The use of timber–concrete composite (TCC) bridges in the United States dates back to approximately 1924 when the first bridge was constructed. Since then a large number of bridges have been built, of which more than 1,400 remain in service. The oldest bridges still in service are now more than 84 years old and predominately consist of two different TCC systems. The first system is a slab-type system that includes a longitudinal nail-laminated deck composite with a concrete deck top layer. The second system is a stringer system that includes either sawn timber or glulam stringers supporting a concrete deck top layer. The records indicate that most of the TCC highway bridges were constructed during the period of 1930–1960. The study presented in this paper discusses the experience and per-formance of these bridge systems in the US. The analysis is based on a review of the relevant literature and databases complemented with field inspections conducted within various research projects. Along with this review, a historical overview of the codes and guidelines available for the design of TCC bridges in the US is also included. The analysis undertaken showed that TCC bridges are an effective and durable design alternative for highway bridges once they have shown a high performance level, in some situations after more than 80 years in service with a low maintenance level.
As the interest in timber buildings is increasing, more attention is pointed towards highrise timber buildings. Partly because it is one of the main areas pushing the development within the field of timber structures. As the current tallest timber building, Mjöstornet in Brumunddal is approximately 10 times shorter than the world’s tallest building, Burj Khalifa, the intuition says that there is room for major improvements regarding tall timber structures. The aim of this thesis is therefore to investigate the possibilities to build a 200 m tall timber tower while still fulfilling the requirements for strength, stability and dynamics. In order to anchor the project in reality, the assumed building location is Gothenburg with the ground conditions of solid rock.
Early in the study it was concluded that in order to push the height limits, the building design had to be improved compared to the existing timber buildings. The main geometries of interest turned out to be the circular shape thanks to its aerodynamical benefits. This base shape was applied in various ways, generating five different concepts ready for evaluation.
Each of the five concepts were modelled and preliminary sized using Grasshopper and Karamba 3D, whereafter they were evaluated based on their dynamic performance, global stiffness, and a few other evaluation criteria. The evaluation was primary made with structural performance in mind and secondary with regard to comfort, quality and economical aspects.
The results show that one of the concepts have great potential of reaching 200 m despite the uncertainties regarding joint stiffness and structural damping. Also, a few of the other concepts might be able to reach 200 m if subject to some structural and dynamical improvements.
Ease of construction and favorable overall costs relative to other construction types are making high-rise (i.e., 4- and 5-story) wood frame construction increasingly popular. With these buildings increasing in height, there is a greater impetus on designers to address frame and finishes movement in such construction. As we all know, buildings are dynamic creatures experiencing a variety of movements during construction and over their service life. In wood frame construction, it is important to consider not only absolute movement but also differential movement between dissimilar materials.
This article focuses on differential movement issues and how to recognize their potential and avoid problems by effective detailing.
In this paper a precise model is established for deflection prediction of mechanically jointed beams with partial composite action. High accuracy of the proposed method is demonstrated through comparison with a comprehensive finite element (FE) modelling for a timber-concrete partial composite beam. Next, the obtained numerical results are compared with gamma-method, a well-known simplified solution for timber engineers according to the Eurocode 5. Validity and accuracy level of the gamma-method are investigated for various boundary conditions as well as different values of beam length-to-depth ratio, and discussed in details.
Project contact is Peter Dusicka at Portland State University (United States)
Summary
The urgency in increasing growth in densely populated urban areas, reducing the carbon footprint of new buildings, and targeting rapid return to occupancy following disastrous earthquakes has created a need to reexamine the structural systems of mid- to high-rise buildings. To address these sustainability and seismic resiliency needs, the objective of this research is to enable an all-timber material system in a way that will include architectural as well as structural considerations. Utilization of mass timber is societally important in providing buildings that store, instead of generate, carbon and increase the economic opportunity for depressed timber-producing regions of the country. This research will focus on buildings with core walls because those building types are some of the most common for contemporary urban mid- to high-rise construction. The open floor layout will allow for commercial and mixed-use occupancies, but also will contain significant technical knowledge gaps hindering their implementation with mass timber. The research plan has been formulated to fill these gaps by: (1) developing suitable mid- to high-rise archetypes with input from multiple stakeholders, (2) conducting parametric system-level seismic performance investigations, (3) developing new critical components, (4) validating the performance with large-scale experimentation, and (5) bridging the industry information gaps by incorporating teaching modules within an existing educational and outreach framework. Situated in the heart of a timber-producing region, the multi-disciplinary team will utilize the local design professional community with timber experience and Portland State University's recently implemented Green Building Scholars program to deliver technical outcomes that directly impact the surrounding environment.
