Sensitivity Study of Axially Load Bearing Cold-Formed Steel Framing

The behavior of axially load-bearing cold-formed steel (CFS) framing systems is influenced by uncertainties in material properties, geometric characteristics, initial imperfections, and fastener stiffness in the bridging components. The purpose of this study is to present a sensitivity study of axially loaded CFS wall studs, using data collected from current manufacturing processes. Key parameters, including steel yield strength, member thickness, initial geometric imperfection amplitudes, and screw stiffness were randomly varied in the sensitivity study. The variation of the yield strength and thickness of the CFS studs was based on data collected from manufacturers. Screw stiffness and initial geometric imperfection amplitudes of the studs were collected from published research. A nonlinear finite element (FE) modeling framework was developed using FE modeling software package ABAQUS. The framing assembly includes CFS studs, tracks, bridging elements, and screwed connections between CFS elements. The numerical model considers material nonlinearity, geometric imperfections, and connector element properties to represent screw connection behavior between CFS elements. Also, contact behavior was defined between various elements to allow sliding, separation, and load transfer. All the CFS elements of the system were modeled with S4R shell elements. The effect of each parameter on framing system stiffness, peak axial load capacity, and post-peak response is analyzed in this study. The comparison of the effects of randomness in different parameters on the performance of the system and the most dominant variables affecting the behavior are presented.