Mass Timber Buildings Research Articles

Leveraging Structural Health Monitoring Data Through Avatars to Extend the Service Life of Mass Timber Buildings

Mass timber construction systems, incorporating engineered wood products as structural elements, are gaining acceptance as a sustainable alternative to multi-story concrete or steel-frame structures. The relative novelty of these systems brings uncertainties on whether these buildings perform long-term as expected. Consequently, several structural health monitoring (SHM) projects have recently emerged to document their behavior. A wide and systematic use of this data by the mass timber industry is currently hindered by limitations of SHM programs. These limitations include scalability, difficulty of data integration, diverse strategies for data collection, scarcity of relevant data, complexity of data analysis, and limited usability of predictive tools. This perspective paper envisions the use of avatars as a Web-based layer on top of sensing devices to support SHM data and protocol interoperability, analysis, and reasoning capability and to improve life cycle management of mass timber buildings. The proposed approach supports robustness, high level and large-scale interoperability and data processing by leveraging the Web protocol stack, overcoming many limitations of conventional centralized SHM systems. The design of avatars is applied in an exemplary scenario of hygrothermal data reconstruction, and use of this data to compare different mold growth prediction models. The proposed approach demonstrates the ability of avatars to efficiently filter and enrich data from heterogeneous sensors, thus overcoming problems due to data gaps or insufficient spatial distribution of sensors. In addition, the designed avatars can provide prediction or reasoning capability about the building, thus acting as a digital twin solution to support building lifecycle management.

Disproportionate collapse prevention analysis for post and beam mass timber building

Disproportionate collapse prevention of mass timber buildings is becoming a relevant design consideration due to the increasing height of these buildings. Linear static alternative load path analysis (ALPA) is well-established with extensive details and worked examples for concrete, steel, and light-frame wood buildings. The research presented herein illustrates its application to a mass timber building with floors supported by beams and columns, referred to as ‘post and beam’ system. The performance of a six-storey post and beam mass timber building, using predominantly wood-to-wood bearing-type connections, following three notional element removal scenarios (removals of ground floor internal, edge, and corner columns) is investigated. It is evaluated whether the case study building’s structural system can trigger floor collapse-resistance mechanisms by checking if its primary elements and connections satisfy disproportionate collapse acceptance criteria, defined by the demand-to-capacity ratio after element removals. The results demonstrated that: i) element removal analyses should be conducted in 3D and should include all primary structural elements, with floor carrying its own weight at every level; ii) compressive arching is dominant for members with small span over depth ratios, whereas catenary action governs for larger spans; iii) continuous beams and slabs help the floor system to cantilever over the removed elements; and iv) the considered connection detail may be improved by the addition of axial connectors to trigger catenary action.

Numerical assessment of the interaction between shear and moment actions in LVL bolted connections

Mass timber buildings are becoming the new sustainable choice in construction due to their reduced carbon footprint and benefits of prefabrication. As the height of timber buildings increases and floors with longer spans are employed, the role of connections in the structural integrity becomes more noticeable. There is limited knowledge available on structural performance and ductility of bolted LVL timber connectors in combined shear and bending actions. The current study uses a series of physical tests to interpret the interaction between bolts and timber in different loading scenarios and bolt arrangements. Finite element analyses (FEA) are conducted to interpret the experimental test results and to predict the interaction behaviour of a bolted beam-to-column connection and the same connection retrofitted with self-tapping screws. Structural responses and failure modes under combined loading of each connection are discussed, and interaction curves and expressions are developed.

