gable end wood buildings 3

[rittz]

We are designing a wood building 80 x 100 16 ft side wall roof slope 3/12 thus peak height about 22 ft. We plan using 16 ft studs 2x8. At the gable end would you use laminated studs from foundation to roof? Or build the end to same height as the sidewall and then frame from there to the roof with regular studs and brace the "hinge" at the 16 ft mark to the roof structure in the attic. Many builders seem to be doing that

 

[msquared48]

The latter scenario is normal.

Mike McCann
MMC Engineering

 

[tadeng]

I agree with Mike. This lets the contractor set all the top plates at the same height.

 

[msquared48]

Unless stick framed, with a truss package there is usually a gable end truss on top of the top plate of the end wall.

Mike McCann
MMC Engineering

 

[Ron]

Don't mix two framing systems. The first you described is balloon framing. The second is platform framing. Platform is much more common.

 

[Robert216]

As long as something is bracing the hinge, platform framing is more practical. However, I have noticed that quite a few contractors claim to "platform frame tall wall systems all the time". If there is a.) no diaphragm at the hinge location or b.) nothing "kicking" (diagonal bracing) up to another (typically a roof) diaphragm, the platform system is almost always an unstable condition. Every once in a while, when components and cladding loads are very small and the gable end wall is not very tall, it may be possible to resolve a moment with coil strapping. This mechanism is most often times limited by the compression component of the force couple, crushing the wood plate. When I have tried to explain this to contractors, they give me the 'ol "I've been framing for 38 years and I've never had to do this...".

 

[rittz]

Robert, I have heard your last sentence uttered roughly 500 times in my 50 years as an Engineer. I have never been able to come up with a dignified rebuttal.
j

 

[msquared48]

Engineering, as the medical field, is a practice. Therein lies the answer. As knowledge grows, the noose tightens. Deal with it.

Mike McCann
MMC Engineering

 

[MiketheEngineer]

I get that "This is the way we have been doing it for xxx years"

Two responses:

"By now - you should know better"

"Well - you have been doing it wrong all that time"

Usually does the trick and when push comes to shove: "If you do it that way - you now own it - not me"

 

[FSS]

Just tell them to turn the wall on its side and imagine walking on it like a floor. Would they frame it the same way? They usually pick up on the hinge effect real quick that way.

 

[woodman88]

My response have been "I have been designing buildings for 20+ years and have never seen or done it that way."

Garth Dreger PE
AZ Phoenix area

 

[msquared48]

Or...

After you have attended college for five years and obtained your BSCE, taken and passed your one-day EIT, done your four-year internship so that you could sit for your one-day Civil test, then done your two year internship so that you could sit to take your two-day structural exam and pass it the first time, give me a call.

Until then, shut up and get a life.

Mike McCann
MMC Engineering

 

[rittz]

MIke if I tell a guy what you suggest I want to make sure he is smaller than me .... hee hee
J

 

[msquared48]

I understand, but I have heard it too many times in my career, and since the responsibility is mine, not theirs - it's talk to the hand dude. I really don't care anymore.

Cheers.

Mike McCann
MMC Engineering

 

[Rick90210]

Yes, the "hinge" is the issue. Diagonal bracing from the wall plate works, but I prefer full height gable end walls where the heights are manageable.

 

[COEngineeer]

It is a problem only if you dont have ceiling diaphragm.

If it is vaulted ceiling, baloon framing is a must.

Never, but never question engineer's judgment

 

[msquared48]

I would not rely on a sheetrock ceiling diaphragm and do not believe that is even allowed by code. I would use periodic diagonal struts connected at the knuckle joint in the wall and to special additional blocking in the roof diaphragm.

As to the use of balloon framing, I agree. However, I have never been able to figure out how many balloons to use.


Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[woodman88]

msquared48, In the IBC 2009 the shear capacity for horizntal gypsum diaphragm ceilings are given in Table 2508.5.

Garth Dreger PE
AZ Phoenix area

 

[msquared48]

Thanks - had not seen this table yet as I never use gyp for shear.

These are very low values that have to be halved for Seismic D or higher. Would help in wind though at the connection being discussed.

To be honest, it would probably still be my decision to use the diagonal struts. I will have to look at this with the next project I get with a similar connection and see what the results are.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[RockEngineer]

2009 IBC 2308.9.1 now states "Studs shall be continuous from a support at the sole plate to a support at the top plate to resist loads perpendicular to the wall. The support shall be a foundation or floor, ceiling or roof diaphragm or shall be designed in accordance with accepted engineering practice". The only exception is Jack studs, trimmer studs and cripple studs at openings in walls.

My understanding is this change came about because of gable end framing on structures with cathedral ceilings where the builders were putting the the top plate level all around the structure and then continuing the framing up to the roof which formed the hinge at the top plate.

As previously well stated you either need to balloon frame the end walls with full height studs or brace at a level top plate with a ceiling or diagonal braces perpendicular to the wall up to the other rafters or truss top chord and diaphragm. 2009 IBC just eliminates the builders argument that they have used level top plates and no bracing for many years without a problem.