Throughout the last two decades the timber building sector has experienced a steady growth in multi-storey construction. Although there has been a growing number of research focused on trends, benefits, and disadvantages in timber construction from various technical perspectives, so far there is no extensive literature on the trajectory of emerging architectural typologies. This paper presents an examination of architectural variety and spatial possibilities in current serial and modular multi-storey timber construction. It aims to draw a parallel between architectural characteristics and their relation to structural systems in timber. The research draws from a collection of 350 contemporary multi-storey timber building projects between 2000 and 2021. It consists of 300 built projects, 12 projects currently in construction, and 38 design proposals. The survey consists of quantitative and qualitative project data, as well as classification of the structural system, material, program, massing, and spatial organization of the projects. It then compares the different structural and design aspects to achieve a comprehensive overview of possibilities in timber construction. The outcome is an identification of the range of morphologies and a better understanding of the design space in current serial and modular multi-storey mass timber construction.
Forest Service/USDA Wood Innovations Grants
Recipient Point of Contact: Nicole K. Knobloch
Location: Arlington, Massachusetts
Summary
Building on successful work creating demand for mass timber as a climate solution in the Boston area through a 2019 Wood Innovation Grant, Olifant and a national group of AEC partners will do the same for three sister cities and their states/ surrounding regions: Atlanta, Minneapolis, and Denver. The goal is to enable each city to make mass timber a centerpiece carbon reduction strategy for the built environment and to be ready to offer a USFS Mass Timber Accelerator grant program to developers and/or other incentives for mass timber construction. Working in collaboration with AIA chapter partners, our AEC industry leaders will conduct regionally-based comparative studies on carbon benefits of local mass timber construction, cost and procurement considerations, forest sourcing, and current and potential U.S. mass timber manufacturing, nationally and regionally, developed into educational materials for use by AEC professionals and city planners. The overarching goal is to create robust, long-term demand for mass timber construction in these cities and nationwide that will encourage more U.S. mass timber manufacturing investment.
Forest Service/USDA Wood Innovations Grants
Recipient Point of Contact: Annie Perkins
Location: Washington, DC
Summary
The mass timber sector needs to gain greater market share of the broader building industry in order to increase demand for wood procured from U.S. forestlands. This project helps to increase demand for mass timber in three key ways by:
1. tapping into the industrial building sector currently not leveraging wood
2. quantifying the social benefits of building with wood procured from responsibly managed forests
3. telling the story of how building with wood procured from responsibly managed forests contribute to social and environmental benefits.
Through a collaboration of forest, sustainability and building experts, this project will:
(1) provide a replicable, scalable roadmap leveraging the use of mass timber in a traditional industrial building application
(2) quantify social Return on Investment (ROI) and act as a template for how an otherwise traditional industrial building can positively impact society
(3) meet Environmental, Social, and Governance (ESG) and sustainability goals
(4) promote healthy communities all while meeting urban design aesthetic criteria
This innovative and unique, showcase-worthy project helps bridge the gap and tell the story of how building with wood procured from responsibly managed forests helps address numerous benefits in and beyond the forest. Furthermore, it will illustrate how these benefits can be realized when constructing in-demand, industrial buildings.
The lateral resistance of dowel-type connections with CLT is related to its lay-up, species of the laminations and even the manufacture method. Treating the CLT as homogeneous material, current methods develop new equations through test results or make use of the existing equations for the embedment strength already used in design codes; thus, the lateral resistance of dowel-type connections of CLT can be calculated. This kind of approach does not take the embedment stress distribution into account, which may lead to inaccuracy in predicting the lateral resistance and yield mode of the dowel-type connections in CLT. In this study, tests of the bolted connections and the screwed connections of CLT were conducted by considering the effects of the orientation of the laminations, the thickness of the connected members, the fastener diameter and strength of the materials. The material properties including yield strength of the fasteners and embedment strength of the CLT laminations were also tested. Using analysis of the dowel-type connections of CLT by introducing the equivalent embedment stress distribution, equations for the lateral resistance of the connections based on the European Yield Model were developed. The predicted lateral resistance and yield modes were in good agreement with the test results; the correctness and the feasibility of the equations were thus validated.
In the construction of modern multi-storey mass timber structures, a composite floor system commonly specified by structural engineers is the timber–concrete composite (TCC) system, where a mass timber beam or mass timber panel (MTP) is connected to a concrete slab with mechanical connectors. The design of TCC floor systems has not been addressed in timber design standards due to a lack of suitable analytical models for predicting the serviceability and safety performance of these systems. Moreover, the interlayer connection properties have a large influence on the structural performance of a TCC system. These connection properties are often generated by testing. In this paper, an analytical approach for designing a TCC floor system is proposed that incorporates connection models to predict connection properties from basic connection component properties such as embedment and withdrawal strength/stiffness of the connector, thereby circumventing the need to perform connection tests. The analytical approach leads to the calculation of effective bending stiffness, forces in the connectors, and extreme stresses in concrete and timber of the TCC system, and can be used in design to evaluate allowable floor spans under specific design loads and criteria. An extensive parametric analysis was also conducted following the analytical procedure to investigate the TCC connection and system behaviour. It was observed that the screw spacing and timber thickness remain the most important parameters which significantly influence the TCC system behaviour.
