Behaviour and design of concrete structures for sustainability and resilience

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Steel-reinforced concrete has played a critical role in the development of modern infrastructure. Unfortunately, most of the durability-related problems observed in concrete structures flow from corrosion of steel reinforcement that makes structures deficient even when the concrete is still healthy. Another issue addressed in this proposal is the alkali-silica reaction that weakens the concrete and the structure. As a result, the concrete infrastructure in most countries is in a dire state. In Canada, the problem is further exacerbated by freeze-thaw cycles and the use of de-icing salts on bridges. Residents of many cities in Canada routinely observe this phenomenon in the form of falling concrete pieces from bridges.An economical alternative to steel reinforcement is fibre reinforced polymers (FRP) that can be used as external reinforcement to upgrade existing structures or internal reinforcement for new ones. Use of FRP as internal reinforcement in concrete slabs, beams and other flexural members has been investigated in recent years and design guidelines developed that are now available in design codes such as “Design and construction of building structures with fibre-reinforced polymers” and Canadian Highway Bridge Code. Although further work is needed and underway in many of these areas, it is the use of FRP bars to resist compressive loads that needs immediate attention. Current codes do not allow the use of FRP bars to resist compression loads in structures primarily due to a lack of experimental and analytical evidence. Another challenge in the use of FRP bars is the behaviour of bent bars, which show significant reduction in strength as a result of curvature. Code committees consider these issues as the most urgent research needs. The proposed work will focus on the challenges in the use of FRP in structures some of which are discussed above. The methodology includes development of analytical models for material behaviour and structural behavior. These models will be supported by, and corroborated with data from a large variety of experiments that will be conducted in state-of-the-art laboratories at the University of Toronto. Large and small specimens will be tested under realistic loads including repeated and simulated seismic forces, and will include large scale columns and beam-column joints. The small specimens made with normal and reactive ASR concrete will be used to develop constitutive models and will investigate such effects as confinement and freeze-thaw. This work will draw significantly from the work on steel-reinforced concrete members carried out by the PI over the years.The ultimate goal is to develop design guidelines that can be included in various codes. This work would also help structural designers gain confidence in using these new materials to retrofit, design and construct more durable and sustainable infrastructure producing significant economic benefits.