- As mass-timber building construction rises around the globe, there exists the need to verify the long-term, in-situ behavior and performance of these structural systems. Structural health monitoring (SHM), generally defined as a damage detection strategy consisting of a network of sensors, a data acquisition system, and algorithms for data analysis, can be implemented for this scope. However, there are no clear guidelines or standards for implementing timber or mass-timber SHM programs. Although guidelines exist for SHM of other building material types, they do not address some key considerations for timber monitoring. As wood is a natural, hygroscopic material, it absorbs and releases moisture from or into the surrounding air, changing the moisture content of the wood. As the moisture content changes, so do many of the physical and mechanical properties of the material. Therefore, to understand the structural performance of timber and mass-timber buildings, quantifying the hygrothermal performance is critical. The lack of standards however leaves ambiguities associated with sampling criteria for timber monitoring, how to clean and analyze data, and how to account for hygrothermal behavior in damage detection algorithms. It has also been attributed to the limited number of timber SHM programs as well as the reason these programs often cannot be compared with one another.
To move towards standardization of SHM for timber and mass-timber buildings, this project focused on the development of a methodological approach for monitoring these buildings during construction. The approach intends to simplify the necessary steps associated with implementing SHM into these buildings during the construction phase, address methods of pre-processing and cleaning data, and develop tools for data analysis and visualization. The construction phase was specifically considered as this phase can provide valuable insight into environmental and mechanical loads experienced during construction as well as insight into construction procedures and performance of them. However, implementing an SHM program during construction has additional challenges compared to in-service monitoring, for example using only temporary power supply to collect data, coordination with building stakeholders, and uncontrolled environmental conditions that may affect data. The approach was to be validated through the implementation of an SHM program in a mass-timber building under construction. To be validated, the approach must provide data that could be used by the industry to document construction performance. The study was accomplished in two steps: (i) literature review, surveys, and design development of an SHM plan for a real building, and (ii) the proposal of a methodological approach with validation in a mass-timber building through analysis and use of data to provide insight into the construction performance of the building.
The first phase of this project focused on a literature review and survey of researchers in the mass-timber monitoring field. The results of both were used to gather necessary background information related to monitoring programs, specificities for mass-timber monitoring, phenomena of interest, sensor limitations, and common sensors used. Further consideration included identification of project objectives, sampling criteria, budget, architectural constraints, phasing of sensor installation, limitations of monitoring equipment, and a long-term plan for data acquisition, storage, and analysis. The outcome of this phase was that the state-of-the-art for timber and mass-timber SHM did not exist and guidelines were not available. For this reason, there have been inconsistencies in monitoring programs, repeated errors among projects, and even failed monitoring projects. Therefore, the development and validation of a methodological approach must attempt to piece together best practices, state-of-the-arts from various subsections of monitoring, and compile lessons learned to adequately develop a benchmark to implement SHM of mass-timber buildings under construction.
The second phase of this project was the development of the methodological approach for mass-timber building monitoring under construction. The procedure was validated using SHM data from the George Peavy Forest Science Complex, or “Peavy Hall,” a mass-timber building at Oregon State University. The building was monitored for its hygrothermal and static performance over the last ten months of construction. The measurands of interest were tension loss in post-tensioned self-centering cross-laminated timber (CLT) shear walls, displacements, rotations, and movements of cross-laminated timber shear walls, moisture content of CLT panels and slabs, glulam beams and columns, and mass plywood panel (MPP) roof slabs, heat transfer in CLT panels, and indoor and outdoor environmental conditions, including relative humidity, temperature, precipitation amounts, as well as wind speeds, directions, and gusts. A significant step in this approach involved data cleaning, visualization, and analysis, which were implemented into data platforms for locations of interest throughout the building. The data platforms were implemented using opensource programs such that minor modifications can be made for use on previous or future projects to compare data and processing techniques.
Outcomes of the methodological approach included documentation of construction performance as it relates to the post-tensioned self-centering shear walls, and the moisture performance of the CLT and MPP roof slabs. Thus, the methodology was considered to be validated. The approach will be further developed and refined for in-service monitoring with continued validation in the studied case. Lastly, specific datasets will be used for model verification, further testing and analysis, development of digital twins, and other future research purposes.