Wind on House. 1

[dgkhan]

Please see attached sketch
I have a house 30’ x 45 ‘.Wind perpendicular to 45’ will eventually engage roof diaphragm and floor diaphragm both from windward and leeward side.
Roof diaphragm will be resisted by two 30’ long shear walls and will go to 30’ side footing. Floor diaphragm will go to 45’ side footing. Am I right?

 

[msquared48]

For wind against the 45' long face, the forces for the roof and floor will go to the 30' endwalls and footing.

Mike McCann
MMC Engineering

 

[dgkhan]

Mike,
Wind against 45’ side . Top half portion will go to roof dia. Bottom half will go to floor dia.
Floor dia. is one feet above the footing along 45’ side. What makes this load to travel and
go into 30’ side footing and not to footing just below it. I am just trying to understand please.

 

[Lion06]

The out of plane stiffness of the walls on the 45' side is much less than the in-plane stiffness of the walls on the 30' side. If you have a rigid diaphragm then it's all stiffness based. If you have a flexible diaphragm then the diaphragm is acting like a beam (which is spanning such that the wind force is perpendicular to the longitudinal axis of the "beam", not parallel to it).

 

[UcfSE]

Are you calling the floor slab on grade a diaphragm? Is this one story?

 

[msquared48]

Except fopr the size of the overall force, it doesn't matter if it's one story or two. What StructuralEIT says is true,

Unless you are dealing with a cantilever diaphragm, the wind force will only go to the 30 foot endwalls for application against the 45 foot face. The opposite is true for wind applied perpendicular to the 30 foot walls - the 45 foot walls will resist it.

Mike McCann
MMC Engineering

 

[dgkhan]

Oh my God, I am getting hit by big fishes, where is JAE & hokie66 .

UcfSE,
Floor is with 2x10 wood joist. There is basement floor below it but basement walls are of concrete which I am considering as footing for wood wall above it.

 

[msquared48]

I would still use the endwalls...Even considering the concrete walls in weak axis bending, which I assume is your concern.

I also assume that you are a fisher of men?

Mike McCann
MMC Engineering

 

[Lion06]

That "big fishes" comment went right over my head.

 

[dgkhan]

I was not expecting that very knowledgable ones will answer on this small issue. But thanks to all of you. Right now I am not buying it totally (Downside of 18 years experience)but I will swallow it eventually as it clicks my mind.

 

[msquared48]

OK. I will clarify here...

If the flundation the lower floor diaphragm is tying into only seel one to two feet of wind pressure below it, as a short stem wall would, then ingnore the contribution of the lower floor diaphragm to the endwalls. However, if it is a full story that does not have earthfill around it, then, with the floor diaphragm still being flexible, distribute the additional lateral load from the wind eto the endwalls.

Mike McCann
MMC Engineering

 

[dgkhan]

Mike,
Can you explain
"Unless you are dealing with a cantilever diaphragm"
Thx

 

[msquared48]

If the diaphragm has shear walls on three of the four sides, then if the force is parallel to the single shear wall, the other two shearwalls resist the torsion of the system by generating enough shear to counter the torsion. Professionally, I do not like this method as it means greater deflections, but it has been used.

Mike McCann
MMC Engineering