Washington Monument engineers, rappelling way up high

Dan Ruff shot this wonderful photograph of structural engineers rappelling down the face of the Washington Monument to inspect possible earthquake damage. More shots here. Shared in the Boing Boing Flickr Pool. Maggie wrote about this the other day, but it's neat to see a Boing Boing reader out on the scene taking photos!


  1. Someone call DHS, I think Al Qaeda was taking pictures of the washington monument to plan how to blow it up.

  2. My question is: how the heck did they get the ropes hooked around the top so they could rappel in the first place? Just thinking about it gives me vertigo.

  3. Some jobs, you gotta wonder how often those folks get to work. I mean, how often is the skillset shown here required? “You gotta be able to rappel AND make structural assessments”. They probably travel all over the world to all kinds of neat projects. Probably a young person’s game.

  4. Any climbers or physicists here? Seems like they rigged a system that would amplify the forces on their anchors. Given they’re not protecting leads and the only failure possibility is really the runners themselves, I could see the decision but it still seems odd. Especially since you’d expect an operation like this to be super-safe, and they’ve got, like, 12 runners around the top of it with the corners padded. And double ropes. Those runners will fail long before the ropes, if I’m right.

    For the rest, by clipping vertical ropes into horizontal runners, they create a system that magnifies the forces experienced by their anchors.  Better to try and create an acute angle between the fall vector (straight down, in this case), and the direction of force on the anchor as translated by the system (forgive me, I’m not a physicist). From what I know, this is a textbook mistake. As I understand, this is basically the same situation as the death triangle (en.wikipedia.org/wiki/American_death_triangle). I’m not an anchor guru and would love to hear from an expert.

    1. Any climbers or physicists here?

      No, not me but I think a structural engineer is required anyway. One problem with the death triangle case you pointed to is that each anchor point has to be reliable in several different directions. Putting ropes around the monument is almost the opposite of this in that if the monument and the ropes are infinitely strong there is no way they can come loose. But as you point out there are some significant concentrated loads at the corners. The climbers seem to have a safety line going directly into the hatch which is presumably considered safe, so maybe that helps the situation.

      1. Thanks for the insight. Interesting point about the concentration at the corners. The forces must be large. As I was taught, direction of pull on anchors is a separate issue from the death triangle. One preferred solution, the “magic x”, causes the forces to change direction and size based on rope movements. In any case, anchors are usually built to withstand forces in many directions. The problem with the death triangle is that it magnifies, greatly, the forces, and can cause failure. Dynamic climbing ropes are  stronger than the stuff usually used to build anchors with, but after looking around it seems like the system most riggers would use would be rated to about 22-27kn.  I think the interesting question here is if the riggers knew this, and decided to go ahead with this setup anyway, knowing that even the magnified forces would still be withing their equipment’s ratings. This is almost certainly true. It’s a complicated setup, as there seems to be a lot of stuff up there not directly clipped to the rope. The other possibility is that the death triangle fear is unique to climbers. I’ve noticed that different “schools” (climbers, cavers, riggers) tend to have very different approaches to this stuff.

  5. Brad – as a climber/architect – your reasons for being concerned about that setup are right.  The fundamental physics that make “death triangles” problematic, are, well, fundamental – but I have the same sense as you that different user-groups are much less concerned about it than climbers.  

    Think about webbing slacklines – in a sense, they are the ultimate “death triangle” type of setup – the slackliner’s straight down vertical force vector is multiplied by the tangent of the angle formed by the webbing.  (and the value of tangent shoots off to infinity as the angle increases.)  Nonetheless, it’s rare for the webbing in a slackline rig to fail.  

    My thoughts about the Monument rig are that they’re probably aware of the issues – and hopefully everyone on the team can literally do the math to calculate the loads involved!  But that it’s the best of several possible alternatives.  (I wonder if any consideration was given to drilling and placing anchors in the rock up there?  Not that they would leave hangers or chains in place, but a few holes and epoxyed-in sleeves would have added safety, without leaving much of a trace.)  If anything, I’m impressed by how much this looks like a more basic climbing setup, rather than some crazy, overkill OSHA rig.

    It’s not like climbers can be too critical either.  Simul-rapping is a zero-gear/zero-redundancy setup:

    And we do use something call the “Euro Death Knot” after all…. http://en.wikipedia.org/wiki/One-sided_overhand_bend

  6. For some reason, someone at the USDA put up a time lapse of the start of the rigging: http://www.flickr.com/photos/usdagov/6189688240/in/gallery-yahooeditorspicks-72157627767654186/

    Once the full setup was in place, I’d be pretty comfortable on it, but I have to admit that the first small loop placed above the hatch would freak me out a bit if I was the one starting the rigging.  Consciously, I know that it’s not likely to “slip off” but without something actually holding it down, that little thought of it somehow lifting up and over the top would be a bit hairy.  (But I’m sure that there was a second safety line running back in through the hatch anchored to some structure inside.)

    All in all though, by working your way up in complexity, height and exposure, rigging anchors in situations like this isn’t that scary.  It should be a little scary, but with some experience to tell you when you SHOULD be scared and when things are under control, it’s not that bad!

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