Softwood is more in demand than hardwood because it is used primarily in the US's largest wood-consuming industry, construction, resulting in increased importation of softwood annually to meet this demand. Hardwood, used for non-structural purposes like furniture and interior designs, is more abundant in US forests. However, some hardwood species are underutilized and undervalued. Cross-laminated timber (CLT) has increased the demand for softwood. A study evaluated the mechanical and physical properties of three underutilized hardwood species (321 yellow poplar, 393 sweetgum, and 262 red oak specimens) for CLT industrial mat manufacturing. The results showed that red oak had a higher density than southern yellow pine, and all species had an average modulus of elasticity greater than the CLT lumber requirement. The study confirmed the viability of these underutilized hardwoods for CLT fabrication, suggesting they could be a suitable substitute for softwood in CLT manufacturing.

Knots are usually regarded as defects when grading lumber. In order to evaluate a member under out-of-plane loading, shear strength is one of the major mechanical properties, specifically, rolling shear (RS) strength is one of the critical mechanical properties of Cross-Laminated Timber (CLT), which determines the flexural strength of CLT under short-span bending loads. Lower grade lumber with a higher percentage of knots is recommended to be utilized for the cross-layer laminations which are mainly responsible for resisting shear stresses. Firstly, shear tests were performed in order to evaluate the effect of knots on longitudinal shear strength using shear blocks. After that, the effect of knots on the RS strength of 3-ply southern yellow pine CLT were investigated by experimental tests and an analytical model. Center-point bending tests with a span-to-depth ratio of 6 and two-plate shear tests with a loading angle of 14° were conducted on six CLT configurations composed of different types of cross layer laminations: clear flatsawn lumber with/without pith, lumber with sound knots with/without pith, and lumber with decayed knots with/without pith. The shear analogy method was implemented to evaluate the RS strength values from the bending test results, which were also compared against the results from the two-plate shear tests. It was found that: (1) The shear blocks containing sound knots had higher shear strength than matched clear shear blocks, the shear blocks containing unsound knots had lower shear strength than the matched clear shear blocks. (2) CLT specimens with cross-layer laminations with either sound knots or decayed knots had higher RS strength. (3) In general, the shear analogy method underestimated the RS strength of CLT specimens containing knots and pith.

I dagens samhälle ligger fokus på hållbarhet vilket ställer höga krav på konstruktören vid utformningav stommen till flerbostadshus. En stor del av CO2-utsläppen inom byggprocessen kan härledas tillmaterialvalet där förbränning av kalk inom cementindustrin och framställning av stål ur järnmalm ärbland de främsta faktorerna till utsläppen. Denna rapport ämnar sig åt att ta fram vilka skillnader och likheter som ställs mellan två stomsystemmed olika bjälklag; ett utförande i korslimmat trä, hädanefter benämnt KL-trä, och ett utförande ihåldäcksbjälklag. De båda objekten har givits identiska förutsättningar, med reservation förbjälklagsmaterial, med en stomme i stål med varierande tvärsnittsprofiler. Data för CO2-ekvivalenter och pris av respektive stommaterial har undersökts och sammanställts itabellform där de två byggnaderna utvärderas och där resultatet diskuteras i analysdelen. Resultatetger svar på vilket element som presterar bäst till en kontorsbyggnad med två våningar med hänsyn tillkostnad och CO2-ekvivalenter för enskilda profiler sammanställts för de två byggnaderna. Dimensionering av balkar har genomförts med avseende på momentkapacitet, pelare med avseende påknäckning av centrisk tryckkraft, plan böjknäckning med moment av vindlast och normalkraft motpelare. Till visualisering av stommen har Tekla Structures använts och för verifiering avlastnedräkningar har FEM-Design 20 nyttjats. Rapportens ekonomidel avser kostnader av de två byggnaderna, vilka redovisats i tabellform medkostnad per stål- och bjälklagsprofil. Klumpsumma för respektive fall har sammanställts och idiskussionsdelen till denna rapport ges förklaringar och slutsatser. / In society today, the focus is on sustainability, which places high demands on the designer when designing the structural frame for apartment buildings. A large part of the CO2 emissions in the construction process can be traced to the choice of material, where the combustion of lime in the cement industry and the production of steel from iron ore are among the main factors for the emissions. This report intends to provide answers to the differences and similarities between two frame systems with different floors slabs; a version in cross-laminated wood, hereinafter referred to as KL-trä (CLTwood), and a version in hollow core slabs. The two objects have been given identical conditions, with a reservation for flooring material, with a steel frame with varying cross-sectional profiles. Data for CO2 equivalents and price of each frame material have been examined and compiled in tabular form where the two buildings are evaluated and results are discussed in the analysis part. The result provides an answer as to which element performs best for an office building with two floors with regard to cost and CO2 equivalents for individual profiles compiled for the two buildings. Dimensioning of beams has been carried out with regard to bending moment capacity, columns with respect to buckling of concentric pressure force and flat bending buckling with elements of wind load and normal force against columns. Tekla Structures has been used to visualize the frame and FEM-Design20 has been used to verify load counts. The financial part of the report refers to costs of the two buildings, which are reported in tabular form with cost per steel and floor profile. The lump sum for each case has been compiled and in the discussion section of this report explanations and conclusions are given to the financial part.

