Fundamental Frequency of Lightweight Cold-Formed Steel Floor Systems

Abstract

As an alternative to traditional wood framing in residential building construction, cold-formed steel (CFS) framing inherits many advantages of steel construction. However, if not appropriately designed, CFS floors with longer spans and lighter weight are likely to be susceptible to annoying vibrations induced by human activity such as walking. The fundamental frequency is a critical parameter for floor vibration serviceability. In current practice, the floor frequency is evaluated based on the simplification of a floor system to a simply-supported beam, which results in a considerable disparity in frequencies obtained from field tests and evaluation. In this research, based on current construction practice, the CFS floor system is modelled as an orthotropic plate with edges of joist-ends being partially restrained and edges that are parallel to floor joists being either freely or simply supported. The deflection of the partially restrained CFS floor joist is adopted as the admissible function of the plate in the derivation of equations to evaluate the fundamental frequency of the equivalent orthotropic plate. Simplified equations and equivalent rigidity properties are proposed for CFS floor systems.