Tacoma Narrows Bridge
Foss has supported several critical milestones in building Washington State's new 5,400-foot Tacoma Narrows suspension bridge. For the first phase of this complex project, Foss positioned huge caissons that formed the bases of the bridge towers, and then helped contractors string pilot lines for the main cables. In the final phase, Foss is helping to move and position 46 huge pieces of steel roadway, each about 120-feet long and weighing up to 600 tons. This is a major a challenge in the strong tidal currents in the Narrows, which can swirl at up to 8 knots.
Requiring complex project management and engineering savvy, the Foss shipyard modified a barge, Marmac 12, to carry each of the steel sections from a ship to its pre-assigned positions under the bridge's main cables. Manufactured in Korea and transported in stacks on dockwise semi-submersible vessels, each roadway section is loaded by crane onto the Marmac 12, which moves them into position for lifting one by one. Four large thrusters, linked by computer from the Dynamic Positioning System, automatically adjust to changes in the current
The sections were then hoisted into position, attached to vertical suspension cables, and bolted together. Foss' tractor tug, Pacific Explorer, provided extra muscle. Working on this project has special meaning for Foss, which provided maritime support during the construction on the original Tacoma Narrows Bridge in 1939.
Carquinez Bridge
Construction of the Carquinez Bridge in San Francisco required lifting 24 roadway segments – each weighing in excess of 800 tons – from a heavy lift ship using strand jacks. This was the first time that such a project was attempted in high current waters. In collaboration with the bridge contractor, Foss Maritime engineers and operations personnel determined the best way to effectively hold both the barge and ship to a tolerance of 250 mm in currents exceeding 4 knots by using a combination of anchors and tug assistance. Foss also succeeded in the difficult task of transferring four roadway sections to a barge for positioning in the shallow water on the inside of the towers. On the marine operations side, the project involved 28 lifts, over 110 anchor sets and anchor retrievals, and running 2” cable from the ship to the anchor gear. The bridge was completed on schedule and without injury.
A Foss barge with a bridge section during construction of the Carquinez Bridge.
Foss engineers assisted in fabrication and modification of vessels and equipment to move bridge sections.
Foss Enhanced Tractor Tugs at work towing a giant caisson.