This research aims to develop a new bridge inspection approach using unmanned aerial vehicle (UAV) coupled with digital image correlation (DIC) system. The DIC system incorporating UAV images can measure displacements or strains by analyzing patterns of reference and deformed images. As part of this research, a commercially available UAV, DJI Matrice 210, was integrated with the DIC system using a 3D printed mounting plate, and the joint UAV-DIC system was utilized to inspect a timber bridge girder in the Structure Lab. Then, the UAV-DIC system inspected an existing timber slab bridge in Pipestone, Minnesota, but the system was not able to efficiently identify critical damage due to its instability caused by windy conditions. Therefore, only the UAV equipped with a gimbal camera was operated to perform the bridge inspection. A significant number of images from the UAV were used and analyzed through a conventional image analysis algorithm within ImageJ software for damage quantification. The major conclusion from this research was that the UAV-DIC system was only able to detect and quantify damage (i.e., crack) on the considered girder under almost zero ambient wind conditions, and the UAV integrated with the image analysis algorithm was capable of damage identification and quantification for the inspected bridge.
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.
Cross-laminated timber (CLT) is a type of mass timber panel used in floor, wall, and roof assemblies. An important consideration in design and construction of timber buildings is moisture durability. This study characterized the hygrothermal performance of CLT panels with laboratory measurements at multiple scales, field measurements, and modeling. The CLT panels consisted of five layers, four with spruce-pine-fir lumber and one with Douglas-fir lumber. Laboratory characterization involved measurements on small specimens that included material from only one or two layers and large specimens that included all five layers of the CLT panel. Water absorption was measured with panel specimens partially immersed in water, and a new method was developed where panels were exposed to ponded water on the top surface. This configuration gave a higher rate of water uptake than the partial immersion test. The rate of drying was much slower when the wetted surface was covered with an impermeable membrane. Measured hygrothermal properties were implemented in a one-dimensional transient hygrothermal model. Simulation of water uptake indicated that vapor diffusion had a significant contribution in parallel with liquid transport. A simple approximation for liquid transport coefficients, with identical coefficients for suction and redistribution, was adequate for simulating panel-scale wetting and drying. Finally, hygrothermal simulation of a CLT roof assembly that had been monitored in a companion field study showed agreement in most cases within the sensor uncertainty. Although the hygrothermal properties are particular to the wood species and CLT panels investigated here, the modeling approach is broadly applicable.
Project contact is Shiling Pei at the Colorado School of Mines
Nail and Dowel Laminated Timber (NLT and DLT) are efficient technologies to build mass timber floor systems directly out of dimension lumber. It is relatively inexpensive to construct and has substantial potential to help expand the mass timber building market, particularly when the floor spans mainly in one direction. There have been multiple NLT projects constructed in the seismic region, which represents a large portion of the CLT construction market. The lateral design of NLT/DLT floor systems is currently based on very conservative assumptions (essentially equating its performance to a traditional joist-sheathing light-frame wood floor system) due to this lack of validated performance examples. This project will systematically demonstrate the potential of NLT/DLT floor systems under extreme lateral loads through component level testing and full-scale building level shake table tests. Through collaboration with manufacturers and designers (StructureCraft and Magnusson Klemencic Associates (MKA)), several full-sized NLT/DLT floor will be tested to failure in the structural engineering laboratory at Colorado State University. Based on component level test results, 2 or 3 floors of NLT/DLT diaphragms will be incorporated into a (planned) full-scale 10-story full-scale mass timber building that will be tested on the world’s largest outdoor shake table for demonstration and education/outreach.
Project contact is Paulo Tabares at the Colorado School of Mines
Cross Laminated Timber (CLT) is a mass timber material that has the potential to expand the wood building market in the U.S. However, new sustainable building technologies need extensive field and numerical validation quantifying environmental and economic benefits of using CLT as a sustainable building material so it can be broadly adopted in the building community. These benefits will also be projected nationwide across the United States once state-of-the-art software is validated and will include showcasing and documenting synergies between multiple technologies in the building envelope and heating, ventilation and air conditioning (HVAC) systems. However, there are no such studies for CLT. The objective of this project is to quantify and showcase environmental and economic benefits of CLT as a sustainable building material in actual (and simulated) commercial buildings across the entire United States by doing: (1) on-site monitoring of at least four CLT buildings, (2) whole building energy model validation, (3) optimization of the performance and design for CLT buildings and (4) comparison with traditional building envelopes. This knowledge gap needs to be filled to position CLT on competitive grounds with steel and concrete and is the motivation for this study.
