Impact of Monitoring Strategies on the Reliability of a Fatigue-Critical Detail in Steel Bridges

This paper presents a reliability-based framework to quantify the impact of monitoring and inspection strategies for fatigue-critical details in steel bridges. The aim is to quantify the added value of different information sources, namely, destructive tests (DTs), sensor measurements, and nondestructive inspections (NDI), in improving residual fatigue-life predictions and structural reliability. The framework combines Bayesian updating with a fracture-mechanics based reliability model. Three updating approaches are demonstrated in a case study of a welded vertical stiffener detail in a steel girder: (1) updating the fracture toughness with limited fracture tests (DT); (2) updating the global model uncertainty from strain or deflection measurements (sensors); and (3) updating crack information through inspections (NDI). The results for this case study indicate that the DT leads to only a marginal absolute change in the reliability index β of 0.03. In contrast, NDI and sensor-based updating yield substantial gains, with the maximum absolute increase in β occurring at the inspection time, rising from 3.1 to 4.36 and 4.0, respectively. The combined use of sensor data and inspections is the most beneficial, particularly as the number of cycles accumulates, ultimately doubling β at the end of the fatigue life. Although the numerical results are specific to the investigated case study, the strength of the proposed framework lies in its broad applicability across different structural systems and diverse sources of information.