enclosed structure - wind load basic question 2

[delagina]

do you consider sidewall pressure for MWFRS (global design)?

 

[msquared48]

If I understand your question correctly...

For the direction considered, I consider the front, rear and roof pressures. The side wall, for that direction, I don't, but wind up doing so when considering the opposite direction as the sidewall becomes either the front or the back.

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

 

[ToadJones]

I have included all pressures in models before
It turns into a giant jumble-#@4% mess.
Then you toss in the wind torsion cases and it gets really fun!

 

[ToadJones]

Look at the wind load cases Figure 6-9

 

[ron9876]

Use the diagrams and loads in ASCE7. Often the side walls won't have an impact but should always be considered.

 

[delagina]

How about for foundation design if individual footing.

Sidewall pressure + winward pressure will cause individual footing to have bi-axial moment.

 

[Lion06]

It's almost a moot point. Does anyone actually do a wind load analysis of a structure by hand with all of the different cases required by ASCE 7? I know I never have, and probably never will.

I let RAM generate the cases and combinations. The first time I saw over 200 different combinations I knew I would never do it by hand.

Just to talk about it, though, there are only two cases where you have wind in pure "X" or "Y" directions. Every other case has some kind of quartering wind, or torsional wind case, or some other case you can't/won't do by hand. So there's always pressures on the side walls (if you want to call them that when the wind isn't really acting in the pure "X" and "Y" directions).

 

[delagina]

I am talking about figure 6-6

 

[slickdeals]

Sidewall pressures will cancel each other out for an enclosed building without expansion joints. There won't be any net force on the diaphragm.

 

[a2mfk]

Lion- yes and no. I consider all of the cases but can usually quickly decide which ones will control, therefore its not necessary to go through the exercise of doing a full MWFRS analysis for each case.

A lot of buildings out there are still designed without a 3-D model... On many low rise structures its less effort.

 

[CTSeng]

I've heard it argued various ways but the primary cases of ASCE Figure 6-9 states 'projected area perpendicular to each principal axis.' Since sidewall and roof are not perpendicular to the principal axis considered they are not required.

 

[delagina]

mike is the only one that really answered my basic question and he said he doesnt consider sidewall pressure.

but fig 6-6 got me confuse if i should consider sidewall pressure.

i am not asking about fig 6-9 wind load cases.

 

[WillisV]

slickdeals actually answered your basic question...

Sidewall pressure is generally irrelevant as it is less than the windward/leeward pressures, so when the wind blows from the other direction (so that the "side" walls are now the windward leeward walls), the main windward/leeward pressures will control.

 

[Ron]

No. The sidewalls, in the scenarios required by code, are in shear. No normal force. The only condition where sidewalls come into play is the oblique wind analysis.

 

[msquared48]

Ron got it.

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

 

[JAE]

Well...I hate to differ...but

Generally the comments above are correct - the sidewall pressures don't normally come into play. But there are certain structural systems where they do:

[blue]Say you have a one story, warehouse type of structure with wind blowing in the North-South Direction.

The sidewalls are on the west and east sides.

The structural system is steel columns and beams/joists using some type of concentric brace system, or a moment frame. Some of the side wall columns could be part of the lateral force resisting system and receive stresses from the North-South wind pressures - this due to lateral shears in the plane of the sidewalls and these would be either axial forces for a concentric brace, or bending and axial for a moment frame.

But if those same columns also supported horizontal wind girts, the columns would be recieving load from the MWFRS North-South wind pressures (windward and leeward) and ALSO the columns would be recieving bending outward due to the MWFRS sidewall pressures. [/blue]

Thus, the sidewall wind pressures can come into play in a necessary, code-required design check.

This is not to be confused with C&C loading as that would be a separate check for those side wall columns, independent of the MWFRS loads brought into the columns as part of a brace.

 

[ToadJones]

I tend to agree with most of what has been said here ....the fact that what JAE said makes sense, means the wind code is totally out of control.
I have designed some new industrial facilities. I once had a FEM model with building loads and crane loads together. I figured for the hell of it I would blindly create all of he possible load combinations in a spreadsheet. It took me about two days (had plenty of time of this job and there were many buildings on one site that i figured would have similar load combos).

I literally wound up with something like 500 load combinations. I figured I'd run the models and see if most of the member designs were based on "obvious" load combos...turns out there were plenty of members designed by load combinations I never would have thought of had I not blindly made the combinations.

 

[Ron]

TJ...ignorance is bliss...don't do that!

JAE...hadn't thought of secodary effects, but you're right...under some systems there will be some. The OP was regarding sidewall pressure, which would be direct but incidental application....in that case I would not apply pressure to the sidewalls as a result of pressure on the primary walls.

 

[delagina]

what does ASCE fig 6-6 mean?

thanks,

 

[ToadJones]

Ron-
Not sure what you mean.
Am I proud that I created 500 load combos? Not at all.

That doesnt less the fact that L/C 168, 275, 289, 120, 54, 98, 65, 333 controlled the designs of certain members.
The overwhelming majority of these cases was the result of various wind + crane loadings.