Calculating load/force for an adjustable climbing wall

[athlon2k2]

TL;DR Summary

I'm building an adjustable climbing wall based on a pulley system but need to figure out the forces involved to adequately reinforce the supports.

The construction of this climbing wall is all done with 2x6 boards and 3/4" plywood. With some base calculation I estimate the wall to weigh roughly 400 lbs. Assuming the max weight of a climber is 200lbs. That would put me at 600lbs. Since this wall is on a hinge the maximum weight at the top when the climbing wall is perpendicular to the floor would be half the weight (300lbs). I intend to use a pulley system with a pulley on each upper corner of the wall. So dividing the load by 2, I estimate each corner to weigh 150lbs.

Here is where it gets little tricky. When I look up some specs on pulleys they state that the force can be up to double the load. This means each pulley could have up to 300 lbs of force. If assuming that being perpendicular to the ground is worst case, then the angle of force on the pulley would be down and out at a 45 degree angle.

In the end this means each pulley would need to support 150lbs of downward force and 150lbs of outward force (away from the wall).

Can someone please valid this is the way to calculate this? Here are some pictures of the project and supporting data.

I have 152 linear feet of 2x6 studs and 3 sheets (4'x8') of 3/4" plywood



https://www.engineersedge.com/commercial_lumber_sizes.htm

http://theplywood.com/weight

 

[jedishrfu]

Here’s a cool video on snatch blocks which are a form of pulleys.



it might get you thinking about your setup.

 

[athlon2k2]

Hey jedishrfu,

Thanks for the video. I love watching Destin's videos. I have been looking into this when I saw that most bike hoists uses a snatch block style system. The great thing is you can set it up so you can use a lot less force to move something. The unfortunate thing is it adds more force to the pulley and this is my issue. I'm cutting the force it takes to lift the wall in half but I'm doubling the force exerted on the pulley. My biggest fear is one of the pulleys being ripped out of the wall while I'm 10 feet in the air and landing on my back.

 

[athlon2k2]

I guess one thing to think about is that I could add more pulleys and therefore spread the load across the wall instead of just one point. I have 24" between the 2x6s so that doesn't give me much room but I'll look into that option. Thanks again.

 

[anorlunda]

Aren't you likely to get sued if someone gets injured on your wall?

Shouldn't you be looking for mandated construction and safeguard details from applicable safety codes rather than on the Internet?

Are you insured? What does your insurance company require?

If someone does get hurt and your defense is, "Well, some guys on the Internet (don't know their names) said it was OK," then your chance of winning is nil.

 

[athlon2k2]

Hey anorlunda,

I appreciate the concern. I am building this wall for myself. That said, I'm sure other people close to me will use it. This is not something I would let children use and all adults would be warned that I built it (maybe a sign "cliimb at your own risk" would be useful). Just like having a pool or stairs I run the risk of someone getting injured at my house. Thankfully I rarely have people over and I do have very good insurance.

In regards to safety codes, I am being very careful to only purchase items that have been rated well past the weight I intend to have and are ASME certified. I also have been consulting with a structural engineer (loosely) as well as looking at the UBC and other sources.

My main goal here was to look at the physics involved and to make sure I was using the right formulas and math to get load on the pulleys. I'm not holding anyone liable (because I can't and wouldn't). This is a physics forum and thought this would be the right place to bounce my theory off of or get more insight. I only took physics in college so I'm pretty rusty, but this has been fun and challenging.

 

[berkeman]

Thankfully I rarely have people over and I do have very good insurance.

Have you talked to your insurance company about this climbing wall that you are adding to your home? Probably it is similar to adding a pool to your home -- it can change the premiums that you pay for some insurance coverages.

 

[athlon2k2]

I have not, but I will talk to my agent.

 

[anorlunda]

I appreciate the concern. I am building this wall for myself. That said, I'm sure other people close to me will use it.

It is not just your safety in question. This is not a private conversation. Anybody, including children, can find it via search. We have no way to judge how they might apply or misapply advice here.

Our guidelines say "no dangerous topics." Thread closed.