Influence of the Residual Tensile Strength on the Factor for Quasi-permanent Value of a Variable Action ψ2

Abstract

Steel fibres are known to aid in deflection control, control the process of cracking and mainly improve the toughness of structural elements and the whole structure. Large experimental program was performed at the Faculty of Civil Engineering-Skopje to find out how steel fibres and the residual tensile strength affect the time-dependent deformation properties and deflections of concrete. Specific realistic loading with permanent and repeated variable loads in loading interval of 8 h per day was applied on full scale beams that were monitored up to an age of concrete of 400 days. The beams were with cross section dimensions 15/28 cm and total length of 300 cm, manufactured from concrete class C30/37. They were reinforced with same percentage of longitudinal and shear reinforcement, but with different amount of steel fibres (0, 30 kg/m3 and 60 kg/m3). Using the experimental results, detailed analysis of the time-dependent deformation properties of concrete and their effect on the time-dependent behaviour was done. A value for the factor for quasi-permanent value of variable action ψ2 is proposed for each type of concrete. It was concluded that the factor for quasi-permanent value of a variable action ψ2 depends linearly on the residual tensile strength.