Main Cable Inspection and Strength Evaluation of Helicoidal Strand Main Cables Using a Modified NCHRP Evaluation Approach

The A. Murray MacKay Bridge (MacKay Bridge) opened to traffic in 1970 and carries four lanes of traffic over the Halifax Harbour between Dartmouth and downtown Halifax, Nova Scotia, Canada. The Bridge's main cable has been opened for detailed visual inspections several times beginning in 2002. The Owner, Halifax Harbour Bridges, retained COWI North America to perform a strength evaluation in accordance with the National Cooperative Highway Research Program (NCHRP) Report 534– Guidelines for Inspection and Strength Evaluation of Suspension Bridge Parallel Wire Cables. As the MacKay Bridge main cable is composed of 61 parallel strands with helicoidal wires, the NCHRP 534 approach (intended for parallel wires) was modified to perform the strength evaluation for cables with helicoidal wires. Based on the analysis performed, it was determined that the main cable of the MacKay Bridge has adequate capacity at this time. Additional measures to protect the cable, mainly through dehumidification, could be considered to prevent further deterioration of the main cable and extend the service life of the cable and therefore the bridge.