The mechanical plant for an office building in downtown Washington, DC was being expanded and two new turbine packages weighing 42,000 lbs. each needed to be set in the courtyard of the building at a radius of approximately 220ft. All crane related activities had to take place within one day, requiring the use of hydraulic cranes. W. O. Grubb Crane Rental had two 550-ton class all-terrain hydraulic cranes with heavy lift attachments, but neither was sufficient by itself to reach over the office building to set the package in place. It was observed that if they worked in tandem, they could handle the load, but they would have to be placed close together in order for both to stay within a radius that would assure adequate capacity. It was not feasible to place the load between the cranes so that they could both be attached to the load from the beginning. Instead, only one crane would be able to make the initial lift of the turbine package. Once lifted, there would be no surface available to support the load until it was placed on its permanent supports. It appeared that a larger crane would have to be brought in by a competitor.
Unwilling to give up on this opportunity, the Salesman and the Operations Manager for W. O. Grubb asked if there was a way to lift a load with one crane and then pass it over to a second crane in mid-air. At first we considered a fabricated lift fixture in the shape of a triangle, but with the lift scheduled to take place in just over a week, there was no time to procure, fabricate and certify such a device in a cost-effective manner. Looking at it again, it was determined that an inverted spreader bar would accomplish the same thing as the proposed lift fixture, but at a fraction of the cost since the crane company already owned the spreader bar and slings. The only items to be fabricated were some small link plates and equalizers. This was quickly accomplished as was the load testing and operational testing needed for certification. A lift plan using this method was developed and submitted for approval.
The cranes were setup at the work site throughout the morning of the lift and the first turbine was delivered to a location about 145 ft from the crane making the initial lift. The rigging was attached to the turbine with many agreeing that it looked pretty ugly and with some bystanders worrying about whether it was going to work. The unit was lifted and swung over the the roof and boomed out to a radius of 170ft where it was held suspended over the roof of the building. The second crane positioned its hook over the loose end of the upper spreader bar and lowered the hook to enable the attachment of the sling hanging from the loose end of the bar. The second crane hoisted slowly until 50% of the load was transferred to the second crane. From that point, both cranes boomed out to the final radius and lowered the unit on to its permanent supports. The second turbine was set in the same manner and, after a long day, the cranes were demobilized from the site and the street was re-opened as scheduled.
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