Yerba Buena Island Transition Structure

THE YERBA BUENA ISLAND TRANSITION STRUCTURE (YBITS)

The Yerba Buena Island Transition Structure (YBITS) will connect the Self-Anchored Suspension Span (SAS) to Yerba Buena Island (YBI), and will transition the new East Span’s side-by-side road decks to the upper and lower decks of the YBI tunnel and West Span.

Crews face the challenge of building the YBITS without disrupting traffic. To accomplish this daunting task, eastbound and westbound traffic were shifted off the original roadway over YBI and onto a temporary detour during Labor Day weekend in 2009. The detour, built by prime contractor CC Myers, connects the East Span traffic to the tunnel. Drivers are using the detour, just south of the original roadway, until traffic is moved onto the new East Span. Due to a conflict between the YBITS and the original East Span, traffic was routed to the detour so crews can demolish the conflicting portion of the bridge leading to the YBI tunnel, and build the YBITS while traffic safely travels adjacent to the construction. MCM Construction is the prime contractor on the YBITS.

Crews are particularly careful during construction as to protect YBI’s rich military history, which dates back to the 1800’s. YBI, which currently has an active coast guard station, saw its first military post and depot built in 1868. Since then the island has hosted a torpedo station (the torpedo shed still stands on the eastern shore) and a U.S. Naval Training Station. Many of those structures remain, including the Nimitz House, a classic revival-style naval commandant’s house used by Admiral Nimitz during World War II.

Labor Day Weekend 2007

During Labor Day weekend 2007, crews demolished a piece of the original Yerba Buena Island viaduct to slide in a new section of the new East Span. The new section, known as the West Tie-In, also marked the first step toward building the temporary 900-foot-long detour. During this historic milestone, the entire Bay Bridge was closed—for the first time since the Loma Prieta earthquake—so crews could replace a 350-foot-long, 6,500-ton section of original viaduct on YBI, just east of the tunnel. Workers cut through the concrete between the girders of the existing roadway using hydraulic hoe rams and other heavy demolition equipment. A giant ringer crane lifted out massive multi-ton chunks of roadway which were hauled away.

With the old viaduct demolished, crews installed special rails and computer-controlled skid jacks to replace the roadway with a seismically upgraded section that functions as a connection to both the YBITS and detour. The new section was slid into place with a mere 3-inch tolerance on each side; the entire roll-in of the new viaduct was a first in California transportation history. While crews had only 81 hours to complete the entire project, they finished ahead of schedule and reopened the bridge to traffic 11 hours early. This marked the completion of the first part of the new East Span that drivers are already using.

With the new section in place, work shifted to the rest of the detour – the viaduct and the East Tie-In; the latter was slid into place in 2009. Much of the steel for the middle section was fabricated in South Korea. The steel for the supports holding the eastern end was produced in Washington state, while the steel for the eastern end’s trusses was fabricated in Arizona.

Labor Day Weekend 2009

Two years later and for only the second time since the Loma Prieta earthquake, the entire Bay Bridge closed to accommodate the connection of the YBI Detour. During Labor Day weekend 2009, a few hundred construction workers spent their holiday weekend making history. While the rest of the Bay Area enjoyed the warm weather at barbecues with friends and family, crews on the Bay Bridge moved 7,000 tons of steel perched more than 150 feet in the air.

Crews used oxygen-acetylene torches, jackhammers and excavators equipped with hydraulic hammer attachments to cut through the steel truss, double decks of a 300-foot-long, 3,300-ton section of the original bridge. With the section cut free, workers used a unique mix of high- and low-tech to push it out of the way. They lifted the section using eight 600-ton hydraulic jacks, and then moved it on stainless steel and Teflon pads, powered by 250-ton hydraulic push/pull units. Of interest is the fact that common household liquid dish soap was actually used to literally grease the skids.

Using that same system of hydraulics and dish soap, crews slowly but steadily moved the 3,600-ton connector (known as the East Tie-In) to the new detour into place, and set it down within a mere half inch variance. Once the new section was rolled into place, three-inch thick steel plates were placed at both ends to create expansion joints and connect the detour to the original bridge. Five such plates were installed at either end, on both decks, for a total of 20 plates. The plates are approximately 10 feet by 10 feet and weigh nine tons each.

Yerba Buena Island Detour

When the bridge reopened to traffic, motorists experienced a slightly different drive. The roadway curves to the south, requiring drivers to slow down while approaching or leaving the Yerba Buena Island Tunnel. On the detour, the speed limit was reduced from 50 mph to 40 mph, and 35 mph for trucks.

Construction of the YBITS has not sat idle during this time. Construction of the YBITS’ 13 supports (footings and columns) was attached to the contract to build the YBI Detour. Having the foundation work done in advance reduces risk to the schedule, as such work is a notorious source of delay due to unknowns encountered in the ground. Work on the foundations is completed and in 2011 the focus has been on beginning to build the main structure, the first phase of YBITS construction.

The second phase will include demolishing the detour once traffic has been shifted to the new East Span, as well as building a new eastbound on-ramp.

More on the 2009 Labor Day weekend closure here.

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