Advanced sustainable lateral load resisting systems that combine ductile and recyclable materials offer a viable solution to resist seismic load effects in environmentally responsible ways. This paper presents the seismic response of a post-tensioned timber-steel hybrid braced frame. This hybrid system combines glulam frame with steel braces to improve lateral stiffness while providing self-centreing capability under seismic loads. The proposed system is first presented. A detailed numerical model of the proposed system is then developed with emphasis on the connections and inelastic response of bracing members. Various types of braced frames including diagonal, cross and chevron configurations are numerically examined to assess the viability of the proposed concept and to confirm the efficiency of the system. A summary of initial findings is presented to demonstrate usefulness of the hybrid system. The results demonstrate that the proposed system increases overall lateral stiffness and ductility while still being able to achieve self-centring. Some additional information on connection details are provided for implementation in practical structures. The braced-frame solution is expected to widen options for lateral load resisting systems for mid-to-high-rise buildings.
In this paper, we examined the effects of extreme tornadic wind loads on mass-timber buildings. In general, mass-timber buildings utilize pre-engineered wood panels to form their main gravity and lateral load resisting systems. The lightweight nature of timber makes these types of emerging buildings lighter and more flexible than buildings made from concrete, masonry or steel. In general, global lateral instability of buildings can occur when the overturning forces due to wind loads exceed the dead load of the structures. In the present study, wind loads were obtained from laboratory simulations of tornado-like wind field and atmospheric boundary layer flow at Western University, Canada. Tornado wind loads from the laboratory tests were scaled to five Enhanced Fujita wind speeds representing various levels of damage. Dynamic structural analyses were carried out to assess floor level demands. It is shown that extreme tornado wind loads may pose significant damage to mass-timber buildings designed for 1-in-50 wind speed using a load factor of 1.4. Based on the obtained results, design strategies are suggested for mass-timber buildings in tornado-prone areas.
A new type of mass timber structural system has been developed in New Zealand over the last decade. Timber members made of engineered wood products are used in combination with post-tensioning cables to produce highly efficient structural components suitable for multi-story moment resisting frames or shear wall-based lateral load resisting systems. Both systems are particularly useful in structures designed in high seismic regions. The post-tensioning also ensures self-centering of the components and the structural systems after a seismic event. In addition to the post-tensioning, the systems can use energy dissipating devices within the connections that further enhance the ductility of the systems and make them good candidates for low damage structural applications. Extensive experimental and numerical studies have been conducted to determine the performance of these systems and design procedures have been developed for practical applications. In an effort to bring this system closer to the North American designers, this paper contains a summary of the evolution of the concept and the most important research projects and findings to date. In addition, a number of applications within and outside New Zealand are reviewed to demonstrate the applicability of the concept. Finally, potential and recent initiatives for adoption of the technology in North America are discussed.