Effect of Fibres on the behaviour of Bottle shaped strut

Sagi, Murali Sagar Varma and S, Suriya Prakash (2021) Effect of Fibres on the behaviour of Bottle shaped strut. In: IOP Conference, 2021.

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Abstract

Bottle-shaped struts are the critical elements in the design of D-regions using Strut- and-Tie method. The transverse tension develops due to dispersion of compression load which further leads to splitting crack in bottle shaped strut. Due to this, the strut fails before reaching its ultimate compression capacity. Higher resistance to the transverse tension can improve the strut capacity and its efficiency in load transfer. Transverse tensile stress can be resisted by providing the steel reinforcement or through the addition of discrete fibres in the concrete. Many international codes like ACI, AASTHO, and CSA have suggested guidelines about the addition of steel fibre reinforcement in the bottle-shaped struts for resisting the transverse tension. Still, the influence of the discrete fibres on the performance of the bottle-shaped strut is not well established. The performance of the bottle-shaped strut in terms of efficiency factors, crack pattern and failure mode for different amounts of macro steel fibres and micro polypropylene fibres are studied using experimental investigation. Specimens of 600mm x 600mmx 100mm size were tested under compression. Steel fibres are added in the proportions of 0.7%, 0.9% and 1.1% volume fractions to the concrete. Effect of fibre hybridization also studied by adding micro polypropylene fibres in the proportions of 1% and 2% in addition to the steel fibres. Experimental results showed that adding discrete fibres in concrete significantly improved the resistance to the transverse tension in bottle-shaped struts and led to the increased load-carrying capacity of the specimens. A 75% improvement in the efficiency factor is observed at 0.9% volume of steel fibre addition. Addition of micro polypropylene fibres to the macro steel fibres further enhanced the load-carrying capacity of the bottle-shaped struts. Microfibres in the concrete effectively arrested the micro-cracks and delayed the occurrence of a first splitting crack in the strut region. Due to this the mode of failure changed to ductile through the formation of a greater number of small cracks with less crack width at the ultimate load. Results of this study clearly show that the addition of discrete fibres to the concrete is an effective solution to improve the performance of the bottle-shaped struts in terms of ultimate strength and serviceability. © 2021 Institute of Physics Publishing.

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