San Francisco 4-Th Street bridge picked up with trailers at low tide

Project Summary

In order to refurbish one of the old San Francisco South of Market bridges, it needed to be completely removed and stored "high and dry". A barge was to be used to lift the bridge structure out of its hinges and then using low bed trailers, roll the structure onshore. Because of the conflicting requirements (low barge for entry at low tide and high barge for rolling off the trailers at high tide) many barge configurations were analyzed before the final selection was made. In order to improve initial stability as well as the ballast capacity of the selected barge, 3 sectional barges were mounted to the outboard side. These could be filled with ballast water to provide the counter moment during roll-off.

On June 30, 2003 during early morning low tide, the cargo barge 220, outfitted with the sectional barges on one side, crane mats and multi-wheel trailers on deck, was carefully maneuvered under the bridge. Once in position, the barge was deballasted to take the weight of the bridge and lift it free of its supports. After waiting for high water, the barge was moved to the south shore and while continuously ballasting the sectional barges, the bridge was successfully rolled off onto the street, under the watchful eyes of a number of San Francisco dignitaries.

Scope of Work

The project scope included:

• Concept feasibility study;
• Verify feasibility of each of the available barges and select final configuration;
• Check of stability throughout the various phases of pick-up and roll-off;
• Design of detailed ballast procedures for roll-off of the bridge onto the street;
• Provision of on-site assistance during the operation.

Project Photographs

Barge with trailers maneuvered into position under the bridge at early morning low tide.	Bridge pin lifted free of its hinge saddle by rising tide combined with deballasting of the barge.	Deballasting of the outboard sectional barges to compensate for the weight going off at the other side.	At high tide, bridge is slowly rolled from barge onto the street while barge is deballasted to keep it level.