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enclosed structure - wind load basic question
2

enclosed structure - wind load basic question

enclosed structure - wind load basic question

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

RE: enclosed structure - wind load basic question

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

RE: enclosed structure - wind load basic question

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!

RE: enclosed structure - wind load basic question

Look at the wind load cases Figure 6-9

RE: enclosed structure - wind load basic question

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

RE: enclosed structure - wind load basic question

(OP)
How about for foundation design if individual footing.

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

RE: enclosed structure - wind load basic question

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).

RE: enclosed structure - wind load basic question

(OP)
I am talking about figure 6-6  

RE: enclosed structure - wind load basic question

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

RE: enclosed structure - wind load basic question

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.

RE: enclosed structure - wind load basic question

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.

RE: enclosed structure - wind load basic question

(OP)
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.

RE: enclosed structure - wind load basic question

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.   

RE: enclosed structure - wind load basic question

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.

RE: enclosed structure - wind load basic question

Ron got it.

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

RE: enclosed structure - wind load basic question

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:

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.


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.
 

RE: enclosed structure - wind load basic question

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.


 

RE: enclosed structure - wind load basic question

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

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.

RE: enclosed structure - wind load basic question

(OP)
what does ASCE fig 6-6 mean?

thanks,

 

RE: enclosed structure - wind load basic question

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.  

RE: enclosed structure - wind load basic question

Great point and example JAE. This is probably on the checklist for PEMBs, which is a popular building type for the example you described. And their calcs often look like what Toad was talking about, I can barely ever understand them for doing foundation design. It can take an hour to find the stinkin' worse case, which for base plate bolt design on a PEMB may be one of these cases we may not normally check, as JAE explained.

I think we are all thinking for your average box-like structure, low rise, with tilt or CMU walls, the side wall pressures usually do not come into play...

RE: enclosed structure - wind load basic question

delagina,

The whole discussion above is based on the Figure 6-6 that shows sidewall pressure.  Your question:  "what does ASCE fig 6-6 mean?" is too general.  Please be more specific.

Thanks.

RE: enclosed structure - wind load basic question

(OP)
jae,

fig 6-6 shows direction of wind in horizontal but it shows there are sidewall pressure. so i am confuse why i shouldnt add sidewall pressure.

others say it will cancel out but i dont agree if you have isolated footings. isolated footings will have bi-axial moment due to sidewall pressure.

i do see in wind load guide by mehta examples that sidewall is not considered for mwfrs.

RE: enclosed structure - wind load basic question

Sidewall pressures are in the code, and we know from large quantities of test data that it certainly exists, so there shouldn't be any reason not to consider it in some way. Now when I say consider it, it doesn't mean that you have you have necessarily add another several load cases and a dozen more load combos. I usually take the strategy of doing some back of the envelope calculations to evaluate if it might be critical locally so that I can design accordingly. Usually the buildings we design have the facade anchored directly to rigid diaphragms, so I wouldn't worry about it for the primary members of the MWFRS unless it happens to combine with the local effects.

Structural Design Engineer
New York, NY

RE: enclosed structure - wind load basic question

delagina- quite simply, there are as many building types and structures as architects' and engineers' imaginations can dream up...

So if sidewall pressures will affect your structure, consider it in design. For your average box-like structure with shear walls, it will not control.

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