Safety assessment of in-service reinforced concrete T-girders of bridge decks

Reinforced concrete bridges located in coastal environment are known to undergo structural degradation due to chloride-induced corrosion of reinforcement. In this paper, reliability-based methodologies have been formulated for safety assessment of in-service reinforced concrete T-girders against shear and cracking limit states. The proposed methodologies incorporate the following features: (a) gain in concrete compressive strength with time, (b) the time-dependent diffusion of chlorides into cover concrete, (c) the chloride-induced corrosion of both stirrups and main rebar of pitting type, (d) the corrosion current variation along the span, (e) the reduction in yield strength of stirrups after it starts corroding, and (f) corrosion crack formation due to the accumulation of the corrosion products. The system reliability concept is embedded in the framework of Monte Carlo simulation, for estimating the time-variant failure probabilities. The usefulness of the methodology is demonstrated on a typical in-service Chennai flyover, designed according to MORTH. The girder fails to meet the target reliability index consideration in the case of shear limit state and also fails the required serviceability criteria even before the end of 50 years. This example brings out the need to consider time-variant reliability considerations at the design stage itself.