Dynamic behaviour and inelastic performance of steel roof deck diaphragms

Modern building codes such as the NBCC 2005 require the use of capacity-based seismic design principles in which a ductile energy dissipating element, typically the bracing members of the vertical braced frames of the lateral force resisting system in single-storey structures, must be clearly identified. The diaphragm, used to transfer inertia loads to these vertical elements, must then be designed for the probable resistance of the braces. Furthermore, the code-proposed formula to calculate the fundamental period of vibration of single-storey structures does not account for the inherent flexibility of the diaphragm; whereas research has shown that accounting for this effect can result in longer building periods and, thereby, lower seismic forces and result in a more economical design.;An experimental test frame mimicking the roof assembly of a single-storey steel structure was constructed in the laboratory. Corrugated steel sheets were fastened to the frame to complete the diaphragm assembly. Nine diaphragm specimens, with varying deck sheet thicknesses and orientations, fastened using typical construction methods, were tested dynamically to evaluate their stiffness, strength and ductility. Loading protocols, including one developed to induce inelastic deformations at the fasteners, were applied. Retrofit and repair strategies were subsequently evaluated in attempts to restitute the properties of the original specimens. From testing, it was determined that the stiffness of the diaphragm diminishes with increased excitation amplitude resulting in a longer fundamental period potentially beneficial for design.;The design of a single-storey structure with a steel roof deck diaphragm, laterally supported by an eccentrically braced frame (EBF) was completed according to the NBCC 2005 and CSA S16-09 seismic provisions. When compared to a concentrically braced structure, it was determined that the overstrength of the eccentric brace system did not have as negative an impact on the diaphragm design. Furthermore, when the design incorporated the flexibility of the roof diaphragm, the structure had an increased drift demand compared to the case in which the roof diaphragm was considered rigid.;In-situ ambient vibration measurements have demonstrated that the period of single-storey structures may in fact be shorter than determined from structural models. It is believed, however, that ambient levels of loading are not representative of larger seismic motions.