(Thanks to Jerry Follen for the heads-up on this article and image!)

Why did the cable at the Arch break?

By Todd C. Frankel at STLtoday.com

A series of problems, ranging from the use of the wrong-sized parts to improper installation, led to a tram cable snapping last summer at the Gateway Arch, according to a new engineering report.

The braided steel cable dropped more than 500 feet inside the national monument on July 21, 2007, knocking out power to the Arch for two hours and resulting in a nighttime evacuation. While the tram was never in danger of falling and no one was hurt, a safety engineer said a falling cable can cut through metal "like a knife through butter." The south tram, which at first was going to be closed just two months, ended up being shuttered for eight months as officials tried to determine what went wrong.

"The main goal was to fix it, not to point fingers," said Justin Struttmann, Metro's director of operations at the Arch, which runs the trams.

But an investigation by Pennsylvania-based Maida Engineering blamed the incident on the workmanship of the National Park Service, which maintains the tram, and outside contractors hired to work on the tram system, according to the report obtained by the Post-Dispatch through a Freedom of Information Act request.

There was nothing structurally wrong with the equipment used to ferry visitors to the top of the 630-foot Arch. The cables were strong. The machinery worked. Engineers even used scanning electron microscopes to look for the smallest weaknesses. Still, a series of small missteps culminated in the first cable failure in the Arch's 43-year history, the engineering firm concluded.

"I was surprised by a couple of things (in the report)," said David Bubac, chief of facility management at the Arch grounds. Yet, he felt the report showed "we were doing a good job, but a couple of procedures needed to be reviewed."

The report, requested by the Park Service, highlighted the difficulties in working on a tram system unlike any other in the world. The trams in the Arch's two legs are part-elevator, part-Ferris wheel. Nine hoist cables pull the tram cars using a counterweight as the cars ride along rails in the Arch's curved portions.

In the curves, the hoist cables need to move and flex.

Investigators focused on one area in particular: the metal shackles connecting the hoist cables to the counterweight.

Maida discovered that the shackles were too big and did not meet the Arch's original specifications. Grouped tightly together on the counterweight, the shackles rubbed and banged against one another, straining the hoist cables.

Arch officials were unaware of the problem until Maida measured the shackles. It turned out suppliers were making shackles thicker on the outside than the inside. The shackles met federal size standards, which are less stringent than the Arch's standards. Arch officials were in the dark.

"We did not know there was such a variance in size," Bubac said.

Maida measured the spare shackles at the Arch and found only a small percentage "were acceptable dimensionally."

A contractor hired to help with the repair work earlier this year was more critical of the shackles' quality. "They gave us shackles so old and damaged we had to call a meeting because we couldn't use them," Dennis Parker, president of Authorized Elevator of St. Louis, said.

The company clashed with Arch officials over several issues and ended up leaving the repair job to be finished by others. Maida, in its report, noted concerns about Authorized Elevator's work being more appropriate for a vertical elevator and redid some of it.

To make the oversized shackles fit properly, Maida suggested the shackles be carefully ground to fit.

Maida also discovered the shackle pins were not lubricated. The Arch's original drawings did not call for lubrication, but Arch workers added lube in recent years as a precaution. It was not known why the step was skipped just prior to last summer's incident, according to the report. But, Maida wrote, "There should be no question that lubrication is critical to a proper assembly."

The south tram reopened in March after Maida inspected the repair work. The north tram remained open throughout, with Maida finding no signs of problems.

Maida's final report was delivered in June to Metro and Park Service officials.

"I believe the tram is very safe," Maida project manager Harve Hnatiuk said in an interview.

He estimates he rode the south tram to the top probably 30 times during his investigation, even when the one cable was missing.

In the report, Maida noted another contributing factor to the cable break was sand-like material found in the broken cable's shackle. Maida urged Arch officials to work more carefully to keep the shackles clean of debris.

Routine maintenance on the tram is conducted by Park Service staff. But major projects — like installing new hoist cables, which are replaced every two years — is handled by contractors. For a decade, Interlift Industries of Muskego, Wis., did the work.

Both Maida and Interlift suggested stepped-up oversight by Arch officials. Last summer, tram mechanics noted fraying of the No. 2 hoist cable. But they didn't identify any problems with the No. 5 cable — the one that ended up breaking.

"There should be a more stringent examination of the rope connection at the counterweight," Maida wrote.

The firm suggested a wireless video camera be installed to provide constant surveillance of the health of the cables. But Arch officials said that was not feasible.

Interlift suggested more training in elevator operation and maintenance for Arch officials. Tram inspections are handled in-house by Arch mechanics, none of whom meet the national standard of a Qualified Elevator Inspector.

Arch officials have resisted calls in the past for this qualification. The Arch is not a true elevator, they say. Bubac reiterated that stance.

"We can always use more training. We can always use an outside pair of eyes," Bubac said. But "I do not believe we need (elevator inspectors) on staff because we are not an elevator."

For now, tram mechanics alone will inspect the trams. But Bubac left the door open to changes.

"If we feel we need someone to come back and re-evaluate," he said, "we could do that."

If you look closely at Image 31 you may notice that the rope leading out of the shackle that is labeled looks somewhat damaged.

 I know more! 

Image 45A
Cross-section through a tapered rope socket showing maximum & minimum
projection of turned-back strand loops above embedment medium.
Image provided by:
American Society Of Mechanical Engineers - A17.3 - 2005 Safety Code for Existing Elevators and Escalators

Do cable bands or seizings need to remain on the rope after the rope fastening has been attached?

I would argue no...and the above image of rope damage beneath a cable band is why I say that.

But what do our codes require?

A17.1S-2005 Section 2.20.9.7.2(b) reads in part, "The seizing shall be done with annealed iron wire, provided that other methods of seizing be permitted, which give the same protection from loss of rope lay." (Emphasis mine) Other forms of seizing would include cable bands.

A17.1S-2005 does not forbid the removal of the last seizing (or cable band) from the rope after the fastening is applied.

A17.2-2001 (Inspectors Manual) Section 3.22.1.1(d)(3) reads, "When the embedment medium has cooled or cured, and the seizing at the small end has been removed, make a visual inspection." (Emphasis mine)

The Handbook on A17.1-1996 (page 260) reads, "The seizing may be removed after the fastening has been completed, as it serves no further purpose." (Emphasis mine)

I would suggest to all Authorities Having Jurisdiction that they require the removal of the last seizing once the fastening is applied.

 I know more!