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Flexural and Shear Response of Deteriorated Prestressed Concrete Girders Taken from a Decommissioned Bridge in Alberta
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- Author / Creator
- Wu, Zhaohan
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Prestressed concrete (PC) bridges are a major component of North America’s transportation network. As this network ages, the response of deteriorated PC bridge girders is of interest since rehabilitation and repairs are constrained by limited infrastructure budgets. Bridges are often evaluated using a largely qualitative rating system which results in differences in opinions between evaluators. As part of a larger initiative to develop reliability-based bridge management tools for deteriorated structures, this thesis presents results and analysis from a series of full-scale destructive tests on a 28-year old PC bridge removed from service near Barrhead, Alberta.
There are many studies on PC girders, but these studies are limited to non-deteriorated systems, systems with accelerated deterioration (corrosion, debonding), non-destructive testing, and normal density concrete. The impact of deterioration on semi-lightweight PC girders subject to real-world environmental effects is rarely studied. Destructive testing was carried out on four 11 m single span, semi-lightweight PC voided slab girders taken from a decommissioned bridge with different types and degrees of deterioration. Both flexural and shear testing was conducted to provide insight on the deteriorated behaviour of the girders. Four-point bending was used for flexural test. Shear tests were conducted using three-point bending with different shear spans (1.0 m and 1.5 m). Modifications on some girders simulated further damage. Flexure tests indicated that all girders resisted the design factored load based on CSA S6:19 but no girders satisfied live load deflection limits of span/800. Deterioration significantly affected the flexural strength of the girders with a 23% decrease in strength for the most deteriorated girder relative to the baseline girder. More concerning, corrosion led to undesirable strand rupture failure prior to yielding which greatly reduced failure deflection. Material tests confirmed that strand corrosion greatly affected the strength and ductility of the strands.
Shear tests showed that shear span-to-depth ratio affected failure mode. All specimens with 1.0 m load scheme failed by strut crushing. For 1.5 m load scheme, girders in fair condition failed by shear compression. However, when stirrups were corroded, diagonal tension failure occurred leading to excessive yielding and wide cracks. Anchorage failure may occur when anchorage is inadequate leading to sudden failure from reinforcement or strand pull out. All girders performed well above design ULS loadings; deterioration did not greatly impact the peak load for the tested girders. However, deterioration affected events leading up to failure. Struts formed at a 29% lower load for 1.0 m load scheme and 32% lower load for 1.5 m load scheme due to induced prestressed strand loss, but the ultimate load only decreased by 9.6% and 9.9% for 1.0 and 1.5 m respectively. Anchorage failure resulted in the lowest peak load and sudden unexpected failure away from load point. Corrosion that leads to anchorage issues, such as end cracking, needs to be carefully examined by bridge inspectors.
After testing, forensic investigation found the average as-built concrete strength was 51% larger than the design value; four extra 25M bars were also discovered that were not included in the stock drawings for this bridge. These bars were initially added for camber control but served as a major backup system since corrosion was much more present in the strands. With updated material properties, CSA S6:19 accurately predicted the baseline girder capacity within 5% of the test value for flexure. CSA S6:19’s sectional approach based on MCFT was conservative in predicting the shear capacity of the girders for both load schemes due to the assumption of plane sections remaining plane. Considering both flexural and shear results, it was concluded that the deteriorated PC girders were flexure dominant and safely resisted the design load at the time of testing. -
- Graduation date
- Fall 2021
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.