helps analyze the effects of parameter variation on the rotational ductility of the connection, define parameter ranges, specify design constraints and nominate parameters for further evaluation. Stiffening the column web to limit its rotation is also studied as a practical solution to the problem.