Recycling Potential Comparison of Mass Timber Constructions and Concrete Buildings: A Case Study in China

The recycling potential (RP) indicates the ability of building materials to form a closed-loop material flow, that is, the material efficiency during its whole life cycle. Mass timber constructions and concrete buildings vary widely in RP, but the differences are difficult to calculate. This paper proposed a level-based scheme to compare the RP of mass timber and concrete buildings, and a BIM-Eco2soft-MS Excel workflow coupling Material Cycle Database and digital design tools were established to obtain information on building materials, resource consumption, and environmental impact for the RP calculation. Taking a residential building as an example, the difference in RP between mass timber and concrete at the material-level is firstly discussed. Then at the component-level, the RP of the wood structure component and concrete component is compared, and the optimization methods are proposed. Finally, the difference in RP between the mass timber building and reinforced concrete building at the building-level are illustrated. The results show that the RP of mass timber building is higher, and the disassembly ability is better. Within a 100-year service life, the RP of mass timber buildings is 73% and that of the reinforced concrete building is 34%. The total amount of material consumption and waste of the Variant CLT is 837,030 kg and 267,237 kg respectively, which is less than one-third of that of concrete buildings (3,458,488 kg; 958,145 kg). The Global Warming potential (GWP) of these two variants is −174.0 kgCO2/m2 and 221.0 kgCO2/m2 separately, indicating that the Variant CLT can realize negative carbon emissions and gain ecological benefits. A sensitivity analysis is conducted to explore the potential impacts of certain parameters on GWP and RP of buildings. The research can provide the reference for material selection, component design, and RP optimization of mass timber buildings. In addition, new ideas for assessing the potential of circularity as a design tool are proposed to support the transition towards a circular construction industry and to realize carbon neutrality.

Effect of partition walls on the seismic response of mass-timber buildings with a post-tensioned rocking wall system

The structural-nonstructural interaction effects of nonstructural partition walls and post-tensioned CLT rocking walls in mass-timber buildings were evaluated in a parametric study. Representative 2D rocking wall units in 5-story and 12-story mass-timber archetype buildings were modeled in OpenSees. Moreover, concentrated spring models were developed to represent effective force-deformation for four different variations of partition wall detailing, and applied to the building models to represent wall densities associated with apartment and hospitality occupancies. Eigenvalue, pushover, and response-history analyses were performed on 2D models of the bare structure and those with partition wall variations. Including partition walls with fixed connection details was found to decrease story drifts and rocking wall story shears compared to the bare frame model by up to 50% in a service earthquake and up to 30% in a maximum considered earthquake. However, partition walls with deformation-compatible details were found to have negligible influence (less than 5%) on the response.

A building information modeling‐fire dynamics simulation integrated framework for the simulation of passive fire protection in a mid‐scale cross‐laminated timber compartment: Numerical implementation and benchmarking

AbstractConstruction fires are a big threat to worker safety and property safety. Mass timber buildings under construction are largely unprotected as they are not yet equipped with active fire protection systems. With the addition of Types IVA, B, and C, the 2021 International Building Code adopted stricter requirements for mass timber buildings that are under construction. Cross‐laminated timber (CLT) is used as the primary structural element for high‐rise mass timber buildings. However, to date, limited number of research studies investigated the impact of passive fire protection for CLT buildings that are under construction. To facilitate a better understanding of construction fires and their consequences, it is necessary to develop a numerical modeling solution for the early phases of a CLT construction project, which can be achieved by using building information models together with fire dynamics simulation (FDS). However, the numerical modeling technique must be benchmarked against experimental data first to then extrapolate the modeling technique to explore other parameters and conduct FDS analysis. Therefore, this paper develops and benchmarks a numerical modeling solution against a mid‐scale CLT compartment fire test by applying the FDS tool to simulate the fire behavior within the CLT compartment. The FDS analysis results are expected to validate the practicality of simulating the fire behavior in CLT structures using the numerical model proposed in this study. The overarching goal of this study is therefore to develop a comprehensive numerical modeling solution to simulate and assess passive fire protection sequencing in CLT buildings that are under construction.

