Reliability-Based Maintenance Strategy for Gusset Plate Connections in Steel Bridges Based on Life-Cost Optimization

This paper focuses on the maintenance decision of vulnerable parts that need rehabilitating within the design service period under repetitive vehicular loads in steel bridges based on the time-variant performance deterioration and life-cost optimization. A practical life-cost reliability-based method was developed to characterize the performance deterioration of critical parts without and with maintenance, and then evaluate maintenance strategies according to life-cost indicators. The time-variant reliability index was mathematically derived according to the damage accumulation rule and life-cost optimization was established to determine the optimal maintenance strategy using particle swarm optimization. The developed method was effectively applied in the optimization analysis of the tube–gusset connection. Four maintenance measures, including plug welding, drilling the crack-stop hole, the welding plate, and changing the bolted channel–gusset connection, were used in longitudinal truss diaphragms of the Second Nanjing Yangzi Bridge and analyzed in a single form and in combination, respectively. It is observed that a single maintenance cannot protect the tube–gusset connection from damage failure within the expected service life (i.e., 100 years) for the restriction on the maintenance frequency, while the combined maintenances with bolted channel–gusset connection do much better than those with welded plate in protecting the detail from damage failure. The optimization results can provide an important basis for maintenance and design, where the optimal maintenance is effectively addressed.