Reinforced concrete bridges are continuously subjected to increased traffic load and exposed to harsh environments causing bridge members to deteriorate, thus, affecting their durability, safety and performance. This work aims at a probabilistic assessment of a reinforced concrete bridge girder under critical loading considering the flexural and shear failure modes of the bridge. A limit state function for the failure modes was generated and, the stochastic variables and statistical parameters were determined. Additionally, the safety indices for each failure mode were determined using First Order Reliability Method (FORM) procedure. Mathematical models were developed and the uncertainties in structural resistance, applied loading as well as structural components were included using the probabilistic method. A computer program in FORTRAN language was developed and deployed for the reliability analysis of the bridge girder to ascertain the level of safety using First-Order Reliability Method. The results revealed that the safety index for shear and flexural failure mode decreases as the span is increased. For concrete strength of 30 N/mm2 and a depth of 1000 mm, the safety index for shear and flexural failure reduced from 4.5 to 2.0 and 10.7 to 3.37 respectively as the span increases from 10 m to 19 m. This indicates that the shear and flexural failure modes are sensitive to increase in span. In order to obtain a minimum safety target of 3.8, it is recommended that the depth of the beam should not be less than 1200 mm while the span should not exceed 16 m, and concrete grade should not be less than 35 N/mm3.
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