C LT Cu be Team:
Cat Do Tara Runyan Sarah Walker
School of Architecture + Design
1 Applied Research Laboratory / Digital Material Systems / Wood / CLT Cube
Abstract Cross-laminated timber (CLT) usage is a relatively new wood innovation that has been developed since the 1990s in Europe, but has limited to no use currently within the United States. However, CLTs are a green building material that has advantages over typical usage of both concrete and steel, making it an attraction option for sustainable building. CLTs also offer the advantage of customization and prefabrication before assembly, therefore the proposal also features the usage of computer numerical control (CNC) systems and other digital technologies in order to further develop the materiality of CLTs. In order to further examine the creation of CLTs and their viable use in the United States, the project proposal states the creation of CLT panels from typically available lumber in order to create a structural section of a pavilion designed for student use as a inhabitable and protective space.
The cube is altered by three other rectangular prisms to form the program of the structure.
Facing page: Diagram of the buidling and volumetric relationships 2 Virginia Tech / School of Architecture + Design / Center for Design Research / Spring 2016 / King + Clark
3 Applied Research Laboratory / Digital Material Systems / Wood / CLT Cube
Int ro d u ct i o n Current Page: 1. Picon, A. (2004). Architecture and the Virtual: Towards A New Materiality. PRAXIS 6: New Technologies//New Architectures. 2. Stauder, C. (2013). Cross-Laminated Timber: An analysis of the Austrian industry and ideas for fostering its development in America.
Cross-laminated timber (CLT) was first developed in Europe (specifically in Austria and Germany in the 1990s) in an effort to combat both lumber deficiency and production of wood waste product (Stauder, 2013). While the development and use of CLTs is still relatively recent, CLTs are a particularly attractive building material due to its production from a sustainable resource, as well as allowing for the creation of a solid structure. However, CLTs are currently only used in the design of mid to large-scale products, such as multi-story buildings and parking structures. Not only that, but because of the diversity of wood present in North America, the use and development of CLTs are nearly nonexistent within the United States. Therefore, it becomes critical to research the creation of CLT from typically available lumber, as well as examining its viable usage on a smaller scale. In addition to the idea of creating CLT panels, the consideration of digital technologies was also critically important to the project proposal. In his essay “Towards a New Materiality”, Antoine Picon discusses the impact of current and future digital technologies on the architectural world, specifically its impact on the current usage and future creation of materials. He discusses how technology and the usage of computers in architecture have transformed our perception of reality, “[presenting] us with new perceptual entities and objects,” allowing for the evolution and revolution of material (Picon, 2004). He suggests that with the use of digital technologies, the difference between representation and materiality is minimal, allowing the design process to design the material itself. Ultimately at its highest form, the computer will act as a gateway between representation and the necessary technical specifications.
In a similar way, CLTs, while already a new and innovative building material, can be further developed with the usage of technology. Technology already plays a critical role for the production of CLTs, such as the usage of CNC machining to prefabricate and refine each constructed panel, theoretically leading to minimal effort during the actual construction stage. In the project proposal, CLT panels were to be made manually, with usage of robotic and CNC machining in order to create refined finger joints, as well as perforations that would help to distribute the overall weight of the CLT panel. These perforations would allow each panel to become a lighter solid structure, leading to increased ease in assembly, as well as a shift in CLT materiality.
a
b
c
d
Facing page: a. Front Elevation b. Right Elevation c. Back Elevation d. Left Elevation 4 Virginia Tech / School of Architecture + Design / Center for Design Research / Spring 2016 / King + Clark
5 Applied Research Laboratory / Digital Material Systems / Wood / CLT Cube
Program The CLT cube is designed to allow for various interactions by users. It serves as a place to gather, to relax, and to wait. Raised one foot off of the ground, the user must step up into the cube’s entrance. A large bench is formed by an imaginary volume pushing against a corner of the cube. The oversized bench provides seating inside of the structure as well as a shaded cover on the exterior. A third volumetric alteration is a spot in the middle of a wall which forms an angled place to lean against while standing on the interior and an inclined seat to rest at on the reverse side. Only inhabitable by about three occupants at once, the cube is a cozy getaway.
Current page: Aerial perspective of Fusion 360 model. Facing Page: Floor plan & section of cube. 6 Virginia Tech / School of Architecture + Design / Center for Design Research / Spring 2016 / King + Clark
7 Applied Research Laboratory / Digital Material Systems / Wood / CLT Cube
Environmental Strategies Cross-laminated timber (CLT) has an inherent environmental advantage because of its usage of wood, which is a renewable resource that can be regrown for future usage in ethically managed forests. Wood also outperforms other materials such as concrete and steel in terms of embodied energy, solid waste, and both air and water pollution (Fuentes, 2015). Additionally, CLTs are considered a green building material due to Facing Page: Fuentes, A. K. (2015). a “significant number of benefits including carbon sequestration, reduced RECONCILING emissions (from harvest to construction), and cost effectiveness when SUSTAINABLE AND RESILIENT DESIGN IN compared to concrete and steel.” (Stauder, 2013). Originally developed CITIES: CROSS LAMINATED in order to combat wood waste production in Europe, the manufacturing TIMBER AND THE FUTURE OF JAPANESE WOODEN of CLTs has allowed for low-grade waste wood to be repurposed into BUILDINGS. a solid green-building material, as well as allowing manufacturing facilities to become more efficient and nearly waste-free. In addition, CLTs typically have a significant seismic performance, fire resistance, as well as allowing for thermal insulation through the creation of a solid building envelope. Current Page: Stauder, C. (2013). CrossLaminated Timber: An analysis of the Austrian industry and ideas for fostering its development in America.
