Impact of load combinations on structural reliability determined from testing cold-formed steel components

• Show the base for the reliability determination in Chapter F of AISI Specification and its originating from a specific load case.
• Determines the sensitivity of the reliability determination implemented in AISI Specification to controlling load combinations and load ratios.
• Present the required statistics for Dead, Live, Snow, Wind, and Earthquake loads used in reliability determination.
• Develop values for Cϕ and VQ (coefficients used for reliability determination) based on a parametric study.

The objective of this paper is to explore the impact of load combinations on the method used to assess the structural reliability of cold-formed steel components determined by testing. Chapter F of the AISI Specification (AISI-S100-07) provides a means to determined the resistance, ϕ or (safety, Ω) factor of cold-formed steel components by direct testing. The procedure uses the standard (United States) Load and Resistance Factor Design format, but simplifies the load side to a single load combination and single dead-to-live load ratio. The impact of this assumption on the resulting component reliability is the focus of this work. To complete the work the bias factors and variances for all loading conditions are established. In addition, a range of practical load ratios, for all loads, is assumed. Parametric studies are performed to explore load case and load ratio dependency for use in the determination of the resistance factor, ϕ; specifically, the pre-factor term Cϕ and the load variance term VQ. The parametric studies are simplified into a table that provides load case dependent Cϕ and VQ factors. Design examples demonstrating the impact of current methods and the load combination dependent solution are provided.