Mass Timber Buildings Research Articles

Quantifying acoustic performance and embodied carbon of acoustic solutions for mass timber buildings: Comparing common approaches around the globe

As mass timber continues to increase in popularity as a building method to shifting away from high embodied carbon concrete structures to utilize wood as a renewable and lower embodied material. As whole building life cycle assessments (LCA) become more essential in meeting environmental emissions targets and qualifying for sustainability linked financing, quantifying the embodied carbon of both the structure and all other elements is necessary. The acoustic challenges of mass timber have been well documented and studied in previous works with a range of solutions now commonly utilized. Like most elements of construction, regionality results in different techniques being more popular and practical in different parts of the world. This work will compare the airborne and structure borne sound transmission and associated embodied carbon of four common acoustic designs for mass timber construction: floating concrete toppings, isolated board and batten floor systems, isolated dry floor linings, and raised access floors.

Investigating the deformation characteristics of balloon-type CLT shearwall

Balloon-type cross-laminated timber (CLT) shearwalls represent a valuable alternative to traditional platform-type construction for use as lateral load resisting systems in mid-rise mass timber buildings. Limited information is available on the behaviour of balloon-type shearwalls, and the system is not included in design codes and standards. The research aims to investigate the lateral deformation contribution and kinematic behaviour of balloon-type CLT shearwall system. A simplified analytical model to establish the lateral displacement of shearwalls is presented and discussed. The methodology involves a validated finite element model, and the result of sensitivity analysis is used to develop the analytical model. The study revealed that the stiffness of hold-downs and vertical joints, and aspect ratio of panels and vertical loads are contributing factors influencing lateral stiffness. The proposed analytical model was verified against 45 cases implemented in numerical models yielding an average error in the prediction of top lateral displacement of less than 4.7%.

Innovating Bhutan's residential construction with mass timber for economic and environmental sustainability

The global construction industry lacks innovation and contributes substantially to world energy consumption and greenhouse gas (GHGs) emissions. This study posits emerging mass timber construction (MTC) as an innovative alternative to Bhutan's archetype mid-rise residential structure, focusing on voluminous assemblages of wall and structural systems. Using an analytical approach, we compared the existing concrete building's essential economic and environmental sustainability with its hypothetical MTC equivalent. The economics focused on the life-cycle cost analysis (LCCA), while the environment focused on the embodied energy and CO2 emissions, estimated using the process-based method in a cradle-to-gate boundary limit. The environmental assessment unsurprisingly showed superior performances for the mass timber buildings relative to the conventional concrete ones. In contrast, the LCCA showed that mass timber buildings had material and built-up costs greater than concrete buildings by 30 and 38%, respectively, which is driven primarily by the high cost of timber in Bhutan. However, the scenario analyses regarding the end-of-life benefits and timber price reduction possibilities presented irrefutable evidence that the construction costs of MTC are cheaper or competitive with the concrete option. Integrating economics and environmental assessment establishes mass timber building as a viable innovative alternative, providing essential information to building developers and policymakers.

Effects of Re-drying on properties of cross laminated timber (CLT) connections

As mass timber buildings continue to gain widespread acceptance in North America, there is the need to address concerns, which might impact the performance of these novel buildings. Moisture intrusion poses significant levels of risks to mass timber elements and has been associated with durability concerns and possible reduction in performance of structural elements and connection systems. While it is recommended to employ design approaches that eliminate moisture accumulation in buildings, the possibility of elements getting wet during, or post construction remains reasonably high. Hence, it is important to re-dry elements once wet to avoid these issues. Additionally, connections constitute an important part of the lateral force resisting system and must be well studied for optimum performance under all conditions. This study therefore characterized the wetting and redrying performance of Cross Laminated Timber (CLT) angle bracket connections made from four CLT species. The effects of three different drying methods on the load carrying capacity, stiffness, and energy dissipating capacity of the connections were studied. Load carrying capacity of the connections was barely affected, but aggressive drying induced brittleness in some connections, and consequently impacted energy dissipating capacity. Physical observation of the connection assemblies also showed varying degrees of damage, which can be attributed to accumulation of drying stresses depending on the drying method employed.