Furthermore, because CLTs are generally prefabricated construction elements, they allow for the reduction of development and assembly time, as well as creating a “significantly reduced construction footprint when compared to concrete and steel construction.” (Stauder, 2013). Because of the reduced assembly time, on-site waste during construction is significantly lowered, disruption to neighbors due to construction is minimal, and the need for specialized labor is lowered due to the prefabrication of the elements (though movement of the panels does require the use of cranes or brute force despite being lighter than concrete or steel). Ultimately, the environmental strategies of CLTs can also lead to an economic benefit, calling for a lower capital cost and faster assembly time.
8 Virginia Tech / School of Architecture + Design / Center for Design Research / Spring 2016 / King + Clark
The creation and use of CLTs is in line with the necessary trend for sustainable design, and though CLT production is well-developed in Europe, production is still at its starting stages in other areas of the world. However, it is necessary to note that interest in CLTs as a sustainable material is present in various research circles. In Japan, for instance, both the government and scientific groups agree that “CLT is a special material that has a place in recent initiatives that support domestic procurement of timber and harvesting of wood from local, responsibly managed forests”, though specific and lawful usage of the material has still not been completely approved in the country (Fuentes, 2015). In the United States, CLT production is still extremely limited due to lack of wood specificity and uniformity across the United States, and is currently confined to only two domestic manufacturers in the Pacific Northwest, though research suggests that the consistency of tree species in the Eastern US would be better suited for CLT production. Overall, further development of CLTs and other lumber materials would allow for the reinvigoration of lumber industries and local economies across the States, particularly where lumber industries have declined due to the misconception of wood as a wasteful material.
9 Applied Research Laboratory / Digital Material Systems / Wood / CLT Cube
Building Analysis Current Page: Stauder, C. (2013). CrossLaminated Timber: An analysis of the Austrian industry and ideas for fostering its development in America.
CLTs are a relatively new example of how digital fabrication can allow for great innovation, bringing the precise efficiency of industrialization to the customization of hand-craft. While maintaining the presence of the designer, digital technologies allow for the creation of larger and more ambitious projects. CLTs, for example, allow for the transformation of exceedingly common dimensional lumber into massive panels, which allows for potential far beyond its typical components. For example because of its large components, CLTs have good fire resistance, allowing for a slow and steady burn of fire. One study of CLT fire resistance showed that the CLT burned for 3 hours and 6 minutes before failing (Stauder, 2012). CLTs are more structurally sound than typical panels due to their strength is both directions, as well as their shearing resistance. This also allows for strong seismic resistance, making it an attractive building material in seismic-prone regions such as East Pacific and the Eastern United States. Furthermore, because CLTs are formed from laminated solid layers, there is an inherent level of insulation, as well as the creation of a solid building envelope. Even though CLTs are usually machined with a commercial CNC router in order to custom-make openings and joints, much of the project’s production of CLTs was done manually. In order to avoid having to cut more joints than necessary, the proposed CLT designs incorporated finger joints into the creation of the CLT by cutting every other board (or adding blocks every other layer). This finger joint construction method is highly unusual with CLTs, likely due to its difficulty in execution because of human error, there were mis-measures and mis-cuts that led to misalignment of finger joints. Generally, finger joints are reliant on careful craftsmanship and can be difficult to maintain on a small scale, making it difficult for a CLT of this scale. In addition to this, a CLT is only as good as the material it is made with. Working with dimensional lumber, there were issues not only with uniformly planing and joining all of the boards, but also in storing them in order to prevent bending and warding. Because of these flaws in manually creating the proposed panels, some of the joints were cut and refined during assembly, though still leaving some gaps. These gaps likely affect the structural integrity of the structural section model, but were remedied with addition of screws.
Facing Page: Axonometric drawing of CLT layers including built-in finger joints. 10 Virginia Tech / School of Architecture + Design / Center for Design Research / Spring 2016 / King + Clark
11 Applied Research Laboratory / Digital Material Systems / Wood / CLT Cube
Materials & Identity Current Page: 1. Fuentes, A. K. (2015). RECONCILING SUSTAINABLE AND RESILIENT DESIGN IN CITIES: CROSS LAMINATED TIMBER AND THE FUTURE OF JAPANESE WOODEN BUILDINGS. 2. Stauder, C. (2013). Cross-Laminated Timber: An analysis of the Austrian industry and ideas for fostering its development in America.