An Empirical Analysis of Barriers to Building Information Modelling (BIM) Implementation in Wood Construction Projects: Evidence from the Swedish Context
Building information modelling is gradually being recognised by the architecture, engineering, construction, and operation industry as a valuable opportunity to increase the efficiency of the built environment. Focusing on the wood construction industry, BIM is becoming a necessity; this is due to its high level of prefabrication and complex digital procedures using wood sawing machines and sophisticated cuttings. However, the full implementation of BIM is still far from reality. The main objective of this paper is to explore the barriers affecting BIM implementation in the Swedish construction industry. An extensive literature review was conducted to extract barriers hindering the implementation of BIM in the construction industry. Secondly, barriers to the implementation of BIM in the wood construction industry in Sweden were extracted using the grounded theory methodology to analyse expert input on the phenomenon of low BIM implementation in the wood construction industry in Sweden. Thirty-four barriers were identified. The analysis of this study also led to the development of a conceptual model that recommended solutions to overcome the barriers identified to help maximise BIM implementation within the wood construction industry. Identifying the main barriers affecting BIM implementation is essential to guide organisational decisions and drive policy, particularly for governments that are considering articulating regulations to expand BIM implementation.
The fiber-reinforced polymer is one kind of composite material made of synthetic fiber and resin, which has attracted research interests for the reinforcement of timber elements. In this study, 18 glued-laminated (glulam) beams, unreinforced or reinforced with internally embedded carbon fiber–reinforced polymer (CFRP) sheets, were tested under four-point bending loads. For the reinforced glulam beams, the influences of the strengthening ratio, the modulus of elasticity of the CFRP, and the CFRP arrangement on their bending performance were experimentally investigated. Subsequently, a finite element model developed was verified with the experimental results; furthermore, a general theoretical model considering the typical tensile failure mode was employed to predict the bending–resisting capacities of the reinforced glulam beams. It is found that the reinforced glulam beams are featured with relatively ductile bending failure, compared to the brittle tensile failure of the unreinforced ones. Besides, the compressive properties of the uppermost grain of the glulam can be fully utilized in the CFRP-reinforced beams. For the beams with a 0.040% strengthening ratio, the bending–resisting capacity and the maximum deflection can be enhanced approximately by 6.51 and 12.02%, respectively. The difference between the experimental results and the numerical results and that between the experimental results and analytical results are within 20 and 10%, respectively.
In this paper, the bending properties of a 3-ply cross-laminated bamboo and timber (CLBT), prefabricated with the bamboo mat-curtain panel and hem-fir lumber, were examined in the major and minor strength directions, and a 3-ply hem-fir cross-laminated timber (CLT) was taken as a control group. The analytical model for the sum of the orthogonal apparent bending moduli with the two types of layer classifications were proposed, and the two kinds of contribution models were developed to analyze the apparent bending modulus variation behavior of the CLBT and CLT panels in the major and minor strength directions. The experimental results showed that since the CLBT group had more internal orthogonal structures, its difference in the bending properties between the major and minor strength directions was lower than that of the CLT group. Furthermore, the proposed contribution models quantitatively analyzed the relationship between the apparent bending moduli of the CLBT and CLT panels and the corresponding composition layer characteristics. The contribution model to characterize the apparent bending modulus in major and minor strength directions demonstrated good agreement with the test results. Based on this model interpreted by three-dimensional figures, the contribution variation characteristics in the major and minor strength directions were revealed.
Forest Service/USDA Wood Innovations Grants
Recipient Point of Contact: Karl R. Englund
Location: Pullman, Washington
Summary
The durability of wood has always limited mass adoption into many markets. With CLT, wood’s perceived ineffective performance when exposed to bio-deterioration and fire has many customers hesitant to commit to a mass timber structure. Our project will evaluate a commercial ready process to pretreat the lamstock of CLT panels with a variety of borate-based treatment options. By treating the lamstock prior to CLT fabrication, a more homogeneous treatment is realized, making a more durable panel that can be implemented in areas prone to high humidity and mitigate risks associated with durability. Our work will provide a commercial-ready solution that can be easily implemented in-line, lowering costs and not interrupting process flows or outputs.
A framework for the probabilistic finite element model updating based on measured modal data is presented. The described framework is applied to a seven-storey building made of cross-laminated timber panels. The experimental estimates based on the forced vibration test are used in the process of model updating. First, a generalized Polynomial Chaos surrogate model is derived representing the map from the model parameters to the eigenfrequencies and the eigenvectors. To overcome the difficulties caused by mode switching, we propose a novel approach to mode tracking based on partitioning an extended and low-rank representation of the mode shapes resulting from different setups of the finite element model into clusters by the k-means clustering algorithm. Second, the surrogate model derived with the help of mode pairing is used to efficiently perform sensitivity analysis and uncertainty quantification of the first five frequencies and the corresponding mode shapes. Finally, the surrogate-based Bayesian update of the model parameters is efficiently performed, providing engineers not only with a finite element model that gives a good fit to the experimental modal data, but also a stochastic model that represents the uncertainties originating from the initial model and the uncertainties of measuring modal properties.
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