An urban ‘age of timber’? Tensions and contradictions in the low-carbon imaginary of the bioeconomic city

What will the low-carbon cities of tomorrow be made from? We see an unexpected answer today in the return of ‘premodern’/‘preindustrial’ materials to central cities and skylines. Champions of new mass timber materials have driven a race on iconic ‘plyscrapers’ and, increasingly, novel systems of industrial prefabrication. Drawing on the notion of sociotechnical imaginaries, we explore how advocates attempt to ‘fix’ desirable future cities and urban bioeconomies through this biomaterial. In doing so, we suggest that mass timber's emergent sociotechnical imaginary embodies a distinct kind of futuring, which we label ‘nostalgic futurism’, conjoining ‘technofuturist’ and ‘nostalgic-reparative’ visions. We find that, on the one hand, mass timber proponents embrace competitive novelty, uniting drives for architectural distinction and high-tech disruption. On the other hand, aesthetic advocates put forward visions around the material's more traditional premodern/preindustrial associations, in narratives of biophilic design which claim therapeutic benefits of contact with visible nature in buildings. These conjoined forward- and backward-looking compulsions pose tensions and internal contradictions. Nostalgic-reparative visions risk greenwashing and reproducing unequal access to environmental amenities, while reinscribing regressive appeals to an imagined past. Meanwhile, technofuturist drives extend late capitalist growth imperatives and pressures for accelerated material churn in both forests and urban centres—while obscuring tough questions about mass timber buildings’ expected lifetimes and claims for long-term carbon sequestration. Conversely, a reimagined mass timber project might support more progressive movements for climate restoration, repair, and reparations.

Reinforced cross-laminated timber-concrete composite floor systems

This paper presents full-scale experimental investigations on cross-laminated timber concrete composite (TCC) systems. The primary objective was to determine the stiffness, ultimate load-carrying capacity, and failure modes of TCC systems using three different shear connectors: self-tapping screws, steel kerf plates, and proprietary glued-in perforated steel plates. The secondary objective was to determine the effectiveness of shear reinforcement in the CLT panels. The TCC system was comprised of 245 mm thick, 7-ply CLT panels with a 150 mm concrete topping. A total of 24 half-span (4.6 m long) and 9 full-span (9.2 m long) CLT and TCC floor segments were tested under symmetric four-point bending as well as torsional bending. For all test series, the CLT panels were either unreinforced, or reinforced using self-tapping screws. The shear reinforcement increased rolling shear capacity which helped to avoid CLT shear failure. Adding the concrete topping increased the shear capacity by up to 167%. The tests showed that the floors with steel kerf plates exhibited the highest capacity and stiffness, while also being the most easy-to-install solution. The results from this research guided project-specific design decisions for “Limberlost Place”, a mass timber building for George Brown College, in Toronto, Canada.

Performance of Beam-Column Connections with Mass Ply Lam and Steel Dowels under Cyclic Loads

A mass timber lateral force resisting system (LFRS) is proposed using a mass timber buckling restrained brace (TBRB) to improve the seismic resilience of mass timber buildings. To develop a resilient braced frame, it is essential to understand and quantify the behavior of the connections, including the possible failure modes and moment-rotation capacities. Cyclic and monotonic tests were conducted on six mass timber beam-column connections to study the response of a mass timber joint connected with slotted-in steel plates and mild steel dowels. The primary goal of the subassembly tests was to measure the maximum rotation, stiffness, ductility, and failure modes of such connections for both monotonic and cyclic loads. The tests showed that the connections with three steel dowel details reached a maximum rotation of 0.11 radians (6.3 degrees) with no loss of strength. In addition, a numerical model was developed to represent the moment-rotation relationship of the mass timber beam-column connections.

