Customer

Burkhalter Rigging, Inc.

Location

San Francisco, California, USA

Products

Jack-Up System

Challenge

The San Francisco–Oakland Bay Bridge spans San Francisco Bay in California. As part of Interstate 80 and the direct road between San Francisco and Oakland, it carries about 270,000 vehicles a day on its two decks, and has one of the longest spans in the United States.

The bridge is in two sections--the western section, known as the Willie L. Brown Jr. Bridge connecting downtown San Francisco to Yerba Buena Island and the newer unnamed eastern section connecting the island to Oakland. The Willie Brown Bridge is a double suspension bridge with two decks, westbound traffic being carried on the upper deck with eastbound carried on the lower one. During the 1989 Loma Prieta earthquake, a section of the eastern span's upper deck collapsed onto the lower deck, and the bridge was closed for a month. Following the earthquake, the western suspension span underwent extensive seismic retrofitting to replace much of the structural steel supporting the bridge deck. For various reasons, the eastern span would have been too expensive to retrofit compared to replacing it, so the decision was made to replace it.

Reconstruction of the eastern section of the bridge began in 2002 and was completed in September 2013. Unlike the west span and the original east span, the new east span is a single deck with the eastbound and westbound lanes on each side, making it the world's widest bridge. Demolition of the old east span is expected to last until 2018.

Solution

Removing the East Span

Dismantling and removal of the old Bay Bridge East Span is in three phases: Phase I was completed at the end of 2015, with the demolition of the cantilever section and S-curve to Yerba Buena Island. Phase II of the demolition process involved the removal the bridge's 1.7 million-pound truss sections, which stretch east to the Oakland shore, and included five 504-foot segments, followed by (14) 288-foot sections stretching from Pier E9 to Pier E22, approximately three quarters of a mile.

Burkhalter Rigging, Inc., a specialized lifting, rigging and transport service provider, was awarded the contract to remove the 288ft segments. The project posed significant challenges. At its highest point, the bridge is 36m (135ft) above water level, with a progressive downward slope to the shore to 40ft above the water. This meant that each span was at a decreasing angle as the segments reached the shoreline. Moreover, lifting would need to take account of tidal changes and wind/weather on the bay. Importantly, all the bridge segments had to be removed between November 2016 and April 2017 ahead of migratory birds returning to the area and nesting on the bridge, after which further removal work would have to be suspended until the birds migrated again.

Burkhalter proposed the use of their Enerpac hydraulic jack-up system to lift each 288 ft bridge section. Earlier removal of the 504 ft truss sections has been accomplished using strand jacks mounted within a supporting frame. The same lifting method was considered for the 288ft sections; however, it would have required more time to set up and lift each truss than using the jack-up technique.

"We already had some experience of the speed and ease of deploying the Enerpac jack-up system on a barge from installing the Fore River bridge in Boston. The major difference here was that although the Fore River bridge lift was twice as heavy as the Oakland bridge sections, the height was much lower at 20m. For the Oakland project, we’d have to almost double the lift height to 36m," says Mike Cassibry, Director of Special Applications at Burkhalter.

The Enerpac’s JS-Series jack-up system is a multi-point lifting system comprising four jack-up towers positioned under each corner of a load. The lifting frame of each jack-up tower contains four hydraulic cylinders, which lift and stack steel barrels. The load is lifted in increments as barrels are inserted via an automated system, lifted, and stacked, forming the lifting towers. The lift capacity per tower ranges from 125 ton to 750 ton. Burkhalter used a JS-750 jack-up system for the Oakland bridge lift with barrels measuring 2.3m x 2.3 x 1m or 7.5 feet x 7.5 feet x 39 inches high.

In reaching the highest truss section at 36m above the water, side load on the jack-up towers is a major factor in planning the lift. Following extensive analysis and modelling by Enerpac, the concept of a box type bracing system was developed for lifts above 20m. This is based on using a special fabricated intermediate barrel with connection points for crane booms and steel wires attached to strand jacks to provide horizontal bracing – creating a hydraulic tensioning device used to stabilise and monitor the side load. As the towers are raised, the crane booms, resting on steel supports above ground are automatically latched on. The bracing wires and strand jacks resting on the boom sections were pinned to the special barrels. Each of the towers was then raised to the height required to lift the bridge section. For lifts below 20m, the bracing system was dispensed with.

In addition, Burkhalter also minimized the side load during movement of the jack-up on the barge by performing additional lift and trim calculations and maintaining the spans’ center of gravity at a precise point to keep the barge level, as well as constant monitoring of tide levels, during truss removal. "Using the bracing system keeps the lift stable, and there is no opportunity for instability," notes Mike Beres, sales leader – Americas, Enerpac Heavy Lifting Technology, "while the stiffer and heavier intermediate barrel provided the support and rigidity needed to facilitate the bracing arrangement."

Truss Section Removal

Given the length of each truss section, the four jack-up towers were deployed on a twin barge assembly to form a single floating platform, with two jack-up towers on each barge. Ahead of the arrival of the barge, the bridge sections were cut from the adjoining segments ready to be lifted from their foundations. The barge was floated in position under the segment and the jack-up towers raised. The west and east facing towers were each connected by a beam on which the truss would rest when lifted. Because of the angle of the segment, the west side towers were approximately 1m higher than the east side towers. The East Span removal began in the middle section, at the intermediate fixed pier, and removed progressively towards the shoreline in the direction of the lowest section. Then, the spans were removed from the middle working towards the highest truss section. Height flexibility of the jack-up system meant that the same process could be used for the highest span and lowest near the shore, where only a single barrel was needed. Once the bridge section was removed, the barge was then moved away from the bridge, the towers lowered, and the span transported to the Port of Oakland for disposal and recycling.

"Using the Enerpac jack-up system was a massive advantage. It has great lateral stability and the elevation is quick and simple to change. Moreover, the speed with which each span was removed using the jack-up was a pleasant surprise. Once in position, the time to stroke up and take the load took just a couple of minutes to lift the span clear. Using the Enerpac jack-up system, we were able to cut each span removal from six weeks to about one week per span," concludes Mike Cassibry.