Research outcomes will advance knowledge at the system performance level as well as at the critical component level. The investigated building system will incorporate cross laminated timber cores, floors, and glulam structural members. Using mass timber will present challenges in effectively achieving the goal of desirable seismic performance, especially seismic resiliency. These challenges will be addressed at the system level by a unique combination of core rocking combined with beam and floor interaction to achieve non-linear elastic behavior. This system behavior will eliminate the need for post-tensioning to achieve re-centering, but will introduce new parameters that can directly influence the lateral behavior. This research will study the effects of these parameters on the overall building behavior and will develop a methodology in which designers could use these parameters to strategically control the building seismic response. These key parameters will be investigated using parametric numerical analyses as well as large-scale, sub-system experimentation. One of the critical components of the system will be the hold-down, a device that connects the timber core to the foundation and provides hysteretic energy dissipation. Strength requirements and deformation demands in mid- to high-rise buildings, along with integration with mass timber, will necessitate the advancement of knowledge in developing this low-damage component. The investigated hold-down will have large deformation capability with readily replaceable parts. Moreover, the hold-down will have the potential to reduce strength of the component in a controlled and repeatable way at large deformations, while maintaining original strength at low deformations. This component characteristic can reduce the overall system overstrength, which in turn will have beneficial economic implications. Reducing the carbon footprint of new construction, linking rural and urban economies, and increasing the longevity of buildings in seismic zones are all goals that this mass timber research will advance and will be critical to the sustainable development of cities moving forward.
Project contact is Jianhui Zhou at the University of Northern British Columbia (Canada)
Summary
Building acoustics has been identified as one of the key subjects for the success of mass timber in the multi-storey building markets. The project will investigate the acoustical performance of mass timber panels produced in British Columbia. The apparent sound transmission class (ASTC) and impact insulation class (AIIC) of bare mass timber elements as wall and/ or floor elements will be measured through a lab mock-up. It is expected that a database of the sound insulation performance of British Columbia mass timber products will be developed with guidance on optimal acoustical treatments to achieve different levels of performance.
The growing diffusion of cross-laminated timber structures (CLT) has been accompanied by extensive research on the peculiar characteristics of this construction system, mainly concerning its economic and environmental benefits, lifecycle, structural design, resistance to seismic actions, fire protection, and energy efficiency. Nevertheless, some aspects have not yet been fully analysed. These include both the knowledge of noise protection that CLT systems are able to offer in relation to the possible applications and combinations of building elements, and the definition of calculation methods necessary to support the acoustic design. This review focuses on the main acoustic features of CLT systems and investigate on the results of the most relevant research aimed to provide key information on the application of acoustic modelling in CLT buildings. The vibro-acoustic behaviour of the basic component of this system and their interaction through the joints has been addressed, as well as the possible ways to manage acoustic information for calculation accuracy improvement by calibration with data from on-site measurements during the construction phase. This study further suggests the opportunity to improve measurement standards with specific reference curves for the bare CLT building elements, in order to compare different acoustic linings and assemblies on the same base. In addition, this study allows to identify some topics in the literature that are not yet fully clarified, providing some insights on possible future developments in research and for the optimization of these products.
Advanced industrialized construction methods enable complex building components and systems to be built with high precision and quality. This manufacturing technique has an advantage to provide cost-competitive and high energy efficient building components and systems for both retrofits and new construction. This document gives an overview of the use of prefabricated panels in building Net Zero Energy Ready wood-frame multi-unit residential buildings (MURBs) in Edmonton.
