The main hoisting work was undertaken by a GP500 hoist powerpack with a Tier 4 QSB6.7 rated 260 hp at 2300 rpm, with a second powerpack available with a Tier 4 QSB4.5 rated 160 hp. The GP500 hoist travels at a high speed of 85 feet per minute, which gave a 14,000-lb line pull, and nearly 50 feet per minute in low speed, with a 50,000-lb pull. The total capacity of the ASD35/120 derrick is 70,000 lb (35 tons).
Given the need for environmental considerations working in such a sensitive location, the Tier 4 engines provide clean, fuel-efficient power for the derrick. Engine dependability was critical, as any issue with the derrick could severely impact a very tight job completion schedule and soon run up a high cost.
Although preceded by a long process of logistical planning with the crane rigging contractors, the Timberland derrick was situated on the roof for just six weeks, including a week to build and test. The ASD35 derrick proved strong enough to work in winds of 30 mph at the top and 15 mph at the bottom on the building, with only five days lost due to clouds or fog preventing work.
With all lifting work complete, the derrick was demobilized and taken down using the elevator, being broken down into sections of about 8 feet, which allowed it to be
man-handled. The Tier 4 QSB6.7- and QSB4.5-powered derrick worked perfectly on the 432 Park Ave. project, and the contractor – Able Rigging – so impressed that it ordered a second ASD35 derrick for its supertall building crane fleet.
1 World Trade Center
As the new 1 World Trade Center neared completion in May 2013, Timberland supplied a 35-ton capacity ASD35 Stiffleg derrick with double-drum hoist using 1-inch (25-mm) wire rope to perform the required pickup and lowering of the tower crane used throughout its construction.
The dismantling project was completed smoothly and without incident by rigging contractor DCM Erectors. Powered by a Tier 4 QSB6.7 engine rated 260 hp, the derrick’s first job was to carefully lower the big tower crane’s 160-foot-long boom down to ground level, some 105 floors below the roof.