Demag AC 500-8 for bridge replacement

14 October 2020

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W.O. Grubb Crane Rental based in Richmond, Virginia, has operated its Demag AC 500-8 all terrain crane for nearly two years, most recently on a bridge replacement project in Lockhart, South Carolina.

The operation required hoisting and placing concrete girders onto piers for construction of the new SC Highway 9/49 Broad River Bridge, which replaces a functionally obsolete, 730ft (222.5m) structure, where the piers dated back almost 100 years. The new structure is part of a $20m project to update multiple bridges in this area.

W.O. Grubb deployed the AC 500-8 along with twelve truckloads of supporting materials from its Greensboro, North Carolina, branch roughly 150 miles (240km) from the bridge site. Within a day, the company’s six-man rigging crew had the crane, counterweight, Sideways Superlift, hook block and rigging material on site, staged and ready for rigging.

The following day, workers rigged the crane in its HA-SSL configuration with 396,800lb (180t) of counterweight and had it ready to lift the girders. The installed Sideways Superlift was set to a 30° angle to provide the required lift capacity. “The speed at which we can mobilize the crane and have it set up helped us to keep to the customer’s schedule,” said Ken Dawson, assistant branch manager for W.O. Grubb.

The crane had to cross uneven ground from the highway to river level, hen manoeuvre into position on compact gravel crane pads constructed in the river.

Craig Hunt, branch manager for W.O. Grubb said: “We had to derig, move the crane and then set it up four times to complete all lifts.” Dawson added: “It could not have been efficiently completed within the time frame needed with a crawler.” Lift capacity, compact manoeuvrability and quick set-up offered by the AC 500-8 were substantial benefits on this job.

Once the all terrain crane was in position, it completed all girder lifts planned for that location, with working radii reaching 100ft. Crew members then derigged the crane by removing the 396,800lb of counterweight in preparation for the move to the next pad. “Since we moved the crane over uneven ground and crossed the existing bridge, the counterweight had to be removed,” added Dawson.

The crew retracted the main boom and kept the Sideways Superlift and outriggers installed. “The way we were able to derig, move and set up the AC 500-8 allowed us to complete the cycle in one shift and stay on schedule,” said Hunt.

The girders weighed in a 160,000lb and were all roughly 80ft long. The Demag crane lifted the girder from transport trucks in tandem with the assistance of one of the bridge contractor’s 200USt (180t) crawler cranes.

In addition to the 396,800lb of counterweight and 30° Sideways Superlift, 169.9ft of boom was needed to complete the lifts. With this configuration, the AC 500-8 offers greater than 85,000lb capacity at the 100ft maximum working radius.

In total, 30 concrete girders were hoisted onto the new piers, so the bridge contractor could continue with constructing the new Broad River Bridge. W.O. Grubb’s crew was on site three weeks and completed the project on time.