Mass timber products are rapidly growing in fascination and popularity across the North American construction market, in which wood products are tested for durability and resiliency according to standards set by the American Wood Protection Association. Presently, the American Wood Protection Association (AWPA) E1 Standard calls for a test sample size of 2.54cm x 2.54cm x 0.64cm, which may be too small to encompass the large spacing between the bond lines of CLT, a multilayered mass timber product composed of layers of kiln-dried lumber alternating in grain direction. The objective of this study was to evaluate the resistance of untreated CLT against subterranean termites (Reticulitermes spp.) found in the southeastern United States using two-sample choice testing and extend the AWPA E1-17 Standard to accommodate the larger building material. Choice-testing methods were evaluated over a 4-week period for mass loss, visual rating, mold formation, and termite mortality.

Sports have grown to be one of the largest industries in the United States and the world. Groups such as the National Football League, the Major League of Baseball, and the National Basketball Association, make billions of dollars every year.[1] Along with this growing popularity has come the development of some of the most incredible pieces of architecture, showing off power, strength, and elitism. Teams are constantly competing to give their fans the best experience possible, including the greatest stadiums in the country. However, these technological and architectural feats come with environmental costs. Stadiums that hold over 80,000[2] spectators and a couple of thousands of employees are typically made entirely of steel and concrete and are responsible for incredible amounts of carbon dioxide. Often, they are fully utilized for a short amount of it. After a team relocates or decides their current stadium is not good enough, they destroy it to build a new one. In a field that is more concerned with the spectacle, this architectural study explores how the design of athletic facilities can be more sustainable through the use of long-span mass timber structures. It explores the history of stadium design and the desire to create the next big thing. The author goes into detail exploring the use of mass timber in the field and presents how it not only can be sustainable but also a demonstration of the spectacle they desire. The design portion of this project will center around a new Indoor Track Facility for the University of Massachusetts. The structure will highlight the research from beginning to end, constructed from mass timber arches, beams, and columns. Sports have grown to be one of the largest industries in the United States and the world. Groups such as the National Football League, the Major League of Baseball, and the National Basketball Association, make billions of dollars every year.[1] Along with this growing popularity has come the development of some of the most incredible pieces of architecture, showing off power, strength, and elitism. Teams are constantly competing to give their fans the best experience possible, including the greatest stadiums in the country. However, these technological and architectural feats come with environmental costs. Stadiums that hold over 80,000[2] spectators and a couple of thousands of employees are typically made entirely of steel and concrete and are responsible for incredible amounts of carbon dioxide. Often, they are fully utilized for a short amount of it. After a team relocates or decides their current stadium is not good enough, they destroy it to build a new one. In a field that is more concerned with the spectacle, this architectural study explores how the design of athletic facilities can be more sustainable through the use of long-span mass timber structures. It explores the history of stadium design and the desire to create the next big thing. The author goes into detail exploring the use of mass timber in the field and presents how it not only can be sustainable but also a demonstration of the spectacle they desire. The design portion of this project will center around a new Indoor Track Facility for the University of Massachusetts. The structure will highlight the research from beginning to end, constructed from mass timber arches, beams, and columns. [1] Gough, “Total Revenue of All National Football League Teams from 2001 to 2020.” [2] Steinbach, “7 Ways Stadium Design Has Changed.”

