Seal Island Bridge - Deck Replacement

Deck Replacement

By 2001 it was found the existing cast-in-place concrete bridge deck was in poor condition. Forty years of wear and tear from traffic, and exposure to wind and salt spray, necessitated a major overhaul of the Seal Island Bridge. The road deck needed complete replacement, and the steel truss work needed reinforcement. Engineers had thoroughly inspected the rest of the bridge structure and found it to be sound and safe. A major deck replacement project was undertaken.

Over the next three years the original cast-in-place concrete bridge deck was removed and replaced using full-depth, precast, prestressed, half-deck width concrete panels. It was necessary to complete one lane at a time, starting with the south lane, leaving the other deck in place so the bridge could continue to be used for vehicular traffic. Construction was completed with minimal traffic disruptions and the bridge remained open to single lane traffic throughout construction, with the exception of three, six-hour overnight closures planned per week. This project added several decades to the useful life of the bridge.

The new high performance precast concrete deck system is much more durable than conventional systems since it is less permeable and crack-free under service load conditions. The deck system adopted is significantly lighter than a conventional cast-in-place concrete deck system. This has resulted in considerable savings in the amount of truss reinforcement required, while providing sufficient mass and stiffness for damping purposes. At the same time the guard rails (traffic barriers) were replaced over the entire length of the bridge, with the new guard rails set inside the main bridge trusses to better protect them from vehicle impact. Unfortunately this made the new bridge deck too narrow to retain the sidewalks so they were not replaced. This modification did result in wider traffic lanes. The overall cost of the bridge deck reconstruction was $15 million. There are now "No pedestrian traffic" signs on each end of the bridge.