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The Threat to the Gateway Arch’s Stainless Steel Skin

The towering Gateway Arch is unique among the world’s monuments. Its gleaming stainless steel exterior reflects the light in continually changing patterns, creating a lovely effect of movement and energy that is different every time you see it. Visitors are dazzled both by its beauty and by the amazing feat of construction that was necessary to create the monumental structure that towers high above the city skyline.

The outer stainless steel skin and carbon steel interior are both important parts of its orthotropic design, which utilizes the inner and outer welded steel skins as structural elements of this massive memorial. The Arch is internationally renowned as a major piece of midcentury modern architecture by a master of the form, Eero Saarinen. In addition, Dan Kiley’s landscape design of the 90-acre park surrounding the Arch is also an important historic feature.

The Arch has become an iconographic symbol of the St. Louis, recognized the world over and a great source of pride for residents who regard the area as their “front porch,” a place for civic gatherings, including the annual Fair St. Louis event held on the Fourth of July weekend.

For almost 50 years, the National Park Service has faced the many challenges involved with maintaining a memorial of this type in an urban area, but today the Arch is facing another possible threat. The stainless steel skin of the structure has suffered a mysterious staining during the past decade. Theoretically, a stainless steel structure like the Arch should not tarnish, corrode, or develop stains over the course of time. The appearance of these stains was obviously a matter of great interest and concern to the National Park Service and St. Louis-area residents and public response and media treatment of the issue called for a swift investigation and solution to the problem. However, a 630-foot tall arch with no precedent for its design or construction did not lend itself to a “quick fix” solution.

After a prolonged period of study, a report issued by Wiss, Janney, Elstner Associates of Chicago indicated that the staining was largely a cosmetic problem and likely caused by atmospheric soiling or rust migrating from field welds. The study concluded that the welds are not losing their structural integrity.

Recommendations made to eliminate the streaking on the exterior of the Arch include further close-up testing of the welds to determine the best method of cleaning the metal and stopping the streaking at its source. Samples will need to be taken from the exterior of the structure and studied to determine the exact type of corrosion present. This would be followed by the final step, a gentle cleaning of the stainless steel surfaces and dressing and polishing the original welds to reduce future staining.

The challenge of finding a way to access the areas where the staining is present is significant. Most of the stains are above the 400-foot level, on a smooth triangular structure constructed of stainless steel, with angled sides and no exterior access save for a work hatch at the apex. The work will attract a great deal of public and media attention, with professionals harnessed and making their investigations high up on the structure of the Arch—much like the recent work done on the Washington Monument.

St. Louisians adopted the Arch design from its very inception. Even before construction began, the Arch appeared on merchandise and in advertising. The Arch became a symbol of the city and of the will of its people to create a better, modern, improved St. Louis. As a symbol, the Gateway Arch is an outward manifestation of the health and well-being of the city; if it is in good physical shape, it serves as a sign that all is well in the community.

Together with World Monuments Fund and park partners, the National Park Service is working to alleviate this flaw in the otherwise majestic Gateway Arch and to preserve it for the 1,000 years that Eero Saarinen predicted it would last.