Enerpack solves heavy falsework lowering problem

Contractor C.C. Myers faced a difficult problem when constructing the Galena Creek Bridge – one of nine bridges for a new 13.7km highway I-580 extension between Reno and Carson City in Nevada. The Galena Creek Bridge comprise two arches, each carrying three lanes of traffic and will be 525m long, with a 210m main span that rises 90m feet from the creek to the bridge deck. On completion in 2011 it will become the longest concrete-arch bridge in the U.S.

Concrete for the arch bridges is poured within a complex falsework structure, with the falsework subsequently lowered away from the hardened concrete. However, in the planning stage it was found that the falsework would be too heavy to lower with the usual cables and winches.  Myers chose a novel solution to the lowering challenge - strand jacking.

The jacks work by grabbing and lifting or lowering cables passing through their hollow centres (see pic) and twelve 77t jacks are needed to lowering each of the giant falsework sections. However uniform lowering at all twelve points is critical if uneven lowering (which could overload some cables) was to be avoided.

To cope with this requirement Enerpac Integrated Solutions provided a system whereby each jack is electronically controlled and networked to a digital controller. The jacks have built-in sensors for closed-loop operation with the controller, and movement of the jacks is synchronized to within 1mm between leading and lagging jacks as they lower the falsework to the ground. In addition to stroke and load alarms, the controller provides individual stroke and load readouts.
Myers sent two employees for factory training on the strand jacking system and its staff designed and fabricated a dozen steel enclosures to protect the jacks against the weather.  Each enclosure houses a strand jack, an 11kW electric hydraulic supply (powered by on-site generators) and a Myers-designed cable coiler.

According to Bill Kidwell of C.C. Myers, the suspended loads at Galena Creek average 50t per jack, and falsework sections are lowered at about 18m/hr. The controller architecture is modular allowing up to 32 jacks to be controlled by a single controller and even these can be networked together for even bigger projects and its overall flexibility should enable Myers to utilise the equipment on future projects.