Originally developed in Europe, self-tapping screws (STS) have become the proprietary fastener of choice in recently built mass timber buildings in North America. STS offers some advantages over other types of fasteners, such as (a) installation of STS inside wood members is easier as it does not require pre-drilling of holes inside members, (b) the yield moment, torsional strength and tensile strength of STS is comparatively high as the material forming the screw is usually hardened after rolling the thread, (c) the stiffness of the resulting connection is higher and the chances of slipping are less (Frese and Blass, 2009), and (d) STS with long threaded lengths makes it feasible for use in large structural members, e.g., mass timber products.
Recently, issues have been raised on failures of STS due to shrinkage and swelling of wood products resulting from moisture content changes, particularly during construction in the coastal climates. Failures of STS have been reported by structural engineers and contractors of several mass timber projects in NA. This has greatly increased the liability of practitioners involved in mass timber construction.
This project will investigate the material properties of several types of mass timber products and self-tapping screws. These material properties will be used in an analytical and numerical prediction model to describe the behaviour of self-tapping screws in mass timber products under moisture content variation.
A number of test series have been conducted at FPInnovations to evaluate the lateral resistance, fire resistance, and acoustic performance of the new Midply shear wall configuration. The results showed that the seismic force modification factors prescribed in the NBCC can be used, along with the enhanced lateral strength and stiffness. Moreover, with some minor design
considerations, it was found that the new Midply with the resilient channels and insulation materials in both sides of the wall and both cavities can provide at least 1 hour of fire-resistance rating and provide at least an ASTC of 47.
Un certain nombre de séries d'essais ont été réalisées à FPInnovations pour évaluer la résistance latérale, la résistance au feu et la performance acoustique de la nouvelle configuration de mur de contreventement Midply. Les résultats ont montré que les facteurs de modification de la force sismique prescrits dans le CNBC peuvent être utilisés, avec une résistance et une rigidité latérales améliorées. De plus, avec quelques considérations de
conception mineures, il a été constaté que le nouveau mur de refend Midply avec les profilés souples et les matériaux d’isolation des deux côtés du mur et dans les deux cavités peut fournir au moins une heure de degré de résistance au feu et un ITSA d’au moins 47.
La présente InfoNote décrit brièvement les systèmes de résistance aux forces sismiques (SRFS) en bois massif qui seront inclus dans l’édition 2020 du Code national du bâtiment (CNB) du Canada, leurs limites de hauteur et les principales exigences de conception selon la norme Règles de calcul des charpentes en bois de l’Association canadienne de normalisation CSA O86-19. Elle explique aussi les différences de limite de hauteur entre les différents systèmes de résistance aux charges de gravité et aux charges latérales.
La présente InfoNote décrit brièvement les SRFS en bois massif prometteurs, de même que les modèles analytiques et par éléments finis correspondants dans le but d’encourager leur adoption par les entreprises de conception structurale.
Mass timber (MT) products, such as Glued Laminated Timber (GLT), Cross Laminated Timber (CLT), Laminated Veneer Lumber (LVL), Nail Laminated Timber (NLT), Dowel Laminated Timber (DLT), Laminated Strand Lumber (LSL), Parallel Strand Lumber (PSL), Mass Plywood Panels (MPP) and others, provide options for developing efficient structural systems to resist gravity and lateral loads. Such systems can be competitive alternatives to their steel and concrete counterparts. This InfoNote briefly introduces the MT Seismic Force Resisting Systems (SFRSs) that will be implemented in the 2020 National Building Code (NBC) of Canada, their height limits, and the main design
requirements according to Canadian Standard for Engineering Design in Wood CSA O86-19. Differences among height limits for MT gravity and lateral load resisting systems are also
discussed. Mass Timber
National Building Code of Canada (NBC) 2020 is the latest edition of the national model code that will be published towards the end of 2021. Based on the best available information from the Standing Committee on Earthquake Design (SCED) at the time of writing this report, the seismic design demand in the NBC 2020 has increased for all site classes for many locations across the country. Also, there are other changes in NBC 2020 that might impact the seismic analysis and design of timber buildings. The main objective of this report is to compare the NBC 2020 to the 2015 edition, with emphasis on the level of the seismic design loads (demands), and potential impacts on the analysis and design of timber buildings.
Computer modelling is an essential part in the analysis and design of mid- and high-rise residential and commercial buildings as well as long-span structures. It is also a valuable tool in the optimisation of wood-based products, connections, and systems. An FPInnovations’ survey shows that practicing engineers are unfamiliar with timber structure modelling, and researchers generally lack resources for advanced modelling of timber systems. Furthermore, wood analysis and design modules currently implemented in a few structural analysis software are usually not suitable for complex or hybrid timber structures. This does not bode well given that performance-based design which is the future direction of building codes and material standards will rely even more on demonstrating the structural performance through computer modelling. In this project, a modelling guide for timber structures is being developed by FPInnovations with a global collaborative effort involving experts in various areas, with the aim of (a) assisting practicing engineers apply computer modelling to timber structures; (b) enriching researchers’ resources for advanced computer modelling of timber systems; and (c) assisting software companies to identify the gaps and upgrade their programs accordingly to accommodate advanced computer modelling of timber structures.
Midply shear wall, 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 shear walls and make it easier to accommodate electrical and plumbing services. In this study, a total of 12 midply shear wall specimens in four wall configurations with different sheathing thicknesses and nail spacing were tested under reversed cyclic loading. Test results showed that the modified midply shear walls have 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 wall. Seismic equivalency to standard shear walls in accordance with ASTM D7989 was also conducted. Results show that an overstrength factor of 2.5 and can be used to assign allowable design strengths of midply shear walls with 7/16” and nail spacing at 4” or 3” on center. For midply shear walls with 19/32” OSB, a higher overstrength factor must be used to meet the ductility criteria. The information from this study will support code implementation of the midply shear walls in Canadian and US timber design standards, thereby providing more design options for light wood frame structures in North America.