Numerical Evaluation of Failure Mechanisms and Retrofitting of Connections in Mass Timber Buildings

With the growing trend in industry towards zero carbon construction, mass timber structures are becoming more accepted globally. Beam-to-column connections in mass timber buildings are currently designed to carry shear actions. However, the connections may be considered to take moment actions and large rotations to comply with ductility and robustness requirements of the building standards. The current study deploys finite element analysis (FEA) to investigate the failure due to large deformation and rotation of a typical bolted beam-to-column connection and provides an economic retrofitting design solution using self-tapping screws (STS). The FEA is validated against current or published experimental results and is used to conduct a thorough assessment of the retrofitted connection. It is shown that a proper arrangement of screws can delay the brittle failure, develop significant moment-resisting capacity, and enhance the rotational ductility of the connection.

Multicriteria Decision Analysis of Steel and Mass Timber Prototype Buildings in the Pacific Northwest

This study used multicriteria decision analysis to quantitatively compare two prototype buildings, both designed using equivalent mass timber and steel structural systems across four decision criteria of seismic resiliency, global warming potential, superstructure cost, and durability. The 5-story and 12-story prototype buildings were both located at an arbitrary site in Seattle, WA. The first three decision criteria were quantitatively measured for each prototype building and durability was assumed to be equivalent between the alternatives. Seismic resiliency was measured using the median expected annual loss calculated using as a percentage of predicted building replacement cost using a procedure in line with FEMA P-58. The global warming potential was measured over the production, construction, and end-of-life stages using the life-cycle analysis program Athena Impact Estimator for Buildings (IE4B). The superstructure cost was calculated as the average cost per square meter using 10 estimating variations that attempt to account for uncertainty in market rates of material, labor, and mass timber design efficiency. Five decision-maker scenarios were analyzed that span the practical range of decision-maker priorities, as informed by discussions with architects and engineers active in the Pacific Northwest. Results from this study showed that for decision-maker cases where the global warming priority was low, steel buildings were the preferred choice. For cases with moderate to high global warming priority and low priority on cost, mass timber buildings were the preferred choice. However, for decision-maker scenarios with moderate priority on both global warming potential and cost, the steel and mass timber buildings were approximately equivalent. Finally, a hybrid steel–timber alternative was presented as a possible sweet-spot solution that merged the benefits of each building material and minimized their drawbacks, making it the most-preferred solution for the case of moderate priority on both cost and global warming potential. The hybrid case was also close second in ranked choice for all other scenarios examined.

Quantifying and Reducing Embodied Carbon in the Acoustic Design of Mass Timber Buildings

An adoption of mass timber construction is the construction industry's best shot at reducing its significantly large contribution to global CO2 emissions. Acoustic design in mass timber buildings typically relies on mass and facing materials in order to meet design criteria, and can account for a high proportion of the embodied carbon (CO2e) per m² on a build. In order to fit with the ethos of mass timber construction; low embodied carbon, reusable, cradle to cradle materials must be adopted. This paper presents the findings of a study into the relationship of acoustic performance and CO2e, and proposes alternate approaches that reduce the CO2e/m² of the acoustic design by up to 66% with little to no detriment to acoustic performance. Through single variable analysis in third party laboratory testing, and in situ testing, it has been found to be possible to utilise low CO2e acoustic systems that reduce the CO2e/m² in not only the acoustic design, but structural, M&E and architectural disciplines, too.

