Usually the closest a structural engineer’s work will get to experiencing the forces of climbing is a maintenance worker ascending a tower or bridge… or a trespasser scaling a skyscraper via suction cups…
In terms of engineering, climbing structures are their own unique animal, involving all the usual suspects—wind loads, seismic loads, gravity loads—but with a little extra thrown in.
“Several people are hanging on these structures at once,” he explains. “You have to account for the activity loads and fall loads.”
In other words, people are constantly working against, and surrendering to, the forces of gravity on a climbing wall. It’s a component that triggers strict standards set forth by the Climbing Wall Association (CWA).
THE "LOAD" DOWN ON CLIMBING STRUCTURES
Portland DCI Principal Wade Younie explains there are essentially three types of climbing structures: stand-alone “monument structures,” bouldering structures and “slabs” that lean against another structure.
“The monuments are most challenging to design. They are like a Frank Gehry building with all of the changing angles and surfaces,” Wade says. “The challenge is to keep the steel tonnage as efficient as possible, but keep the monument stiff for the safety of climbers, as well as being seismically stable.”
For bouldering structures, climbers use thick floor pads to cushion their fall. This technique is also used on taller structures, as well. However, climbing above a certain height, usually between 10 and 15 feet, necessitates a system of ropes, belays and anchors to prevent falling. Or, as they say in the climbing world, “hitting the deck.”
Greg and Wade note the biggest load factor is at the top of the wall on the belay bars, themselves; and they need to be anchored in adequately in order to withstand the force of the climber’s fall.
Many facilities also use auto-belay, which are anchored with the belay bars at the top of the wall and a retractable rope is clipped into the climber’s harness. This load not only accounts for the climber, but the weight and action of the auto-belay, itself.
A GROWING, EVOLVING INDUSTRY
Since 2012, the climbing industry has experienced a nine percent average growth rate every year. DCI averages over a dozen climbing projects annually, ranging from small-scale bouldering projects to large-scale, top-rope monuments.
In fact, just six miles from DCI Engineers’ downtown Seattle office is what is believed to be the world’s first climbing structure. Located in West Seattle’s Camp Long, it was designed and built by expert mountaineer Clark Schurman in 1939.
Comprised of concrete and protruding rocks of various sizes for handholds, the 20-foot-tall monument structure served as a training piece for many notable climbers, including Jim Whittaker (the first American to ascend Mount Everest) and Fred Beckey, one of climbing’s most iconic figures.
To say the least, climbing structures have come a long way. The same goes for technology. Greg recalls some of his earlier projects where the designer would send photos of Styrofoam block models.
“I’d be looking at a foam block thinking, can we fit a frame in it?” Greg laughs. “Now they’ve got 3D sculpting software that feeds into a 5 Axis CNC Router. The communications are better and the process is much more sophisticated.”
The Portland office applied this same technology on expansion projects for the Portland Rock Gym, which is the second oldest climbing facility in the country.
“We imported the climbing wall artist’s 3D ACAD model into our 3D structural modeling program to size the members, which are typically steel angles welded together,” Wade notes. “The footing is sized for the overturning reactions at the base.”
However, with better technology comes bigger, grander and more complicated designs, which translates to more involvement in structural integrity and activity loads. Take for example, large overhangs at the top of a wall. As we’ve learned, this area of the structure already carries significant fall loads with top-rope and auto-belay anchors.
“The challenge is that very few climbing walls are the same,” Greg explains. “We normally use a tube steel frame, but sometimes we’ll use concrete frames. It just depends on the shape of the wall, location circumstances and design the client wants.”
“The outside surface is what the artist cares about. So the trick is providing a steel frame that is flat to mount the plywood skin on,” Wade notes of their approach to the Portland Rock Gym projects. “On both the slabs and monuments, we used a layer cake approach. We designed a series of eight-foot-tall frames that stack on top of each other.”
Nowadays, you’ll find climbing structures on private properties all over the country, from small bouldering walls in children’s playrooms to 30-foot-tall slabs on the backside of pole barns. Regardless of the project, a licensed structural engineer will work with you to build a solid, safe structure for you to practice your Sylvester Stallone moves.
So, “Climb on!”
About the Author
Erin Spaulding, Communications Coordinator / Erin comes from a journalism background with an emphasis in feature writing. She enjoys capturing the unique details of a story and is a firm believer that every person (and every project, for that matter) has a story to tell. Erin loves running, fly fishing and learning about unique spaces. Back in Michigan, she owns a little studio condo readapted from an asylum into a mixed-use residential building.