Cross-laminated timbers (CLTs) are strong and lightweight structural building materials. CLTs are made from renewable wood resources and have significant economic potential as a new value-added product for the United States. However, market penetration has been obstructed by product affordability and lack of availability for use. Previous studies and projects have surveyed opinions of designers and contractors about the adoption of CLTs. No previous study was found that surveyed cost estimators, who serve the essential function of creating economic comparisons of alternative materials in commercial construction. CLTs are not included in these current cost estimation tools and software packages which may be limiting the potential use of CLT in construction. The purpose of this study was to discover if cost estimation is being used to make structural decisions potentially affecting the marketability of CLT use in construction and building design because of the ability to estimate CLTs adequately. Through the use of a survey, the re-designing of a building, and discussions with subject matter experts, this study examined the knowledge level of cross-laminated timbers of under-surveyed building construction professions and the relationship between cost estimation and structural material choices. Their responses are demonstrating the need for better cost estimation tools for cross-laminated timbers such as inclusion in the Construction Specifications Institute's classification systems in order for CLTs to become a more competitive product. The study concluded that cost estimation is important for CLT market development, because it is being used extensively in the construction industry. / Master of Science / Cross-laminated timbers (CLTs) are strong and lightweight structural building materials that also serve as a method of sequestering carbon rather than emitting carbon like more traditional construction materials. CLT construction is straightforward and quick to assemble, requiring minimal time and labor. CLTs are made from abundant and renewable wood resources and have significant economic potential as a job creator and as a new value-added product for the United States. However, market penetration has been obstructed by product affordability and lack of availability for use. Previous studies and projects have surveyed opinions of designers and contractors about CLT use. However, no previous study has been found that examined the opinions of cost estimators, who serve an essential function in providing economic comparisons of different construction systems for designers and building owners to select in the commercial construction area. CLTs are currently not included in these cost estimates, and this lack of information may be limiting the potential of this construction system. The purpose of this study was to discover if cost estimation is being used to make structural decisions potentially affecting the marketability of CLT use in construction and building design because of the ability to estimate CLTs adequately. Through the use of a survey and discussions with subject matter experts, this study examined the knowledge level of crosslaminated timbers of under-surveyed building construction professions and the relationship between cost estimation and structural material choices. They are demonstrating the need for better cost estimation tools for cross-laminated timbers such as inclusion in the Construction Specifications Institute’s classification systems in order for CLTs to become a more competitive product. Cost estimation is performed early in the design process before the structural material has been chosen. However, making cost estimates of CLT materials early in the design process is not a practical solution at this point due to the lack of cost data available. As an alternative solution, this project developed a design tool that is meant to accelerate the design process and allow companies to approach suppliers for quotes, which require mostly complete designs. While this is not a complete solution, if designs are made faster and more effortless, they should also be a more affordable investment for clients. 5 | Page Building construction professionals perceived CLT construction as too expensive, unavailable to the consumer, or unwanted by the client. It was found that the lack of data, due primarily to the material being new to the US construction industry, was a significant barrier to CLT cost estimation. The custom design of many previous CLT projects, due to the lack of CLT construction in the current building codes, limits the collection of standard CLT construction data. There is also an issue with the discrete sizes of CLT panels limiting their competitiveness. These barriers were identified in this study, and further research is needed to develop complete solutions.

The invention of mass timber products, including cross laminated timber (CLT), over the past two decades has made tall wood building possible. In CLT structures, angle brackets are commonly used in wall-to-floor connections to transfer the shear in seismic and wind loads. In reality, these connections could experience loads in various directions, as well as multi-directional forces. This research consists of two parts: an experimental study carried out in Part 1, followed by a numerical program completed in Part 2. The research aims to investigate the performance of wall-to-floor CLT angle bracket connections under various loading situations. In Part 1 of the research, a two-phase experimental program consisting of 12 monotonic tests in the first phase, and 24 monotonic and 24 cyclic tests in the second phase was conducted to investigate the behaviour of wall-to-floor CLT angle bracket connections. Connections were assembled using two different sizes of steel angle brackets and four types of fasteners, under uplift, in-plane shear, and out-of-plane shear loads. The performance of the connections was evaluated in terms of strength, stiffness, ductility, energy dissipation capacity, and failure modes. Results show that small diameter fasteners are more desirable for wood-to-wood angle bracket connections in terms of failure modes, load-bearing capacity and stiffness. Specimens exhibited considerable ductile performance under both uplift and in-plane shear loads due to combinations of yielding of brackets and yielding or pull-out of screws. Connections loaded under out-of-plane tension may fail in the splitting of CLT panels. Fully-threaded screws led to higher strength, stiffness and energy dissipation capacity but less ductility compared to partially-threaded screws in angle bracket connections. In Part 2 of the research, a two-phase numerical program was carried out to assess the coupling effect of biaxial loading on the performance of CLT wall-to-floor angle bracket connections. In Phase I, a 3D finite element model of connections was developed using ABAQUS software and verified with the data from experimental tests carried out in Part 1 of the research. In Phase II of the numerical program, the verified model was used to simulate the performance of connections under three biaxial loads, i.e., shear and in-plane uplift, shear and out-of-plane tension, and shear and out-of-plane compression. The coupling effect on the performance of the connections was evaluated in terms of strength, stiffness, ductility, and failure modes under biaxial loads, and compared with the scenario where the connection was only loaded in shear. Results show that the application of biaxial loading may considerably decrease the shear performance of the connections. Additionally, the results confirm the analytical equation suggested by the European Technical Assessment to predict the resistance of angle bracket connections under biaxial loads. / Graduate / 2022-08-04