External fire plumes from mass timber compartment fires—Comparison to test methods for regulatory compliance of façades

AbstractPost‐flashover fires inherently lead to external fire plumes, constituting a hazard for rapid fire spread over façades. As multi‐storey mass timber buildings with internal visible timber surfaces become more common, there are concerns that such buildings would produce larger external plumes and hazards (assuming all other parameters equal). The literature reveals only indications of this, and how the actual exposure relates to different test methods for assessment is unknown. Here we utilise a series of full‐scale mass timber compartment tests to quantify the exposure to the external façade. An incombustible external façade is instrumented with gauges at positions corresponding to reference data from several different assessment methods. The results show that there is an increase in plume duration, height, and temperatures when increasing the areas of exposed timber, but that this increase is less for normal‐ to large‐opening compartments, than was previously seen in small‐opening compartments. Also, normal variations in external wind speed have a larger influence on plume heights than the effect of doubling exposed timber surfaces. Test methods used for regulatory compliance differ significantly not only in exposure but also in pass/fail criteria. The proposed European large exposure method and the BS8414 method exhibit exposures on par with the severe end of what could be expected from mass timber compartments, whereas methods like SP Fire 105 and Lepir II produce significantly less severe plumes. However, the safety level is always a combination of exposure and assessment criteria. This data can help justify assessment criteria from a performance perspective.

Further application of the 1/3 oct band heavy/hard impact prediction method

Previously, the author presented a 1/3 octave band heavy/hard impact prediction method based on force pulse measurements from a drop tower. Since then, we have been applying the method with a variety of success. The previous paper was based on concrete structures in North America. This paper will be looking at the validity of the method on lighter weight mass timber buildings primarily located in the United Kingdom as well as traditional concrete buildings. The discuss will be focused on the accuracy of the method across several structures and describe why the method was less accurate in some applications. The primary cause of disagreement between predicted and in-situ measurements was high levels of background noise and other site conditions.

The Vibration Reduction Index of Typical Canadian Cross-laminated Timber Junctions

In support of the National Building Code of Canada, The National Research Council Canada has published research report RR-335 which describes the results of measurements of the transmission of structure-borne noise through junctions between mass timber elements. The Code only allows for the use of measured data for the vibration reduction index from the NRC's reports or reports from other research institutes. The Code does not currently allow for the use of empirical data for the calculation of the apparent sound transmission class of mass timber buildings. A lack of published data for typical mass timber junctions used in Canada can result in the overdesign of buildings or buildings which don't meet the acoustic requirements of the Code. The NRC has embarked on a program to measure the vibration reduction index of a number of mock junctions of typical junctions used in Canada including junctions between cross-laminated timber floors and lightweight timber framed walls. The new data will aid in the development of empirical models of typical Canadian mass timber constructions.

Impact of partial encapsulation on the fire dynamics of an open‐plan compartment with exposed timber ceiling and columns:CodeRed #04

AbstractThe use of mass timber in construction is becoming a compelling option when faced with the high carbon footprint of traditional concrete and steel production. However, fire safety standards are yet to evolve to support these designs. Encapsulation is commonly used to protect all, or some, of the timber surfaces and reduce the risks introduced. This paper presents the results fromCodeRed #04, the final experiment of theCodeRedexperimental campaign. This experiment was carried out inside a purpose‐built facility to capture fire dynamics in large compartments with exposed timber.CodeRed #04had identical characteristics toCodeRed #01with the exception that ~50% of the cross‐laminated timber (CLT) ceiling was encapsulated. The experiments were intentionally similar to the traveling fire experiments,x‐ONEandx‐TWO, which had a non‐combustible ceiling to enable a direct comparison. The overall fire dynamics experienced inCodeRed #04, intersect the characteristics observed inCodeRed #01andx‐ONEandx‐TWO.1. InCodeRed #04, there was a delay in the ignition of the CLT ceiling as the CLT directly above the crib was encapsulated. Once the CLT ceiling ignited, the fire spread rapidly throughout the compartment. The peak heat release rate (HRR) was estimated to be approximately 100 MW, a 17% decrease fromCodeRed #01. Following CLT ignition the resulting fire duration, maximum temperatures, and heat fluxes were broadly similar toCodeRed #01. Flame heights of approximately 1.5 m were observed from the windows while flame heights of 2.5–3 m were observed inCodeRed #01. Therefore, flame heights were found to be comparable tox‐TWO.1, though over a greater number of windows, reflecting the greater extent of simultaneous burning within the compartment. The average charring depth of the exposed CLT panels was ~25 mm, which is similar to that measured inCodeRed #01‐suggesting that the fire severity near the ceiling was not strongly impacted by the 50% encapsulation of timber. No charring was observed where the ceiling was encapsulated and loaded service fixings installed through the encapsulation were found to be less likely to fail than when attached directly to the exposed timber. Smoldering was observed after the cessation of flaming and, in a few locations, was observed to progress through the thickness of the CLT panel and continue behind the encapsulation. This illustrates that, while encapsulation can succcessfully prevent flaming, it cannot be completely relied on to avoid smouldering. The findings fromCodeRed #04contribute to the development of evidence‐based fire safety design methodologies for exposed mass timber buildings.

