Influence of the Time-Dependent Strength Degradation on the Reliability of FRP-Reinforced Concrete Members

Fibre reinforced plastic (FRP) reinforcements are characterised by a time-dependent material behaviour which results from strength losses. In contrast to basalt and glass reinforcements, carbon reinforcements show only minor strength losses, and the long-term durability is significantly influenced by the type of impregnation. Time-dependent reliability assessments can be used to quantify the influence of the time-dependent strength degradation on the safety level of FRP-reinforced concrete members. However, in the design of FRP reinforcements, the assumption of the residual strength at the end of service life is normally on the safe side. This paper presents the results of a structural reliability assessment on FRP-reinforced concrete members subjected to bending loads. By using a First-Order-Reliability Method (FORM) and Monte-Carlo Simulations (MC), the time-dependent strength of the FRP reinforcement is investigated for different reference periods (1 to 100 years). Specific time intervals were chosen to significantly reduce the computational effort that is commonly required by the MC. For the action side, the live loads were considered time-independent by means of a Gumbel distribution. The results of studies in this paper indicate that the time variance has a positive effect on the safety level of FRP-reinforced concrete members when the FRP reinforcement failure becomes governing.