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Recent interest in sustainable design has resulted in timber products being considered for a variety of construction projects. This has especially been the case for engineered wood products (EWPs), such as glue-laminated timber (glulam) and cross-laminated timber (CLT). Research into the performance of these massive timber products has been ongoing, where the methodology employed has generally favoured experimental approaches on undamaged members, combined with simplified analytical methods. Relatively little attention has been given to more sophisticated numerical methodologies and to the effects of repeated loadings on the same specimen. This study intends to contribute to the literature by investigating the viability of full-scale finite element models to simulate the behaviour of timber elements at high strain rates and proposing a generalized structure for dynamic models that is capable of adequately recreating realistic failure modes. Three glulam specimens and three CLT specimens were subjected to simulated blast loads under four-point bending with simply supported boundary conditions using the University of Ottawa Shock Tube Test Facility. The behaviour of the glulam specimens during the dynamic testing was consistently linear-elastic until flexural failure was reached. Conversely, the failure behaviour of CLT panels was more complex and included flexural failure, rolling shear failure, or a combined behaviour where both modes developed simultaneously. Single-degree-of-freedom (SDOF) and finite element analysis (FEA) methodologies were used to predict the behaviour in terms of displacement-time histories and failure modes. The inputs for the analytical methods relied on values sourced from literature or manufacturer data. A finite element (FE) material model was implemented into ABAQUS/Explicit through a dynamic user subroutine (VUMAT). The model used continuum damage mechanics to alter the material stiffness matrix once the elastic strengths were exceeded. SDOF analysis was shown to effectively predict the maximum mid-span displacement of glulam members subjected to blast loads, within a 20% error margin. However, the model was found to be incapable of consistently predicting the displacement and time of failure, especially for CLT panels, where up to 50% error was observed. This degree of error was attributed to the model’s inability to account for multiple failure modes, namely rolling shear and flexural failure. The resistance curves implemented in the SDOF models generally agreed with experimental results, particularly with regard to initial stiffness, and were deemed sufficiently accurate from the perspective of design. The finite element models simulated specimen ultimate behaviour reasonably well. Relatively accurate analytical predictions were also obtained for both maximum mid-span displacements and corresponding times. However, computational issues with damage transfer prevented the modeling of repeated tests on CLT panels. The FE model was capable of producing resistance-displacement relationships which correlated well to experimental results, despite the presence of numerical fluctuations. This is a significant outcome for the potential application of FEA to blast behaviour of timber components, since SDOF models require resistance curves as input and are unable to predict the force-displacement response of members.

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How can we as design professionals contribute to increase the use of less carbon-intensive materials to build our growing cities? Cities are experiencing a resurgence in population growth and therefore the building industry ought to attend this demand with sustainable solutions. One way of responding to the growing urban population and increase demand for housing as well as to make efficient use of our limited resources is to increase the density in our cities. Since steel and concrete have high material strengths, we currently use either steel, concrete or composites of them to build skyscrapers. Unfortunately, both of these materials have a large carbon footprint. The design community has the challenge to achieve net-zero emissions buildings by the year 2030, and the efforts now should be focused on using less carbon intensive materials, such as timber. While cultures around the world have built with wood for centuries, recent technological innovations, such as Cross Laminated Timber (CLT), is allowing for new applications of wood as the main structural material and the potential to use it for large-scale projects. However, as expected with a new building material some constrains have still to be overcome. For my thesis, I desired to explore this issue through the design of a tall building using mass timber as its main structural material. Engineered timber is here, the future is bright! / Master of Architecture / Urban population is growing faster than ever before and at the same time, we have started to suffer the scarcity of resources. One way of responding to the growing urban population as well as to make efficient use of our limited resources is to increase the density in our cities. We currently use either steel, concrete or composites of them to build skyscrapers. Unfortunately, both of these materials have a large carbon footprint. While cultures around the world have built with wood for centuries, recent advances in wood-based building materials and construction techniques have made it possible to use wood even in large-scale projects. However, as expected with a new building material some constrains have still to be overcome. For my thesis, I desired to explore these issues through the design of a tall building using timber as its main structural material.

