What magnitude of minor lateral force on Great Room wall makes it shake

[Ron247]

I was pushing laterally on a 20'Hx25'W Great Room wall the other day to show the builder how weak the wall was. With only me pushing on the wall at about 4' to 4.5' from the floor, you could easily see it moving in and out. The wall is almost all windows and doors. It was framed with 2x4 syp wall studs. The upper half is mostly windows and the lower half is windows and doors. It passed city inspection I am told but that may not be true.

There are several framing issues that created the problem, but in shoving on the wall, I told the builder I cannot push horizontally on the wall more than about 1/3 my body weight and that was minor in comparison to the wind the wall was supposed to resist (5,000 lbs or more). The builder claims people can push more than their body weight and used someone bench pressing as an example. I know the bench pressing is not applicable to this.

My question is mainly, how hard can someone push laterally from shoulder level against something when they have nothing bracing them from overturning themselves. I used 3' spread of my feet and 4' to 4.5 for the distance to my shoulder and that is where I get my 1/3 approximation. Does that sound right? (3'/2)xP = 4.25xH ---> H = .375P -----> Ballpark 1/3 your weight.

 

[XR250]

In my experience, if you can shake it, it is not ok. With a lot of windows, that wall would likely need to be 2x8 construction. Might be easier to show the builder a quick calc. with code C&C wind loads on it.

 

[271828]

Calculations aside, I'm pretty sure I've never seen a wall that I could push laterally and detect any noticeable deflection.

If someone short of a World's Strongest Man competitor can move the wall enough to see it, that's good enough proof for me.

 

[RWW0002]

I agree that the wall has problems. No question.

But in terms of putting a number to the force, why not put a bathroom scale between your hands and the wall? I would try to find an analog version, digital ones make you wait until it is at equilibrium sometimes..

Those of you at home today could probably give the OP the rule of thumb he is seeking (% of body weight while standing at a normal stance pushing on a wall) in a few minutes..

All of this assuming bathroom scales work vertically, but I think they should (accurately enough for this anyway).

 

[bones206]

I confess I already did the bathroom scale test this morning. Partly curious, partly procrastinating from my real job.

Static push was ~35 lbs, shoving hard was ~70 lbs. I weighed in at 155 lbs and was wearing socks

 

[ChorasDen]

Is this 2x4 20ft tall wall braced at all for out of plane loading? If not, you've exceeded the allowable code prescribed slenderness using 2x4 framing at 20ft, nevermind the lateral forces involved. Refer to AWC NDS section 3.3.3, I get a slenderness of 68.6.

 

[RWW0002]

Some versions of IRC technically allow crazy tall gable walls as long as they are nonloadbearing,and contains very little as far as full-height king stud requirements. I do not do much residential design, but I had to chase down the requirements for a friend a while back and I was stunned how flexible of a wall was allowed.. No doubt they need a beefier wall, but If you have a sharp contractor, you may have an uphill battle from a code perspective. However I think even these (woefully inadequate in my opinion) requirements call for at least 2x6 studs..

 

[271828]

I confess I already did the bathroom scale test this morning. Partly curious, partly procrastinating from my real job.

Static push was ~35 lbs, shoving hard was ~70 lbs. I weighed in at 155 lbs and was wearing socks

Sounds about right to me.

I would think the absolute upper bound would be what the person can overhead press, not bench press. 200 lb is a lot for a recreational athlete. 300 lb is a lot for almost anybody. The world record clean and press is about 500 lb iirc. Take those times the cosine of about 45 deg.

 

[Ron247]

Several have mentioned the use of scales. I am 2 states away from home in a motel and even at home, I think we threw the scale away because it quit working and have not bought another one yet. Not sure how rotating it 90 degrees affects accuracy but probably close enough.

Thanks bones206, at least that gives a starting point. 1/3 of body weight woudl be 50. You hit between 35 and 70.

 

[BAretired]

If bathroom scales are used, the weight of the scale has to be included in the equation. This would give a somewhat exaggerated value for F_max. (See below)

Available friction underfoot would be another consideration.

W*e + W_bs*d = F_max*h

BA

 

[dik]

I think you are using a scalpel where an axe would be more appropriate.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[kissymoose]

I think it's important to note in BA's diagram the answer to your overturning question. Without e, there's no force against the wall. Try it now, standing vertically see how much purely horizontal force you can apply to the wall while remaining vertical.

Also this whole scenario is interesting. In my opinion, if the builder finds an engineer to qualify this without changes, feel free to report them to the board.

 

[dik]

Without e, there's minimal force against the wall, I suspect.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron247]

I rotated my hips and put one foot against the base of the wall and the other foot was about 3' away. Other than that I was abotu what BA depicts.

I doubt an engineer will sign off on this. The ball is in his court. Find one that will, let them do their calcs and submit them for review. At 10 psf wind and 500 square feet compared to maybe 100 lbs max a person can push.

 

[BAretired]

Even sumo wrestlers could not exceed their weight unless they were wearing special shoes with a static friction value greater than 1.0 on the floor finish.

BA

 

[dik]

Superglue on the Sumo wrestler's bare feet.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dauwerda]

While I completely agree that the wall is not adequate by the sounds of it, I do feel that everyone is missing one key item when it comes to maximizing the horizontal force you can apply on the wall. That is the vertical friction between your hands and the wall.

Rather than pushing the wall over with a purely horizontal force, one would push both horizontally and up, essentially becoming an axial member. This does two things, it eliminates the overturning problem and it also increases the friction force between your feet and the floor (by increasing normal force). This will allow you to exert much more force on the wall, which will only be limited by your strength or the frictional resistance between you and the wall or floor.

 

[271828]

While I completely agree that the wall is not adequate by the sounds of it, I do feel that everyone is missing one key item when it comes to maximizing the horizontal force you can apply on the wall. That is the vertical friction between your hands and the wall.

Rather than pushing the wall over with a purely horizontal force, one would push both horizontally and up, essentially becoming an axial member. ...

I agree. I think we can set a reasonable upper bound as I described above. The maximum axial force in the person (LOL) is how much he or she can overhead press. For people who are pretty strong, that's about 200 lb. Take that and multiply it by 0.707 to get about 140 lb maximum horizontal force.

I'd guess an average man can overhead press no more than 120 lb, so that's about 85 lb maximum horizontal force.

 

[dauwerda]

Why would you need to overhead press it? Your legs are much stronger than your arms. Start with your arms straight out (or use your shoulder and eliminate your arms all together) and use the muscles in your legs to increase the axial force.

 

[271828]

Still have to maintain the axial load in the arms and spinal column.

I can't hold a lot more above my head than I can overhead press. It becomes a stability problem. LOL. I guess I'm making the leap that this is about all anybody could muster.

 

[Ron247]

In my case, my arms were horizontal. It makes sense that pressing upwards with your hands while pushing horizontal will increase your vertical stabilizing force and would be related to wall friction value and how hard you are pushing horizontal.