The need to lower the embodied carbon impact of the built environment and sequester carbon over the life of buildings has spurred the growth of mass timber building construction, leading to the introduction of new building types (Types IV-A, B, and C) in the 2021 International Building Code (IBC). The achievement of sustainability goals has been hindered by the perceived first cost assessment of mass timber systems. Optimizing cost is an urgent prerequisite to embodied carbon reduction. Due to a high level of prefabrication and reduction in field labor, the mass timber material volume constitutes a larger portion of total project cost when compared to buildings with traditional materials. In this study, the dollar cost, carbon emitted, and carbon sequestered of mass timber beam–column gravity system solutions with different design configurations was studied. Design parameters studied in this sensitivity analysis included viable building types, column grid dimension, and building height. A scenario study was conducted to estimate the economic viability of tall wood buildings with respect to land costs. It is concluded that, while Type III building designations are the most economical for lower building heights, the newly introduced Type IV subcategories remain competitive for taller structures while providing a potentially significant embodied carbon benefit.
The report describes a new structural system in wood that is the first significant challenger to concrete and steel structures since their inception in tall building design more than a century ago. The introduction of these ideas is fundamentally driven by the need to find safe, carbon-neutral and sustainable alternatives to the incumbent structural materials of the urban world. The market for these ideas is quite simply enormous. The proposed solutions have significant capacity to revolutionize the building industry to address the major challenges of climate change, urbanization, sustainable development and world housing needs.
Both the BCBC and the NBCC are objective-based codes whose provisions are deemed to be acceptable solutions. Alternative solutions are permitted; however, they must be demonstrated to provide a level of performance equivalent to that of the acceptable solution they are replacing.
There is interest in Canada in constructing tall wood buildings. To aid in the design and approval of such buildings, FPInnovations oversaw the development of a Technical Guide for the Design and Construction of Tall Wood Buildings in Canada. Chapter 5 of the Guide addresses Fire Safety and Protection in tall buildings. Rather than developing site-specific regulations for tall wood buildings, a more robust approach, recommended in Chapter 5 of the Tall Wood Guide, would be to demonstrate quantitatively that the fire safety provisions proposed for the building yield fire risks that are not greater than the fire risks associated with the acceptable solutions of the code.
Unfortunately BCBC and NBCC do not provide a quantitative method for assessing the level of fire safety (or risk-to-life) inherent in the design of a building. However, CUrisk, the most comprehensive model available for assessing the fire risk in buildings, can assess how fire protection measures work together to ensure life safety by computing the risk-to-life due to fire in the building.
In this project, CUrisk was employed to assess and compare the risk-to-life due to fire in mid-rise and high-rise residential and office buildings of wood construction and of non-combustible construction and to demonstrate how fire protection measures can be tuned to ensure a mid-rise or high-rise building of wood construction is as safe as a similar building of non-combustible construction.
This article outlines the structural design approach used for the Brock Commons Student Residence project, an 18-storey wood building at the University of British Columbia in Vancouver, Canada. When completed in summer 2017, it will be the tallest mass timber hybrid building in the world at 53 meters high. Fast + Epp are the structural engineers, working in conjunction with Acton Ostry Architects and Hermann Kaufmann Architekten. Total project costs, inclusive of fees, permits etc. are $51.5M CAD.
This study explores the use of Cross Laminated Timber (CLT) in a 10-story residential building as an alternative building method to concrete and steel construction. The study is not meant to be exhaustive, rather a preliminary investigation to test the economic viability of utilizing this new material to increase density, walkability and sustainable responsiveness in our built environment.
Based on international precedent, CLT is an applicable material for low-rise, as well as mid-rise to high-rise construction and has a lighter environmental footprint than traditional concrete and steel construction systems. Cross-laminated timber is a large format solid wood panel building system originating from central Europe. As a construction system it is similar to precast concrete in which large prefabricated panels are lifted by crane and installed using either a balloon frame or platform frame system. The advantages to using CLT are many, but the main benefits include: shorter construction times, fewer skilled laborers, better tolerances and quality, safer work environment, utilization of regional, sustainable materials, and reduction of carbon footprint of buildings. As a new, unproven material in the Pacific Northwest, this study investigates the cost competitiveness of CLT versus traditional materials for “low high-rise” buildings.
The US housing construction market consumes vast amounts of resources, with most structural elements derived from wood, a renewable and sustainable resource. The same cannot be said for all nonresidential or high-rise buildings, which are primarily made of concrete and steel. As part of continuous environmental improvement processes, building life-cycle assessment (LCA) is a useful tool to compare the environmental footprint of building structures. This study is a comparative LCA of an 8360-m2, 12-story mixed-use apartment/office building designed for Portland, OR, and constructed from mainly mass timber. The designed mass timber building had a relatively lightweight structural frame that used 1782 m3 of cross-laminated timber (CLT) and 557 m3 of glue-laminated timber (glulam) and associated materials, which replaced approximately 58% of concrete and 72% of rebar that would have been used in a conventional building. Compared with a similar concrete building, the mass timber building had 18%, 1%, and 47% reduction in the impact categories of global warming, ozone depletion, and eutrophication, respectively, for the A1-A5 building LCA. The use of CLT and glulam materials substantially decreased the carbon footprint of the building, although it consumed more primary energy compared with a similar concrete building. The impacts for the mass timber building were affected by large amounts of gypsum board, which accounted for 16% of total building mass. Both lowering the amount of gypsum and keeping the mass timber production close to the construction site could lower the overall environmental footprint of the mass timber building.
