Sitka Bridge
Sitka Harbor / John O’Connell Bridge in Sitka, AK is a historic civil engineering landmark and one of the oldest cable-stayed bridges in the US. Under Alaska DOT’s inspection program, this structure requires a special in-depth inspection every decade. As part of the inspection team, BDI conducted a comprehensive evaluation of the stay cables. Our work included:
- Cable Dynamic Testing: Using BDI’s custom-built accelerometers and STS (Structural Testing System) hardware and software, high-frequency acceleration data was collected from vibrating cables. Our engineers analyzed the data to identify vibration modes and determined in-situ cable forces using the Taut Cable Vibration Method.
- Magnetic Flux Leakage (MFL) Testing: All 24 cables were tested for potential loss of cross section and/or wire breaks. This technology works by magnetizing the cables and detecting flux leakage through the magnetized cables.
- Ultrasonic Testing (UT): Critical anchorage components—including all pins and spanner nuts—were tested using ultrasonic waves to detect internal flaws (indications) not visible through standard visual inspection.
This project required a diverse set of certifications and expertise, including ASNT UT certification, SPRAT rope access certification, and specialized training for MFL and STS. BDI’s team used rope techniques to access pins and rig the MFL device. MFL provided valuable insight into the in-situ cable forces, cable condition, and integrity of the anchorage components including the spanner nuts and pins.
