Shuddering/deflection of upper storey bedrooms in 2 storey framed house due to wind

[Euler07]

Hi all, just wondering if anyone can provide advice on this.

I am designing a 2 storey steel stud framed house. Due to architectural reasons, the lower storey walls will be taller than normal, 4.5m tall (about 15 ft). While I can calculate the required bracing walls in the lower storey for strength, I am concerned about serviceability shuddering of the upper bedrooms during wind. Do people consider this in calculations?

When people are lying down or trying to sleep, they become very sensitive to minor shuddering/movement of the bed. I am aware of a previous court case where the builder was successfully sued because the owner was sensitive to the movement, and therefore the house was not fit for purpose.

Thanks

 

[jhnblgr]

What deflection are you seeing? Typically the conventional stud maxes out at 12’ and then you have to go with engineered lumber.

 

[Euler07]

What deflection are you seeing? Typically the conventional stud maxes out at 12’ and then you have to go with engineered lumber.

Thanks jhnblge. The walls are 90mm steel stud; for this height they would be back-to-back stud. For a normal height lower storey I wouldn't check racking deflection and would only check strength. For this I haven't yet checked racking deflection as I'm deciding on the max allowable deflection of the upper storey floor before design, or understanding the racking deflection issues before design.

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[phamENG]

Does your code have any guidance?

In the US, lateral deflection and story drift due to wind are left up to the engineer (not codified), but the recommended number is between H/400 and H/600 for the serviceability wind load. The exact value and what that serviceability wind load is depends on the type and use of the structure. For what you're talking about, I'd shoot for H/500 but would accept H/400 if things get too costly, and I'd use a 10 year MRI for the wind speed used to calculate my wind load (as opposed to a 700 year MRI that is used for strength).

 

[XR250]

What deflection are you seeing? Typically the conventional stud maxes out at 12’ and then you have to go with engineered lumber.

You can go 16 ft +/- with 2x6's sometimes. I'll switch to 2x8's before I go engineered lumber due to cost and availability.

 

[jhnblgr]

Try getting the drywall to finish on conventional lumber that long. The lumber is so twisted anymore.

 

[EngDM]

Try getting the drywall to finish on conventional lumber that long. The lumber is so twisted anymore.

Sounds like a good 'ol construction means and methods problem to me.

 

[phamENG]

Try getting the drywall to finish on conventional lumber that long. The lumber is so twisted anymore.

You're the only one talking about lumber. It's a steel stud wall.

 

[XR250]

Try getting the drywall to finish on conventional lumber that long. The lumber is so twisted anymore.

Honestly, I never hear complaints about that but I get it that it can be a problem.

 

[Euler07]

Does your code have any guidance?

In the US, lateral deflection and story drift due to wind are left up to the engineer (not codified), but the recommended number is between H/400 and H/600 for the serviceability wind load. The exact value and what that serviceability wind load is depends on the type and use of the structure. For what you're talking about, I'd shoot for H/500 but would accept H/400 if things get too costly, and I'd use a 10 year MRI for the wind speed used to calculate my wind load (as opposed to a 700 year MRI that is used for strength).

Thanks phamENG. No, our code does not have guidance for this. Using H/500 for 4.5m tall wall would result in 9mm racking deflection at the upper floor level. Obviously if the bed is shaking back and forth by 9mm during wind then this is a big issue and would make the house potentially unlivable. Even 5mm would be potentially too much.

Does anyone know how much a bed can move before it's not fit for purpose? Thanks.

 

[phamENG]

Thanks phamENG. No, our code does not have guidance for this. Using H/500 for 4.5m tall wall would result in 9mm racking deflection at the upper floor level. Obviously if the bed is shaking back and forth by 9mm during wind then this is a big issue and would make the house potentially unlivable. Even 5mm would be potentially too much.

Does anyone know how much a bed can move before it's not fit for purpose? Thanks.

There's another hard limit recommendation of 0.4 inches or thereabouts to to prevent damage to drywall. So I'd say your 9mm is pretty reasonable.

As for maximum bed movement...I'll bite my tongue and just say that it's highly subjective, and I seriously doubt you'll find any studies on it. At least not any from the engineering community.

 

[XR250]

As for maximum bed movement...I'll bite my tongue and just say that it's highly subjective, and I seriously doubt you'll find any studies on it. At least not any from the engineering community.

Ha

 

[milkshakelake]

To limit deflection and vibrations in steel stud walls, you can use either plywood, X-bracing straps, or steel sheets. The X-bracing with flat straps is commonly used, but it's also the least stiff. But it definitely works for a 2 story building if you can get enough of them. It relies on the strap being fully tensioned, but I haven't come across any project where that was a real life issue.

I had a project where a different engineer designed a 2 story with full glass facade. It vibrated every time a truck drove by, or if there was a windy day. What you are describing definitely needs consideration using shear walls or something similar to limit the vibrations.

 

[XR250]

It relies on the strap being fully tensioned,

Has that actually ever occurred in real life? . I imagine the sheetrock ends up doing most of the work anyway.

 

[milkshakelake]

Has that actually ever occurred in real life?

I highly doubt it! Though I haven't seen issues so far, and yeah, the sheetrock is probably doing lateral work.