Behaviour of corbels reinforced with headed-end GFRP bars

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Date
2023-12-18
Authors
Allen, Matthew Nicholas
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Abstract

Steel-reinforced concrete (RC) corbels are commonly found in bridges, industrial buildings, and parking structures throughout North America. Corbels are structural elements with low shear span-to-depth ratio that transfer vertical and horizontal loads to other members such as columns or walls. Given that the vast majority of RC infrastructure in North America is aging rapidly due to steel corrosion, engineers face the challenge of designing replacement structures with innovative construction materials to meet or exceed the intended design life. Glass fibre-reinforced polymer (GFRP) bars have electromagnetically inert properties, which alleviate long-term durability concerns due to corrosion. Extensive research over the past two decades have proven that the use of GFRP bars in new structures is desirable to extend the service life. GFRP and steel have different mechanical properties; requiring separate design methods to ensure failure loads are accurately predicted and serviceability requirements are met. Headed-end bars enhance the anchorage achieved by GFRP under tie-action, helping minimize one of the key drawbacks compared to steel. Currently, Canadian building and bridge codes provide strut-and-tie modelling (STM) provisions to design steel-RC corbels, but the American code prohibits the use of this method for GFRP-RC corbels due to lack of research. This research program evaluates the use of GFRP headed-end bars as internal reinforcement for concrete corbel elements. Twelve (12) full-scale GFRP-RC corbels and two (2) steel-RC control specimens were constructed and tested to failure. The test parameters included main tie reinforcement ratio, secondary reinforcement ratio, shear span-to-depth ratio, and concrete strength. The parametric effect on serviceability criteria, strength capacity, and mode of failure were discussed. Performance of the experimental specimens were compared to available design provisions and analytical prediction models. The experimental results confirmed the formation of the STM through flexural and diagonal shear crack patterns. The thermoplastic headed-end bars used were found to be a viable anchorage method. The Canadian standards provided conservative shear capacity predictions for all evaluated corbels. The American code overestimated the shear capacity predictions for all evaluated corbels except one, suggesting that revisions are required to better predict the capacity of GFRP-RC corbels.

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Code provisions, Corbel, Diagonal cracking, Glass fiber-reinforced polymer (GFRP), Headed bars, Secondary reinforcement, Reinforced concrete, Strut-and-tie
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