Cold-formed steel (CFS) floor systems generally consist of a frame with a series of equally-spaced CFS joists sheathed with structural panels. While wood and oriented strand board sheathing are common options for cold-formed steel floor systems, steel deck, either filled with concrete or unfilled is increasingly specified. The advent of new fire-resistant cementitious sheathing materials motivates a dual structural skin system: fiber cement boards fastened to steel deck. However, the capacity and behavior of these dual skin systems is unknown. This paper explores this structural system via a computational approach. The authors developed a three-dimensional high-fidelity shell finite element model to explore the shear strength and stiffness of steel deck floor diaphragms and to better understand the shear behavior and flow of forces in steel deck diaphragms, and steel deck diaphragms sheathed with fiber cement board. The computational model consists of a series of equally-spaced floor joist framed to a ledger beam via clip angle connections and sheathed with steel deck. Diaphragms are designed such that shear capacity is governed by either fastener strength or panel buckling, which can be dependent on fastener scheme. Results indicate that the modeling approach accurately captures diaphragm strength and primary failure mode. Furthermore, bespoke fastener schemas tailored to specific desired structural function are able to tune failure modes for ductility and strength. Fiber cement board panels can restrict buckling of the panel and increase strength and stiffness of the floor system.
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