Tensile behaviour of reinforced UHPFRC elements under serviceability conditions

Tension stiffening is an essential effect that influences the behaviour of concrete structures under serviceability conditions, mainly regarding crack control and deflection behaviour. Serviceability conditions can be studied experimentally by running the so-called uniaxial tensile test. This paper reports an extensive experimental research conducted to study the tensile behaviour of reinforced Ultra-High Performance Fibre-Reinforced Concrete (R-UHPFRC) under service conditions by uniaxial tensile testing. The parameters studied were the reinforcement ratio and the steel fibre content in a experimental programme including 36 specimens. Special testing equipment and methodology to measure the post-cracking deformation of R-UHPFRC ties were developed, and special attention was paid to the shrinkage effect. The tensile elements’ axial stiffness was approximately parallel to the bare bar response after microcracking formation showing a full tension-stiffening response. The average tensile capacity of the reinforced elements (tension stiffening response) was achieved. Concrete’s contribution in the R-UHPFRC ties with the tensile properties deriving from four-point bending tests (4PBTs) on non-reinforced UHPFRC specimens was also compared. The experimental results revealed a slight increase in concrete’s contribution with the higher reinforcement ratio. Moreover, the concrete’s contribution in the tensile elements was higher than the characteristic tensile properties deriving from 4PBTs.