Gateway Arch

What engineering icon's image is more closely associated with its place than the St. Louis Gateway Arch? The Gateway Arch is the nation's tallest monument (630 feet tall) , and is 75 feet taller than the Washington Monument and over twice as tall as the Statue of Liberty. In 1947, architect Eero Saarinen's winning competition entry conceived the Arch in stainless steel. Saarinen asked structural engineer Fred Severud to study its feasibility from the structural engineering point of view, demonstrating the need for joining the skills of more than one discipline in order to create a project of this magnitude.

The stainless-steel-faced Arch spans 630 feet between the outer faces of its triangular legs at the ground level, and its top soars 630 feet into the sky. It takes the shape of an inverted catenary curve.

Each leg is a symmetric triangle with sides 54 feet long at ground level, narrowing to 17 feet at the top. The legs have double walls of steel 3 feet apart at ground level and 7-3/4 inches apart above the 400-foot level. Up to the 300-foot mark, the space between the walls is filled with reinforced concrete. Beyond that point, steel stiffeners are used.

The double-walled triangular sections were placed on top of one another and then welded inside and out to build the legs of the Arch. Sections ranged in height from 12 feet at the base to 8 feet for the two keystone sections. The Arch has no interior structural frame - its inner and outer steel skins joined to form a composite structure and give it its strength and permanence.