Life-Cycle Cost-Optimized Target Reliability Index for Concrete Cable-Stayed Bridge Girders

This paper proposes a method to value the target reliability index of the main girder of a concrete cable-stayed bridge considering the resistance decay and cost optimization in the whole life cycle of the girder. The initial cost during the construction period, the maintenance cost during the service period, and the failure cost of the main girder structure are comprehensively considered, and the calculation model and objective function of the whole life-cycle cost are established. For maintenance costing, a hybrid strategy model (corrective + preventive) is adopted, and the time-variant reliability index is approximated from the recession law of the initial flexural capacity with resistance decay. On this basis, a bridge case with a 100-year design life is analyzed in detail to compute cost-optimized initial resistances and the corresponding initial reliability indices. In addition, to reflect that a target reliability index is defined for a class of structures, we further generate a set of feasible designs (ribbed-deck cable-stayed girders) and construct the class-level E[CT]−β scatter envelope. The minimum of the envelope yields a rational class target reliability, βT=5.865, which exceeds the code lower bound of 4.7. A brief parametric study indicates that increasing the failure consequence cost CF shifts the envelope leftward and slightly raises βT, while a higher discount rate γ moves the envelope downward and tends to reduce βT. The proposed procedure provides a balanced, economics-and-safety-oriented basis for selecting βT of ribbed-deck cable-stayed bridge girders and can support life-cycle design and operation and maintenance decision-making.