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

Ron247 (Structural)

(OP)

16 Jan 22 15:40

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.

3DDave (Aerospace) · Answer 1 · 2022-01-16 15:49:54

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.

Ron247 (Structural) · Answer 2 · 2022-01-16 16:46:58

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.

BAretired (Structural) · Answer 3 · 2022-01-16 16:57:42

W*e = F_max*h
F_max = W*e/h

W = weight of person
F_max = 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 F_max

BA

EdStainless (Materials) · Answer 4 · 2022-01-16 17:47:50

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.

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3DDave (Aerospace) · Answer 5 · 2022-01-16 18:04:18

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

3DDave (Aerospace) 16 Jan 22 18:04

Since you figured it out, why did you ask?

Brad805 (Structural) · Answer 6 · 2022-01-16 18:22:41

20' tall 2x4. Not sure how that would work even if an interior wall with only 5psf wind load.

Ron247 (Structural) · Answer 7 · 2022-01-16 18:42:05

Quote (Ron247)
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?

3DDave- I asked if what I figured out sounds right.

3DDave (Aerospace) · Answer 8 · 2022-01-16 18:51:52

Quote:
My question is mainly, how hard can someone push laterally from shoulder level against something when they have nothing bracing them from overturning themselves.

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.

dik (Structural) · Answer 9 · 2022-01-16 19:20:39

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

JLNJ (Structural) · Answer 10 · 2022-01-16 19:32:20

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.

dik (Structural) · Answer 11 · 2022-01-16 20:16:23

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

BAretired (Structural) · Answer 12 · 2022-01-16 20:23:11

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

BAretired (Structural) 16 Jan 22 20:23

F_max*h = W*e

image edited

BA

Lomarandil (Structural) · Answer 13 · 2022-01-16 23:10:51

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.

Ron247 (Structural) · Answer 14 · 2022-01-17 01:06:26

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.

Ron247 (Structural) · Answer 15 · 2022-01-17 04:55:55

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.

dik (Structural) · Answer 16 · 2022-01-17 06:08:20

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

dik (Structural) · Answer 17 · 2022-01-17 06:09:35

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

IRstuff (Aerospace) · Answer 18 · 2022-01-17 06:40:40

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.

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bones206 (Civil/Environmental) · Answer 19 · 2022-01-17 11:29:17

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" ?

XR250 (Structural) · Answer 20 · 2022-01-17 12:40:36

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 (Structural) · Answer 21 · 2022-01-17 13:12:01

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 (Structural) · Answer 22 · 2022-01-17 14:42:50

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 (Civil/Environmental) · Answer 23 · 2022-01-17 15:18:51

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 thumbsup

ChorasDen (Structural) · Answer 24 · 2022-01-17 16:11:26

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 (Structural) · Answer 25 · 2022-01-17 18:18:17

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 (Structural) · Answer 26 · 2022-01-17 18:20:57

Quote (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

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 (Structural) · Answer 27 · 2022-01-17 19:24:48

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 (Structural) · Answer 28 · 2022-01-17 19:41:20

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 (Structural) · Answer 29 · 2022-01-17 19:58:43

Quote (the weight of the scale has to be included in the equation)

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 (Structural) · Answer 30 · 2022-01-17 20:05:48

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 (Structural) · Answer 31 · 2022-01-17 20:09:41

Quote (Without e, there's no force against the wall.)

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

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

-Dik

Ron247 (Structural) · Answer 32 · 2022-01-17 23:21:32

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 (Structural) · Answer 33 · 2022-01-17 23:39:08

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 (Structural) · Answer 34 · 2022-01-17 23:55:16

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 (Structural) · Answer 35 · 2022-01-18 15:12:25

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 (Structural) · Answer 36 · 2022-01-18 15:30:35

Quote (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. ...

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 (Structural) · Answer 37 · 2022-01-18 15:34:51

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 (Structural) · Answer 38 · 2022-01-18 16:26:43

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 (Structural) · Answer 39 · 2022-01-19 01:50:48

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.

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