Project contacts are Frederico França at Mississippi State University and Robert J. Ross at the Forest Products Laboratory (United States)
Summary
With the rapid development of CLT manufacturing capacity around the world and the increasing architectural acceptance and adoption, there is a current and pressing need regarding adhesive bond quality assurance in manufacturing. As with other engineered glued composites, adhesive bondline performance is critically important. Bondline assessment requires technology in the form of sensors, ultrasonics, load cells, or other means of reliable machine evaluation.
The objectives of this cooperative study are to develop quality assurance procedures for monitoring the quality of mass timber and CLT during and after manufacturing and to develop assessment techniques for CLT panels in-service.
Lack of research and design information for the seismic performance of balloon-type CLT shear walls prevents CLT from being used as an acceptable solution to resist seismic loads in balloon-type mass-timber buildings. To quantify the performance of balloon-type CLT structures subjected to lateral loads and create the research background for future code implementation of balloon-type CLT systems in CSA O86 and NBCC, FPInnovations initiated a project to determine the behaviour of balloon-type CLT construction. A series of tests on balloon-type CLT walls and connections used in these walls were conducted. Analytical models were developed based on engineering principles and basic mechanics to predict the deflection and resistance of the balloon-type CLT shear walls. This report covers the work related to development of the analytical models and the tests on balloon-type CLT walls that the models were verified against.
FPInnovations initiated this project to demonstrate the ability of wood exit stairs in mid-rise buildings to perform adequately in a fire when NBCC requirements are followed, with the intent of changing perceptions of the fire safety of wood construction. The objective of this research is to investigate further the fire safety afforded by exit stair shafts of combustible construction, with the ultimate objective of better consistency between the provincial and national building codes with respect to fire requirements for exit stair shafts in mid-rise wood-frame construction.
Auburn University’s (AU) School of Forestry and Wildlife Sciences (SFWS) in Alabama actively works to increase awareness of the benefits of CLT along with hybrid systems for more widespread adoption in multiple building segments. AU’s two-year project proposal outlines a plan that will establish a preliminary design for the usage of a timber-steel composite system, utilizing CLT or laminated veneer lumber (LVL), as an option that will replace reinforced concrete slabs to improve the structural performance for buildings six stories or more.
Project contact is Kadir Sener at Auburn University (United States)
Summary
While the emphasis in the timber industry understandably focuses predominately
on complete mass timber structures, opportunities to substantially expand the mass timber
market exist using composite timber-steel systems. Timber-steel composite systems have a
high potential to be an economically, architecturally, and structurally feasible system to
expand the usage of timber panels for mid-rise and high-rise structures where mass timber is
currently not a feasible option. In this novel system, prefabricated timber panels replace
reinforced concrete slabs to provide the floor and diaphragm elements that work compositely
with steel beams and to improve the structural performance compared to either individual
material. Considerable testing effort outside the US has explored the feasibility and benefits
of these composite systems. This has led to implementation of this novel system on a number
of international construction projects. However, the topic has not been assimilated by
researchers and practitioners in the US. Hence, this proposal focuses on identifying and
removing barriers and providing design guidance on using steel-timber composite systems in
US construction. The proposal: (i) Engages a diverse body of stakeholders in an advisory panel
and workshop, (ii) Completes engineering-based testing and analysis to demonstrate
feasibility, (iii) Performs constructability studies (i.e., construction cost, speed, env. impact),
and (iv) Establishes preliminary design guidelines and approaches. The goal of the project will
be to demonstrate the performance and economy of a timber-steel composite system(s) and
establish preliminary design guidelines and approaches for target stakeholders. Ultimately,
the project will develop experimentally validated design-detailing configurations and
establish design specifications for new mass timber markets in multiple construction sectors.
Oregon is facing two distinct challenges. Wildfires have become larger and more destructive and wildfire season has become longer and more costly. Similarly, Oregon’s wood products sector faces decreasing supplies of available wood fiber.
