Optimization of retrofitting distortion-induced fatigue cracking of steel bridges using monitored data under uncertainty

This paper focuses on optimization of retrofitting distortion-induced fatigue cracking of steel bridges using monitored data under uncertainty. The optimization problem has two competing objectives: (i) maximization of the fatigue reliability of the connection details after retrofitting and (ii) minimization of the cut-off area. The geometrical restrictions, predefined maximum tensile stresses, and minimum remaining fatigue life of the connection details after retrofitting are all taken into account as constraints. The fatigue reliability assessment with monitored data is based on the formulation used in the AASHTO specifications. The original monitored data may be modified by using a proposed cut-off size adjustment factor (SAF) to represent the fatigue stress ranges at the identified critical locations after retrofitting. The nonlinear relationships between the cut-off size and SAF are established. The proposed approach is illustrated by using an existing steel tied-arch bridge monitored by the Advanced Technology for Large Structural Systems (ATLSS) Engineering Research Center at Lehigh University.