Wood has been utilized by humans for thousands of years in the construction of our built environment. More recently, our expanded understanding of the material and the advancement of engineered wood have allowed us to use wood like never before. Concrete and steel, however, have emerged as the main materials used in large scale construction in the late 19th and 20th Centuries. As we are battling and searching for solutions to climate change, the importance of wood in large scale construction has increased as not only is its carbon intensity is lower than steel and concrete, but its existence stems from sequestered carbon. Yet as timber finds its way into large-scale projects, the forms it takes resemble those of concrete construction. Although this form is functional, it does not take full advantage of its capabilities or mitigate the weaknesses of wood. This thesis is concerned with exploring new options for mass timber, finding forms more appropriate to wood’s mechanical and aesthetic properties. Research began with precedent studies of existing mass timber structures to see which strategies would be useful in the project. Next a theoretical project was undertaken to design an 18-story timber-based high rise in Denver, Colorado. The design uses a variety of Engineered Wood Products (EWP) in the most effective and efficient way. The findings of this study have shown that wood, being an isotropic material, prefers to have forces run parallel to its grain. Combining multiple types of engineered wood arranged to create forces traveling parallel to their fiber grain direction created a system that was efficient, strong, and architecturally effective. The design also works to avoid subjecting wood to forces perpendicular to its wood grain, thus avoiding its weaknesses. Finally, the design uses common, stock, engineered lumber products to make the project more economical. It produced a high rise design that serves as a highly desirable model for future projects across the United States and world. This technology will not be limited to high rises and can be used in a plethora of large-scale building types. Broader implementation of this technology will help to decrease our species’ carbon footprint as our population expands and builds. More material efficient structural solutions will encourage wider spread implementation and their aesthetic qualities will increase their desirability by private and government investors alike.