This thirty-storey apartment tower in wood is an exploration of the potential of a prime building material grown by the sun. The building industry represents approximately one-third of greenhouse gas emissions worldwide. Since buildings are becoming more and more energy-efficient, the effects of the embodied energy in building structures become increasingly important. In this respect, wood structures embody a significantly lighter carbon footprint than steel and concrete and offer a viable approach for meeting the challenges of climate change. Typically the unique architectural qualities of wood have been reserved for low-rise typologies, but the performance characteristics of wood make it a competitive, eco-friendly alternative to steel and concrete in tall buildings. Wood in the form of mass timber panels is a durable and strong material. With increasing demand for housing in large sustainable buildings, wood should be an important structural material for the skylines of the future. / Det här trettio våningar höga typhuset i trä är en undersökning av potentialen för ett utmärkt byggmaterial som produceras av solen. Byggbranschen står för ungefär en tredjedel av världens utsläpp av växthusgaser. Eftersom dagens byggnader är alltmer energieffektiva blir effekterna av den inbyggda energin i byggnadskonstruktioner allt viktigare. I det sammanhanget ger träkonstruktioner upphov till betydligt lägre utsläpp av koldioxid än stål och betong och erbjuder därmed en framkomlig väg för att möta de utmaningar som klimatförändringen medför. Träets unika arkitektoniska kvalitéer har traditionellt varit hänvisade till låga byggnadstyper, men dess materialegenskaper gör det till ett konkurrenskraftigt och miljövänligt alternativ till stål och betong i höga hus. Trä i form av massivträskivor är ett hållbart och starkt material. Genom ökande efterfrågan på bostäder i stora hållbara byggnader torde trä bli ett viktigt konstruktionsmaterial för framtidens skylines.

This document will outline the findings of three separate and independent studies: Study 1: In or around 1972, an experimental building was constructed. One of the intents of the construction project was to demonstrate advancements in wood building construction design. It was value-engineered throughout. That is, its materials and systems were intended to function at or near design capacity. In 2019, part of the roof of the structure collapsed. This case study investigates two potential factors that led to the failure: stress concentration in excess of the 12 allowable stress for 2 × 4 web members and insufficient plywood sheathing to support live loads 13 caused by large rain events. Study 2: As a building material, cross laminated timber (CLT) has exponentially grown in popularity recently. Although performing superior to numerous other popular building materials, a consistent issue presented in wood construction is the effect of moisture on performance. This study looks to investigate the effect of moisture content on the performance of a 2-way dowel type fastener system loaded in shear perpendicular to the major strength axis. It was found that the peak load capacity of the specimens was not affected by the moisture content of the CLT. However, yield strength increased as the moisture content decreased. Lastly it was found that the failure mode changed from ductile to brittle as specimens became drier than 12% moisture content by mass. Study 3: Inherently, the weak point of any structure is the connection system. This phenomenon is particularly apparent in wooden structures as dowel type fasteners place tremendous amounts of stress perpendicular to the grain of the wood, as well as shear stress under the bolt. In hopes of mitigating this behavior, fiberglass reinforcement of these samples is examined to see if both failure mode as well as overall performance of these fasteners could be improved with reinforcement. It was found that fiberglass significantly reduced the standard deviation of failure strength of fasteners, significantly increased the overall strength of the fasteners, increased the efficiency of the fasteners, and finally increased the probability of bearing failure opposed to block shear failure.