System Reliability of Floor Diaphragms Framed from Cold-Formed Steel with Wood Sheathing

Abstract

A high-fidelity simulation-based system reliability calculation methodology was implemented for steel floor diaphragms framed from cold-formed steel joists topped with wood sheathing, leading to design recommendations that consider the sensitivity of the system performance to fastener component reliability and load paths provided by the sheathing and steel. Diaphragm structural response under in-plane equivalent lateral seismic forces was obtained from high-fidelity computational simulations verified with a full-scale diaphragm test. The model included sheathing-to-joist and joist-to-ledger connection load-slip nonlinearities and randomness from the bearing, tilting, and screw shear, obtained from independent and isolated fastener tests. An uncertainty-modeling scheme provided a statistical distribution for the diaphragm system capacity, which was used to calculate the diaphragm system reliability. The variation in diaphragm system reliability with the fastener component reliability, i.e., the reliability sensitivity, was quantified to guide the diaphragm design to a predefined system-reliability target.