Westpark Corporate Center, a venture of Northwestern Mutual Life Insurance Company and the National Automobile Dealer Association, is the first of two nine-story office towers to be located in McLean, Virginia. The project also contains five levels of below grade parking. A long-span reinforced concrete floor system was specified to satisfy the numerous requirements of the tenants.
Typical bay dimensions for the office tower are 30-by-42-feet, with end bays spanning 47 feet. A banded beam system was utilized for the floor framing. Beams spanning in the long direction are 72-inches wide by 16-inches deep. A 9-inch thick post tensioned slab frames between the 72-inch wide beams.
Concrete with a compressive strength of 5,000 psi is used for the slab and beams, while columns in the lower floors utilize a 10,000-psi mix. Concrete was produced from an on-site batch plant, which resulted in high quality control: cylinders for the slab concrete easily reached 3,000 psi in 30 hours. This helped contribute to the five-day floor cycles.
Concrete versus Steel Framing
Structural steel was never really a viable option for this project for a variety of reasons. Due to height restrictions, the floor to floor heights needed to be kept to a minimum. By utilizing the banded-beam system, the floor heights could be reduced by about 8 inches per floor, compared to a structural steel floor system. This also resulted in a substantial cost savings. Column transfers and the curvilinear profile of the building were other reasons why structural steel was not used.
Westpark Corporate Center L.L.C.
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