There was no simple way to install the 4.5t (10,000 lb) filters, said Kerwin Chong, Hawaii Crane and Rigging vice president.
Two bays of a new double-tee roof had been built above the final destination of the filters, and these could not be opened. Access was limited to a side opening measuring 20ft (6m) high by 12ft (3.5m) wide. The filters themselves were 17ft high and 8ft wide and deep. They needed to be carried 15ft (4.5m) inside the building, and lowered into a 16ft sump hole set in the floor.
The roof was not strong enough to be used to hang the filters from. And they could not easily be supported from below, as the bottom of the sump was channelled and crossed with valves and outlets, making conventional skating, rolling and jacking time-consuming. What’s more, the filter was very prone to tipping-its centre of gravity was located within one inch of the inside of its support legs-so rolling would not have been safe.
There was hardly any space beside the sump holes to set up a gantry. Obstacles along the width meant only eight inches of free space were available. These dimensions made it very difficult to install a small hydraulic extending gantry to roll the filter down the length of the sump. The filters needed to be placed with a precision of just a quarter of an inch.
A job for an expert
Chong and 35-year veteran crane operator Gary McKeague developed a cantilevered lifting beam held from a mobile crane.
The beam held the load on one end, with a 6.4t counterweight on the other. The beam hung from a single crane, but from both hooks. Winch one controlled the pitch of the beam, and winch two controlled the vertical movements.
Chong said that his biggest concern with the design was whether it would be too difficult for the operator. After coming up with the idea, he spoke with McKeague, who had never done this kind of work before, but felt confident that he could pull it off, Chong says.
The crane and the rigging can move the end of the beam in three dimensions: it can move in and out, side to side and pitch up and down, independently or in unison. Side to side motion was controlled by light tension on tag lines held by two men on the ground. To keep the cantilever beam level, McKeague manipulated the no 1 and no 2 lines to move the fulcrum point forward or backwards.
“The operator manipulates the beam like a puppet master would manipulate a puppet,” Chong says. Not that it is easy. To move the cantilever in and out, the operator has to simultaneously boom down, swing, and adjust the two lines. “That’s four operations that have to occur in an environment where there is only 1″ of vertical clearance, holding a device that has an insured value of $1m and having the exposure of 20 men in close quarters.”
Hawaii Crane cut the railings to fit the units, but kept the railings in the second bay for safety. Then the lifting began. “We first installed the inner reactor in the sump and moved it as far down the sump as we could manipulate the beam in the first bay,” Chong says. “Then we temporarily set the unit down, cut loose and reached through the inner bay and re-attached the unit and manipulated the reactor all the way down the race way sump to its final location. The outer reactor followed suit.”
Moving the filters down the sump was the most difficult part of the job, Chong says. In addition to McKeague working the beam, two riggers on the ground controlled the side-to-side swing.
After all the preparation, the two units were installed safely. The facility owner was C&C Honolulu; Commercial Electric were the contractors and Brown & Caldwell were consulting engineers.
