Architect: Kendall/Heaton Associates / Pelli Clarke Pelli
Engineer: Brockette, Davis, Drake, Inc.
Construction Management: Crescent
General Contractor: Beck Construction
Concrete Contractor: Beck Concrete
Reinforcing Bar Fabricator: CMC
Total Project Cost: $120 Million
Rebar Producer: CMC
Rebar Placer: Great Western
Total Concrete Yards: 50,000
Reinforcing Tons: 5,300
UNIQUE DESIGN FEATURES
The tower projects continually outward on the north side at a constant slope 45 feet from the ground level to the roof. The aesthetic impact of a tapering tower (growing with elevation) provided the owner with larger lease areas higher in the tower. This resulted in larger floor plates at a more desirable and marketable lease rate. The tapering of the tower allowed for a smaller foot print at grade level enhancing the public plaza and green areas at the tower base. The asymmetry of the structure results in a sustained overturning moment in the lateral load resisting system. The structural frame used bonded post-tensioned shear walls in addition to reinforced concrete moment frames. The vertical post tensioning in the shear walls provided a counteracting sustained force to that induced by the lean of the tower reducing the effects of horizontal drift. In lieu of transferring columns, leaning columns were used to avoid transfer girders. The leaning columns allowed the reinforced concrete frame depth to remain consistent to the pan form depths maximizing available ceiling heights and plenum space. Working with the concrete supplier to optimize the concrete mix designs to provide higher strength while minimizing material allowed for more efficient use of reinforcement. Additionally, the “temporary” retention system for the two and a half levels below grade also served as the permanent basement walls by engaging the structure upon removal of the tie backs.
REASONS FOR CHOOSING REINFORCED CONCRETE
Serviceability along with minimizing structural depth to allow for higher available volumes in a compressed floor to floor height lead to the selection of concrete. A steel frame system was deemed the less desirable option considering those factors and overall cost. The concrete frame floor to floor height reduced overall skin cost without compromising the available ceiling heights in the office floor. Additionally, the reinforced concrete frame was left exposed in many instances further reducing finish out cost.