August 4, 1995

STRATOSPHERE TOWER RISING IN LAS VEGAS

Minnesota-based Grand Casinos Inc. is building Nevada's tallest structure, the Stratosphere Tower in Las Vegas. The project will be 400 feet taller than the Space Needle.

The "mushroom-like" tower begins with three concrete legs positioned like a tripod with a center concrete hexagon core with 20-foot-wide walls ranging from 12 to 24 inches thick. At the tower's base, three 20-foot by 32-foot rectangular legs, ranging from 12 to 32 inches thick, are on a 12-foot-thick concrete pad foundation. All legs taper toward the center, coming together at the 264-foot level.

The legs turn out to rise an additional 535 feet to support the tower's "pad" base at the 775-foot level. This building will house wedding chapels, indoor and outdoor observation decks, a 360-seat revolving restaurant, a cocktail lounge, and two thrill rides -- a roller coaster and a simulated "space shot," which will propel riders toward the 1,100-foot level.

From a construction viewpoint, one critical phase was the use of hydraulics to help form the outward curve of the concrete legs. Power Team hydraulics were used to counteract the natural force of gravity and the concrete leg design, pulling the legs inward towards the core. (Each leg weighed about 4 million pounds from the base to the point where rams were attached at 255 feet.)

In addition to accomplishing this task 255 feet above ground, additional challenges included applying no more than 240 tons of pressure per leg, and applying equal and simultaneous pressure/push on all three legs to induce a 3-to 4-inch outward movement of each leg.

Subcontractor Advanced Steel Systems used a system of six 150-ton Power Team rams with locking collars. Minnesota-based Power Team customized the rams, adding a pad at the base of each cylinder to accommodate 1-inch bolts. A Power Team electric hydraulic pump with pressure switch powered the operation.

Fraser Smith, the project's structural engineer with Mendenhall & Smith Inc. of Las Vegas, designed rectangular steel frames to straddle the distance between each leg and center tower. A crane hoisted the frames to the 255-foot level of the tower, where workers bolted each frame to concrete anchors within the center tower and each leg. Once all three frames were in place, workers mounted the rams horizontally by bolting rams to the end of the beam. With all three frames in place, workers attached manifolds to the pump.

Workers then set the pump in the middle of the tower at the 255-foot level. They set the pressure switch to prevent pressure from exceeding 240 tons per leg. Next, workers connected hoses from the pump to a two-valve manifold connected to each of six rams, two rams per leg.

One person at each of the three converging points monitored the ram, fluid flow and pressure delivered. A fourth worker operated the pump and monitored the leg-to-tower dimension and leg-to-tower parallel (the flat side of the square leg must face the flat side of the hexagon, so every other side of the hexagon will parallel a leg side).

Workers secured the rams' locking collars when the desired pressure and position were achieved. The pressure held the rams in place. The legs each moved between 3 and 4 inches outward, as predicted. The concrete was then poured and cured for two to three weeks, whereupon the rams were removed and construction continued.

The Stratosphere Tower is scheduled to open by April 1 next year. It will include a 354,500-square-foot building at the base of the tower. The first level of the base building will include a 97,000-square-foot casino and restaurants. A second level will lead to the tower's four high-speed elevators, which will carry passengers to the top at a speed of 1,800 feet per minute. The top will include a retail shopping area and specialty restaurants.

Even at a quarter of its completed height, the Stratosphere Tower dwarfs its surroundings. When finished, the tower will stand 1,149 feet.

Hydraulic rams with locking collars were left in place for two to three weeks while the concrete cured.