The East Span comprises four interconnected structures: the 2,047-foot-long Self-Anchored Suspension Span (SAS); the 6,900-foot-long segmental concrete box girder Skyway viaducts (Skyway) that sweep up from the Oakland shoreline to connect with the SAS; the 4,229-foot-long Oakland Touchdown, which links the Skyway to California’s Interstate 80; and the 1,542-foot-long Yerba Buena Island (YBI) Transition Structure that connects the SAS to the YBI tunnel.

The Skyway portion of the East Span is the bridge’s longest component. The parallel eastbound and westbound viaducts carry 10 lanes of traffic in each direction, with 10-foot-wide shoulders to maintain traffic flow and a new bicycle-pedestrian path that enables users to enjoy panoramic views of the region.

The viaducts of the Skyway are three-cell, variable-depth, precast segmental box girders, erected in balanced cantilever, with a typical span of 525 feet. The 452 concrete segments for the Skyway box girders were cast in a special precasting yard and are the largest of their kind ever cast, each weighing up to 750 tons.

After being match cast and stored up to six months to reduce the effects of creep and shrinkage, the segments were barged about 70 miles to the Skyway construction site. Once on site, Self-Launching Erection Devices (SLEDs) were used to lift the massive segments up to 135 feet above the water and into place on the cantilevers. The SLEDs were set up and anchored to the cast-in-place pier tables. The first precast segment was hoisted up from a float barge and a cast-in-place closure was made between the pier table and the first segment. Once the pier table and segments were post-tensioned together, the SLEDs advanced onto the leading segment and were re-anchored. The next pair of segments were then erected and post-tensioned together. The process repeated, with the SLEDs advancing outward from the pier table until all pairs of segments of a typical cantilever were erected.

The balanced-cantilever method of construction was used for the Skyway to compensate for the high cost of constructing seismically-resistant foundations in the soft bay mud. Using this method, the variable-depth segments were erected in both directions, working outward from the piers, and allowed longer span lengths. While this method increased the cost of the superstructure, it reduced the number of spans and lowered the cost of the foundations.

The Skyway superstructure is divided by expansion joints into four frames, three with four piers and one with two piers. The frames are typically connected at midspan by a large hinge pipe beam measuring 6.5 feet in diameter and 60 feet long and are supported on circular bearings. The pipe beams are designed to not unseat during an earthquake, and are constrained against longitudinal movement in one cantilever and free to slide in the adjacent cantilever. This permits the bridge frame to expand and contract at the hinge locations. During an earthquake, the hinge pipe beams constrain the two parts of the structure to move together transversely and vertically, thereby limiting damage to the expansion joint above. In case of overstress, the midsection of the hinge pipe beam absorbs the strain, minimizing damage to the remaining length of the pipe beams.

Carrying 300,000 vehicles per day, the Skyway viaducts also required specially-designed expansion joints that could carry heavy traffic and reduce lane closures during repair procedures. While the expansion joints on the original bridge could only accommodate up to a few inches of movement during an earthquake, the expansion joints used on the new structure can handle up to several feet of movement.

A battery of mock-ups was performed to verify constructability and circumvent challenges in the field, thereby maintaining and/or accelerating erection operations and reducing the risk of impacts to the schedule. While this method has been used to create secure foundations for offshore oil rigs, this is the first time the technology has been used for bridge construction of this scale.