Synthetic fibres or fibre cocktail in terms of shear capacity of concrete after elevated temperatures

•Using cocktail fibres increased the shear strength by 39% compared to the concrete mix of synthetic fibres. The increase is more significant at high temperatures, i.e., 700 °C reaching 108%.•Mixes that contain fibre cocktail showed more ductile behaviour than mixes with synthetic fibres at both ambient and high temperatures.•Elevated temperatures decreased the stiffness of both test series, however using cocktail fibres showed higher stiffness than using synthetic fibres.•At high maximum temperatures, crack widths for both series are characterized with higher stiffness than crack slips to the counterparts.