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Study to Probe Rusting Gateway Arch

Thursday, September 23, 2010

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St. Louis Gateway Arch

The National Park Service has commissioned a structural study of the St. Louis Gateway Arch—the nation’s tallest monument—following reports that the steel structure is showing corrosion.

The $325,000 contract was awarded Sept. 16 to KPB Architects of Anchorage, AK, which subcontracted the work to Wiss, Janney, and Elstner Associates of Northbrook, IL, Park Service contracting officer George Sievers said Thursday (Sept. 23). WJE, an architectural and engineering consultancy, conducted another study of the Arch in 2006.

The new study follows disclosures by the St. Louis Post-Dispatch that the stainless-steel exterior of the iconic structure is suffering from increasing rust and decay. Park officials say the structure is safe, but they do not know the extent of the damage.

‘Ongoing Investigation’

Margaret Sullivan, a spokeswoman for WJE, declined Thursday to discuss the cost, scope or schedule of the upcoming study. “We’re still working out details, and I can’t comment on anything more than that. The project will be part of an ongoing investigation [by the Park Service], and we don’t comment on that.”

The study is expected to start in October or November and should take just over a year, said Sievers, but he would not discuss the scope of the work, either.

The newspaper reports visible corrosion, streaks, spots and discoloration of the structure, particularly in the upper reaches, Multiple engineering reports in recent years have also noted corrosion—some of it aggressive—and discoloration of the structure, which opened in 1967.

The 2006 report by WJE was considered an initial report. An in-depth second study was recommended, but there has been no money for a second study, officials said.

Rust and Mysterious Stains

The 2006 study “identified corroding bolt heads and staircases, a leaky interior sometimes shrouded with its own fog, rusting of interior carbon steel, and a mysterious staining of the glimmering surface,” the Post-Dispatch reported.

"The exterior skin has definitely degenerated since first constructed," said the report, as quoted by the newspaper. "However, it is not possible to accurately determine the rate of visual distress."

Water infiltration is believed to be the cause of the problems.  "Condensation in the legs has been there since day one," Frank Mares, deputy superintendent of the Jefferson National Expansion Memorial, told the Post-Dispatch.

The 2006 report noted a repainted area inside one of the legs and speculated that the original paint layer may have failed because of rusting of the steel, the newspaper said.

Engineering and Design

Designed by architect and industrial designer Eero Saarinen, the Arch has no real structural skeleton. It is composed of double-walled, equilateral triangular sections —12 feet high at the base; eight feet high at the keystones—with a carbon steel interior and stainless steel exterior, stacked and welded with concrete supports.

The walls are three feet apart at ground level and 7-3/4 inches apart above the 400-foot level. The space is filled with reinforced concrete up to 300 feet. Beyond that point, steel stiffeners are used, J.E.N. Jensen, former Associate Director of the National Park Service, explains in “The Construction of the Arch.”

“The complex engineering design and construction is completely hidden from view,” Jensen writes.  “All that can be seen is its sparkling stainless steel outside skin and inner skin of carbon steel, which combine to carry the gravity and wind loads to the ground. Its inner and outer steel skins, joined to form a composite structure, give it its strength and permanence.”

The structure takes the shape of an inverted catenary curve— “a shape such as would be formed by a heavy chain hanging freely between two supports,” Jensen writes.

3 Million Visitors

About 3 million people visit the Arch each year. Two trams shuttle visitors to the top of the structure. In 2007, a steel cable on one of the trams snapped, knocking out power and trapping about 200 people inside for several hours.

The Arch has not had a full-scale cleaning since it opened, officials say. Addressing the rust issue could require anything from a cleaning to full-scale restoration.

Meanwhile, a consortium led by New York landscape architects Michael Van Valkenburgh Associates-- the firm responsible for redesigning Pennsylvania Avenue at the White House--has won a competition to reshape the grounds of the Arch.

That project is expected to be completed by 2015 and is unrelated to the corrosion problem. The selection of the architect was announced this week.

   

Tagged categories: Architecture; Corrosion; Protective coatings; Steel

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