Graduate Thesis Or Dissertation
 

The Fundamental Behavior of CLT Floor-to-Wall Connections in Fire

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/m039kc93c

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  • This thesis focuses on the fundamental behavior of CLT floor-to-wall connections during a fire. Cross-laminated timber (CLT) panelized structures rely on floor-to-wall connections for the load path and stability of the structure. Additionally, the fire performance of these connections is critical to prevent horizontal or vertical fire spread within these buildings, limiting the impact of the fire on the structure. The structural performance of floor-to-wall connections often depends on the performance of connection elements, such as steel plates or dowels, and the embedment of the connection components (e.g. screws) into the CLT itself. However, little is known about the behavior of such connections during a fire, where the strength and stiffness of metal connectors degrades with increasing temperature and the cross section of the CLT panels reduces due to charring. Therefore, research into the behavior of these connections during fire exposure is an important step in developing engineering solutions for fire safe mass timber buildings. The aim of this research was to improve the understanding of CLT floor-to-wall connections throughout a fire event. The specific objectives were: 1) compile a review of the state-of-the-art on the fire testing of CLT floor-to-wall connections, 2) use the conclusions of the review to develop and evaluate a prototype testing method to quantify the structural behavior of CLT floor-to-wall connections during a standard fire, and 3) use the prototype test method to observe and measure the mechanical and thermal behavior of specific CLT floor-to-wall connections during both the heating and cooling phases of a fire event. To meet these research objectives, a comprehensive literature review was performed on eighteen experimental studies that investigated the fire performance of CTL floor-to-wall connections. The varying testing methods and data reporting practices of these previous investigations were synthesized and analyzed for consistency. The results of this analysis showed that previous studies on the fire performance of CLT floor-to-wall connection have used varied testing methodologies and did not report data consistently. These variations and inconsistencies can impede the synthesis of the developed knowledge into new design methodologies for fire safe buildings. However, the previous experimental research results highlighted the criticality of the behavior of CLT floor-to-wall connections during the fire cooling phase. Observational data from previous experiments included smoldering of the timber components and flames visible through the connection, all during the cooling phases of the fire exposure. Previous researchers used these observations along with the quantifiable data collected during the experiments to estimate self-extinguishment within the timber compartments or specimens. However, previous researchers defined self-extinguishment inconsistently, again making the synthesis of data for new design methods difficult. The results of the literature review analysis were used to develop a testing method, to explore the behavior of four floor-to-wall connections during the heating and cooling phase of a fire event. The specimens were subjected to residential mechanical loading and exposed to the ASTM E119 (ASTM 2020) standard fire for one hour while load was maintained on the specimen. After one hour of exposure, the specimens were allowed to cool naturally for one hour. Temperatures of the specimens were measured on both the fire exposed surface and the unexposed surface. In addition, thermocouples were embedded within the connection itself to measure temperatures at the locations of connection elements (e.g. screws and angles) and through the floor panels. Displacements were measured along the length of the specimen and within the connection region. Temperature data collected from thermocouples embedded within the connection elements and through the floor panels were used to calculate char rates, and displacement measurements in the connection region were used to calculate settlement of the connection as the timber charred. Thermocouple data from the experiments showed that heat continued to propagate through the connections even during the cooling phase. Flame-through was also observed during the cooling phase of one of the tests. Wood-wood connections did not exhibit flame-through and exhibited minimal connection settlement. Connections with exposed steel elements exhibited charring across the entire bearing surface as well as within dowel embedment, leading to increased settlement.
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  • The research presented was funded by the USDA Forest Service (Grant #20-DG-11062765-741).
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  • Pending Publication
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  • 2022-09-14 to 2023-10-15

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