Braced timber frames (BTFs) are one of the most efficient structural systems to resist lateral loads induced by earthquakes or high winds. Although BTFs are implemented as a system in the National Building Code of Canada (NBCC), no design guidelines currently exist in CSA O86. That not only leaves these efficient systems out of reach of designers, but also puts them in danger of being eliminated from NBCC. The main objective of this project is to generate the technical information needed for development of design guidelines for BTFs as a lateral load resisting system in CSA O86. The seismic performance of 30 BTFs with riveted connections was studied last year by conducting nonlinear dynamic analysis; and also 15 glulam brace specimens using bolted connections were tested under cyclic loading.
In the second year of the project, a relationship between the connection and system ductility of BTFs was derived based on engineering principles. The proposed relationship was verified against the nonlinear pushover analysis results of single- and multi-storey BTFs with various building heights. The influence of the connection ductility, the stiffness ratio, and the number of tiers and storeys on the system ductility of BTFs was investigated using the verified relationship. The minimum connection ductility for different categories (moderately ductile and limited ductility) of BTFs was estimated.
Midply shear wall (hereafter Midply), which was originally developed by researchers at Forintek Canada Corp. (predecessor of FPInnovations) and the University of British Columbia, is a high-capacity shear wall system that is suitable for high wind and seismic loadings. Its superior seismic performance was demonstrated in a full-scale earthquake simulation test of a 6-storey wood-frame building in Japan. In collaboration with APA–The Engineered Wood Association and the American Wood Council (AWC), a new framing arrangement was designed in this study to increase the vertical load resistance of Midply and make it easier to accommodate electrical and plumbing services. In this study, a total of 14 Midply specimens in six wall configurations with different sheathing thicknesses and nail spacing were tested under reversed cyclic loading. Test results showed that Midply has approximately twice the lateral load capacity of a comparable standard shear wall. The drift capacity and energy dissipation capability are also greater than comparable standard shear walls. For Midply to use the same seismic force modification factors as standard shear walls, seismic equivalency to standard shear walls in accordance with ASTM D7989 was also conducted. Although Midply has superior lateral load and drift capacities, it does not seem to be as ductile as the standard shear walls at the same over-strength level. Additional testing and dynamic analysis are recommended to address this issue.
Braced mass timber (MT) frames are one of the most efficient structural systems to resist lateral loads induced by earthquakes or high winds. Although braced frames are presented as a system in the National Building Code of Canada (NBCC), no design guidelines currently exist in CSA O86. That not only leaves these efficient systems out of reach of designers, but also puts them in danger of being eliminated from NBCC. The main objective of this project was to develop the technical information needed for development of design guidelines for braced MT frames as a lateral load resisting system in CSA O86.
In the first year of the project, the seismic performance of thirty (30) braced MT frames with riveted connections with various numbers of storeys, storey heights, and bay aspect ratios were studied by conducting non-linear pushover and dynamic time-history analyses. Also, fifteen (15) glulam brace specimens using bolted connections with different slenderness ratios were tested under monotonic and cyclic loading. Results from this multi-year project will form the basis for developing comprehensive design guidelines for braced frames in CSA O86.
