04 - 0435U4 -WEST SPAN SUPERSTRUCTURE



October 5, 1999





PROJECT CONTACT PERSONS
PROJECT MANAGERKen Terpstra(510) 286-4679
PUBLIC INFORMATION OFFICE(510) 286-4444
CONTRACTORCalifornia Engineering Contractors/
Modern Continental

CONTRACT INFORMATION
CONTRACTOR'S BID$146 million
NUMBER OF WORKING DAYS
CONTRACT AWARDED09-24-99


ISSUES

On Route 80 in the City and County of San Francisco at San Francisco-Oakland Bay Bridge, West Spans, Bridge No. 34-0003, PM 5.3/7.7. The west span of the bridge extends from the San Francisco Anchorage in the City of San Francisco to the Yerba Buena Island Anchorage on Yerba Buena Island in the central San Francisco Bay. The seismic retrofit will occur within the same alignment as the existing bridge. The San Francisco-Oakland Bay Bridge (SFOBB) is a major transportation link between San Francisco and the East Bay cities. A closure of this bridge due to a seismic event, and subsequent repairs, would create a major economic impact to the region. As such, the SFOBB qualifies as an "Important Bridge" as defined in "Seismic Performance Criteria for the Design and Evaluation of Bridges". In addition, the Bay Bridge is designated as an emergency "lifeline" route to be used in disaster response activities. As a lifeline route, the state would use the bridge to provide a high level of post-earthquake transportation service for emergency response and support for the regionšs economy. The objectives of the seismic retrofit for SFOBB West Spans are to improve operational and safety standards to the greatest extend possible and to allow the SFOBB to remain open and functional following a Maximum Credible Earthquake.

RETROFIT PROPOSAL

West Bay Suspension Span Towers

This segment of the contract involves the seismic retrofit of the steel towers atop Piers W-2, W-3, W-5 & W-6. These towers are similar in configuration, and therefore the proposed retrofits are alike in concept, though the amount of work at each tower will vary. The proposed retrofit measures include replacing rivets with high strength bolts throughout portions of the towers. Adding new plates and replacing all the rivets with high strength bolts will retrofit many of the existing gusset connections. Also, additional plates will need to be placed along portions of the longitudinal faces of the tower legs and at W-6, along the longitudinal and transverse faces, and at various strut and diagonal locations at all towers. Replacing existing rivets with high strength bolts will strengthen the Cable Saddle connections at the top of towers. A new upper deck wind tongue will be constructed. Additionally this contract will involve the installation of viscous dampers at the truss-to-tower connection of the suspended spans. These dampers will allow the structure to behave in its "as-built" condition under service loads. However, under seismic events these dampers will engage and prevent the superstructure from ramming into the towers and thus will enhance the overall seismic performance of the structure. These devices are similar to the ones proposed for the Golden Gate Bridge and for which fairly large scale testing has been done. It is anticipated that the work on these towers will be done from a barge type vessel and from equipment located up on the decks. A maximum of four lanes will be allowed to be closed on the decks during the off-peak hours. In addition, some limited full closures of the entire upper deck will be allowed Sunday Morning. All barges will be anchored up to the pier based on the Coast Guard approved tie down configurations so as to minimize delays or obstructions to shipping traffic. The barge will serve as more of a support vessel for the work on the tower bases. The contractor may elect to put a large crane on the barge to complete some of the work planned for the tower below the lower deck. Depending on the contractor, some equipment could be placed the pier and the work will be from there. The retrofit work at and above the lower deck will likely require cranes and other large hoisting equipment on the upper and lower decks.

West Bay Suspension and Span Superstructure

This segment of the contract includes the "twin" suspension and the Continuous Span Truss. The East and West Suspension Trusses are located between Pier W1 and Yerba Buena Island Anchorage. The Continuous Span Truss is located between Pier W1 and the San Francisco Anchorage. This seismic retrofit involves strengthening the existing bottom lateral bracing under the lower deck and placing a new lateral bracing on the upper deck of the suspended truss. Additionally several of the chords and all the diagonal members for all the trusses need to be strengthened. This will be accomplished by installing additional plate sections and replacing existing lacing with perforated plate. Many of the connections require replacing the rivets with bolts to increase capacity. The connection of the floor beam to the chord will be strengthened to ensure its ductility. Selected gusset will be strengthened. All rocker posts on the suspended truss will have new cover plates installed. Bearings will be modified at both ends of the Continuous Truss with dampers being installed at the lower deck only at the San Francisco Anchorage. It is anticipated that the contractor will be able to do most of this work from the upper and lower decks. Temporary lane closures will be needed for the construction equipment such as cranes and other large hoisting equipment. A maximum of three lanes will require to be closed on the lower deck during the off-peak hours. The contractor can use existing traveling scaffold rails.

Electrical Work

This contract will also temporarily or permanently replace electrical conduits. A new lower deck lighting system will be installed to replace the entire existing lower deck lighting system. Abandoned system in conflict with the retrofit work will be removed.

The following electrical lighting systems will also be modified: