Jack-up system performs huge bridge lift safely
An Enerpac heavy jacking system of a type being deployed throughout Australasia has demonstrated its power, precision and safety in international use by removing more than a kilometre of high bridge spans in the United States in record time.
Burkhalter Rigging Inc used the world’s tallest JS-70 multi- point incremental jack-up system to remove a total of 14 bridge sections, each of 87.78 m, stretching more than 1200m on the eastern section of the old San Francisco- Oakland Bay bridge, which was damaged in an earthquake. Use of the jack-up system cut each span removal from six weeks to about one week per span.
The engineering task – which involved total weights of hundreds of thousands of tons of steel at up to 20m above a surging tide in fluctuating winds – is highly relevant to Asia- Pacific nations located on the region’s earthquake- prone “Rim of Fire”, which circles the Pacific, says Enerpac Australasia Mining and Heavy Lifting Technology Manager Warren Baltineshter.
In addition to repairing damaged road and rail structures, the jack- up technology is used for the lif ting and lowering of heavy equipment such as mining shovels, excavators and electrical plant; lif ting and lowering of structures and buildings; and de- propping and load transfer from temporary steel work.
The San Francisco– Oakland Bay Bridge – which carries about 270,000 vehicles a day on its two decks, and has one of the longest spans in the United States – was built in two sections, the eastern one of which was damaged extensively during the 1989 Loma Prieta earthquake.
The eastern span would have been too expensive to retrofit so it was reconstructed as 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, meanwhile, is expected to last until 2018.
REMOVING THE EAST SPAN
Dismantling and removal of the old Bay Bridge East Span is proceeding in three phases: Phase 1 was completed at the end of 2015, with the demolition of the cantilever section and S- curve to Yerba Buena Island. Phase 2 of the demolition process involved the removal the bridge’s 771,000kg truss sections, which stretch east to the Oakland shore, and included five 153.61m segments, followed by the 87.78m sections stretching from Pier E9 to Pier E22.
Burkhalter Rigging, Inc., a specialised lifting, rigging and transport service provider, was awarded the contract to remove the 87.78 segments. The project posed significant challenges. At its highest point, the bridge is 36m above water level, with a progressive downward slope to the shore to 12.192 metres above the water.
This meant that each span was at a decreasing angle as the segments reached the shoreline. Moreover, lif ting 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 lif t each 87.78m bridge section. Earlier removal of the longer truss sections has been accomplished using strand jacks mounted within a supporting frame. The same lif ting method was considered for the 87.78m sections; however, it would have required
more time to set up and lif t 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 lif t 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 lif t height to 36m,” said Mike Cassibry, Director of Special Applications at Burkhalter.
Enerpac’s JS-Series jack- up system is a multi- point lif ting system comprising four jack- up towers, one positioned under each corner of a load. The lif ting frame of each jack- up tower contains four hydraulic cylinders, which lif t and stack steel barrels. The load is lif ted in increments as barrels are inserted via an automated system, lif ted, and stacked, forming the lif ting towers. The lif t capacity per tower ranges from 113.398 – 680.389 tonne. Burkhalter used a JS-750 jack-up system for the Oakland bridge lif t with barrels measuring 2.3m x 2.3 x 1m.
In reaching the highest truss section at 36m above the water, side load on the jack-up towers was a major factor in planning the lif t. Following extensive analysis and modelling by Enerpac, the concept of a box type bracing system was developed for lif ts 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 lif t the bridge section. For lif ts below 20m, the bracing system was dispensed with.
In addition, Burkhalter also minimised the side load during movement of the jack-up on the barge by performing additional lif t and trim calculations and maintaining the spans’ centre of gravity at a precise point to keep the barge level, as well as constant monitoring of tide levels, during truss removal.
“The stiffer and heavier intermediate barrels provide support and rigidity for the bracing system, which keeps the lif t stable,” notes Mike Beres, Sales Leader – Americas, Enerpac Heavy Lifting Technology.
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 lif ted 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 lif ted. 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 lif t 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,” said Cassibry.
PRODUCTS: JACK- UP SYSTEM
The JS-series is part of the Enerpac range of heavy lif t, shift, balance and place solutions, which includes the world’s largest portfolio of heavy lif t and load control applications. Enerpac systems – such as hydraulic gantries, strand jacks, skidding systems, self- erecting towers, self- propelled modular transporters (SPMTs) and synchronous lif t systems – can handle some of the world’s most challenging lif ts, including awkwardly shaped and sometimes massive structures weighing tens of thousands of tons in maritime, mining, energy and heavy industrial applications.