ABSTRACT
Single-storey steel buildings comprise a significant portion of the building stock in North America. They typically include a cold-formed steel roof deck diaphragm which transfers the lateral forces due to wind or strong ground motion to the vertical bracing bents (Fig. 1a). These roof deck diaphragms are generally composed of corrugated steel deck panels which are integrally connected at their side laps and to the underlying structure. Current design principles require that inelastic demand should be limited to the vertical bracing bents of the building, while the roof diaphragm and the other remaining elements in the seismic force resisting system (SFRS) are designed to carry loads corresponding to the probable capacity of the bracing bents (Fig. 1b). These design requirements have forced engineers to choose thicker deck panels and more closely spaced fastener patterns for the roof diaphragm compared with past practice, causing the structural system of a building to become more costly. An increase in cost is more pronounced when one has to design this type of building with tension/ compression braces (Tremblay & Rogers 2005). The braces, which are selected based on their compression resistance, inherently possess significant reserve strength in tension; the surrounding elements including roof diaphragm must be designed accounting for the large force in the braces as defined by the probable tension yield capacity AgRyFy, where Ag is the
member cross-sectional area and RyFy is the expected yield strength. An alternative design approach is to consider the steel deck roof diaphragm to act as the ductile fuse element in the SFRS instead of the braces (Fig. 1c). A reduction in the structure cost is possible because the probable force used in capacity design may come close to matching the actual shear resistance of the diaphragm, thus the SFRS would be subjected to much lower loads than assumed in current practice (Tremblay & Rogers, 2005). Furthermore, past studies have shown that the dynamic response of low rise buildings can be affected by the in-plane flexibility of the roof diaphragm (Naman & Goodno 1986, Medhekar 1997, Tremblay & Stiemer 1996, Tremblay et al. 2003, 2004, Rogers et al. 2004). It has been shown through analytical means that the period of a single-storey steel building with a flexible roof diaphragm may be longer than that which is based on the stiffness of the vertical SFRS (Tremblay & Stiemer 1996, Medhekar 1997, Tremblay et al. 2008a). Significant savings in the cost of the lateral load resisting system could be achieved if this longer period of vibration were exploited in the design of single-storey steel buildings, mainly because of the lower seismic load (Tremblay et al. 2002, Tremblay & Rogers 2005). In contrast, ambient vibration studies of these buildings have shown that the overall period of vibration may not be as long as that obtained from analytical predications (Medhekar 1997, Paultre et al. 2004, Tremblay et al. 2008a).
