MCGrawHill - Sept-14_Cassidy Breaux - 17

Second and 23 (Months): The Retractable Roof and Those Amazing Arches I n a move as gutsy as any seen on a football ﬁeld, Jerry Jones and crew decided to build the new Cowboys Stadium — all $1.12 billion, 3 million square feet of it — on just two arches. But as with anything Cowboys, they’re not just any arches. Each 17 foot wide by 35 foot deep arch box truss spans 1,225 feet (about a quarter of a mile), is 292 feet high at its apex, and weighs 6.5 million pounds (about as much as 20 777 airplanes). The weight of the entire stadium rests on these two arches, eliminating the need for interior columns and giving fans an unobstructed view of the ﬁeld. It is the largest column-free room in the world. So large, in fact, that the Statue of Liberty, at a height of 151 feet, 1 inch, could easily ﬁt inside — even with the roof closed. The arches began their journey in Luxembourg at ArcelorMittal, which was able to provide the stronger grade of steel (ASTM A913 Grade 65 steel) necessary. From Luxembourg, the steel was shipped to Houston, then taken by truck to W & W Steel in Oklahoma City for manufacturing. Getting the 56-foot beams to Arlington, Texas, was an arduous process, as some of them were so heavy (as much as 44,000 pounds each) only one could ﬁt on a truck. In order to stay within the shape limit (W14 x 730) and reduce the stress, a Quadrangular Warren web conﬁguration was used along each vertical side of the truss. One of the most ancient three-di- 23 mensional designs, it creates a diamond or checkerboard pattern. According to John Aniol, Operations Manager and Senior Project Manager in the Dallas ofﬁce of Walter P Moore, the arches were erected in nine sequences with the use of six temporary shoring towers, beginning at one abutment and then progressing to the 50-yard line, where two bracing truss- es were installed. The sequence was then repeated on the other side. Each arch was completed in about ﬁve months with the erection of a 56-foot keystone segment at the 50-yard line. In all, 46,500 ASTM A490 bolts were used. To erect the trusses, Derr Steel Erection Company used a Manitowoc 18000, a Terex-Demag CC 2800, a Link-Belt LS-1018, a Link-Belt LS-918, a Liebherr LR1200SX, and a Manitowoc 999. In the constructing of the arches, Bob Derr said, “When the arches were connected at the center ‘keystone’ sections, we found that the length of each arch came within a fraction of an inch of the expected overall dimension, which was addressed with a minor amount of shimming at the joints. That kind of accuracy says a lot about the quality of the fabrication by W&W Steel and Manhattan’s construction of the abutments, which were almost a quarter of a mile apart.” In order to handle the enormous 19million-pound thrust reaction from the trusses, there are four 64,000-pound cast solid-steel arch truss pin bearing Special Advertising Supplement to Texas Construction 17

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