Diaphragm performance of cold-formed steel floors with steel form-deck and gypsum-based self-leveling underlayment

Abstract

Cold-formed steel composite floor systems are being widely used in cold-formed steel framing for mid-rise building construction, primarily because of their structural and economic efficiency. This study investigated the diaphragm performance of cold-formed steel composite floors through cyclic load testing and numerical simulation. The composite floors consist of cold-formed steel C-shaped joists and a subfloor with cold-formed steel form-deck and gypsum-based self-leveling underlayment. The test results indicated that the primary failure mode of the specimens was shear failure of the self-drilling screws that connected the steel form-deck and end joists. A finite element model was developed and validated with the test results in terms of hysteretic curves, failure modes, and seismic performance indices such as the ultimate load-bearing capacity and stiffness degradation. Moreover, extensive parametric studies were conducted using the proposed models. The results of analyses showed that the spacing of the screws connecting the steel form-deck to the joists at the floor perimeter and as well as the floor aspect ratio have significant impacts on the diaphragm performance. By contrast, the thickness of the gypsum-based self-leveling underlayment, joist depth, and web perforations exert only a minor influence on the diaphragm performance. Finally, a simplified method was proposed to calculate the central displacement of composite floors based on theoretical analysis. This study provides a useful design basis for the design and application of cold-formed steel composite floors in engineering practice.