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Point load applied to roof diaphram

Point load applied to roof diaphram

Point load applied to roof diaphram

(OP)
A building I'm working on has had some changes per the architect.  I now have a point load from a newly added wind girt that was never anticipated.  I've looked and looked for a way to resist the girt's reaction of 4500 lbs from wind loading.  Not that big, but something has to do it.  

Load is applied at roof level.  3/4" plywood diaphragm.  Would you feel comfortable just using a long piece of glulam blocking with a couple rows of 16d nails through the plywood into the top of the blocking to resist the load?  I have up to 10' available for the length of the blocking.  I have mono trusses framing perpendicular to the blocking... trusses are parallel to girt.

Any better ideas?

RE: Point load applied to roof diaphram

(OP)
I know this just sounds like a collector of sorts, wish I could show you the plans...

RE: Point load applied to roof diaphram

some kind of sketch would definitely help

RE: Point load applied to roof diaphram

4.5 kips is fairly large for a wood diaphragm, depending on the length is distributed over.  You'll need a lot of nails to develop 4.5 k.   

RE: Point load applied to roof diaphram

If you can't show a plan of the roof, show a crude sketch.  Your problem is not clear at the moment.

BA

RE: Point load applied to roof diaphram

A couple of MSTI60 straps could do that if properly positioned.  

Again, a sketch would help.

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

RE: Point load applied to roof diaphram

Please DO NOT post the picture of that block wall again.

I was laughing so hard last night I couldn't sleep.

RE: Point load applied to roof diaphram

If I understand the wind girt is for framing the end gable wall opening? Can you do a sketch of that elevation?

If I understand what you are trying to do, I don't think I like it.

I need more info to give you any helpful advice. For wood framing the architect is really trying to do a lot here... You may need some steel.

RE: Point load applied to roof diaphram

NOW THAT HAS ME LAUGHING
HAHAHAHAHAHAHAHAHAHAHAHA

Unneutral ...Thank you. That was funny.  

RE: Point load applied to roof diaphram

Unneutral-
Can you put sway bracing in the lower mono trusses (in the plane perpendicular to your sketch)?
You should be able to transfer your load into the sway braing and back into the diaphragm.  

RE: Point load applied to roof diaphram

Tear down that wall, Mr Gorbachev!

RE: Point load applied to roof diaphram

you may also be able to put sheathing on the backside of the lower monotrusses and make it a shear wall of sorts.  

RE: Point load applied to roof diaphram

(OP)
ToadJones-
That was my original idea.  It is a total pain because the state I'm in does expedited foundation/site plans for construction while the framing is being approved.  Footings are already in.  I don't have anything substantial enough below the truss to create a shear wall at the mono truss.  I am hoping to get through this without a big change order.  

Keeping it in the roof diaphragm is ideal.  Your bracing idea in the monotrusses is something else I have considered and will likely include that too along with the strut.

a2mfk-
This is a gable end wall.  There is no opening, just a half-@$$ed sketch.  What isn't drawn is underneath the wind girt is a tall wood framed wall.  An open stairwell is to the left side of the ridge.  I posted about another tall wall a couple days ago, but this is a different situation.  I haven't convinced myself that I like it either, that's why I'm questioning it. :)  

RE: Point load applied to roof diaphram

What about using light gage studs or LVLs to full-height frame the gable rather than using the wind girt? Then you have a standard roof shear diaph. situation. That connection will be nasty to design at the end of the girt for 4500lb into wood, and I assume you will have to design for forces in either direction depending on the wind direction...  Good chance your average framer would botch this no matter how nice and fancy your detail may be..

RE: Point load applied to roof diaphram

good idea- balloon frame the end wall to the top of the truss....or -3 1/2" from the top to allow for you rake ladder for the overhang as in a drop-gable truss.
I'd say 100% that is the way to go.
Set your last truss inside the balloon framed wall.  

RE: Point load applied to roof diaphram

(OP)
a2mfk - I think you are right.  I've spent several hours on details and it is just too detailed.  A very critical component of the building and due to other items of the building (that I won't get into) would be very difficult to "observe" that it was installed correctly.  

I appreciate the help.  Usually the simplest approach is the best, I've found.

RE: Point load applied to roof diaphram

balloon framing will give you a nice flat wall too.  

RE: Point load applied to roof diaphram

if balloon framing, be sure you install fire blocking, whether required by code or not.  

RE: Point load applied to roof diaphram

Yea...  

You'll need the fireblocking to prevent the fire from igniting the helium-filled ballons.  The results could be catastrophic!

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

RE: Point load applied to roof diaphram

(OP)
Since we are in an engineering forum here... it's actually hydrogen that is combustible, not helium.  :)

Thanks for the lesson on balloon framing though, Mike.

RE: Point load applied to roof diaphram

Mike-
you poking fun at my terminology?  

RE: Point load applied to roof diaphram

Ohhhhhhhh the humanity!!!!!!!

RE: Point load applied to roof diaphram

Toad:

Even though I use the same terms, I have fun wherever I can.  After 40 years of this stuff, I need it.  Thanks for the opportunity.  bigsmile

By the way, just checkin that you guys were reading my posts with the helium comment, OK?  (just kidding) bigsmile

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

RE: Point load applied to roof diaphram

Mike-
No offense taken...I have been accused being a smart a$$ here and there too.  

RE: Point load applied to roof diaphram

No worries mate.
 

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

RE: Point load applied to roof diaphram

Helium, hydrogen, they both are lighter than air, but hydrogen is more abundant. Lets just use that to fill our dirigibles, what could go wr.....

RE: Point load applied to roof diaphram

(OP)
Following up here.  What is the largest point load you guys would feel comfortable putting in a wood diaphragm?  I know it depends on the exact situation and a thousand other factors.  I've thought about this quite a bit the last couple days.  There's really no really good way to theoretically arrive at it... more a judgment call than anything else.  I have some thoughts on the matter, but wanted to hear others'.    

RE: Point load applied to roof diaphram

The limits are your diaphragm, the drag strut length and member design, and making the connection from the girt to the drag strut. Most pre-fab steel connections for timber are not designed for this, but may be able to be used for that application. You can always design your own steel buckets/plates, I have done that several times. With wood, I try to avoid this type of detail.

Also, if you are balloon framing the end wall, remember anchorage for suction on that wall. You may have to use some tension straps at the top of the framing to get the load into the roof...

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