...reinforced-concrete thrust-block abutment with a steel-pin bearing assembly that ties together truss chords. The assembly, cast in a special sand mold, weighs 32 tons. Each abutment bears the brunt of a 9,500-ton thrust reaction and is founded on a 3,400-cu-yd buried concrete box that is 176 ft long, 71 ft deep and 18 ft wide.

The shoebox scheme, its 30-in.-thick walls made using the slurry-wall method, was an idea of Clyde N. Baker Jr., senior principal (geotechnical) engineer at STS/AECOM, Vernon Hills, Ill. The foundations took five months. Sliding the shoebox rebar cage into the trench was “quite a feat,” says Manhattan’s Penny.

Derr Steel Erection Co., Euless, Texas, started 18 months of roof steel erection last July. Cranes picked 156-ft-long truss panels assembled on site. Each assembled panel weighed 150 tons.

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UNI-Systems Steep slope inspired a rack-and-pinion drive system to move the roof panels.

The original plan called for concurrent arch erection, like a giant ladder with transverse box trusses as stabilizing rungs. But there was not enough laydown area or room for cranes to maneuver for Derr to erect both arches at once. Also, serial arch erection would save $1-million on shoring towers, which could be reused. WPM, as Derr’s erection engineer, reanalyzed the structure for the asymmetrical loading produced by the new strategy.

As Derr erected an arch, it left a space for the keystone. When the keystone went in on one arch, “we were within 2 in. of the halves being exactly where they needed to be,” says Penny.

Derr left one end of the keystone loose as a temporary expansion joint so the arch could “breathe” with air temperature swings until crews finalized all other structural connections. This prevented overloading of falsework during cold weather when the arch wanted to shrink and lower itself, says Adam Younkin, Derr’s project manager.

When Derr decentered the arch, it deflected 4 in. That was 2 in. less than the maximum deflection WPM predicted.

Manhattan Construction

Daryl Shields / HKS Rebar cage (top) for arch abutment part of buried concrete box.

Derr is on schedule to finish fixed roof steel this month before beginning final alignment of the 850-ft-long wheel rails and support beams atop the arches. The catch is that alignment is happening before the arch shape is stable. To help, the team is using real-time survey data of the arch shape. “We need a smooth curve for smooth operation of the transporters,” says Uni-Systems’ Waldron.

Through the job, the stadium team has been trying to keep up with the Joneses—the Cowboys’ ruling family bearing the city-owned stadium’s cost beyond the city’s $325-million share. One problem is that the Joneses keep expanding scope and budget. Despite this, Manhattan is on track to finish on time, says Penny.

But the job is not out of the woods yet. Last month, a worker died by electrocution and three were injured during a crane operation. Manhattan has responded by leaning on its team and the subcontractors to enforce safety procedures.

In August, workers will begin erecting steel for the 286-ft x 220-ft biparting panels. The test of the 0.3-mph ride is expected in November; five years of effort for a 12-minute slide.