This effort will demonstrate that forest resilience treatments on federal forests can make forests and communities safer from wildfire while simultaneously providing small-diameter fiber to serve the growing mass timber industry.
Planned actions:
1. Advance forest health and community wildfire resilience on three to four 70-acres project areas within the Willamette National Forest.
2. Partner with the Willamette National Forest to prepare supporting documentation necessary for NEPA determinations (including categorical exclusions and determinations under other environmental laws such as ESA and NHPA) by the applicable federal agencies.
3. Collaborate with the Willamette National Forest to plan, layout, and administer three to four Good Neighbor Authority (GNA) timber sales to provide additional wood fiber to the regional mass timber supply chain.
4. Provide restoration fiber to the regional supply on three to six approximately 70-acre areas.
5. Develop robust track and trace program to bring additional transparency and accountability to the restoration mass timber supply chain in partnership with Sustainable Northwest.
6. Develop multi-media communication and outreach efforts to raise public awareness of socio-economic and ecological benefits of building affordable mass timber housing from restoration fiber.
The objective of this research is to address a knowledge gap related to fire performance of midply shear walls. Testing has already been done to establish the structural performance of these assemblies. To ensure their safe implementation and their broad acceptance, this project will establish fire resistance ratings for midply shear walls. Fire tests will provide information for the development of design considerations for midply shear walls and confirm that they can achieve at least 1-hour fire-resistance ratings that are required for use in mid-rise buildings.
This research will support greater adoption of mid-rise residential and non-residential wood-frame construction and improve competition with similar buildings of noncombustible construction. This work will also support the development of the APA system report for midply walls, which will be a design guideline for using midply walls in North America.
Project contact is Nicole K. Knobloch (United States)
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.
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.
Project contact is Keri Ryan at University of Nevada, Reno (United States)
Summary
A landmark shake table test of a 10-story mass timber building will be conducted in late 2020. The test program, funded by other sources, will help accelerate the adoption of economically competitive tall timber buildings by validating the seismic performance of a resilient cross-laminated timber (CLT) rocking wall system. In this project, we leverage and extend the test program by including critical nonstructural components and systems (NCS). Including NCSs, which are most vulnerable to rocking induced deformations of the CLT core, allows investigation of the ramification of this emerging structural type on building resiliency. Quantifying interactions amongst vertically and horizontally spanning NCSs during earthquake shaking will allow designers to develop rational design strategies for future installation of such systems. The expected research outcomes are to expand knowledge of rocking wall system interactions with various NCS, identify NCS vulnerabilities in tall timber buildings, and develop solutions to address these vulnerabilities. Moreover, this effort will greatly increase visibility of the test program. The results of this research will be widely disseminated to timber design and NCS communities through conference presentations, online webinars, and distribution to publicly accessible research repositories.
In this paper, possibilities and challenges of novel robotic manufacturing processes for segmented timber shells are presented and evaluated. This is achieved by comparing two newly developed construction systems for segmented plate structures: one system consisting of cross-laminated timber elements that are connected with crossing screws, and one system consisting of light-weight, hollow components with finger joints as well as bolted connections. Segmented timber shells are introduced as an emerging structural typology transitioning from applied research to the building industry, enabled by new developments in computational design and digital fabrication methods. Although the two construction systems share their underlying segmentation strategy, they differ in their joint design approach and ensuing fabrication complexity. While the first construction system can be produced with conventional machining technology in the timber industry, the second system was developed in conjunction with innovative robotic manufacturing methods. In order to evaluate the relationships and trade-offs of fabrication complexity and performance, the two systems are compared on a range of metrics, including material use, environmental impact and costs.
Wood preservation is an important issue for agricultural buildings with timber structure. This is among others due to their halfway opened construction, high level of moisture release from livestock breeding or storing goods. However, regarding the possibly high moisture content in the building structure and the potential threat caused by wood-destroying organisms, there is still a substantial need for research. The latest results of the research work carried out by Technical University of Munich, in cooperation with the Bavarian State Research Center for Agriculture, show that, for the most agricultural buildings built from spruce, no preventative chemical wood preservation is necessary to ensure a durable construction.
