Rugged conditions are no match for the Demag AC 500-8
W.O. Grubb Crane Rental, Richmond, Virginia, has operated its Demag® AC 500-8 all terrain crane for nearly two years. In that time, Craig Hunt, branch manager for W.O. Grubb, has used the crane in just about every imaginable application.
It’s the company’s go-to crane for infrastructure, power plant, industrial, petrochemical, tower crane erection and commercial maintenance projects. “The AC 500-8 is compact, easily maneuvered and navigates well in off-road conditions,” comments Hunt.
It was specifically for these reasons W.O. Grubb used the AC 500-8 on a bridge replacement project in Lockhart, South Carolina. The task required hoisting and placing dozens of concrete girders onto piers for construction of the new SC Highway 9/49 Broad River Bridge, which replaces a functionally obsolete, 730-ft (222.5-m) structure, where the piers date back nearly a century and the steel span superstructure nearly 70 years. The new structure is part of a $20 million project to update multiple bridges in this area.
W.O. Grubb mobilized the AC 500-8 all terrain crane plus 12 truckloads of supporting materials from its Greensboro, North Carolina, branch roughly 150 mi (240 km) to the project site. The crane meets axle load limits with 183.7 ft (56 m) of main boom installed and travels to project sites at highway speeds reaching 50 mph (80 kmph). 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 396,800 lb (180 t) of counterweight and had it ready to lift the girders. The installed Sideways Superlift was set to a 30-degree angle to provide the required lift capacity, especially when working at a long radius. “The speed at which we can mobilize the crane and have it set up helped us to keep to the customer’s schedule,” says Ken Dawson, assistant branch manager for W.O. Grubb.
The process of lifting the girders into position was not an issue. All lifts were straight forward, according to Dawson. Site access and mobility were the challenges. “Ken worked the project off-and-on for about a year,” recalls Hunt.
The crane had to traverse uneven terrain to get from the highway to river level. Then it had to maneuver into position on compact gravel crane pads constructed in the river.
If the crane was able to place all the girders from one location, perhaps the job could have been completed using a crawler crane. However, Hunt explains, “We had to derig, move the crane and then set it up four times to complete all lifts.” Dawson adds, “It could not have been efficiently completed within the time frame needed with a crawler.” Lift capacity, compact maneuverability 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 100 ft (30.5 m). Crew members then derigged the crane by removing the 396,800 lb (180 t) 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,” offers 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,” adds Hunt.
Maneuverability and fast set-up aside, the Demag AC 500-8 all terrain crane was brought in to provide the heavy lifting. The girders weighed in a 160,000 lb (72.6 t) and were all roughly 80 ft (24.4 m) long. The Demag crane lifted the girder from transport trucks in tandem with the assistance of one of the bridge contractor’s 200-U.S.-ton (180-t) crawler cranes. “Because we moved the crane several times to position the girders, it was impractical to use the on-site crawler for the lifts,” says Hunt.
In addition to the 396,800 (180 t) of counterweight and 30-degree Sideways Superlift, 169.9 ft (51.8 m) of boom was needed to complete the lifts. With this configuration, the AC 500-8 offers greater than 85,000 lb (38.6 t) capacity at the 100-ft (30.5-m) maximum working radius.
In total, 30 of the 160,000-lb (72.6-t) 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, a feat attributed to the crew’s hard work and the AC 500-8 crane’s ability to be quickly derigged, moved and set up for a series of lifts.
“It’s satisfying to see nearly a year’s worth of work come to fruition, especially since everything worked as planned,” says Dawson. “The AC 500-8 went together very well and performed as expected, especially with regard to the moves. We were incredibly pleased with the crane’s overall performance.”