$1-Billion Jigsaw Puzzle Has Builder Modeling Supply Chains
The virtual heart of the $1-billion project, whose lead contractor is Skanska USA Buildings Inc., Boston, is a Web-browser-accessible, color-coded, 4D building information model that tells the team at a glance the status of 3,200 precast risers being manufactured and assembled to form the bowl of the 84,000-seat stadium. The data is refreshed several times a day, about as frequently as Skanska’s supervisors at the precast yards or on the jobsite dock their pen-sensitive tablet PCs.
“The old method was to use spreadsheets and color-coded drawings to track things,” says Nery Pascoa, Skanska’s quality-control manager on the project. “Now we can, at a glance, figure out if the manufacturer is producing in the correct construction sequence, which tends to be a problem with precasting yards. They like to produce all of the various types of pieces when they have the forms in place. It’s more efficient and reduces their cost, but it can cause problems with the sequence,” Pascoa explains.
The interoperability of two independent software products that flow supply-chain information between databases is key to the process. Vela Systems, Burlington, Mass., supplies the hardware and software for capturing radio-frequency identification (RFID) registration tag numbers on individual pieces as they move from casting to assembly. It marries status and condition information to the record of each individual part.
That information is then integrated into the 4D structural design and construction sequence model created with software from Tekla Inc., Atlanta. Skanska is piloting a new Tekla offering called Tekla Structures for Construction Management that is due out next fall.
The structural model was turned into a construction model by importing scheduling data from Primavera Systems' P5 and using Autodesk's Navisworks to run clash detection. It became a materials-tracking model during a month of collaborative software development last fall between Skanska, Vela and Tekla. "The interoperable interface took two product managers and two �bertechs a month to develop," says Andy Dickey, product manager for the contractor segment in North America for Tekla. "That's really the beauty of it. The technology has matured so much you can do this," he explains.
Just-in-time material flow is critical. There is no lay-down yard and only a small holding area for trailers. The 44-ft- by-10-ft precast elements, weighing an average 45,000 lb, become the seating risers as they are racked into the stadium’s structural frame, but they have very limited interchangeability.
Casting is going on at four plants within a four-hour radius of the site, says Dave Campbell, a Skanska vice president and director of SIMCon—an acronym for Skanska Integrated Modeling for Construction. He says he borrowed the idea of using RFID and data management tools to track the precast components from another Skanska project in Finland. The technology it was using was not transferrable, but the idea was; so he brought Vela and Tekla together and worked with them to develop the system. “I came up with the idea that we needed to separate out the statuses. The real power is to be able to look at it visually and see just where we are,” Campbell says.
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Skanska Buildings USA
Model colors change as units move to assembly. Tablet PCs and RFID tags keep track.
To demonstrate, on April 20, he logged onto the Internet from a remote location and viewed the model to find that between Feb. 14 and that afternoon, 102 pieces had been erected and 78 more had been received on site. The yards had another 79 pieces cast, of which 26 had been approved for shipping. “It is quite challenging,” Campbell says.
For smooth assembly, every undamaged, next-in-line piece needs to arrive on trucks in the correct sequence and roll under the hook on cue. And the process needs to happen 3,200 times. The assembly is planned from the outside in to, minimize the movements of two 450-ton tracked cranes working from the center and to limit their boom-out to 50 ft.
Pascoa says top elevation of the finished bowl will be 184 ft above grade. It will be supported by 13,600 pieces of steel, weighing 22,000 tons. The exterior will be clad with a metal-fin system now being fabricated in China that will give the appearance of a solid curtain wall but allow ventilation and preserve the structure’s code status as an open-air facility. Pascoa says Skanska is considering applying the materials-tracking technology to the cladding fins, but for now is concentrating on the critical pre-cast elements.
Unique precast risers are kept in proper sequence to avoid crane shifts.
“They are not highly interchangeable pieces,” says Campbell. The construction managers only need two pieces of information to keep things sorted out: a unique identifying number attached to each piece and a location in the model where it belongs. Vela handles the rest of the process by associating metadata with the number on each piece. “Aside from the ID numbers, there is no information stored on the tag,” Campbell says. “It has an ID that is referenced to information in the database.”
The ID number is on a chip in a plastic tag hanging near one end of each precast part. “We started out with the least costly tag possible, about 40¢, but have gone to the key-fob-style tags, which cost about $2,” says Josh Kanner, one of the founders of Vela Systems. “They’re durable. This is RFID on a super-rugged information tracker for...