Drilled standoff screws for shear connection in light composite steel–concrete trusses

Composite steel–concrete flexural members have become increasingly popular in the design and construction of floor systems, structural frames and bridges. A particularly popular system features composite trusses (open web joists) that can span large lengths and provide open web space for installation of typical utility conduits. One problem that arises with respect to composite joists has been the installation of welded shear studs. As the joist span gets smaller, the top chord also gets smaller. The thinner the top chord member becomes, the more difficult it is to weld studs without burning through the base member. Likewise, as the joists get smaller, the greater the sweep (lateral out-of-straightness) tends to become. For these reasons, a form of shear connector other than welded shear studs is of interest. This paper presents research results for a new type of shear connector, the standoff screw. This type of connector is drilled, rather then welded, and represents a viable alternative to headed shear studs in light composite trusses or open web joists. Results of experimental and analytical research are presented, as well as the development of a recommended design methodology.