The building construction industry has seen the emergence of Cross Laminated Timber (CLT) as a renewable replacement for structural application of steel, concrete, and masonry. However, CLT has not been researched extensively as a nonstructural component of the building envelope/facade. In the presented research, the application of CLT is introduced in the form of lightweight CLT (CLT-L) panels and presents a framework to evaluate the opportunities and application of CLT-L panels as an alternative construction method for non-load-bearing exterior wall systems. Since exterior walls as part of the enclosure system have a significant role in energy consumption and human comfort level, the research evaluates application opportunities of the CLT panels for US climates, by conducting a life cycle environmental analysis, and a thermal evaluation of CLT-L systems for Phoenix, Arizona, and Minneapolis, Minnesota. The life cycle analysis was conducted to assess the environmental impact of a typical CLT wall system as compared to three conventional panelized wall systems. The results of the analysis have shown that CLT wall systems exhibit the lowest cumulative life cycle environmental impact indicators, including acidification potential, fossil fuel consumption, global warming potential, and human health particulate when compared to other wall systems. These results suggest that CLT wall systems could be a viable alternative to conventional panelized exterior wall systems from an environmental impact perspective. In the next step, a parametric study was conducted to determine the optimal configuration of a CLT-L wall system for enhanced thermal performance. This was achieved through dynamic thermal simulations by employing the conduction transfer algorithm and analyzing various thicknesses and locations of the thermal insulation layer. Through analysis of the annual thermal transmission load and decrement factor, the optimum insulation thicknesses for CLT wall systems in two climate regions were determined. The results showed that the exterior insulation location yields better thermal efficiency. The results of this phase were employed in the development of the CLT wall system model and conduction of a comparative parametric study on the thermal mass behavior of CLT and CMU wall systems via finite difference algorithm. One significant outcome of the simulation data analysis was the heat transfer dynamics within the CLT and CMU wall system when exterior insulation is applied. The analysis revealed that in the presence of exterior insulation, the CLT layer continues to be the primary contributor to the reduced thermal transmission of the wall. However, in the CMU mass wall configuration, the insulation layer assumes a dominant role in the reduced thermal transmission of the wall. The findings of this research present CLT as a potential environmentally efficient envelope alternative for framed buildings and provide insights into the thermal performance of CLT wall systems, which can lead to the opening of a new market for CLT panel application in the U.S. / Doctor of Philosophy / The construction industry has witnessed a notable shift with the advent of Cross Laminated Timber (CLT), presenting itself as a renewable substitute for conventional materials like steel, concrete, and masonry in structural applications. However, the potential of CLT as a building component, particularly as a component of building exteriors wall, remains relatively underexplored. This research endeavors to fill this gap by introducing lightweight CLT (CLT-L) panels, which are three-layer CLT panels, and exploring their viability as an alternative construction method for non-load-bearing exterior wall systems. Non-load bearing exterior wall panels do not carry any structural support for the building. Recognizing the significant influence of exterior walls on both energy consumption and human comfort levels, the study assesses the applicability of CLT panels across diverse climates in the United States including states Minnesota and Arizona which show exterior temperature swings. The investigation began by conducting a comprehensive life cycle environmental analysis, comparing the environmental impact of a typical CLT wall system with three conventional panelized wall systems. Results revealed that CLT wall systems exhibit the lowest cumulative life cycle environmental impact indicators suggesting their potential as a sustainable alternative. The environmental indicators included acidification potential, fossil fuel consumption, global warming potential, and human health particulates. Subsequently, a parametric study delved into optimizing the thermal performance of CLT-L wall systems through dynamic thermal simulations. The dynamic simulation considered the exterior temperature changes during the day. By varying insulation thicknesses and locations, the study identifies optimal configurations for different climate regions. Notably, the analysis underscores the efficacy of exterior insulation placement in enhancing thermal efficiency. Furthermore, the study investigated the thermal mass behavior of CLT compared to concrete block (CMU) wall systems under different scenarios. Findings revealed that while CLT retains its significance as a primary contributor to thermal mass, particularly with exterior insulation, CMU configurations see a shift in thermal mass dynamics towards the insulation layer. These findings collectively underscored the potential of CLT as an environmentally efficient envelope alternative for framed buildings, shedding light on its thermal performance and paving the way for broader adoption in the US construction industry.

