No_5_May_1969 — Page 29

IT

張鈞

Ladsi

U.S. arena features

cable-suspended roof

THE cable-suspended roof of a new arena, which forms part of a multi- purpose sports complex in the centre of the San Fransisco Bay area, is one of the largest of its type. It rests on, and is visible through, a ring of X- columns, giving the 420ft. diameter structure a spectacular appearance.

Inside the X-columns a glass wall is independently supported by open-web joists, hanging down from the com- pression ring. The draped cables sup- port not only the roof but also a 260ft. diameter penthouse containing the mechanical equipment.

The X-columns rise up from the promenade level to carry the 420ft. diameter concrete suspension ring from which the roof cables are suspended. Cables span from this compression ring to a 45ft. diameter steel tension ring at the centre. There are ninety-six 2 3/16in. galvanished bridge strands supporting the roof.

Precast concrete radial ribs rest on top of the cables and are interconnected by diaphragms that form six annular rings to tie the roof structure together. The penthouse is steel-framed with

OAKLAND-ALAMEDA COUNTY COLISEUM

SKIDMORE, OWINGS & MERRILI

AMMANN & WHITNEY

GUY F. ATKINSON CO.

columns resting on top of the radial ribs, and a cast-in-place gypsum roof rests directly on top of the radial ribs and the penthouse steel framing.

The 32 pairs of X-columns were cast in place using prefabricated steel forms. The columns act as compression members for both gravity loads and for lateral seismic forces.

The concrete compression ring, lo- cated 100 ft. above the floor of the arena, has a trapezoidal section mea- suring 6 ft. across the base and standing 6 ft. at the inner and 5 ft. at the outer face. The ring was poured in eleven segments that had to be cured for a minimum of seven days before the keys could be poured between them. The compressive force in the 1320 ft. ring is of the order of 4800 kips, making this an unusually long column.

Very close tolerances were required

owners

architects

consulting engineers

general contractor

to eliminate any eccentricity in the ring and the roof. The base was re- quired to be within 1⁄2 in. of the plan grade, the inner face within 1⁄2 in. of correct radius, and the anchor points for the roof cables within 4 in. of position in regard to the base and the inner face. Pipe sleeves were embedded in the ring to anchor the cables. Block- outs formed pockets 2 ft. square by 3 ft. deep so that cable sockets pushed through the pipe sleeves could be secured by slotted washers. When all the cables were strung, the pockets were concreted.

The tension ring is a steel box mem- ber welded together from A441 plates. The 45 ft. diameter ring, was fabricated in four pieces and assembled on scaf- folding 65 ft. above the floor of the arena. The four splices were bolted up with 1/4 in. high-strength bolts.

Far East BUILDER, May 1969

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