Abstracts Engineering

Inelastic performance of welded cold-formed steel strap braced walls

by Gilles Comeau

As cold-formed steel construction grows in North America the void in our building codes must be filled. The NBCC and the CSA S136 Standard currently have no seismic provisions for cold-formed steel construction. Recently, the AISI has made available an updated version of AISI S-213 which includes adaptations for use with Canadian codes. This standard gives guidance on the design and construction of cold-formed steel systems to be used for lateral load resistance and prescribes the use of a capacity approach for seismic design. Seismic force modification factors to be used in conjunction with the NBCC are recommended for two CBF categories; one for limited ductility (Rd = 2.0, Ro = 1.3), examined herein, and one for conventional construction (Rd = 1.25, Ro = 1.3). A building height limit of 20m for the limited ductility system is also recommended. The main objective of this research was the verification of the capacity based design approach, the Rd and Ro values and the building height limit as found in AISI S-213 for limited ductility CBFs. In order to achieve this, the lateral load carrying behaviour of weld-connected cold-formed steel strap braced walls was examined by means of laboratory testing (30 wall specimens). The wall aspect ratio was varied from 1:1 to 1:4 to look at its effect on stiffness and overall performance. Each of the wall specimens was tested using both a monotonic and the CUREE reversed cyclic protocols. Further to these laboratory experiments, non-linear dynamic time history analysis of a multi-storey structure, designed using the Canadian specific AISI S-213 provisions and the NBCC, was carried out. ATC-63, a newly available method for determining the validity of R values, was used to check the AISI S-213 design parameters. Input earthquake records (both synthetic and recorded) were scaled to the UHS for Vancouver, site class C. Walls with aspect ratios of 1:1 and 1:2 showed the ability to sustain lateral loading well into the inelastic La croissance des constructions en structure d'acier laminé à froid dans l'Amérique du Nord nécessite le colmatage des carences pertinentes dans les codes nationaux du bâtiment. En effet, le Code National du Bâtiment du Canada (CNB) et la norme CSA S136 de l'Association Canadienne de Normalisation ne contiennent aucune directive portant sur la conception de structures en acier laminé à froid sous les charges sismiques. Récemment, l'American Iron and Steel Institute (AISI) a publié une mise-à-jour de la norme Américaine AISI S-213 accommodant des ajustements aux codes Canadien. Cette norme comprend des recommandations visant la conception et la construction de structures en acier laminé à froid pour résister des charges latérales, et exige l'adoption d'une approche de conception sismique basée sur la capacité de la structure. Des facteurs de modification de force, utilisés en concordance avec le CNB, sont prescrits pour deux catégories de cadres à contreventement concentriques (CC): la première catégorie, traitée ci-dessous, est liée à un système…