Project contact is Jacob Mans at the University of Minnesota
As the acceptance of cross-laminated timber (CLT) grows among commercial and institutional clients, the hospitality industry, in general, has been hesitant to adopt CLT. This reluctance is linked to several real and perceived factors. One, the industry has fire safety and fire rating concerns with the construction system; these concerns have been largely addressed through independent research and building code updates. Two, the industry is concerned with the acoustic rating of standard CLT panels, which do not currently meet the elevated performance standards of the hospitality industry – specifically the sound transmission class (STC) rating -- and will require additional design research. Three, the industry is concerned with the aesthetics of the system and the dual challenges of exposing wood and simultaneously integrating Mechanical Electrical and Plumbing (MEP) systems. Image, brand identity, and indoor air quality are all key variables that factor into whether this rapidly-growing industry adopts CLT as a viable system for hotel construction. There is an opportunity to reframe these individual challenges as a collection of assets in order to provide a holistic solution that can will demonstrate the feasibility of CLT within the hospitality industry.
This grant will address these barriers and to facilitate the increased utilization of CLT within the hospitality industry. Such utilization has the potential to divert a substantial amount of fuel from federal forest and timber lands and to sequester its embedded carbon in buildings. Market analysis estimates that 715 hotels of 8 floors or lower (the target size for this project) will be built in the United States in 2020. If constructed out of CLT, this market represents approximately 94 million board feet of potential wood utilization through CLT per year (over 1 million metric tons of sequestered CO2). The opportunity to capture a fragment of this market warrants feasibility research to prove the viability of CLT for the hospitality industry.
The University of Minnesota and DLR Group will work with CLT manufactures and established hospitality partners to construct a modular hotel room prototype that can test acoustical and MEP systems integration strategies – as well as spark future research projects. This experimental apparatus will also double as a show unit to educate possible users and developers of the potential for a mass timber hotel. In addition to developing, constructing, and testing the prototype, the team will develop informational materials and a detailed cost analysis of the project that will encourage hospitality partners to implement these ideas with confidence.
The building sector is increasingly identified as being energy and carbon intensive. Although the majority of emissions are linked to energy usage during the operation part of a building's life cycle, choice of construction materials could play a significant role in reducing greenhouse gas emissions and other environmental end-point damages. Increasing the use of wood products in buildings may contribute to the solution, but their environmental impacts are difficult to assess and quantify because they depend on a variety of uncertain parameters. The present cradle-to-gate life-cycle analysis (LCA) focuses exclusively on a glued-laminated wood product (glulam) produced from North American boreal forests located in the province of Quebec, Canada. This study uses primary data to quantify the environmental impacts of all necessary stages of products' life cycle, from harvesting the primary resources, to manufacturing the transformed product into glulam. The functional unit is 1 m3 of glulam. This is the first study based on primary data pertaining to Quebec's boreal forest. Quebec's boreal glulam manufacturing was compared with two other LCAs on glulam in Europe and the United States. Our results show that Quebec's glulam has a significantly smaller environmental footprint than what is reported in the literature. From an LCA perspective, there is a significant advantage to producing glulam in Quebec, compared with the European and American contexts. The same holds true in regard to the four end-point damage categories.
Project contact is Shiling Pei at the Colorado School of Mines
NHERI Tallwood project is an effort to develop and validate a resilient-based seismic design methodology for tall wood buildings. The project started in September 2016 and will last till 2020. The project team will validate the design methodology through shake table testing of a 10-story full-scaled wood building specimen at NHERI@UCSD. It will be the world's largest wood building tested at full-scale.
Project contacts are James Wacker at the Forest Products Laboratory, Justin Dahlberg and Brent Phares at Iowa State University
The use of cross-laminated timber (CLT) has gained popularity over the past decade, with many advances stemming from completed research and construction projects in Europe. Many inherent advantages of CLT (such as, it is prefabricated, relatively lightweight, dimensionally stable, and environmentally sustainable) have been utilized in vertical construction projects. Despite these advances, the use of CLT in bridge structures has been limited, and the adoption of CLT into governing design codes has been slow. However, CLT shows promise as a complementary or alternative construction material in bridge decks, and additional research would help characterize the structural attributes of CLT decks to guide their use in bridge projects.
Project contacts are Frederico França at Mississippi State University and Robert J. Ross at the Forest Products Laboratory
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.
Project contacts are Robert J. Ross at the Forest Products Laboratory and Rubin Shmulsky at Mississippi State University
Notches, particularly when incorporated on the tensile face, influence the ultimate capacity of members, such as beams and floor panels. Understanding and quantification of failure modes, ductility, and strength of notched CLT floor panels can allow the safe application of notches on building construction. Despite wood’s ductility, notches are known areas of stress concentration. The 2018 International Residential Code for one- and two-family dwellings (International Code Council 2017) restricts the use of notches on engineered wood products by requiring structural calculations instead of elucidating the ways notches might be used. To employ CLT to its maximum potential, there is a current and pressing need for better knowledge regarding the influence of notches on flexural performance.
This research seeks to review the literature regarding notches in solid and engineered beams, review typical CLT design details that employ or utilized notched panels, and conduct pilot-scale testing of notched CLT panels.
