Tuesday, May 2, 2017

Engineers Hang from Ropes to Inspect Dam Gates

Major Doug Droesch, engineer with the U.S. Army Corps of Engineers – Tulsa District, inspects the gates at Robert S. Kerr Lock and Dam south of Sallisaw as part of a periodic inspection. Droesch is using the rope access technique, which allows him access to areas he would not have easily accessed by using the fall arrest method. Rope access allows the inspectors to ascend and descend via ropes, while fall arrest requires them to scale the structure with only a safety line to keep them from falling. (Photo by Thomas Mills, USACE)

Engineers were on the ropes, literally, at the Robert S. Kerr Lock and Dam south of Sallisaw, last month.

Major Doug Droesch and David Jarvis, both with the U.S. Army Corps of Engineers – Tulsa, were dangling from ropes on the dam’s gates. Droesch, a structural engineer in the civil design section, and Jarvis, hydraulic steel structures engineer for maintenance and operations and the bridge program manager, were in the process of inspecting the dam’s tainter gates for a periodic inspection.

The technique they are using, called rope access, is quite different from the old way of doing things, called fall arrest, they said. With the fall arrest system inspectors climb onto the structure, relying on their ability to scale the gates with their hands and feet. If they fall the self-retracting lifeline of the fall arrest system will catch them, but it also may allow them to swing into the structure.

The rope access system is different because the inspectors are actually suspended from the top of the structure, allowing them to get into positions they couldn’t get to if they were just climbing, said Droesch, allowing them to more thoroughly and more efficiently inspect the dam.

At some point in the 1980s, said Jarvis, inspectors on large structures realized they could reach difficult areas using techniques from ascending and descending cliffs. That has translated into industrial rope access and three levels of training for rope access technicians. Level one rope access technicians are the people who perform the rope access work. Level two technicians do rope access work and safety evaluations, and level three technicians are responsible for the work site.

While rope access requires a level three technician on site to ensure the rigging and practices are safe, it still requires less people and equipment than using a crane or cherry picker, said Jarvis.

“For us to do our inspection really requires only one other person to be our safety lead and level 3 rope access technician,” said Jarvis. “He sets up all the rigging, the anchors, ties all the knots on the ropes.”

The periodic inspection occurs every five years and determines cost, repair methods and repair techniques for the future, said Jarvis.

“As Major Droesch and I are down on the gates we’re identifying areas that may have to be replaced, areas that will have to be painted and areas where we may have to reweld things,” said Jarvis. “We also report to management and say ‘these are the things we could do to better maintain the gates and give them longer life.’”

Droesch said they look at critical areas of the gates where there are higher forces and higher stresses on the steel structure.

“We’re looking at welds, looking for cracks in the welds, looking for corrosion, any rust that will start to deteriorate the metal,” Droesch said.

With less metal because of corrosion the ability to resist the water behind the gate is lessoned as well, he said.

“So we’re checking all of that to see what the condition of the gate is,” he concluded.

Sally Maxwell, Senior News Director

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 Green Leaf Properties

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