Concrete-Steel Interfacial Bond Strength in Composite Flooring: Shoring and Form Removal

Composite floor systems, constructed with cold-rolled corrugated steel decking covered with concrete, are a common design scenario in current construction practice. The limit state that most frequently controls the design strength of such composite floor systems in the finished structure centers on a breakdown in the interfacial bond strength between steel and concrete due to horizontal shear stresses developed during flexure. It is assumed in current practice that this same interfacial bond strength limit state governs during construction of the floor system as well. Existing design guides base recommendations regarding the timing of shoring removal, during the construction phase, on concrete compression strength alone. Such an approach is philosophically consistent with development length equations from reinforced concrete design, wherein it is assumed that the interfacial bond strength between rebar and the surrounding concrete is related to fc′ of the concrete. A series of experimental tests are carried out to study the influence that curing time and concrete strength, fc′, have on the interfacial bond strength of composite floors. Results from full-scale flexural tests of floor slabs under uniformly distributed loading, as well as from deck pullout testing, are reported herein.