Saarinens’ design was for a gateway arch of heroic proportions. He wanted his arch to taller than any in the world and to eclipse the 550 foot tall Washington Monument. Massive reinforced concrete foundations go down sixty feet to bedrock and because he wanted it to require little or no maintenance he encased it in stainless steel. The legs are hollow, equilateral triangles, with sides that taper gradually from fifty-seven feet in width at the base of the arch to seventeen feet at the top. The height and distance between the legs at the base is 630 feet.
Building the sections
The stainless steel sections of the arch were built by the Pittsburgh – Des Moines Steel Company at Neville Island, Pittsburgh. The U.S. Steel’s Homestead Works at Pittsburgh and the Eastern Stainless Steel Company in Baltimore, Maryland, supplied 886 tons of one-quarter-inch thick 18-8 stainless steel sheets with a 2B finish. The sections were built to meet unusually high dimensional tolerances. Scratches and dents could not be tolerated.
Erection of the sections was one of the most challenging feats of the twentieth century requiring the design and building of two special fifty-ton cranes that could creep up the sloping sides as each segment was welded into place. A structural steel skeleton went inside the legs as each section was set in place.
As each section was set in place the legs leaned a little more towards the center as workers momentarily held their breaths for fear that the leg might keep on leaning like the famous Italian tower. Putting the last ten foot long keystone section into place 650 feet above the ground proved to be one of the most difficult problems of the entire project. As was to be expected, the legs were quite close to each other and would have to be spread apart by a powerful hydraulic jack. In addition, one leg was somewhat taller than the other because of unequal thermal expansion. Fire hoses were brought in to try to cool the leg, at least the largest sections near the bottom. As if by a miracle, however, the final section was set into place by late afternoon. The St Louis Arch opened on October 25, 1965 and cost $13 million.