The Gateway Arch

The simple appearance and design of the Gateway Arch in St. Louis, Missouri hide some complex mathematics, geometry, and technology.  It should be a geek mecca. When I visited the monument, the stark elegance satisfied my love for modern forms of sculpture.

The geometric basis of the Gateway Arch is readily apparent to anyone who views it. The monument is described as a “weighted catenary”.  Imagine a length of chain Arch-03handing from its two ends under its own weight. The resulting curve is the curve of a hanging chain. “Catenary” is derived from the latin word for chain.  If you could invert that hanging chain, you would have the basic outline of the Gateway Arch.  By the way, this is not a “catenary arch” as it is often mistakenly called.

The catenary design is ideal for a freestanding arch of consistent thickness.  Because the actual monument’s cross-section varies from thicker at the bases to decreasingly narrower toards the top, it is sometimes called a “modified catenary”.  The design was adopted so as to create an optical illusion.  The eye of the viewer senses that the arch is much taller than its width.  In reality, the structure is approximately as wide as it is high.

The actual monument consists of equilateral triangles that measure 54-feet per side, at the bases. The triangles’ measurements become gradually smaller along the height of the legs. The very top segment is an equilateral triangle that measures 17-feet per side. Each cross-section unit is double-walled, with each wall constructed of carbon steel panels.  The outer walls are finished with quarter-inch thick stainless-steel panels.

Both legs of the Arch are embedded in 23,570 tons of concrete, 18-metres (60-feet) deep. The material was reinforced with 252 high-tension rods. All of the materials work together as a single unit.  The entire loading is described as “orthotropic”. That is, the external surface and the support system are “one and the same”.

The Gateway Arch is the main feature of the Jefferson National Expansion Memorial Park, located on the west bank of the Mississippi River. The park was conceived as an early urban renewal project to beautify a blighted area of St. Louis. The old industrial area had deteriorated to its worst state, following the end of the Great Depression of the 1930s. The US Park Service contract was won by Earo Saarinen, in 1947. His team refined the original, massive arch design, into the more sleek, triangular cross-section design.

The ground breaking ceremony took place in 1959.  Actual construction began in February of 1963.  Macdonald Construction of St. Louis oversaw the construction work. The panels of the triangular sections were pre-fabricated in Warren, Pennsylvania. The “walls” were shipped to the construction site by railroad train, then were assembled into sections.  The sections were then attached together to build the arch.Arch-01

Each leg’s hollow inner core houses a specially designed elevator, transport system.  It’s a combination of an elevator with a Ferris-wheel like train of capsules. Each tram consists of eight, five passenger capsules.  It takes four minutes for each tram to climb to the observation room at the apex of the Arch and three minutes for the descent.

On October 28, 1965 the top or “keystone” section was welded in place during a ceremony attended by school children, local citizens and dignitaries. Vice-President Hubert Humphrey oversaw the activities from a helicopter.

Work continued to complete the visitor’s center which opened in June of 1967.  Finishing touches and testing of the trams were completed as well. The first trips to the top began in late July of that year.Arch-02

On May 25, 1966 the Gateway Arch was officially dedicated.   Rainy weather caused the outdoor ceremony to be cancelled.  250,000 people were initially expected, but the cancellation meant that an indoor ceremony in the visitor center could only accomodate 500 individuals. Vice-President Humphrey returned to officiate the dedication.

This year, is the 50th anniversary of the Arch’s completion.  Meantime, upgrades and added features to the surrounding park are being finished for the 50th anniversary of the Gateway Arch’s dedication celebration, next year.

1984aThe Blue Jay of Happiness found this quote by Seneca: “Human society is like an arch, kept from falling by the mutual pressure of its parts.”

About swabby429

An eclectic guy who likes to observe the world around him and comment about those observations.
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