The concrete mix included a corrosion inhibitor and ultrafine fly ash for the lower decks, which will be a parking structure. These decks were built during the winter months, so Hensel Phelps heated them from below to keep the concrete setting on schedule. They also installed intelliRock maturity meters to check strength gain for post tensioning, although they had a little trouble calibrating the readings at first due to all the additives.

Hensel Phelps found that the MevaDec formwork went up quickly and allowed them to progress rapidly with the job.

There's no reshoring with this system, since the shores stay in place as the form panels are dropped out from below. “The craftspeople have really taken ownership for this,” says Berry. “They have learned it quickly and really like how it makes them more productive.” The resulting decks are very smooth across the bottom due to the Alkus panels. To complete the floors, workers returned after 28 days to place the final pour strips after all shrinkage had occurred.

The hotel opened to rave reviews in December 2005.

Tilt-up for stairwells

The Polaris Hilton Hotel and Conference Center, in Columbus, Ohio, recently nabbed the number five spot in the TCA's list of the tallest panels ever built. The facility is a 253-room, nine-story hotel with a 40,000-square-foot conference center that will open in April 2008. The tall panel, part of the stairwell shaft, measured 85 feet high, 11 feet 3 inches wide, and weighed almost 54 tons. A large area was used for the casting bed and a 300-ton Liebherr crane was used to lift the big panel. Other panels on the project also are noteworthy, measuring in at 84 feet tall.

The tall panels presented several challenges, including the determination of how to brace them. According to Scott Collins, assistant chief engineer at Meadow Burke Products, each stairwell shaft for the nine-story hotel had an overall height of 95 feet 8 inches and inside dimensions of 12 feet 7 inches by 20 feet 4 inches. Erection began by tilting up a shorter 20-foot-4-inch-wide panel, which was braced to a deadman. Then its opposite panel was placed and braced. “Then we placed a tall 84-foot piece to form the third side and the connections were welded,” says Colin Smith, project coordinator for tilt-up subcontractor Lithko Contracting. “Then the opposite tall panel was placed and its connections welded. At that point we had a box, so the bracing could be removed and we didn't need to brace any more panels in this core to complete it. We just added the additional panels on top and welded the connections all the way up.”

In addition to the stairwell shafts, tilt-up also was used for the elevator shafts, which were even taller than the stairwells. “The elevator shafts had an overall height of 101 feet 5 inches,” explains Collins. “Six 84-foot-tall panels were used to construct the three elevator shafts (two for each shaft).” After the box had been built, Lithko placed 17-foot-5-inch panels on top of the 84-foot panels to get the shaft to its ultimate height.

According to Eric Messerly, P.E., an associate for structural engineering firm Shelley Metz Baumann Hawk, the main reason for using tilt-up panels for the shaft walls was the schedule. “This project was on a tight construction schedule and using tilt-up panels saved valuable time,” says Messerly. “In addition, the cost of constructing the walls using tilt-up was less than cast-in-place.”

The time advantage also was extremely helpful to the tilt-up subcontractor Lithko Contracting. Colin Smith, project coordinator for Lithko, says using tilt-up for the stairwell shaft enabled the concrete work to be completed before the other trades (structural steel and prefabricated walls and floors) started on the project, which eliminated the safety issue of workers below the formwork and fighting for crane boom time. With a cast-in-place method, Smith says, two cranes would have been needed, one for each pair of shafts for the duration of the core construction. “Using tilt-up construction allowed us to finish before any of the subs started,” Smith says. “We were safer and more cost effective, and we were able to beat the weather.” The casting beds went in on December 4 and the shafts were completed on January 12.

In addition to speed of construction, tilt-up also resulted in fewer connections since the panels were so tall, and a smooth interior face on the shaft wall because the panel does not contain construction joints at each floor. If the walls were cast-in-place, Messerly says, construction joints typically would occur at each floor and these joints can be ugly due to formwork misalignment. The cores provided most of the shear resistance needed for the hotel and the embedded connection plates were designed to transfer this load. And since the shaft walls are structurally stable after the panels are connected, the wall bracing can be removed to allow the floor framing to take place unencumbered.

“Although I have used tilt-up as a solution for office buildings and other structures before,” says Messerly, “this project opened my eyes and will prompt me to consider tilt-up panels on future projects.”