Outrigger Beam-Wall Connections. I: Component Testing and Development of Design Model

A key factor behind successful performance of outrigger beam-core wall connections in hybrid structures is the adequacy of headed studs that are typically used to connect a stud plate, onto which the outrigger beam is connected through a shear tab, to the wall. In an effort to better understand cyclic behavior of stud groups under combined action of gravity shear and cyclic diaphragm forces, the research reported was undertaken. Six 1/3-scale subassemblies that involve a portion of the wall, connection, and outrigger beam were fabricated and tested. The test results suggest that a design method which closely follows available equations for computing stud capacity results in connections that reach the design loads; however, the mode of failure is stud pullout. This mode of failure does not have any ductility and lacks energy dissipation capabilities. Moreover, the available design equations fail to capture the substantial increase in strength due to wall boundary element reinforcement around the studs. The boundary element also alters the mode of failure from stud pullout to stud fracture. A new design technique based on dissipating the input energy through yielding and eventual fracture of the shear tab was developed. The performance of a test specimen designed based on this methodology was found to be satisfactory in terms of strength, ductility, and energy dissipation characteristics. Two simple adjustments to available equations were also identified to account for the effects of confinement, by wall boundary element reinforcement, around headed studs.