Circular economy in mass timber construction: State-of-the-art, gaps and pressing research needs

The building and construction sector is a major contributor to human environmental impact on the planet. It follows that the sector's contribution is also crucial for transition towards a low carbon society and circular economy (CE). Mass timber products, are one of the sustainable alternatives to traditional building materials and have led to the recent revolution in timber construction. While environmental benefits of mas timber manufacturing and construction is well documented the end-of-life (EOL) and the post-EOL options for mass timber buildings, their environmental benefits and CE potential are discussed much less. Short history of construction technology involving prefabricated mass timber panels compared to traditional building types results in virtually no documented cases of panelized mass timber structures reaching the EOL stage and no practical examples of incorporating CE concepts in such projects. In this study, a two-step systematic literature review was used, to define and classify 23 CE-based governing principles from six categories in the construction industry, and to use those principles to analyze the state-of-the-art circular approach in mass timber research. The study covered a total of 90 papers, of which 68 focused on the general construction industry and 22 specifically on the mass timber construction. Results of this review suggest substantial gaps in knowledge and pressing research needs for the development of holistic approaches to prepare the mass timber construction for circular economy.

A Case Study on the Impact of Transportation of Mass Timber Products on the Cradle-to-Gate LCA Results for an Institutional Building

Mass timber products (MTPs) are being adopted in new building constructions and remodels in the last three decades, credited to their renewable and low carbon footprint characteristics. However, there are no mass timber manufacturers currently existing in Atlantic Canada. Extended distances of transporting MTPs to this region from other Canadian provinces may sacrifice the environmental benefits of using MTPs. This study was aimed to understand, via conducting a cradle-to-gate life cycle assessment (LCA), the environmental impacts of a mid-rise institutional building, which is located in the Province of New Brunswick Canada. By comparing the current steel frame design of this building with an alternative mass timber building design with the same height range and function including the transportations of major building materials. It was found that the mass timber building design could still have environmental advantages over the steel structure, as much as 19.5% lower global warming impact and 16.8% lower ozone depletion impact, even with MTPs delivered from the furthest location considered in this study. However, the disadvantages in other impact categories, such as 31.9% higher smog impact, 13.6% higher acidification impact, and 248.2% higher eutrophication impact were found when using the TRACI impact assessment in this whole building LCA study.

Experimental investigation and numerical modeling of rocking cross laminated timber walls on a flexible foundation

AbstractWith recent developments of engineered wood products such as cross laminated timber, mass timber buildings in areas of high seismicity are becoming feasible and offer benefits such as faster construction and unique architectural features. It has also opened the door to creating seismically resilient lateral systems that sustain minor and reparable damage during large earthquakes. This paper presents a numerical modeling procedure for mass timber rocking wall lateral system with distributed spring elements to model base rocking. This modeling technique was validated by comparing the behavior with results from the full‐scale two‐story shake table test on a mass timber building with coupled CLT rocking walls completed as part of the NHERI TallWood Project. Although the lateral system performed better than expected during testing, it was determined that the flexibility of the foundation actually limited damage to the rocking wall panels. By adjusting the numerical model to represent a rigid foundation boundary condition, it was determined that the wall system would have experienced more damage, but would have still met design performance objectives had it been tested on a rigid foundation.

The embodied carbon of mass timber and concrete buildings in Australia: An uncertainty analysis

This research uses uncertainty analysis to determine and compare the range of embodied carbon outcomes of mid-rise mass timber and concrete buildings in Australia. In doing so, it measures the variability in inventory databases, transportation distance, lifetime of building components, biogenic carbon emissions, carbonation of concrete materials and end-of-life scenarios. Through the use of Monte Carlo analysis, the research found that the embodied carbon of a mass timber building ranged from 196 kgCO2-e/m2 to 590 kgCO2-e/m2 with a mean of 417 kgCO2-e/m2. For a post-tensioned concrete building the range was 307 kgCO2-e/m2 to 618 kgCO2-e/m2 with a mean of 465 kgCO2-e/m2. This equates to a 48 kgCO2-e/m2 reduction in mean embodied carbon for the mass timber building. Using deterministic analysis, previous research suggested a more substantive 129 kgCO2-e/m2 reduction. These results demonstrate that mass timber buildings do typically have a lower embodied carbon, compared to concrete buildings, however the significance of this depends on the assumptions made, and the input data used. For the concrete building, the variation in embodied carbon is primarily influenced by the inventory data and building products' lifetime. The greater range of embodied carbon in the mass timber building is due to variations associated with the inventory data, allocation of biogenic carbon emissions (sequestration, and forest management losses) and, different end-of-life scenarios associated with timber products. Despite this, the research suggests that with a carefully planned end-of-life strategy, mass timber mid-rise buildings have the potential to benefit from lower embodied carbon emissions, as compared to concrete buildings, across their full lifecycle.

