As work nears completion on the Bay Bridge’s West Approach in San Francisco, it is accelerating on the new East Span between Oakland and Yerba Buena Island (YBI), where an entirely new bridge is being constructed to the north of the existing truss-cantilever structure. When completed in 2013, the new span will consist of several primary structures, including a 1.2-mile elevated Skyway, a signature Self-Anchored Suspension (SAS) span, a permanent transition structure connecting the SAS to the YBI Tunnel, and a new Oakland touchdown structure connecting the Skyway with the Oakland shore.
The monumental work that was performed on the West Approach over Labor Day weekend in 2006 served as a “dry run” for the even more complex work that was performed this past Labor Day weekend near YBI, when a large section of roadway on the bridge’s upper deck was removed and a 350-foot-long, seismically upgraded replacement section was rolled into place. This work required a full bridge closure—the first since the 1989 Loma Prieta earthquake closed the bridge for a month.
The YBI Viaduct Replacement
The process of performing this work was nothing short of an engineering wonder. Although this procedure had been performed elsewhere, this was perhaps the first time that such ambitious work was attempted within such a narrow timeframe.
The objective over Labor Day weekend was to close the bridge on Friday at 8 p.m.—after the rush of holiday traffic had diminished—and to open it to traffic at 5 a.m. on Tuesday, in time for heavy weekday traffic to resume. Contractor CC Myers, Inc., which completed the repair of the MacArthur Maze freeway structure in record time, has built a career performing major demolition and construction work under tight deadlines and was well prepared for the task at hand.
When the bridge was closed on Friday night, demolition began on a 350-foot (6,500 ton) section of the upper deck, known as the YBI Viaduct. A new replacement structure had been previously constructed to the south of the existing roadway and was resting on temporary support columns. Working with near surgical precision to avoid damaging the new columns, crews cut through concrete between the girders on the old structure, and a giant ringer crane lifted out huge, multi-ton sections of roadway and loaded them onto trucks to be hauled away. By late Saturday evening, crews had carved out a precise football-field-sized hole on the upper deck and had laid rails across the lower deck. The rails would be used to glide the new section of seismically upgraded roadway into place.
As soon as the demolition was completed and the tons of debris had been cleared, the new structure was lifted by computer-controlled hydraulic jacks and skidded into place along the temporary tracks, with a mere three-inch leeway on each side. The operation was unexpectedly fast—requiring slightly less than three hours—roughly half the time that was predicted. Once in place, the new roadway was grouted and striped, electricity restored, the jacks and rails removed, and the bridge reopened to traffic. All this in a mere 70 hours—11 hours ahead of schedule!
When the bridge reopened on Monday evening, the most apparent change to motorists was at the toll plaza, which featured new FasTrak lane configurations and signs. The massive work that had been performed on the bridge was much harder to detect, but essential nonetheless. “The YBI Viaduct will be part of the permanent structures connecting the western end of the SAS to the Yerba Buena Island tunnel. It is critical that it meets the same seismic safety requirements as the new bridge,” said Bay Bridge Project Manager Ken Terpstra. “Replacing this section of roadway under a full bridge closure made sense,” he added. “We now have a new seismically safe roadway with a longer life span, which was placed without jeopardizing the safety of our workers or motorists.”
The Road Ahead: Transition Structures and
YBI Temporary Bypass Structure
The work over Labor Day weekend represents the first in a series of phases to build a 900-foot temporary detour structure and permanent transitional roadways near Yerba Buena Island. These new roadways, which are slated for completion around the same time as the new Self-Anchored Suspension (SAS) span, will connect the western end of the SAS span to the YBI Viaduct, and will segue the side-by-side road decks of the new span to the upper and lower decks of the existing Yerba Buena Island tunnel and the West Span.
Constructing the permanent transitional structures near Yerba Buena Island can only be accomplished with a major traffic shift south of the island onto a Temporary Bypass Structure, which will route both east and westbound traffic from the exiting East Span around the southern side of the island and connect with the existing YBI Tunnel. Traffic is slated to be shifted to the Temporary Bypass Structure in 2009, following the completion of an East Tie-In. This will represent the most complex traffic shift yet on the Bay Bridge.