Understanding structural health monitoring data to support decision-making processes and service life management of mass timber buildings. A preliminary study on use of data scaffolding

ABSTRACT Structural health monitoring (SHM) can be used to support decision-making processes leading to improved building management plans. With advanced engineered wooden buildings on the rise, SHM has emerged as a critical tool to document behaviour of these structures. However, monitoring data need to be easily accessible and understandable to support informed decisions. This study explores the potential benefits of an intentionally designed data scaffolding to support interpretation of SHM data for timber structures. Results suggest that appropriate scaffolding (e.g. pinpointing critical parameter ranges) can enable lay users to better interpret monitoring data of timber structures. Results also suggest that, for more highly educated users, access to graphs linked to metadata can be beneficial. Overall, it appears that documentation related to the monitored phenomena and context, as well as more explicit reference to building performance requirements, could improve data-driven decision making for all knowledge levels for the building maintenance sector.

Whole life embodied emissions and net-zero emissions potential for a mid-rise office building constructed with mass timber

Increasing global interest in sustainable buildings has generated significant investment in the mass timber industry in recent years. Timber products including Cross-Laminated Timber (CLT) and glue-laminated timber beams (glulam) are a structurally sound, aesthetically pleasing, and potentially carbon reducing alternative to traditional steel or concrete framing. This study uses Life Cycle Analysis methodology to determine the total embodied carbon emissions for a four-story (10033 m2) office building using two design scenarios: a traditional design using structural steel framing and a mass timber alternative utilizing CLT and glulam. The work is founded on detailed material lists for the two building designs that were generated by an architectural contractor with both designs subject to strict evaluation regarding building and construction codes. In addition to a comparative embodied carbon emissions analysis, this study utilized building energy consumption models and existing utility data to estimate operational emissions throughout the lifetime of the building. Energy production with rooftop solar arrays was estimated to evaluate grid emissions avoidance and determine the potential to offset whole life embodied carbon emissions when evaluated over a 30-year time horizon with temporal grid emissions accounting. Three end-of-life scenarios were evaluated for the mass timber products to determine the fate of biogenic carbon stored in the wood biomass. For the three scenarios, different mass fractions were sent to the landfill, directly re-used, or processed into particleboard. Results for the cradle-to-grave embodied carbon emissions analysis show the steel design embodies 3999 t CO2-eq. (398.5 kg CO2-eq m−2) whereas the mass timber design offers an 80–99% reduction in embodied carbon totaling 50–795 t CO2-eq. (5–79 kg CO2-eq m−2) dependent on the end-of-life treatment of mass timber products. Of all the evaluated cradle-to-grave scenarios, the smallest required solar array to fully offset embodied carbon emissions in 30 years was 665 kW with the mass timber building and the end-of-life scenario where 75% of CLT and 95% of glulam were directly re-used with the remaining fractions manufactured into particleboard. Discussion focuses on the challenges and uncertainty in using solar arrays to offset emissions from building construction, operation, and end-of-life treatment, requirements for achieving true net-zero carbon buildings, and methodological limitations.

