The use of cross-laminated timber (CLT) in residential and non-residential buildings is becoming increasingly popular in North America. While the 2016 supplement to the 2014 edition of the Canadian Standard for Engineering Design in Wood, CSAO86, provides provisions for CLT structures used in platform type applications, it does not provide guidance for the in-plane stiffness and strength of CLT shearwalls. The research presented in this paper investigated the in-plane stiffness and strength of CLT shearwalls with different connections for platform-type construction. Finite element analyses were conducted where the CLT panels were modelled as an orthotropic elastic material, and non-linear springs were used for the connections. The hysteretic behaviour of the connections under cyclic loading was calibrated from quasi-static tests; the full model of wall assemblies was calibrated using experimental tests on CLT shearwalls. A parametric study was conducted that evaluated the change of strength and stiffness of walls with the change in a number of connectors. Finally, a capacity-based design procedure is proposed that provides engineers with guidance for designing platform-type CLT buildings. The philosophy of the procedure is to design the CLT buildings such that all non-linear deformations and energy dissipation occurs in designated connections, while all other connections and the CLT panels are designed with sufficient over-strength to remain linear elastic.
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.
This paper presents the seismic design and analysis of a 20-storey demonstration wood building, which was conducted as a part of the NEWBuildS tall wood building design project. A hybrid lateral load resisting system was chosen for the building. The system consisted of shear walls and a shear core, both made of structural composite lumber, connected with dowel-type connections and heavy-duty HSK (wood-steel-composite) system. The core and the shear walls were linked with horizontal steel beams at each floor. The wood-based panel-to-panel interface was designed to be the main energy dissipating mechanism of the system. A detailed finite element model of this building was developed and non-linear time history analyses were performed using 10 earthquake motions. The results showed that the seismic response of the 20-storey demonstration building met the various design criteria and the design details are appropriate.
April 3-5, 2014, Boston, Massachusetts, United States
Summary
Cross-laminated timber (CLT) is widely perceived as the most promising option for building high-rise wood structures due to its structural robustness and good fire resistance. While gravity load design of a tall CLT building is relatively easy to address because all CLT walls can be utilized as bearing walls, design for significant lateral loads (earthquake and wind) can be challenging due to the lack of ductility in current CLT construction methods that utilize wall panels with low aspect ratios (height to length). Keeping the wall panels at high aspect ratios can provide a more ductile response, but it will inevitably increase the material and labor costs associated with the structure. In this study, a solution to this dilemma is proposed by introducing damping and elastic restoring devices in a multi-story CLT building to achieve ductile response, while keeping the integrity of low aspect ratio walls to reduce the cost of construction and improve fire resistance. The design methodology for incorporating the response modification devices is proposed and the performance of the as-designed structure under seismic is evaluated.