Cross-laminated timber (CLT) is a type of massive timber, “manufactured products that have fibers, veneers, or wood boards glued or bound together with methods of fixation like adhesives.“ (Fuentes, 2015). In Europe, the preparation for wood before being laminated into panels is specific - wood is usually visually graded first, depending on the company’s standard, and then must be first kilndried to a standard moisture content of 12% (+/- 3%) (Stauder, 2013). Specific visual grades are given for perpendicular and parallel layers (grade 3 and grade 2, respectively), and optional stress grading follows afterwards. The lumber must then be planed on four sides, then the layers are formed by surface bonding with an adhesive. The wood direction alternates each layer, allowing for the strength of the panel to be distributed both directions, therefore allowing it to be stronger than a typical lumber product. Typically, CLT panels will be between 3 to 7 layers thick, with variation depending on what the panel is being used for. Panels are then pressed both vertically and horizontally, then finally being tested (shear strength, bending strength, delamination) for their final grading.
The proposed CLT panels were designed to be built out of typical lumber that would be planed down on all four sides to a dimension of [need dimension here]. The dimensions were created from consideration of both the machines in the wood shop, as well as the necessary dimensions to construct the majority of the finger joints as part of the panel (rather than post-processing the joints later on). The processed boards were then grouped and then cut to specific dimensions, before being grouped and then assembled into their respective panels. Due to the lack of a kiln and adequate space for all 150 boards, the boards were covered with a tarp and stored outside, leading to some moisture variances in the boards that caused some minor warping. Some visual grading was conducted before the boards were grouped into their panels, with some further visual grading during CLT construction. Rather than using typical polyurethanane (PUR), melamine urea formaldehyde (MUF), or phenolresorcinol-formaldehyde (PRF) adhesives for the construction, the boards were adhered together using Titebond II wood glue (Cross-linking polyvinyl acetate). Additionally, lacking professional-grade pressing systems, clamps and CMU blocks were instead used to distribute only vertical weight. The finger joints of the CLT panels were designed to be incorporated into the construction of the panel, with some refinement of specific joints to be done robotically. However because of mechanical difficulties, the finger joints were instead roughly cut and refined using a reciprocating saw (sawzall), a drill, and a hammer.
Current Page: 2x6x8s stacked on top of each other in CLT formation. Facing Page: Planed and joined 2x6x8s. 12 Virginia Tech / School of Architecture + Design / Center for Design Research / Spring 2016 / King + Clark
13 Applied Research Laboratory / Digital Material Systems / Wood / CLT Cube
Prototype Construction For the construction of the full scale section model, all the 2x6x8s were planed and joined to a dimension of 5.375” x 1.35” to give them 90 degree angles to allow for a tighter fit when laminating. Due to room limitations in the shop, only two panels were able to be assembled at a time and then panels were relocated outdoors once dry. This affected the schedule, but was beneficial as it gave time to learn the best method for the gluing process. All parts needed to be placed on top of two 2x4s to give additional height for clamps. While laminating the boards with Titebond exterior wood glue, clamps and CMUs were temporarily put on top of the freshly glued pieces. Once all pieces were laminated, a tabletop was laid on top of the panel to provide an evenly distributed weight. The large majority of joints were built into the panels. Yet there were a few panels that required hand cut joints specific to the angled connections. During the assembly of the prototype, it was discovered that not all the joints lined up exactly or were too snug of a fit. Using a hand saw and the sawzall, joints were adjusted to achieve the necessary finger joint connection. For added precaution, 8” screws were drilled in at each finger joint to ensure the structural integrity of the wooden joints. By assembling the prototype with the back on the ground, trimming joints became more accessible and it prevented a roughly 500 pound panel from being lifted into the air 8’ for placement. a
d
e
f
g
b
c
Current Page: a. Ripping boards to size with the table saw. b. Cutting angle specific joints with the sawzall. c. Lining up boards while laminating them together. Facing Page: d. Clamps and CMUs were used to hold wood together before a tabletop was placed on top. e. Lining up finger joints during assembly. f. CLT panels in prepartion of assembling. g. Prototype ready for the final panel. 14 Virginia Tech / School of Architecture + Design / Center for Design Research / Spring 2016 / King + Clark
15 Applied Research Laboratory / Digital Material Systems / Wood / CLT Cube
a b
Current Page: a. Final protoype with the additional column. b. View of the opening and bench. Facing Page: Demonstration of oversized bench. 16 Virginia Tech / School of Architecture + Design / Center for Design Research / Spring 2016 / King + Clark
17 Applied Research Laboratory / Digital Material Systems / Wood / CLT Cube
Rendering of multiple installations in Times Square
18 Virginia Tech / School of Architecture + Design / Center for Design Research / Spring 2016 / King + Clark
19 Applied Research Laboratory / Digital Material Systems / Wood / CLT Cube
Rendering of a single installation
20 Virginia Tech / School of Architecture + Design / Center for Design Research / Spring 2016 / King + Clark
21 Applied Research Laboratory / Digital Material Systems / Wood / CLT Cube