System Reliability Benefits of Repetitive Framing in Cold-Formed Steel Floor Systems

Abstract

Typical cold-formed steel floor systems involve many repetitive joist members laid in parallel, yet the design specifications are based upon the reliability of individual members and fail to account for the potential benefits imparted by repetitive framing. A repetitive member factor, similar to that used in the United States National Design Specifications (NDS) for wood, could be used in cold-formed steel (CFS) design to recognize these benefits and allow for more economical and efficient design that does not compromise safety. This paper introduces and validates procedures based on Monte Carlo simulation for assessing the performance of repetitive floor systems under current code assumptions, and elastic and inelastic load redistribution mechanisms, and uses these procedures to examine two floor systems of varying complexity. Load redistribution is found to provide a benefit of at least 3% to the capacity of the floor system based on a target reliability index of 2.5 and therefore justifies applying a 1.25 factor to the design of joist capacity for the systems studied.