Abstract
The results of sixty-five double-sided pushout tests utilizing the Elco grade
8, 5/16 in. diameter, standoff screw functioning as a mechanical shear connector
are presented. In all tests, the base material, through which the screw was
fastened, was fabricated out of back to back angle to simulate the top chord of
an open web steel joist. Varied test parameters include: steel deck profile, base
angle thickness, screw embedment depth, slab thickness, and slab width. The
objectives of the testing were (1) to provide an understanding of the strength of
the standoff screw in various test geometries and (2) to provide an
understanding of the slip characteristics, or ductility, of the connector.
A review of literature presents several applicable existing welded stud
strength models based on post-test observations of failure mechanisms.
Modeled failure mechanisms include: concrete splitting, concrete pullout, rib
shear, and stud shear. After applying the existing models to the pushout test
data, the following conclusions are drawn: (1) the concrete splitting model
developed by Oehlers (1989) can be used to predict the strength of the standoff
screw in flat slab geometries and (2) no existing model adequately predicts the
strength of the standoff screw in geometries utilizing profiled steel deck. An
equation, based on a rederivation of a wedged shaped shear-cone pullout model
(Lloyd & Wright 1990), is presented which predicts the strength of the standoff
screw in geometries with steel deck with acceptable accuracy.
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