Five full-scale fire experiments were conducted to observe the performance of a two-level apartment-style structure constructed of mass timber. Each level consisted of a one bedroom apartment, an L-shaped corridor, and a stairwell connecting the two levels. One of the primary variables considered in this test series was the amount and location of exposed mass timber. The amount of mass timber surface area protected by gypsum wallboard ranged from 100% to no protection. For each experiment, the fuel load was identical and the fire was initiated in a base cabinet in the kitchen. In the first three experiments, the fire reached flashover conditions, and subsequently underwent a cooling phase as the fuel load from combustible contents was consumed. The first three experiments were carried out for a duration of up to 4 h. In the fourth experiment, automatic fire sprinklers were installed. Sprinklers suppressed the fire automatically. In the fifth experiment, the activation of the automatic fire sprinklers was delayed by approximately 20 minutes beyond the sprinkler activation time in the fourth experiment to simulate responding fire service charging a failed sprinkler water system. A variety of instrumentation was used during the experiments, including thermocouples, bidirectional probes, optical density meters, heat flux transducers, directional flame thermometers, gas analyzers, a fire products collector, and residential smoke alarms. In addition, the experiments were documented with digital still photography, video cameras, and a thermal imaging camera. The experiments were conducted in the large burn room of the Bureau of Alcohol, Tobacco, Firearms and Explosives Fire Research Laboratory located in Beltsville, Maryland, USA. This report provides details on how each experiment was set up, how the experiments were conducted, and the instrumentation used to collect the data. A brief summary of the test results is also included. Detailed results and full data for each test are included in separate appendices.
In Phase I (2018-19) of this project on Prefabricated Heavy Timber Modular Construction, three major types of connections used in a stackable modular building were studied: intramodule connection, inter-module vertical connection, and inter-module horizontal connection. The load requirement and major design criteria were identified. The connections were designed and tested to quantify their performance.
Conventional methods to build timber modules based on platform construction may not be most suitable for midrise to tall stackable buildings, due to the weak compression perpendicular to grain property of wood. Balloon construction is proposed here to manufacture individual modules so that non-disruptive vertical load transfer path is maintained along the structural height. Three screwed connections were tested to evaluate the load transfer between the elements, with steel angle brackets and Laminated Veneer Lumber (LVL) blocks. Screws at 90° were found to be inadequate for this application due to the low stiffness and high variation. When screws were installed at 45°, both the steel plates and LVL blocks had high stiffness, high strength, and good ductility.
Cross-Laminated Timber is one of the most widely used engineered wood products, thanks to its numerous advantages, among which construction speed is the most appreciated, both by clients and by designers. However, construction scheduling compression refers exclusively to CLT structures, while the rest of the construction process still requires a longer phase to complete vertical enclosures. The aim of the research work presented in this paper is to outline advantages brought about when the degree of envelope prefabrication of tall timber buildings is increased. Results are presented in two sections. The first includes the definition of a case study together with an overview of possible technical details for entirely prefabricated façade solutions, ready to be installed without the need to work via scaffolds. The second deals with construction site management analysis for the case study building, where the determination of specific factors having an influence on time and costs is achieved by varying the prefabrication degree of the various façade configurations and repeating the analysis process. The main findings of this research work demonstrate that comprehensive façade prefabrication allows not only consistent compression of construction scheduling to be achieved, but also for immediate protection of wooden elements from weather agents.
Modular and Offsite Construction (MOC) Summit Proceedings
In the context of the global trend of designing sustainable structures, the attention towards high-rise timber buildings of 8 to 25 storeys has been increasing in recent years. Balloon construction technique using a relatively new heavy timber material, cross-laminated timber (CLT), has been shown to be promising for high-rise building applications, given its compatibility with off-site construction techniques and its desirable mechanical characteristics. To date, tall timber buildings using CLT have been built mainly in non-seismic or low-seismic locations around the world, whereas their application in high seismic regions has been limited to platform construction. More research on the behaviour of CLT structures during seismic events in terms of system behaviour as well as the behaviour of components, particularly connections, is required. The research presented in this paper seeks to initiate the process of seismic design of tall wood buildings using a balloon construction technique. Two buildings, one three-storey fictitious building and one to-be-constructed ten-storey building, both located on the west coast of Canada, were considered and designed based on the NBCC 2015 seismic provisions. The loads on the shear walls, which span over three storeys, were extracted in order to estimate realistic demands on lateral load resisting systems (LLRS) in the balloon construction. Different connections, including base shear connections, panel-to-panel shear connections, as well as high-capacity hold-downs, were designed accordingly. An experimental program was developed to investigate the behaviour of these connections, focusing on yielding and failure mechanisms in each connection category. This paper explains different phases of the experimental program and introduces connection details designed to achieve the research goals. The results of this study will contribute to the body of knowledge on seismic behaviour of prefabricated mass timber buildings, and will benefit engineers and practitioners using timber to design high-rise structures.