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There has been a limited number of studies about the flexural behavior of unbonded posttensioned concrete (UPC) beams strengthened with carbon fibre reinforced polymer (CFRP) and these studies have not systematically examined the effect of CFRP sheets on the tendon strain as well as the strengthening efficiency. Moreover, current design guides for the FRP strengthening techniques have not provided any design procedure for UPC structures. This study, thus, investigates the influence of CFRP sheet ratio on the flexural behavior of CFRPstrengthened UPC T-beams and quantifies its effect upon tendon behavior in this kind of UPC beams. The testing program consisted of nine large-scale UPC T-beams strengthened by different layers of CFRP sheets with or without CFRP U-wrapped anchors. The experimental results have shown that the use of CFRP sheets and CFRP U-wrapped anchors significantly affected the tendon strain. The FRP reinforcement ratio governed the flexural capacity, the crack width, the mid-span displacement, and the ductility of the beams in which the

The paper presents an improved, fracture-mechanics-based formula for estimation of the ultimate shear resistance of steel fibre reinforced concrete beams. The proposed formula was evaluated using 312 published and 28 new test results and its accuracy was compared with 12 already known formulas. Twenty eight tests on reinforced concrete beams subjected to non-symmetrically placed concentrated loads were carried out, in which two different types of steel fibres: short straight and long hooked-end were used. The influence of the volume of fibres on shear resistance and cracking behaviour of the beams for each type of fibre as well as their combination was investigated. The obtained results indicate the validity of the new formula for a wide range of beam and material parameters and prove its applicability for a reasonably precise estimation of the ultimate shear resistance of steel fibre reinforced concrete beams.

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