Graduate Thesis Or Dissertation
 

In-plane Creep Behavior of Cross-laminated Timber and Mass Plywood Panels: A Methodology to Evaluate the Long-term Performance of Post-Tensioned Mass Timber Walls

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/nv935b140

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  • Post-tensioned (PT) self-centering shear walls were designed to reduce structural damage from seismic activity. However, these lateral force resistant systems experience post-tension loss negatively affecting the re-centering capability due to delayed deformations experienced by engineered wood products over time. The long-term mechanical response of mass-timber panels to in-plane PT loads is a complex, multi-physics problem involving moisture diffusion, constrained hygroexpansion, and viscoelastic and mechano-sorptive response of the panel to the PT load, which is mitigated by the deformation of the panel. Changes in the relative humidity of the surrounding environment affects the wood moisture content and results in additional creep due to the mechano-sorptive effect. Methodologies developed to accurately measure creep and post-tension loss and improve the visualization of monitoring these phenomena in an existing building to-date proved insufficient. Therefore, a new methodology was developed to measure viscoelastic and mechano-sorptive creep characteristics of small-scale post-tensioned cross-laminated timber (CLT) and mass plywood panel (MPP) wall specimens in two controlled environments. The combined data from these tests will be useful for updating PT loss modeling parameters, or to create a new predictive creep model. Additionally, a full-scale monitoring study of 28 ft tall post-tensioned CLT and MPP walls was proposed to obtain long-term data from a structural system and validate the model. The model will then be used to predict PT losses in a real building based on input data obtained from a structural health monitoring (SHM) system. Furthermore, to streamline SHM, measurands including relative humidity, air and wood temperature, wood moisture content, displacements and deformations of shear walls, and tensile force of post-tensioned rods, were integrated and visualized in a Building Information Model (BIM), as it enables the storage of spatial information, including building geometry and dimensions, and non-spatial attributes, such as material type and sensor readings. The approach intends to simplify the necessary steps required to create a digital model of a structure linked to historical sensor data to improve the visualization of SHM data to assist with maintenance decisions. Specifically, the BIM was proposed to access all the environmental and structural monitored parameters used to describe and predict the long-term response of mass timber post-tensioned shear walls in a building. The east stairwell of the George W. Peavy Forest Science Center (“Peavy Hall”) at Oregon State University was used as a case study to test the proposed approach. Since there was no accurate, as-built BIM available, the BIM of PT CLT shear walls was developed using a Scan-to-BIM approach by converting Light Detection and Ranging (LiDAR) point clouds into a BIM. All sensors included in the BIM were linked to their historical data displayed on the internet and easily accessible through a list that highlights their locations within the digital model. The precise placement of these sensors and the possibility to associate the measured parameters of these entities within a BIM is hypothesized to assist with data management by adding a spatial element to data and analysis results, which could lead to a more streamlined maintenance and service life planning of a building. The creep tests, modeling, full-scale monitoring of post-tensioned systems, and BIM for SHM were developed to assist with the design and maintenance of post-tensioned timber shear walls. The creep tests were designed to capture important data such as load, viscoelastic creep, mechano-sorptive creep, timber moisture content, environmental conditions, and timber shrinkage and swelling, useful for refining material properties to create a predictive model. The creep model currently accounts for the creep of CLT under a constant load, which is a preliminary step towards predicting the post-tension loss of PT shear walls. In future work, the data recorded from the tests should be analyzed to update the creep model to include mechano-sorptive effects and a varying load due to PT loss. Engineers can benefit from a predictive model to design a system that reduces and accounts for expected PT loss, so the building remains seismically resilient. Building managers and occupants of a building can benefit through the improved visualization of SHM data. A future study can incorporate the live sensory data into the BIM and display the data for the public. This would allow occupants to make maintenance requests and be aware of future maintenance tasks that can improve the service life of the building.
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  • This study was funded by the “Design, construction, and maintenance of mass timber PT shear walls” conducted through the TallWood Design Institute with funding by the U.S. Department of Agriculture’s Agricultural Research Service (USDA ARS) Agreement No. 58-0204-9-165. The material presented is also based upon work supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, McIntire Stennis project under 1009740 and the Achievement Rewards for College Scientists (ARCS).
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