Seismic Performance of Outrigger Beam-Wall Connections


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Title: Seismic Performance of Outrigger Beam-Wall Connections

Author(s): B. M. Shahrooz, G. Tunc, and J. T. Deason

Publication: Special Publication

Volume: 211


Appears on pages(s): 223-246

Keywords: beam-wall connections; composite construction; cyclic loading; hybrid structures; outrigger beams; seismic resistance design; shear studs; walls

Date: 2/1/2003

A common connection between steel outrigger beams and reinforced concrete walls involves a shear tab welded onto a plate that is conncected to the wall through headed studs. Previous studies focused on behavior of headed studs have ignored a number of major issues, e.g., (a) cyclic behavior of studs under multiple loads was not studied, (b) the concrete around studs was not reinforced or the reinforcement did not represent what would commonly be present in wall boundary elements, and ( c) effects of cracking and yielding of reinforcement around headed studs were not included. To remedy these deficiencies and to develop seismic design guidelines for outrigger beam-wall connections, a coordinated experimental and analytical research program was conducted. Through a number of tests, involving a wall subassembly and an outrigger beam, the behavior of studs subjected to cyclic tension and constant gravity shear was examined, and a design methodology was developed to control the mode of failure. To further investigate the cyclic performance of outrigger beam-wall connections and to validate the design guidelines, two 1/4-scale walls with two outrigger beams were tested. The wall reinforcement details around the connection were selected according to the anticipated level of cracking and plastic hinge formation. The two outrigger connections were subjected to constant gravity loads and cyclic tensile forces, which were controlled as a function of the wall shear. This paper provides an overview of the experimental program, testing procedures, relevant test results, and design implications. The design methodology followed in this research resulted in connections that could develop and exceed the design forces despite extensive cracking and yielding of wall reinforcement around the headed studs. Presence of heavily confined wall boundary elements around headed studs increases the capacity. A simple method to account for strengthening effects of boundary elements was develped. This model could accurately assess the expected mode of failure and capacity of outrigger beam-wall connections. Test results indicate that the outrigger beam transfers the majority of diaphragm forces directly to the core wall, and participation of floor slab toward transferring the loads to the core wall is negligible. Therefore, floor diaphragm-wall connections can be based on simplle details, and designed to resist only gravity loads.