WALL parapet parallel to roof truss for wind load 2

[johndeng]

WALL parapet parallel to roof truss. Can peremeter truss hold the wall for wind load? Roof is only 3/4" plywood, and I cross braced end three trusses.

Thanks

 

[hokie66]

A parapet is a cantilever. You have to provide structure to fix the base of the cantilever. It is not likely that a truss will have the torsional capacity to resist the cantilever moment. Whether or not your cross bracing is adequate to resist the moment is for you to determine.

 

[johndeng]

Thanks.
But even it's not parapet, say just a wall, can the roof diaphram and cross brace take the load?
Is anyone sure how to check for it?

 

[structSU10]

Model it in RAM, RISA, etc.? you just have to check the cross brace, and see if it can get the load into the diaphragm / LFRS.

 

[XR250]

Model it in RAM - really? This should be a simple statics problem.

 

[IceNine]

This is pretty basic. Hire an experienced structural engineer.

 

[johndeng]

IceNine: It's basic, but you think you know the right answer?
hokie66: you said the cross brace will take the moment, I feel it will be only lateral load. The diaphram as a pin ponit, will take the lateral load. Cross brace will brace the horizontal load on the top chord. And the essential connection would be the tie of the bottom chord to base plate for uplifting.
Just need someone to check whether I am missing anything.

 

[RFreund]

I think you should post a sketch. I'm not even sure how others were able to respond...

EIT

http://www.HowToEngineer.com

 

[johndeng]

ok sketches.

 

[johndeng]

sketch

 

[RFreund]

Ahh, yes. Thank you.

Currently there is not much resisting wind on the back side of the parapet or leeward pressure on the masonry wall.
I think what you have is doable as you do need the cross bracing or at least a kicker to brace the top of the masonry wall. However I think I would add solid blocking at the top cords to so that the force may be developed into the roof diaphragm and add straps top and bottom for tension (leeward wind).


EIT

http://www.HowToEngineer.com

 

[johndeng]

Very good points, you are absolute great! Thanks!
I know kickers would be the best (it would work both windward and leeward), but I want to cut the cost.
Only thing I am worried about the cross brace is that all the truss load will have to pass to both ends of the trusses. The spans of the trusses are weak points actually.

 

[msquared48]

You need a rim 2X continuous nailer at the edge of the plywood diaphragm to the parapet. Otherwise, there is no transfer of the roof diahraqm shear into the parapet and into the CMU shear wall below. You may also need a diaphragm chord member there, depending on your framing.

The lateral support of the CMU wall concerns me also. Diagonal struts would help, specifically detailed to handle the 200#/foot minimum.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[wannabeSE]

I would not call the wall below the roof deck a parapet. I would call it a wall with a hinge at the intersection of the masonry and wood. It may be possible brace the hinge with kickers to the diaphragm and some creative connections. Why don't you continue the masonry all the way to the top of the parapet or at least to the roof deck? Also, the all wood wall section needs detailing for the diaphragm boundary elements.

By the way, do they really want the EFIS on top of stucco? I thought stucco (or some other hard coat) went on top of the EFIS.

 

[RFreund]

Sorry I should have mentioned seismic as well and the 200plf min as msquared mentioned.
It would be easier if you could extend the masonry wall up to the top of the trusses but I think with careful detailing i.e. make sure you have a direct load path to the diaphragm and design the connection accordingly, this could work.

EIT

http://www.HowToEngineer.com

 

[BAretired]

The top of the masonry wall should be tied laterally with continuous horizontal bridging members at reasonable intervals. This means either raising the top of masonry wall or lowering the bottom chords of the trusses so that a positive connection can be made.

BA