Precast Double-Tees Made with Lightweight Aggegrate Big Part of Atlanta’s SunTrust Ballpark
Cranes tower above Cobb County Georgia’s Cumberland District. Down below, SunTrust Park, the new home of the Atlanta Braves, is taking shape. The ballpark and mixed-use development is the first of its kind: a place where fans can shop, eat and even live long after the game ends.
Finding a place for all those fans to park their cars is a big part of the work underway in the Atlanta suburb of Smyrna.
Metromont, a major producer of precast concrete products, is supplying all of the panels, beams and columns that make up the various parking structures scattered across the 60-acre site. They’re also supplying the structural precast components that make up the actual ballpark.
“We’re doing all of the structural precast on the stadium as well as five parking garages,” says Metromont’s Angela San Martin. “All of it is being made at our Hiram, Georgia plant. It’s very exciting.”
San Martin says lightweight concrete is often used in the massive pieces that come together to make up a parking deck. One of the key components of a parking garage are double-tees, which form the structure’s floor and ceiling.
Lightweight aggregate from Trinity Lightweight is used in the concrete mix poured into forms at the Hiram yard. The resulting product easily meets the project’s strict fire-rating requirements. “On a few of the parking decks at SunTrust park they have a fire rating requirement based on the building type classification. We use lightweight concrete. There are other benefits but in this case, it was due to the fire rating; you can achieve over 2-hours,” says San Martin.
Back at the project, trucks bring double-tees to the job site for placement. Transporting each of these pieces safely across busy Atlanta requires careful coordination and is a major expense for any project, especially one this large.
“We’ll put more than one piece on a truck if we can,” says San Martin. “If we can save shipments and the number of loads going to the project that can also help save costs for the owner. We like to use it as much as we can to get the weight down when we’re shipping. It can reduce the weight of the piece and it may let us put two double-tees on a truck versus one. When you are hauling a long distance it can be quite a cost savings.”
Each of the double-tees are carefully hoisted high into position. A specialized crew guides each member into place. Because they’re lighter, precast elements containing structural lightweight concrete often have reduced placement costs.
“The weight of a typical double-tee is probably around 35-thousand pounds,” notes San Martin, “and lightweight concrete keeps the whole weight of the structure down.”
Precast members containing lightweight aggregate are typically 25 to 35-percent lighter than those made with normal weight concrete but just as strong. “You’re able to get the strengths same as normal weight so that’s not an issue. Nothing really changes other than the actual concrete mix. We aren’t limited on the number of hours we can strip the forms so that’s the same. The benefit: you have a lighter structure, you’re able to achieve fire rating requirements that a specific project may have.”
SunTrust Park and its mixed-use village of restaurants, hotels, and residential properties is expected to be completed by the first pitch of 2017.