Nonlinear analytical modeling of mass-timber buildings with post-tensioned rocking walls

Nonlinear analytical modeling of mass-timber buildings with post-tensioned rocking walls

Implementing a Choosing-by-Advantages Decision-Making Method to Evaluate the Critical Success Factors of Mass-Timber Building Materials in the US

Implementing a Choosing-by-Advantages Decision-Making Method to Evaluate the Critical Success Factors of Mass-Timber Building Materials in the US

Impact of ventilation on the fire dynamics of an open‐plan compartment with exposed timber ceiling and columns: CodeRed #02

AbstractThe desire by developers and architects to build mass timber buildings using cross laminated timber (CLT) and glulam has significantly increased globally in the last decade due to its benefits with regards to sustainability as well as other architectural and commercial drivers. This paper presents novel experimental evidence from CodeRed #02, the second in a series of large scale fire experiments carried out inside a purpose‐built, open‐plan compartment to capture fire dynamics in large compartments with exposed timber. The experiment used a continuous wood crib (6 × 29 m) as a controlled movable fuel load. The aim of the CodeRed #02 experiment was to study the impact of reduced ventilation on fire dynamics by keeping all other parameters the same as CodeRed #01 (Kotsovinos et al., 2022), with the exception of ventilation area which was reduced by almost half. The reduction in ventilation was found to significantly impact the fire dynamics by slowing the fire spread and burning rate. The reduced ventilation led to an increased fire duration by 4 min 30 s, which corresponds to 20% longer duration compared to CodeRed #01. The reduced ventilation had a greater overall impact on the rate of flame spread across the CLT (−23%) than the crib (−8%) compared to CodeRed #01. While the maximum temperature and incident heat fluxes inside the compartment were approximately the same as in CodeRed #01, their evolution in time and space were significantly different. The external flames were higher than in CodeRed #01 (3–3.5 m compared to 2.5–3 m) and protruded further laterally (up to ~4–5 m compared to ~1 m) outside of the compartment from the large end openings. Unlike CodeRed #01, the external flaming from CodeRed #02 pulsated between visible flames and dark soot with significantly greater frequency. This was caused by the limited ventilation resulting in incomplete combustion in CodeRed #02. The peak heat release rate of CodeRed #02 was estimated to be 16.5% lower than CodeRed #01, despite having the same fuel load. The average char depth in the ceiling, as measured at the end of the experiment, was 28 mm. This was 11% greater than in CodeRed #01 and was likely due to the increased duration of the fire. After the extinction of the flaming, smouldering occurred for CodeRed #02 as it did for CodeRed #01. One of the glulam columns lost its restraint and fell to the ground because smouldering spread through the thickness of the member. The findings from this work can help engineers quantify the hazard and therefore identify appropriate solutions for the fire safety design of exposed mass timber buildings.

Prevention of Disproportionate Collapse for Multistory Mass Timber Buildings: Review of Current Practices and Recent Research

The expanding height of multistory mass timber buildings makes the development of guidance to prevent disproportionate collapse an increasingly important area of engineering design; however, there is no guidance available in building codes or design standards on how to prevent disproportionate collapse of multistory mass timber buildings. In this paper, practical project-specific solutions applied in constructed prominent multistory mass timber buildings to prevent disproportionate collapse are presented. Various approaches have been successfully used for different construction types of multistory mass timber buildings to decrease the potential risk of disproportionate collapse, such as using walls above supports as deep beams and using columns to carry tension forces and hold the floor below in case a supporting column or wall is damaged. Then, recent and ongoing research in the field of prevention of disproportionate collapse of multistory timber buildings is reviewed. Such research is mostly based on numerical simulations of element removal scenarios and pushdown experiments on floor systems and connections and provides valuable insights and guidance to designers on important structural aspects regarding the prevention of disproportionate collapse in multistory mass timber buildings. Finally, the draft provisions for an upcoming standard related to the prevention of disproportionate collapse are reviewed, and the conclusions regarding the state of the art are presented.