Rental firm Bryson Crane employed two spreader beams, manufactured by Modulift, below-the-hook of a Terex all-terrain crane to lift the first of 17 90,000-lb. prefabricated buildings into position at a communications tower in Edgewater, Florida.
The MOD 50 spreaders, which offer up to 50t capacity at 8m or 26 ft. and up to 13m or 42 ft. at a lower capacity, were used with slings, shackles, and rolling blocks, as the 130t capacity Terex Explorer 5500 employed its 60m-long main boom to lift and move the unit 30 ft.
Bryson, of Florida's Dayton Beach, accepted the scope of work from a local power company to relocate the communications buildings. The structures, which measure 12 ft. x 20 ft. x 10 ft. and all weigh approx. the same, contain switches, breakers, and other equipment required to run the substation.
Scott Woodward, facilities manager at Modulift distributor I&I Sling Inc., from where the below-the-hook rig was sourced, explained that Bryson's biggest challenge was presented by an offset centre of gravity, caused by backup batteries that are housed at one end. Four rolling blocks were mounted to the spreader beams to counter the offset in weight.
Ray Rutt, operations manager at Bryson, said: "By adding length to the rigging, we were able to ensure that each bottom sling that was connected to each pair of lifting points was equally tensioned by the wire rope moving over the roller. This particular rig configuration will commonly warrant the use of rolling blocks."
He continued: "We opted for a very compact rig to reduce the height and keep the spreader bars close to the load. This rig is more commonly used when there are four bottom lifting points [not eight as in this case] and the rig height is crucial. As there were a greater number of lifting points, the rolling blocks were a requirement."
Rutt added that Bryson selected the spreader beam configuration versus a lifting frame because it already owned one MOD 50 and it made sense to acquire an additional unit. At the time of going to press, the 17 lifts are scheduled over the coming weeks.
Bryson's crane operators are certified through the National Commission for the Certification of Crane Operators (NCCCO). Its varied fleet offers customers up to 600-ton lifting capacity in addition to forklift trucks and rigging personnel. Utilities, construction, aerospace, and marine industries are just a few of the sectors it serves.