Numerical evaluation of the behaviour factor of lightweight steel lateral force resisting systems according to FEMA P695

Seismic design regulations rely on certain factors to reduce the earthquake actions due to inherent ductility and overstrength of the lateral force resisting systems. The behaviour factors given in Eurocodes are one such example, which when applied during the design process will ensure the life safety performance level of a building. Light-Weight Steel (LWS) structures fabricated with Cold Formed Steel (CFS) profiles are increasingly widespread in earthquake prone regions, however the current in practice edition of Eurocodes fails to acknowledge their seismic performance by not providing behaviour factors for them. The study presented herein addresses this issue by evaluating behaviour factor for the two commonly used LWS systems: CFS strap braced walls and CFS shear walls with gypsum board sheathing through FEMA P695 methodology. For each type of system, a set of archetypes, which represent a range of design parameters and building configurations are designed following the capacity design approach and their response is idealized by nonlinear numerical models. The performance of archetype models is evaluated systematically through the static pushover and the incremental dynamic analysis under a suite of forty-four normalized and scaled earthquake records, representing the probable seismic hazard to the buildings. Finally, by calculating the collapse probability while also considering the uncertainties from various sources, the suitability of a trial value of the behaviour factor used in the design phase of archetypes is evaluated. Based on the results, it is concluded that a behaviour factor of 2.5 and 2.0 for CFS strap braced walls and CFS shear walls with gypsum board sheathing is appropriate.