NBIS Inspections of Moveable Bridges

JMT performed the National Bridge Inspection Standards (NBIS) biennial, re-evaluation survey of five long-span moveable bridges, four of which were historic. The project included hands-on, routine underwater and interim inspections of the Townsends Inlet, Grassy Sound, Corsons Inlet, Middle Thorofare, and Great Egg Harbor Bridges. We completed full inspections of the span locks, load shoes, strike plates, trunnions, and trunnion bearings for all five bridges, as well as a full mechanical and electrical inspection of the Middle Thorofare span drive system. We performed underwater inspections in accordance with New Jersey Department of Transportation and NBIS requirements.

The approach spans to the single leaf bascule spans on each bridge are a combination of fracture critical steel three beam approach spans with pin hangers and two girder riveted steel approach spans, requiring hands-on Fracture Critical Members (FCM) inspections. Visual, hands-on inspections were performed on the FCMs. Special attention was given to section loss, fatigue cracks, weld flaws, fatigue sensitive details, movement, collision damage, live load capacity, and low ratings. We inspected fatigue-sensitive details and welds to locate and assess weld flaws and identify any cracks. AASHTO Fatigue Category details, pin and hanger details, gusset/splice plate connections on main load carrying members, and non-redundant load path members were checked in accordance with the Federal Highway Administration Manual on Inspection of Fracture Critical Bridge Members, and New Jersey Department of Transportation Guidelines Inspection of Fracture Critical Elements. The field inspection required the use of a mobile platform truck and a snooper to access the superstructure and a boat to access the substructure.

Preliminary biennial inspection reports were prepared and submitted to the County for review and comment. Final reports incorporated all County Engineering comments. Sixteen emergency and priority repairs were identified, including the severe section loss of the bascule span floor system and non-functioning span locks on the Townsends Inlet Bridge.