The new marine mammal pavilion at the Baltimore Aquarium presented a problem for the fabricator of the 136-ton space frame and wide-flange truss that would sit atop it.
The fabricator planned to complete the project a the company plant in Norfolk and barge it to Baltimore ready for placement, rather than stick-build it onsite. This would eliminate the need for scaffolding in Baltimore - and the physical risks involved. It would also help to make up for the amount of time the fabricator would need to manually cut the 360 pieces for pipe required to fabricate the 157-by-11-by-111-foot structure.
The Cutting Challenge
The manual cuts were the fabricator's overriding concern. The assembly design would require a number of multiple intersection cuts that would consume significant time in cutting and cleanup.
Of course, intricate pipe cuts are a problem for many fabricators. Those who primarily work with I and H beams find themselves challenged by the need to profitably cut pipe to architect's specifications.
The cutting job was performed by an outside company who used a micro-processor-controlled plasma pipe cutting machine. The machine provided 4-axis control, allowing the operator to make variable weld preparation angles, cuts at both ends without manual measuring or marking, menu drive, no setup changes or overhead lifting, and one-person operation ability.
The architect's and engineer's drawings were turned into working drawings for the cuts. Cut data was simplified, and the drawings were completed, providing the physical dimensions and characteristics of the pipe and cuts.
The requirements were intricate at best and complex at the most demanding. In some cases, the multiple intersections had as many as 11 adjoining pipe ends.
To speed up the handling process, the company given the cutting job used an integraated conveyor system to move the pipe to and from the cutting machine.
When the initial shipment arrived from the cutting procedure, the manufacturer found that the cuts required little or no cleanup and began fabricating by sections. The 360 pieces of 6- and 8-inch-diameter steel pipes were fit together to form 16 small trusses.
The cutting job was completed in just three weeks. These trusses were then welding into one unit - forming the space frame - and joined to a 45-ton, wideflange truss, simulating the Baltimore site conditions with a concrete pad.
Transporting the Structure
The new challenge was to determine how to lift the structure on and off the barge without torqueing it out of shape. The plan to complete and ship the job as a single unit rested on getting the final product safely to its new home.
Computer calculations were worked out to determine central gravity, lengths of lifting cables, and extra bracings. With that information, a three-point pick was used to lift the structure onto a 326-by87-foot, 700-ton barge.
Then the structure arrived in Baltimore two days later, it was lifted up and set down, with the columns matching the base plates. Bolts were tightened, and project was complete.
The information presented in theis article was prepared by Bill Butler, Takagi Communications Inc., Escondido, California. Pipe cutter machine described in the article was from Vernon Tool Company; aquarium frame fabricated by Tidewater Steel, Norrfolk, Virginia, and LBJ Enterprises, Maryland; pipe cutter, Brown & Root, New Orleans, Louisiana.