2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference

Evaluation of proposed Steel Fibre Reinforced Concrete shear predictions against the Modified Compression Field Theory

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Mr. Helmi Alguhi, University of Alberta (Presenter)
Dr. Douglas Tomlinson, University of Alberta

Steel fibre reinforced concrete (SFRC) is used in many applications in construction such as in shotcrete tunnel walls and slabs on grade. Compared to non-fibre reinforced concrete, SFRC has superior post-cracking performance which leads to elements with narrower crack widths. Narrower cracks enhance the service performance of beams and improve aggregate interlock, which increases the shear capacity of SFRC members relative to non-fibre reinforced concrete. However, the benefits of using SFRC are not incorporated into the design standard for concrete buildings (A23.3-14), particularly for crack control and shear resistance.

Numerous empirical models have been developed by researchers to account for the improvement SFRC has on shear resistance in concrete. However, many of these models are calibrated against limited test data, often only from tests performed by one researcher. This applicability of twelve different shear resistance models for SFRC was evaluated in this study using a database of 80 tests on shear-critical SFRC beams. These models were compared to a mechanics-based approach based on the Modified Compression Field Theory (MCFT). SFRC was incorporated into MCFT by modifying the tension constitutive models for concrete. The SFRC contribution is modelled by changing the concrete’s tension stress-strain response based on an inverse analysis of existing test data incorporating fibre material properties (tension stress-strain, end treatment (straight, hooked), diameter, length, and dosage.  Fibre dosages between 0.5 and 2.5% were analyzed. Normal strength concrete (35 MPa) with 19 mm aggregates was the focus in this study. Steel and GFRP reinforced slabs and beams without stirrups, thicknesses ranging from 175 to 600 mm, and varying reinforcement ratios were evaluated.

In the MCFT analysis, it was seen that SFRC has smaller crack widths and enhanced aggregate interlock compared to non-fibre reinforced concrete. The effectiveness of SFRC increased with fibre dosage, particularly for fibres with hooked ends. The results show that SFRC is most effective at improving the shear resistance of members with lower reinforcement stiffness, particularly GFRP reinforced beams. Models that incorporate fibre reinforcement ratio, length, diameter, and end condition are more accurate compared both to test results and MCFT. These models are more suitable candidates for inclusion into future design standards.