Validation and application of rational tying method for robustness design of post-and-beam timber buildings

ABSTRACT The lack of reliable tying methods for the design of low and medium-rise mass timber buildings with regard to progressive collapse constitutes a strong limitation for the timber structural engineering community. In this context, the current work aims to validate and apply a recently developed rational tying force method for robustness design of post-and-beam timber buildings falling in low and medium consequence classes. This rational tying force method, which considers the requisite resistance via tying to the loss of a load-bearing member, preserves the simplicity of the prescriptive rules present in some current standards, while utilising a mechanical basis similar to that considered in alternative load path analysis. An extended example of the application of the new tying force method to a post-and-beam timber structure is reported in this work. The example highlights several critical aspects for achieving a robust design of post-and-beam timber structures. The results presented in this work show that the new tying force method represents a promising and practical strategy for robustness design of post-and-beam timber buildings.

Modelling ambitious climate mitigation pathways for Australia's built environment

• We model operational and embodied GHG emissions for Australia's built environment. • The scope includes residential and commercial buildings. • A high ambition scenario delivers a 94% reduction in emissions compared to BAU. • Includes renewables, electrification, efficiency and material replacement. • Novel pathways analysis highlights options for net zero and net negative emissions. Achieving net zero operational and embodied greenhouse gas (GHG) emissions in the built environment is recognised in Australia and globally as a key strategy to address climate change and achieve the United Nations Sustainable Development Goals (SDGs). However, gaps in knowledge remain regarding potential national pathways to achieve this outcome in Australia. This study further extends and applies a national-scale integrated macroeconomic simulation model to explore coherent pathways to net zero emissions in the built environment sector by 2050. The scope of the study includes residential and commercial buildings and both operational and embodied emissions. It applies scenario analysis incorporating different levels of climate ambition, including a shift to renewable energy, electrifying buildings, improving energy efficiency and replacing carbon-intensive materials. We find that a high ambition scenario (Scenario 2) delivers a 94% reduction in GHG emissions by 2050 when compared against business-as-usual, placing a net-zero target within reach. Improvements on Australia's SDGs performance are also attained. Through subsequent pathways analysis we find that achieving net zero or even net negative operational and embodied emissions is feasible with more ambitious action in key areas, including increasing the share of mass-timber buildings and reducing end-of-life losses in sequestered carbon.

A Lifecycle Assessment of a Low-Energy Mass-Timber Building and Mainstream Concrete Alternative in Central Chile

While high-rise mass-timber construction is booming worldwide as a more sustainable alternative to mainstream cement and steel, in South America, there are still many gaps to overcome regarding sourcing, design, and environmental performance. The aim of this study was to assess the carbon emission footprint of using mass-timber products to build a mid-rise low-energy residential building in central Chile (CCL). The design presented at a solar decathlon contest in Santiago was assessed through lifecycle analysis (LCA) and compared to an equivalent mainstream concrete building. Greenhouse gas emissions, expressed as global warming potential (GWP), from cradle-to-usage over a 50-year life span, were lower for the timber design, with 131 kg CO2 eq/m2 of floor area (compared to 353 kg CO2 eq/m2) and a biogenic carbon storage of 447 tons of CO2 eq/m2 based on sustainable forestry practices. From cradle-to-construction, the embodied emissions of the mass-timber building were 42% lower (101 kg CO2 eq/m2) than those of the equivalent concrete building (167 kg CO2 eq/m2). The embodied energy of the mass-timber building was 37% higher than that of its equivalent concrete building and its envelope design helped reduce space-conditioning emissions by as much as 83%, from 187 kg CO2 eq/m2 as estimated for the equivalent concrete building to 31 kg CO2 eq/m2 50-yr. Overall, provided that further efforts are made to address residual energy end-uses and end-of-life waste management options, the use of mass-timber products offers a promising potential in CCL for delivering zero carbon residential multistory buildings.

