A Novel Methodology for Inspection and Strength Evaluation of Suspension Bridge Main Cables

A novel methodology is proposed to evaluate the ultimate strength of the main cables of suspension bridges using information obtained from site inspections and from tensile strength tests on selected wire samples extracted from the bridge's main cables. A new model is proposed accounting for the spatial variation of individual wires' strength along their length, an important physical attribute of corroded wires considered here for the first time. This model includes (1) mapping the corrosion stage variation along one-panel-long wires that are visible during an inspection; (2) establishing probability distribution functions for the ultimate tensile strength of 0.46 m (18 in.)-long wire segments in each corrosion stage group; (3) generating random realizations of the ultimate strength of all the wires in the cable's cross section, accounting for their strength variation along the entire panel length; and (4) accounting for the effect of broken wires in the evaluation panel as well as in adjacent panels. A Monte Carlo simulation approach is finally proposed to generate random realizations of the ultimate overall strength of the cable, using an incremental loading procedure. The final outcome is the probability distribution of the ultimate strength of the entire cable. The methodology is demonstrated through the cable strength evaluation of the Franklin Delano Roosevelt Mid-Hudson Bridge using results of a 2009 inspection, and compared with corresponding results obtained using current guidelines. The proposed methodology provides estimates of higher accuracy and reliability for the cable's ultimate strength, without essentially increasing the cost of inspections.