Wind not perpendicular to building projection

[rheim]

Is there a standard procedure or reference to design shear walls (stud framing) not parallel or perpendicular to the wind direction? All design examples I found use a standard rectangular box.

Thanks for any input

 

[sdz]

Consider a wall(1) at 45 deg acting with a wall(2) parallel to load.
When wall 2 deflects 10mm then wall 1 will deflect 7mm in plane of wall. Assume wall 1 therefore develops only 7/10 of load in wall 2, which acts parallel to wall 1, i.e, at 45 deg to load direction. Therefore load component in load direction is 50% of design capacity.

ie design capacity of inclined wall = design capacity parallel wall * cos(angle)^2

Does that help?

 

[UcfSE]

Remember that wind loads are applied normal to the surface regardless of wind direction. If the wind comes in at 45 degrees on your box, say toward a corner, you'll get windward and leeward pressures each side, still normal to the surface. You'll just have loads in two prependicular direction at once though the wind is still coming from just one direction. Use a similar procedure if you have nonparallel walls. You'll resolve forces perpendicular to each wall into forces along your major orthogonal axes and proceed as normal.

 

[msquared48]

What I do is determine the length of shearwall, projected, that is parallel to the direction of the wind application, use that length for the shear wall, and proceed normally otherwise.

Mike McCann
MMC Engineering

 

[rheim]

sdz, UcfSE,

thanks for your input. Makes perfect sense to me.

Mike, this is exactly wht I did in the past, all Building Departments have accepted it so far. I just felt it might be very conservative. (I am currently working on a residence with large open spaces and few short shear panels, so I probably can not account for loads that are too conservative)

Thank you guys

 

[sdz]

Actually it is non conservative.
ie design capacity of inclined wall = design capacity parallel wall * cos(angle)^2

a wall at 45 deg is only 50% effective.

 

[kslee1000]

Never got that deep into directional wind effect.
Questions for all wind experts:

1. Why is 45 degree?
2. If the 45 degree wind glancing through half of the wall, thus creating positive pressure on it, won't the wind then turns direction outward, and creating suction on the remaining wall?
3. When and where we need to consider effects from directional wind force?

 

[sdz]

I'm talking about a building where wind loads are assessed in directions orthognal to the building but some of the bracing walls are at angles of other than 0 or 90 degrees. That wall might be at any angle but I used 45 deg as an example.

I have had to check buildings like this myself. e.g.

http://files.engineering.com/getfil...df-400a-879c-14d52f44f6ea&file=ShearWalls.xls

 

[kslee1000]

sdz:

Sorry, I wasn't really pointing in your direction, only borrowed the 45 degree (or between 0 & 90 degrees) from you to construct my questions, which are meant to imply the uncertainties involved when deal with natural forces. It looks like the OP is trying to find a valid/proven method (?) to justify the use of lower wind effect on shear walls, or only a few out of the entire building system. I just want to say to that effort - be prudent, especially for lightly constructed residential buildings.

Actually I think you method (your first response) is quite interesting, worth to dig deep into it.

 

[hokie66]

I can't get my head around sdz's method, and instead agree with what Mike posted. If the two equal length walls (1) and (2) are both attached to a rigid diaphragm, they will deflect the same amount parallel to the load, so will resist the force in proportion to their length in the load direction. This will make both walls see the same total force, as the rotated wall has two components which must be resolved parallel to the wall.