Investigating the effects of hybrid fibres on the structural behaviour of two-way slabs

Pourreza, Ramin (2014) Investigating the effects of hybrid fibres on the structural behaviour of two-way slabs. Masters thesis, Memorial University of Newfoundland.

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Abstract

This research is conducted to examine the effects of hybrid fibres on the performance of two-way slabs. The hybrid fibres were a cocktail of steel and macrosynthetic fibres. An experimental investigation was carried out to examine the structural behaviour of hybrid-fibre-reinforced concrete (HFRC) two-way slabs under static loading conditions. A literature review was carried out on slab-column connections made with steelfibre- reinforced concrete (SFRC). The major experimental findings of previous research were discussed and the data were collected into a databank. The review of the results revealed a large scatter in the data. Nonetheless, there was an apparent size effect in the specimens. The expressions proposed to predict the capacity of the SFRC slabs gave a significant degree of scatter when evaluated using all the test results in the database. In the current study, eight full-scale interior slab-column connections with side dimensions of 1900 mm were prepared and tested. The slabs were all simply supported along four edges and loaded through a 250 ˟ 250 mm central column. The steel fibre volume fraction (0 to 0.96%) and the slab thickness (200 and 250 mm) were the main variables. The structural behaviour of the test slabs was investigated with regard to loaddeflection characteristics, deflection profiles, steel reinforcement and concrete strains, crack patterns, modes of failure, and punching-shear capacity. The test results revealed that an increase in fibre content enhanced the stiffness, energy-absorption, and the capacity of the test specimens. The results also confirmed that using HFRC caused a decrease in the steel strain due to the contribution of HFRC in tension. The addition of hybrid fibres, up to 0.96%, increased the shear strength of the 200 and 250 mm-thick slabs, by 32 and 20%, respectively, compared to the reference slabs. The addition of hybrid fibres caused a ductile punching failure in the slabs. The ductility increased by 154 and 157% with the addition of fibres up to 0.96% for the 200 and 250 mm-thick slabs, respectively. The experimental observations confirmed that the contribution of fibres in the 200 mm-thick slabs was more pronounced than in the case of the 250 mm-thick ones. The results revealed that as the thickness of the test slabs increased, the fibres had less effect on enhancing the capacity of the slabs. Finally, the existing equations for predicting the capacity of SFRC two-way slabs were evaluated using the experimental results from this research. In general, the equations produced a small scatter in the predicted results. The equation proposed by Narayanan and Darwish gave a reasonably safe prediction with least scatter compared to the prediction of Hiroshi Higashiyama et al. which gave the safest prediction, however, it had a large scatter.

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