Finite element modelling of the progressive collapse of post-and-beam mass timber building substructures under edge and corner column removal scenarios

The structural behaviour of mass timber buildings under a load bearing element removal scenario is complex. To well understand this phenomenon and ultimately develop scientifically based design guidelines against progressive collapse for this type of buildings, there is a need to develop a Finite Element model which accurately captures the non-linear response, load redistribution mechanisms (alternative load paths) and failure modes of such buildings. As such, this paper presents for the first time how mass timber post-and-beam systems can be accurately modelled using Finite Element under edge and corner column removal scenarios. The model was validated against published 2D and 3D experimental tests performed on scaled-down substructures. The non-linear structural responses of the main structural connections were experimentally quantified and inputted into the model using the component method. Results show that the model accurately replicated load redistribution mechanisms, ultimate loads, failure modes, and strain developments. The use of the model was then illustrated by running parametric studies to quantify (i) the influence of the Cross Laminated Timber (CLT) floor panels layout and (ii) one alternative load path, typically ignored in design, on the progressive collapse resistance capacity.

An aqueous polyisocyanate adhesive with excellent bond durability for engineered wood composites enhanced by polyamidoamine-epichlorohydrin co-crosslinking and montmorillonite hybridization

Recent trends toward mass-timber buildings and tall timber structures necessitate more stringent requirements for the bond durability of adhesives for engineered wood composites. In this work, a cost-effective strategy for manufacturing a novel aqueous polyisocyanate adhesive with excellent hygrothermal resistance for engineered wood composites was produced via co-crosslinking with polyamidoamine-epichlorohydrin (PAE) resin followed by organic–inorganic hybridization with montmorillonite clay (MMC). Test results confirmed that PAE co-crosslinking effectively increased the crosslinking density of aqueous polyisocyanate adhesive meanwhile prolonged working life. Hybridization of PAE-crosslinked polyisocyanate with MMC resulted in compact crosslinked networks and notably increased hygrothermal resistance. Consequently, this novel aqueous polyisocyanate adhesive exhibited excellent bond durability of plywood in terms of a wet aged strength of 1.73 MPa and a strength reduction ratio of only 18.4% after 7 boiling-dry hygrothermal aging cycles, which satisfies the requirements for manufacturing engineered wood composites as good construction and building materials.

A development cost comparison between a multi-storey mass timber and reinforced concrete building in South Africa

High-rise timber buildings have experienced a resurgence internationally during the past two decades. This paper presents an investigation into the financial feasibility of a multi-storey mass timber building for South Africa through a development cost comparison. Two 8-storey commercial buildings - a mass timber frame and a reinforced concrete frame - were first designed by independent engineering consultants. A focus group workshop, conducted with industry professionals, assisted with the development of construction schedules. Subsequently, a financial model was developed to determine the overall development cost and financial feasibility of each option. Finally, a sensitivity analysis was conducted to investigate the effect ol certain variables on the overall profitability of the mass timber frame development. The focus group workshop identified that the construction of the reinforced concrete frame building and mass timber frame building will take 42 weeks and 21 weeks, respectively. The total capital investment required for the mass timber frame development was found to be 10% more than that of the reinforced concrete frame development (R115 691 000 versus R 105 118 000). A five-year internal rate of return (IRR) of 20.9% and 25.7% was calculated for the mass timber and reinforced concrete frame developments, respectively. A significant finding of the sensitivity analysis was that the mass timber frame building proved to generate a higher five-year IRR than that of the reinforced concrete frame once the mass timber building achieved a rental premium of 7.8% or more. The sensitivity analysis further showed that the importation of the mass timber elements remains an expensive option, with a 16.4% five-year IRR for the imported mass timber frame (at a R17:€1 exchange rate).

