Graduate Thesis Or Dissertation
 

Modular Cross Laminated Timber Structures Using Underutilized Ponderosa Pine

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3t946010h

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  • Conflicts and disasters displace millions of populations worldwide. There is a need for rapid and affordable housing to cater to the needs of the displaced and unhoused population. Experience from previous post-disaster responses shows that temporary housing should be rapidly deployable, planned for months to years, and should be environmentally and economically sustainable. Using products such as cross laminated timber (CLT) can help provide environmentally friendly solutions for the post-disaster response. As CLT is currently perceived as a relatively expensive material, one of the ways to reduce the costs of CLT panels may be to use laminations from low-value logs. One of the sources of low-value underutilized logs is ponderosa pine (Pinus ponderosa or PP) obtained as a by-product of the forest restoration programs that are aimed at mitigating wildfires. The added incentive for the utilization of PP logs in CLT is to offset the high costs of these restoration programs. The use of PP laminations in CLT has been investigated in a preceding study at Oregon State University. PP CLT was deemed suitable for certain types of applications in structures. If PP CLT can be used in temporary housing, then it can help in post-disaster response while offering a high-value use of a by-product from restoration programs. One of the solutions that have been used for temporary housing is modular structures, structures with standardized repeated units. Modular structures can be mass-produced efficiently and designed for quick assembly, which can help in providing quick and affordable post-disaster shelters. Once the need for temporary housing in a post-disaster response is over, the reuse of these structures in providing shelters to others in need would be more sustainable. Hence, to incorporate the aspects of manufacturing, quick assembly, disassembly, and reuse from the design phase, the design of modular structures for post-disaster response benefits from the Design for Manufacturing, Assembly, and Disassembly (DfMAD) principles. Reuse of a CLT structure can be enabled by selecting connections that are suitable for disassembly and reuse. As most of the deformation in a CLT structure occurs at the connections, connections play a crucial role in the behavior of a structure, especially during events such as earthquakes. Although previous research has been conducted on other species of CLT, these results cannot be used directly in the design of PP CLT structures. Hence, there is a need to characterize the behavior of connections in PP CLT. Furthermore, numerical modeling can provide valuable insights into the behavior of the structures and their components. A way to characterize the connections and demonstrate their use in modular CLT structures would be invaluable in the further use of PP CLT in modular structures. The aim of the research is to demonstrate a proof-of-concept for a modular CLT structure that can be rapidly assembled, disassembled, reassembled, and reused made from underutilized PP. The specific objectives were to 1) determine the pertinence of modular CLT construction for temporary housing via analysis of manufacturing, engineering, architectural, and construction features of existing modular CLT construction, 2) develop, assemble, disassemble, and reassemble a prototype design of a rapidly deployable 2D modular structure based on DfMAD principles to test the feasibility and learn limitations and constraints, 3) characterize the mechanical behavior of connections in CLT made from underutilized PP so that these connections can be benchmarked for numerical modeling, and 4) develop finite element model to access the performance of shear walls in modular CLT structures using the experimental results from connections in PP CLT. A review of modular CLT projects was conducted using data collected from published sources. The data were classified into different geographical, dimensional, temporal, functional, production and logistics, and design features and analyzed to determine the suitability of modular CLT construction for temporary housing and in seismic areas. The review concluded that a quarter of the modular CLT structures are temporary structures. Substantially lower average construction duration of modular CLT construction compared to the average construction duration of residential housing in the US and the presence of a third of the modular CLT projects in regions of medium to high seismicity indicated the possibility of use of modular CLT construction for rapidly deployable housing in regions like Northwest US. A prototype unit made of narrow-width PP CLT panels joined with intra-modular connections (butt joints with inclined screws) was designed using 2D modules. The 2D modules were connected via a point-type connection suited for easy assembly and disassembly. The assembly, disassembly, and reassembly of the prototype unit demonstrated the proof-of-concept of the use of modular CLT construction using PP CLT for rapid construction and reuse. The lessons learned during the design and assembly-disassembly-reassembly cycle are presented. In-plane testing on two types of connections used in the prototype unit was conducted in PP CLT: 1) butt joints with inclined screws, and 2) point-type connection that facilitates easy assembly and disassembly. The results from the testing along with the comparison of the behavior of connections in PP CLT with the behavior in other species of CLT from previous tests are presented. The experimental results of PP CLT connection testing were used to benchmark a numerical model and used to access the impact of connections in the behavior of multi-panel shear walls for modular structures. The impact of spacing of screws between the panels on the behavior of multi-panel shear walls, which can affect the behavior of modular CLT structure, was assessed. The multi-panel wall had force-displacement behavior similar to a single panel wall for closely spaced screws and as a coupled wall for widely spaced screws. The research presented provided proof-of-concept of the utilization of PP CLT in modular structures suited for easy assembly, disassembly, and reuse using a prototype studio unit. The experimental works on connections along with the numerical modeling methodology will help the architectural, engineering, and construction community in using underutilized PP in providing post-disaster solutions and mass affordable housing.
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  • Pending Publication
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  • 2022-06-09 to 2023-01-10

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