Shear Behavior of Steel Fiber Reinforced Self Compacting Concrete

Sharma, Drishan and K V L, Subramaniam (2017) Shear Behavior of Steel Fiber Reinforced Self Compacting Concrete. Masters thesis, Indian Insitute of Technology Hyderabad.

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Abstract

In design of reinforced concrete structures, strength -based design is conventionally adopted, which ignores the contribution of tensile stress carried by concrete after cracking. Further any delay in the onset of cracking can only be considered through an increase in tensile strength. To assess the true potential of fibers; (a) delay in th e onset of cracking due to suppression of cracking and (b) post cracking stress transfer across crack has to be accounted for. The post cracking stress transfer is particularly important for shear where shear transfer by aggregate interlock provides signif icantly to shear capacity of RC elements. Shear displacements along rough cracks also result in dilatancy. The crack bridging provided by fibers can potentially provide for increased mobilization of aggregate interlock, thereby increasing the shear capacit y. An understanding of the influence of fibers on the post -cracking shear stress transfer across rough cracks surface and it influence on the shear capacity of reinforced concrete beams needs to be understood to develop design provisions which consider the influence of fibers on shear capacity. The study aims to investigate the shear capacity of self -consolidating concrete (SCC) reinforced with discrete steel fibers. The influence of hooked -ended steel fibers on the shear transfer across rough cracks in SCC and its influence on the shear behavior of reinforced concrete are investigated. A two stage investigation which involves obtaining information of the material behavior and relating it to the structural response is developed. In the first step, the fractu re behavior of steel fiber reinforced SCC is investigated using digital image correlation (DIC). The formation and propagation in the fiber reinforced SCC is studied using full -field displacements obtained from DIC. The significant increase in fracture ene rgy is shown to be associated with post-cracking resistance to crack opening provided by fibers. The increased resistance to crack opening results in multiple cracking with increasing load. In the second stage, shear behavior of SCC beams with and without steel fibers is investigated. The shear failure in SCC beams i s very brittle, with very visible opening of the shear crack. The sudden failure of internal shear transfer across the shear crack in the SCC beams produces a large slip accompanied by sudden op ening of the crack. The shear responseof the steel fiber reinforced concrete is shown to be directly influenced by the post -cracking stress transfer across the crack. At corresponding loads, the crack opening in steel fiber reinforced SCC beams were vi signif icantly smaller when compared with the SCC beams. In steel fiber reinforced SCC beams the resistance to crack opening provided by the fibers influences the propagation of the shear crack in the beam. The abrupt failure produced by an uncontrolled increase in slip across the primary shear is prevented. The load transfer across the primary shear crack is sustained for a larger crack opening. The crack closing stresses provided by the fibers allow shear stress transfer across the primary shear crack for large crack openings. In the steel fiber reinforced SCC beams, shear failure was produced by the formation of a secondary shear crack, which occurred after the peak load.

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