TORSIONAL STRENGTH OF STEEL FIBROUS CONCRETE

摘要

Failure of reinforced concrete members subjected to shear and torsional loading is initiated in concrete due to the limited resistance of concrete to the induced stresses. Such failures are brittle in nature and should be avoided in design. Presence of discrete short length steel fibres enhance the weak properties of concrete like tensile strength, resistance to cracking, limited ductility and strain capacity. This enhancement will modify the failure mode and improve both the shear and torsional strength of plain concrete. This paper reviewed the previous studies on the torsional strength of steel fibrous concrete and a method is proposed to predict the cracking and torsional strength of steel fibrous concrete. The method utilizes the thin-walled tube, space-truss analogy to predict the torsional strength of plain concrete at the onset of cracking. After cracking the steel fibres starts contributing to the torsional strength through the wall thickness, which is a function of the cross-section dimensions. The steel fibres in this width are transformed to an equivalent closed stirrup area centred in the wall. The stress in this stirrup is estimated from the geometrical properties of the fibres and their bond strength with concrete. The contribution of the equivalent closed stirrups to the torsional strength of the composite is estimated according to the space-truss analogy. Application of the proposed method to square, rectangular and circular concrete specimens containing steel fibres of different types and volume percentages showed good agreement with published experimental results. The method can be further modified or developed to include the contribution of conventional steel reinforcement to the torsional strength of fibrous reinforced concrete members.