Project contact is Jianhui Zhou at the University of Northern British Columbia
The impact sound perceived in the lower volume in a building is radiated by the vibration of the ceiling transmitted from the vibration of the floor generated by an impact source in the upper volume. Thus, the dynamic behaviour of a floor is one crucial intermediate step to understand the impact sound insulation performance of such a floor. A key to reducing the impact sound is to isolate the structural floor from the subfloor. Floating floor construction is a common way of improving the impact sound insulation, which is to float a concrete topping on the mass timber floor with an elastic layer in between. There are two types of floating floor solutions, a) with a continuous elastic layer and b) with point bearing elastic mounts as shown in Figure 1. This study will investigate both solutions and will provide guidance on how to adopt both solutions for mass timber floors with an exposed ceiling.
The objectives of this project are:
1. To measure the sound insulation performance of mass timber floors with full-scale concrete topping on various continuous elastic interlayer materials
2. To measure the sound insulation performance of mass timber floors with full-scale concrete topping on discrete elastic load mounts
Project contact is Frank Lam at the University of British Columbia
The objective of this project is to develop a large span timber-based composite floor system for the construction of highrise office buildings. This prefabricated floor system could span over 10 m under regular office occupation load, and its use will expedite the construction significantly, converting to multi-million financial savings in a typical 40+ story project, besides the impact on reducing carbon footprint and enhancing living experience.
Project contact is Cristiano Loss at the University of British Columbia
This research aims at developing novel multi-material deconstructable hybrid connections for mass timber prefabricated buildings. Connections will be conceived in order to (i) meet multi-objective structural performance, (ii) favour modular construction, (iii) favour quick erection of buildings, (iv) quick disassemble and possible reuse of the timber members, and (v) provide seismic-resistant structural assemblies.
Project contact is Angelique Pilon at the University of British Columbia
The pilot uses whole-building life cycle assessments (WBLCA) to identify major contributors to embodied carbon impacts. More importantly, the project conducts a critical analysis of the procedural requirements, information gaps, systemic barriers and other challenges for project teams seeking to use LCA as an effective tool in reducing their environmental impacts. The second phase of the Embodied Carbon Pilot project builds on the experiences and learning of Phase 1 while addressing a more common and replicable building typology. The first year, we used mass timber buildings at the University of British Columbia for the pilot LCAs and developed a protocol/strategy for adapting project information into the appropriate bill-of-materials (BOM) format for input into LCA tools, while identifying procedural challenges and barriers and variations of different material take-off methodologies and LCA tools. This second year, we will target mid-rise, multi-unit residential buildings (MURBs), a common and growing building type throughout British Columbia. Mid-rise MURBS are between 4 and 8 stories and typically use wood as one of the primary construction materials: stick-frame construction for projects under 6-stories or an increasing number of mass timber projects.
Project contact is Jianhui Zhou at the University of Northern British Columbia
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.
International Network on Timber Engineering Research
Buckling Restrained Brace Frames (BRBF) are a proven and reliable method to provide an efficient lateral force resisting system for new and existing structures in earthquake prone regions. The fuse-type elements in this system facilitate stable energy dissipation at large load deformation levels. Currently, the new trend towards mass timber vertical structures creates a need for a lightweight compatible lateral force resisting system. A Buckling Restrained Brace (BRB) component is possible to construct and feasible to implement when combining a steel core with a mass timber casing herein named the Timber-Buckling Restrained Brace (T-BRB). T-BRBs when combined with mass timber beam and column elements can create a system that will have advantages over the current steel framed BRBF system when considering recyclability, sustainability, framing compatibility, and performance. This paper presents findings on small scale testing of candidate engineered wood products for the T-BRB casing and testing of six full scale 12 ft long 60 kip braces according to code prescribed loading protocols and acceptance criteria.
Katerra has developed its own cross-laminated timber (CLT) manufacturing facility in Spokane Valley, Washington. This 25,100 m2 (270,000 ft2 ) factory is the largest CLT manufacturing facility in the world, and is capable of producing approximately 187,000 m3 of CLT per year. Katerra has also established a vertically integrated supply chain to provide the wood for the CLT factory. Production started in summer of 2019.
Katerra commissioned the Carbon Leadership Forum (CLF) and Center for International Trade in Forest Products (CINTRAFOR) at the University of Washington to analyze the environmental impacts of its CLT as well as the Catalyst Building in Spokane, Washington. The Catalyst is a 15,690 m2 (168,800 ft2), five-story office building that makes extensive use of CLT as a structural and design element. Jointly developed by Avista and McKinstry, Katerra largely designed and constructed the building, and used CLT produced by Katerra’s new factory. Performing a life cycle assessment (LCA) on Katerra’s CLT will allow Katerra to explore opportunities for environmental impact reduction along their supply chain and improve their CLT production efficiency. Performing an LCA on the Catalyst Building will enable Katerra to better understand life cycle environmental impacts of mass timber buildings and identify opportunities to optimize environmental performance of mid-rise CLT structures.
The goal, scope, methodology, and results of this analysis are detailed in this report.