Graduate Thesis Or Dissertation
 

Influence of Uncertainties in Terrestrial Laser Scanning on Structural Reliability and Bridge Load Rating

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/vm40z0370

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  • To ensure the safety of the nation’s bridges, the National Bridge Inspection Standards (NBIS) require all bridges to undergo routine load rating analyses to assess their structural capacity. Accurate geometric information for each structure is necessary for load rating analyses. This information is typically ascertained from as-built plans. Still, when plans are unavailable or unreliable, dimensions must be gathered in the field, typically using traditional survey methods such as tapes and calipers. This process is not only time-consuming, error-prone, and may lead to a disruption of service, but also poses safety risks to workers. Modern survey devices, such as terrestrial laser scanning (TLS), are increasing in popularity. However, the measurement uncertainties associated with acquisition, registration, post-processing, and model development are not well understood. As a result, the implications of these measurement uncertainties to structural assessments are unknown. This thesis first computes uncertainties in dimensions extracted from TLS point cloud data of a reinforced concrete beam specimen and a steel specimen in a controlled laboratory test. In this test, several angles of incidence and scanning ranges were used to determine the scan positions that correlated to the lowest levels of uncertainty. For both specimens, uncertainties were largest for the shorter thickness dimensions (e.g., section width and height) but minimal for the longer length measurements, such as specimen length. Furthermore, scanning at a range of 10m paired with angles of incidence of 30° to 60° yielded mean dimensions with a bias of 0.97 to 0.99 and coefficients of variation of 0.06% to 2% (concrete) and 0.07% to 0.9% (steel width) or 62% (steel web). For incidence angles of 0° and 90°, the coefficients of variation doubled. For the reinforced concrete specimen, a structural reliability analysis quantified the influence of the uncertainties in the extracted dimensions on the reliability indices for the ultimate limit states of shear and bending moment. Overall, uncertainties in dimensions extracted using TLS had minimal impact on the reliability of the reinforced concrete specimen. For the steel specimen, two linear finite element torsional models were developed to compare the change in the specimen yield stress location between the TLS based dimensions and the reference dimensions that were hand measured. The significant uncertainties (coefficients of variation of 44% to 62% and large bias of 0.0073 and 0.0070) in determining the web and flange thicknesses adversely impacted the yield stress location. The TLS developed model non-conservatively predicted the specimen would yield almost 3900mm closer to the fixed end of the specimen than the reference model. Thus, more traditional approaches are necessary to capture the relatively small dimensions of the web and flange thicknesses for steel members. Following the lessons learned from evaluating the uncertainties in TLS derived measurements in a laboratory setting, a bridge load rating was performed for a cast-in-place, five-span reinforced concrete girder bridge in Oregon based on TLS measurements. The results were compared with a load rating based on the geometry extracted from the as-built plans. No significant change was observed in the bridge rating using the TLS measurements. Nonetheless, deviations between the as-built and TLS based dimensions are noted to inform future TLS surveys to support bridge load ratings.
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  • Associated dataset: Influence of Uncertainties in Terrestrial Laser Scanning on Structural Reliability and Bridge Load Rating - Finite Element Models (FEM)
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  • Pending Publication
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  • 2022-03-16 to 2023-04-17

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