Comparative Life Cycle Assessment of Mass Timber and Concrete Residential Buildings: A Case Study in China

As the population continues to grow in China’s urban settings, the building sector contributes to increasing levels of greenhouse gas (GHG) emissions. Concrete and steel are the two most common construction materials used in China and account for 60% of the carbon emissions among all building components. Mass timber is recognized as an alternative building material to concrete and steel, characterized by better environmental performance and unique structural features. Nonetheless, research associated with mass timber buildings is still lacking in China. Quantifying the emission mitigation potentials of using mass timber in new buildings can help accelerate associated policy development and provide valuable references for developing more sustainable constructions in China. This study used a life cycle assessment (LCA) approach to compare the environmental impacts of a baseline concrete building and a functionally equivalent timber building that uses cross-laminated timber as the primary material. A cradle-to-gate LCA model was developed based on onsite interviews and surveys collected in China, existing publications, and geography-specific life cycle inventory data. The results show that the timber building achieved a 25% reduction in global warming potential compared to its concrete counterpart. The environmental performance of timber buildings can be further improved through local sourcing, enhanced logistics, and manufacturing optimizations.

Mass Timber Building Life Cycle Assessment Methodology for the U.S. Regional Case Studies

The building industry currently consumes over a third of energy produced and emits 39% of greenhouse gases globally produced by human activities. The manufacturing of building materials and the construction of buildings make up 11% of those emissions within the sector. Whole-building life-cycle assessment is a holistic and scientific tool to assess multiple environmental impacts with internationally accepted inventory databases. A comparison of the building life-cycle assessment results would help to select materials and designs to reduce total environmental impacts at the early planning stage for architects and developers, and to revise the building code to improve environmental performance. The Nature Conservancy convened a group of researchers and policymakers from governments and non-profit organizations with expertise across wood product life-cycle assessment, forest carbon, and forest products market analysis to address emissions and energy consumption associated with mass timber building solutions. The study disclosed a series of detailed, comparative life-cycle assessments of pairs of buildings using both mass timber and conventional materials. The methodologies used in this study are clearly laid out in this paper for transparency and accountability. A plethora of data exists on the favorable environmental performance of wood as a building material and energy source, and many opportunities appear for research to improve on current practices.

Comparative LCAs of Conventional and Mass Timber Buildings in Regions with Potential for Mass Timber Penetration

Manufacturing of building materials and construction of buildings make up 11% of the global greenhouse gas emission by sector. Mass timber construction has the potential to reduce greenhouse gas emissions by moving wood into buildings with designs that have traditionally been dominated by steel and concrete. The environmental impacts of mass timber buildings were compared against those of functionally equivalent conventional buildings. Three pairs of buildings were designed for the Pacific Northwest, Northeast and Southeast regions in the United States to conform to mass timber building types with 8, 12, or 18 stories. Conventional buildings constructed with concrete and steel were designed for comparisons with the mass timber buildings. Over all regions and building heights, the mass timber buildings exhibited a reduction in the embodied carbon varying between 22% and 50% compared to the concrete buildings. Embodied carbon per unit of area increased with building height as the quantity of concrete, metals, and other nonrenewable materials increased. Total embodied energy to produce, transport, and construct A1–A5 materials was higher in all mass timber buildings compared to equivalent concrete. Further research is needed to predict the long-term carbon emissions and carbon mitigation potential of mass timber buildings to conventional building materials.

CLT concrete composite floors with steel kerf plate connectors

This paper presents experimental investigations on timber-concrete-composite (TCC) floors with transversely installed steel kerf plates as shear connectors. The TCC system was comprised of 245 mm thick, 7-ply cross-laminated timber (CLT) panels with 150 mm concrete topping. Three embedment depths of the steel kerf plates in CLT (35 mm, 70 mm, and 90 mm) were evaluated at hand of 18 small-scale shear tests. It was shown to be beneficial to only engage the top layer of the CLT panel in order to avoid rolling shear failure. Subsequently, two full-scale TCC floor segments were tested under symmetric four-point bending. The tests confirmed that the TCC floors with steel kerf plates can be designed using the established gamma procedure, and that they exhibited adequate capacity and stiffness to provide an economical solution. The results from this research were utilized to make project-specific design decisions for “The Arbour”, a 10-storey mass timber building for George Brown College, located in Toronto, Canada.