Cross-Laminated Timber (CLT) is an engineered wood product made by laminating dimensional or structural composite lumber in alternating orthogonal layers. Compared to Canada and Europe, CLT is a novel product to the US. With the additions included in the 2021 International Building Code (IBC), CLT material properties, especially rolling shear, would need to be explored. The increasing demand for softwood lumber, along with the increase of demand of CLT panel production, could place a burden and surpass the domestic softwood supply. Rolling shear is a phenomenon that occurs when the wood fibers in the cross-layers roll over each other because of the shearing forces acting upon a CLT panel when it is loaded out-of-plane. This study used the two-plate shear test from ASTM D2718 to measure the rolling shear properties of various southeastern US wood species: southern pine, yellow-poplar, and soft maple. A secondary study was conducted, using the same two-plate shear test, to measure the rolling shear properties of re-manufactured southern pine for CLT cross-layer application. The soft maple had the greatest average rolling shear strength at 5.93 N/mm2 and southern pine had the lowest average rolling shear strength at 2.51 N/mm2. Using a single factor analysis of variance (ANOVA), the rolling shear strength values from soft maple were significantly greater than yellow-poplar, which was significantly greater than the southern pine. For the rolling shear modulus, the southern pine and soft maple were of equal statistically significant difference, and both were greater statistically significant different compared to the yellow-poplar. The most common failure found from testing was rolling shear. / Master of Science / Cross-Laminated Timber (CLT) is an engineered wood panel product, similar to plywood, constructed with solid-sawn or structural composite lumber in alternating perpendicular layers. The additions included in the incoming 2021 International Building Code (IBC) has placed an importance in expanding the research related to the mechanical and material properties of CLT. Also, with the increasing demand for softwood lumber and CLT panel production, the demand for the domestic softwood lumber could place a burden and surpass the domestic softwood supply. Rolling shear is a failure type that occurs when the wood fibers in the cross-layers roll over each other because of the shearing forces acting upon a CLT panel. This study used the two-plate shear test to measure the rolling shear properties of various southeastern US wood species: southern pine, yellow-poplar, and soft maple. A secondary study was conducted, using the same two-plate shear test, to measure the rolling shear properties of re-manufactured southern pine for CLT cross-layer application. The soft maple had the greatest average rolling shear strength at 5.93 N/mm2 and southern pine had the lowest average rolling shear strength at 2.51 N/mm2. Using a single factor analysis of variance (ANOVA), the rolling shear strength values from soft maple were significantly greater than yellow-poplar, which was significantly greater than the southern pine. For the rolling shear modulus, the southern pine and soft maple were of equal statistically significant difference, and both were greater statistically significant different compared to the yellow-poplar. The most common failure found from testing was rolling shear.

Ce mémoire de thèse aborde le problème du flambement de murs en bois lamellé-croisé. Ces panneaux de bois, constitués de planches collées perpendiculairement, sont de plus en plus utilisés dans la construction. La tendance actuelle du marché est de concevoir des immeubles de grande hauteur, ce qui soulève la question de la résistance en compression de ces murs. Il s'avère que le bois est fortement anisotrope. En particulier, la raideur et la résistance en cisaillement perpendiculaire aux fibres, également appelé cisaillement roulant, sont beaucoup plus faibles que dans la direction parallèle aux fibres. Ce fort contraste nécessite un critère de conception plus élaboré que les outils classiques utilisés dans l'ingénierie du bois. Ce travail est organisé en deux parties. Dans la première partie, la raideur équivalente de cisaillement transverse d'un panneau de bois lamellé-croisé est étudiée. Des bornes sont établies par une approche théorique. Ces bornes sont validées par un nouveau dispositif expérimental qui permet la mesure de la raideur en cisaillement roulant avec une variabilité plus faible que le test textit{single-lap} classiquement utilisé. Dans la deuxième partie, ces données sont utilisées dans l'analyse du flambement de panneaux en bois lamellé-croisé en raffinant progressivement le problème. Dans un premier temps, la charge critique de flambement linéaire d'une plaque épaisse sans imperfections est établie. Cette charge critique est basée sur une nouvelle théorie de plaque d'ordre supérieur et montre que la charge critique de flambement basée sur une théorie de plaque mince (Kirchhoff-Love) ne peut pas estimer correctement la résistance de murs en bois lamellé-croisé. Dans un second temps, l'influence des imperfections est étudiée en adaptant l'approche classique de Ayrton et Perry à une poutre de Timoshenko. Cette extension a révélé qu'un nouveau critère de résistance doit être satisfait lors du flambement qui est spécifique aux murs en bois lamellé-croisé. Dans un dernier temps, cette analyse est étendue aux charges permanentes en supposant une loi de fluage simple qui conduit à un nouveau critère de conception simple qui pourrait facilement être adopté dans les codes de conception actuels / This PhD thesis addresses the issue of CLT wall buckling. These wooden panels, made of boards which are glued cross-wise, are more and more used in construction. The current trend of the market is to design high-rise buildings which raises the issue of the compressive strength of such walls. It turns out that wood is a highly anisotropic material. Especially, the shear stiffness and strength perpendicular to