Gerald Ratner Athletics Center - Design

Design

The construction employed 2,000 short tons (1,814 t; 1,786 long tons) of steel. The 2,000,000-pound (907,185 kg) roof of the gym is supported by a pair of 125-foot (38 m) steel masts. The pool's roof is supported by three masts. Each mast is composed of three 18-inch (46 cm) diameter steel hollow structural sections (HSS) filled with high-strength concrete that are arranged in a tapered tied-column configuration.

The German-import masts are united by 120 high-strength steel cables that total approximately 6,500 feet (1,981 m) in length. They are inclined at a 10 degree angle from vertical. Each tapered composite mast that supports the flattened S-shaped roof girders is supported by 15 splaying cables; 9 fore-stay cables and 6 backstay cables. During construction, the masts were filled with 10,000 pounds per square inch (69,000,000 Pa) cast-in-place concrete using innovative pumping techniques.

Concrete counterweights totaling 2,500 cubic yards (1,911 m3) — with some as large as 50 by 25 by 13 feet (15 by 7.6 by 4.0 m) — counteract the weight of the roof from below the ground. The masts and counterweights are likened as external form-giving elements to flying buttresses in gothic architecture, which predominates the campus' architecture. The building is said to interpret gothic architecture through structural expressionism. The exterior support design made the interior space more receptive to open natural lighting and more accommodating for free movement.

The roof design incorporated multi-level splayed cables so that the structural roof members could form a 33-inch (83.8 cm) deep uniformly curved roof plane. The roof members are curved and shallow. They support 7 2-inch (5.1 cm) thick 25-foot (7.6 m) metal roof deck spans between the roof girders. The W33x169 girders are cold bent with reverse curves to multiple radii. The curved roof planes are suspended from German “full-lock” steel cables and include three outer layers of interlocking Z-shaped wires designed to minimize water infiltration and corrosion.

The engineering of the masts was complicated because stability was so important to the overall design success of the suspension structure. Mast displacements could significantly alter cable length and tension and redistribute loads through the superstructure contrary to design. The key to successful design was control of the foundation settlement. The sites natural underlying subsurface conditions were stiff silty clay below a medium dense sand layer, which was determined to be too accommodating to settlement to host the structure. Ground improvement, consisting of triple-fluid jet grouting, was performed to reduce the compressibility of the silty clay, stiffen the sand deposit and provide a desirable shallow foundation system. This site marked the first time that these geotechnical ground improvement techniques were employed.

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