the arena containing post-tensioning girders on several levels due to long spans, transfer conditions, and the significant load and deflection requirements in certain areas.A one-way beam-and- slab system was used in the parking structure, which is attached to the arena. Various parts of the project—the parking garage, the arena


and the loading docks—used post-tensioning for different but distinct reasons. In the case of the parking garage, the underground facility


has some special circumstances. RogerWade, a Structural Engi- neer with Qk4, said post-tensioning was used because the owner wanted a long-span structure to accommodate two parking bays and a drive aisle between columns. Also, it was necessary to keep the depth on the parking


garage as shallow as possible. The site is two blocks from the Ohio River; consequently, the water table is very high. The low- est part of the garage is near the normal water table. Having the shallowest structure possible reduced costs, and helped avoid damp conditions. An advantage of using post-tensioned concrete on the garage


was increasing the speed of construction. Using precast would have involved loading and unloading slabs from the city streets. Post-tensioned slabs can be done on-site, and as one slab is fin- ished, it is easy to move on to the next. Other advantages includ- ed the reduction inmaterial by using shallowdepthmembers and decreased cracking. “The arena didn’t need post-tensioning for its typical floor


structure, but it was necessary to have a column-free area to accommodate a practice court,” said Bart Miller, P.E., Senior Associate withWalter P.Moore, structural engineer. (The prac-


tice court is located below the arena seating and runs parallel to themain court.) Additionally, the facility features a curved window wall that


required floors to cantilever up to 17 feet from the structural frame to reach the back of the glass. The structure was designed using stringent deflection limits around the curved window to prevent the concrete from transferring loads to steel supporting the window. Also, two escalators outside the arena yet still within the


building lobby rise 50 feet and apply a 10-ton load to the end of the supporting structure,which cantilevers 16 feet fromthe arena structural frame – all of which was coordinated with Otis. Although chosen primarily for design-build reasons, post-


tensioning has had side benefits. “We saved concrete and we saved formwork,” saidMike Clay, Principal with Populous, the architect. “We really used post-tensioning froma structural stand- point for our spans, deflections and loads. Everything else is an additional advantage.” The projectwas started in late 2008 and is scheduled to open


in late 2010. Other members of the design and construction team, in


addition to Amsysco, Populous, Walter P. Moore and Qk4, include ClasSickle Inc. (associate structural engineer) M.A. Mortenson Co. (construction manager) and F.A.Wilhelm Con- struction (general contractor).


Kimberly Kayler can be reached at kkayler@constructivecommunication.com.


PT


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SEPTEMBER 2009 • PARKING TODAY • www.parkingtoday.com 51


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