the grain (rolling shear) are much weaker than in the direction parallel to the grain. This high contrast requires more elaborate design criteria than classical tools used in timber engineering. This work is organized in two main parts. First, the equivalent rolling-shear behavior of a CLT layer is investigated. Bounds are established for the stiffness of an equivalent layer using a theoretical approach. These bounds are validated by means of a new experimental set-up which allows the measurement of the rolling shear stiffness with less variability than the classical single lap shear test. In the second part, this data is used in the buckling analysis of CLT walls with increasing refinements. First, the linear buckling load of a thick plate without imperfection is established. This load is based on a new higher-order plate theory and reveals that the critical load based on a thin plate theory (Kirchhoff-Love) cannot predict correctly the strength of CLT walls. Then, the influence of imperfections is introduced adapting the classical approach from Ayrton and Perry to the case of a Timoshenko beam. This extension reveals that a new design criterion has to be satisfied under buckling which is specific to CLT. Finally, this analysis is extended to long term loads assuming a simple creep law and leading to a new simple design criterion which may be easily introduced in current design codes

This doctoral thesis addresses questions of how wind loads acting on multistoreytimber buildings can be dealt with by structural design of such buildings.The conventional use of sheathing either nailed or screwed to a timberframework is considered, together with other stabilizing structures such ascross-laminated timber panels.The finite element method was employed in simulating the structuralbehaviour of stabilizing wall units. A series of studies was carried out of walls inwhich the sheathing was nailed to a timber frame. Different structural levelswere studied starting with modelling the performance of single sheathing-toframingconnections, to the use of models for studying the overall structuralbehaviour of walls. The results of calculations using models for simulation ofwalls subjected to different loading agree reasonably well with experimentalresults. The structural properties of the connections between the sheathing andthe frame, as well as of the connections between the members of the frame,were shown to have a substantial effect on the simulated behaviour of shearwall units. Both these types of connections were studied and described inappended papers.Regarding cross-laminated timber wall panels, it was concluded that walls witha high level of both stiffness and strength can be produced by the use of suchpanels, and also that the connections between the solid wall panels can bedesigned in such a way that the shear forces involved are transmitted from onepanel to the next in an efficient manner.Other topics in the thesis include the properties of connections between shearwalls and the rest of the building. Typically high tension forces occur at specificpoints in a timber structure. These forces need to be transmitted downwards inthe structure, ultimately connecting them to the substrate. A lap-joint that maybe used for this purpose has been studied using generalized Volkersen theory.Finally the maximum capacity of a conventional rail to substrate connection hasbeen examined using linear and nonlinear fracture mechanics.

Engineered wood products (EWP) are becoming extremely popular and a viable material option for the construction of residential, commercial, and hybrid buildings. Cross-laminated timber (CLT) is among one of the many EWP available in North America, which can be utilized for many different applications such as: walls, floors, and roofs. Despite the available requirements in the Canadian blast design standard (CSA, 2012) with regard to the design of wood structures, there are currently no provisions on how to retrofit timber structures to improve their performance when subjected to blast loads. The current study is aimed at investigating the effect of different retrofitting alternatives in order to improve the overall behaviour of CLT when exposed to out-of-plane bending. The experimental program examined the behaviour of seventeen reinforced CLT slabs. Testing was conducted at the University of Ottawa by means of a shock tube capable of simulating high strain rates similar to those experienced during a blast event. The current study was divided into two phases. The first consisted of CLT slabs retrofitted with steel straps where strap spacing, location, and order of installation was investigated. The second phase focused on the development of dynamic properties of CLT panels when reinforced with GFRP. Lay-up configuration and fabric orientation were among the parameters explored. The results from the experimental program show that reinforcing the panels with steel straps had minimal effect on the ultimate strength, but significant levels of post peak resistance and ductility was achieved. The horizontal straps were able to restrict the failure to small regions and to promote flexural failure by preventing rolling shear failure. It also eliminated flying debris and enhanced the ultimate strength, stiffness as well as ductility. Applying GFRP layers enhanced the overall behaviour of the slab resulting in a significant increase in peak resistance, ductility, and stiffness when compared to the dynamic results of an unretrofitted panel. The post peak resistance was also greatly improved. In particular, applying stacked quadraxial lay-up configuration significantly improved the ductility and resulted in the greatest post peak resistance. The effect of steel straps on damaged and retrofitted was relatively minimal, and only partial recovery of the resistance and the stiffness was achieved. GFRP with full confinement yielded better performance compared to the unretrofitted and undamaged counterpart. More work is needed to quantify the benefits of using GFRP in these applications.

