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

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Ron247

Ron247

Structural
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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.
 
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The limit will be how high the friction is with the floor, though I suppose if there is high friction with the wall you might go higher.

What might be more valuable is to put a floor weight scale against the wall and see how hard the builder can push. If it is less than 5,000 pounds and the wall moves a noticeable amount then that indicates there might just be a problem.
 
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While the friction would account for sliding, overturning has been my problem. My feet do not slide, but I overturn at some force because my only stability is my body weight and a moment arm equal to half the spacing of my feet.
 
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W*e = Fmax*h
Fmax = W*e/h

W = weight of person
Fmax = maximum force against wall
e = horizontal distance from c.g. of W to c.g. of foot furthest from wall
h = height of horizontal force Fmax


BA
 
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Even if you could push with 500# it is 1/10 the wind load.
Looks like a problem.
Get a scale and ruler on a stand, flex the wall, record load and deflection.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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Since you figured it out, why did you ask?
 
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20' tall 2x4. Not sure how that would work even if an interior wall with only 5psf wind load.
 
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Ron247 said:
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?
Click to expand...


3DDave- I asked if what I figured out sounds right.
 
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My question is mainly, how hard can someone push laterally from shoulder level against something when they have nothing bracing them from overturning themselves.
Click to expand...

Isn't that a question?

Maybe ask only one question if want the answer to only one question.

I told you how to exactly determine that value - you do own a bathroom scale, don't you? You have access to a wall. You could have found out in the time it took to complain about my very correct answer.
 
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2x4 framing is a little light for 20' height... I'm not a 'wood guy' but I've done tall walls in wood, 20' high and they were 2x8@16, including wind loading. Remedy might mean adding and securing another 2x4 stud wall to the face of the existing; the solution may not be easy.

With a coef of friction of about 0.5, I suspect the push would be about 100 lbs max. If on an angle, maybe a little more becaused of the apparent 'added' weight.

Was the wall built from any drawings? or did the contractor just 'build it'? The use of a scale would give a good approximation of the load.

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

-Dik
 
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Not only are 2x4s light for the height, but they would likely be spliced as well. Wood splices can be flexible and problematic.

I don't know too much about the residential code, but there might be some prescriptive designs in the code for which to compare your wall.
 
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No more 20' trees? [ponder]They used LVLs for the ones that I was involved with...

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

-Dik
 
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Fmax*h = W*e

image edited

Capture_lwthix.png



BA
 
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I looked into this once. Professional rubgy players and sumo can sustain about 100% of body weight as lateral force. Average humans top out closer to 70%.

----
just call me Lo.
 
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Lomarandil, do you mean they can create a force of 100% while standing still or while moving? In my case, I would be using the standing still value. I can see that squatting down would increase your ability since the moment arm reduces. In the case I am talking about, BAs sketch is very close.

dik-I think the contractor just built it. I doubt the plans were detailed.
 
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They are full length 20' 2x4s. They may be from a local mill and may not even be graded. This is not the first one I have run into. Last one was replaced with a steel tube frame. One of them I ran into was two 10' walls placed on top of each other to make the 20' wall. It shook very easily too.

Owner was concerned due to movement so that is why I went out. They saw it move with a moderate wind. At this stage, the builder has to get his own engineer involved since he thinks it is ok. I do not know who he will get but I am confident it will not work.
 
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There would be an Fmax at his feet limited by coef of friction.

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

-Dik
 
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Can you introduce a couple of 2x10 or whatever pilasters? may be the easiest fix.

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

-Dik
 
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It looks like most of these calculations assume only body weight, but there ought to be stances that can produce more than body weight, although not necessarily for very long. A weightlifter could potentially a 600-lb force for a clean and jerk and 1000-lb for a bench press or squat.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
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You could apply an impact factor of 2 to the static body weight (BW) force, so 2 x 0.33BW = 0.66BW. That would be more in line with the typical force Lomarandil suggested.

Shouldn't really need calculations to win this argument with the builder though... If a wall is visibly moving under moderate wind or human pushing, isn't that objectively unacceptable for conventional US construction "by inspection" ?
 
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