Protective coatings were never applied to the now-rusting stainless-steel exterior of the St. Louis Gateway Arch because planners considered the 630-foot monument impervious to corrosion.
Moreover, planners had such confidence in the design and construction of the nation’s tallest monument that they never even developed a maintenance plan for the structural steel, according to the Arch’s maintenance director.
As a result, the Arch has been neither fully cleaned nor its carbon steel interior fully recoated since the structure opened in 1967.
‘Could Never Fail’
“People said it was designed to last 1,000 years,” said Edward Dodds, who recently became chief of maintenance for the Jefferson National Expansion Memorial, the National Park Service division that includes the Gateway Arch.
“They thought the exterior structure could never fail,” Dodds said in an interview Friday (Sept. 24). “We found that that may not be true.”
In fact, visible interior and exterior staining and corrosion have led the National Park Service to commission a structural study of the Gateway Arch.
The $325,000 study will be conducted by Wiss, Janney, and Elstner Associates of Northbrook, IL, the same consultancy that conducted an initial study of the monument’s condition in 2006.
WJE will not comment on the scope of the new study, saying the issue remains under investigation by the NPS.
NPS officials say the corrosion problem is not affecting the monument’s structural integrity, but they also admit that they do not know the extent of the damage. Dodds says the NPS has no recent photos of the exterior’s upper reaches, where some of the corrosion has been reported.
The 2006 study did report corrosion throughout the structure. It noted corroding bolt heads and staircases, interior rusting and leaking, and degeneration of the exterior skin.
Today, exterior staining can be seen from the ground, and the St. Louis Post-Dispatch recently reported visible spotting, staining, discoloration and corrosion along the exterior. Those reports prompted calls for the new study, which is considered an in-depth follow-up to the 2006 report.
No Maintenance Plan
Designed by architect and industrial designer Eero Saarinen, the Gateway Arch has no real structural skeleton. Ground for the unique monument was broken in 1959, and the first triangular section was set in place in 1963, according to an NPS history of the monument.
An engineering marvel at the time, the Arch’s reinforced-concrete-and-steel construction was considered so impregnable that planners left no direction for maintenance, Dodds said.
“I don’t think we were given any indication of what we should do to maintain the exterior,” said Dodds. Nor were recommendations made for the interior, except for working mechanisms, he added.
Battleship-gray protective coatings were applied to the interior before the monument opened, but—except for touch-ups around welds and other repairs—no coating has been applied since, Dodds said. He did not know the type of coating applied to the interior.
Stainless steel possesses “unusual resistance to attack by corrosive media,” but it “can corrode in service if there is contamination of the surface,” according to “Stainless Steel Corrosion,” an article by the National Association of Corrosion Engineers (NACE) in its online Resource Library. Welded areas are especially vulnerable, as are components exposed to precipitation, according to the article.
The 2006 report recommended a full-scale cleaning of the Arch within 10 years, but it did not say what the project should include or how it should be done, Dodds said. Meanwhile, he added, the consultants could not determine the cause of the problem because they could not gain full access to the structure.
“That’s one of the biggest hurdles to overcome,” he said. “How do you gain access to the exterior?”
Answering critics who are accusing the NPS of foot-dragging on the problem, Dodds said: “Do you want to do something quickly or do it correctly? The Park Service wants to do it correctly, especially when you’re dealing with something irreplaceable.”
Even a full-scale cleaning—probably the minimal that will eventually be required—would have to be approached with caution. “Would that be a corrective action, or could you be causing another spot?” Dodds asked.
Finding the Culprit
Although water intrusion is a chronic issue with the Arch (“that’s going to happen anytime you have an interior structure like that that’s unconditioned,” Dodds said), there may be other culprits as well, including environmental contaminants.
Several years ago, he said, maintenance workers attempted to determine the presence and type of exterior contaminants by applying some kind of tape to the surface through a hatch at the top of the structure. But the crew could not obtain a large enough sample for analysis, he said.
For now, NPS is adopting a wait-and-see attitude before making its next move. Aggressive sanding or grinding, parts replacements and other remedial measures could all backfire without sufficient information, Dodds says.
NPS is hoping that the new report will spell out causes and make clear recommendations that include cost estimates. The findings, Dodds says, “will hopefully provide guidance for years to come and keep [the Gateway Arch] a national icon.”