In an unprecedented engineering feat, New York City high-rise crews on May 11 successfully hoisted a 150-ft-long replacement luffing boom to the roof of One57, a 1,100-ft-tall residential building under construction in midtown Manhattan, and attached it to an existing tower-crane mast. The new crane is now in service.
In an interview with ENR, construction manager Lend Lease explains how workers pulled off the task, which engineers say has not been done before at such heights.
"It was an extremely involved process," says Paul Finamore, Lend Lease senior vice president and project executive. "Every step required New York City Dept. of Buildings approval." The roughly 10-hour job also required three nearby buildings to be evacuated.
Tower cranes usually are built closer to the ground using a mobile assist crane and then jacked up into position. When construction is complete, the cranes are usually jacked down again. In the case of the original One57 rig, there was no way to lower the mast using the typical jacking method because it had been damaged.
The challenge was to devise a way to rebuild the crane 1,100 feet in the air. The new luffing jib replaces the one that was damaged during Superstorm Sandy, which sent 90-mph gusts or higher to the top of the tower. Winds blew the boom backward over its mast, where it hung precariously over the city.
Planning the job to replace the damaged crane superstructure, which was dismantled earlier this year piece by piece using smaller, roof-mounted cranes, has been in the works since the storm. Two weeks prior to this month's lift, workers first removed two sections—each about 18 ft tall—of the crane's 54-section mast. This strategy allowed a 35-ton Timberland derrick mounted on the roof of One57 to have enough clearance to hoist the boom into position.
Crews then brought up smaller components, such as the cab, rotating gear, counterjib, counterweights, winches and other parts needed to operate the crane. Riggers preassembled the four-section boom on the ground and attached all the necessary rigging the day before the lift.
Starting at 3:30 a.m. on May 11, crews arrived at the site, according to Finamore. At 4:00 a.m., the derrick's hook began its slow journey down to the street. Because the derrick was fitted with multiple parts of line, it took about 45 minutes for the hook to reach the bottom of the building.
The rigging was designed to hoist the boom at exactly a 15° slope. The angle was required to make sure the bolt holes lined up when the boom reached the crane's upperworks, according to Lend Lease.
"It is tied to the location of the replacement crane's upperworks on the tower," Finamore explains. Staten Island-based J.V. Trucking and Rigging LLC performed the job, which was designed by consulting engineer Howard I. Shapiro & Associates. The lift, which began at 5:00 a.m., was complete at 7:30 a.m. Later that day, at 2:50 p.m., the city lifted the evacuation order.