Timber is one of the most common materials that had been use for a long time. The need for new buildings will affect the climate negatively, that is why it’s necessarily to find new ways to build quickly and sustainably. Cross-laminated timber (CLT) product came in the 1990- century. The material was developed to be used in high residential wood constructions buildings. The material considered to have good properties compared with other types of wood material, some of the studies showed the possibilities of building high residential with the CLT material. Such high rises buildings work best when CLT wood constructions combined with other materials, which called, Composite constructions. Case study preformed theoretically in Fullriggaren building in Alderholmen in Gävle city, the building have 14 floors and about 40 m high. With the purpose of trying to investigate the consequences that occur when the concrete floor slabs were replaces  with CLT wood floor slabs, taking into account the rules and standards for fire safety, acoustics, oscillations and vibrations. In order to achieve this and to determine the most suitable alternatives, the different types of CLT-wood floor slabs was compared. The building studied in its design and execution, and a simpler model created in Revit 2018. The challenge was that the building has a long span of maximum 10 m. The different types of CLT floor slabs which compared in the study was, CLT timber joist slaps, flat floor slab and CLT wood floor slabs in combination with steel hat beams and other beam steel types. Each type of floor slabs had its advantages and disadvantages, but the results and studies showed that timber and concrete composite floor slab combined with steel hat beams are the best possible options for the construction in Fullriggaren building, where the floor slab height is the shortest compared to other CLT wood floor types. With the chosen floor slab, the problem of vibration and oscillations will minimize. When using such a floor slab, the building height will increase, which means in this case, removing an entire floor from the building. / Trä är ett av de vanligaste material som har används sedan länge i byggkonstruktioner. Behovet av nya byggnader kommer att påverka klimatet på ett negativ sätt, därför är det bra att bygga snabbt och hållbart. Korslimmat trä (KL-trä) är en produkt som kom under 1990-talet. Trämaterialet utvecklades där den kan användas i träkonstruktioner i flervåningshus.Materialet anses ha goda egenskaper jämfört med andra typer av trämaterialen, litteraturstudier visade på möjligheten att bygga högt med KL-trämaterialet. Liknande höghus fungerar bäst när KL-träkonstruktioner kombineras med andra material s.k. Hybrida konstruktioner. Fallstudien utfördes teoretisk i  Fullriggarenbyggnaden i Alderholmen i Gävle, som består av 14 våningar och är ca  40 m högt. Syftet var att undersöka konsekvenserna som uppstår när betongbjälklaget ersätts med KL-träbjälklag, hänsyn tas till regler och normer när det gäller brandsäkerhet, akustik, svängningar och vibrationer. För att uppnå detta och kunna bestämma lämpligaste alternativ, jämfördes olika typer av KL-träbjälklag. Byggnaden undersöktes beträffande konstruktion och utförande, och en enklare modell skapades i Revit 2018. Utmaningen var att byggnaden har långa spännvidder med max 10 m. Olika typer av KL-bjälklag jämfördes som kassettbjälklag, samverkanbjälklag, plattbjälklag och KL-trä bjälklag i kombination med stålhattbalkar och andra ståltyper. Varje typ av bjälklag har sina fördelar och nackdelar, men resultatet och studierna visade att samverkabjälklag kombinerad  med stålhattbalkar är den bästa lösningen för konstruktionen i Fullriggaren, då dess tvärsnitthöjd är den minsta jämfört med andra KL-träbjälklagtyper. Med det valde  bjälklaget minskas även problemet med vibrationer och svängningar. Vid användning av detta bjälklag kommer byggnadshöjden att ökas, vilket leder till att  en våning måste väljas bort.