Friday, September 30, 2011

Re: Wind forces on the columns of open structure

Along the lines of what Irv noted, I've design flagpole loading per the flagpole design manufacturer's consortium (joking) design guide.  Basically, I've used the design pressures at 110 mph as a uniform load over 2 diameters and use a moment arm of 0.55h, similar to the design of a sign/billboard.  My gut says the tension on the anchors due to uplift on the canopy might govern the overall design.

On Fri, Sep 30, 2011 at 11:41 AM, IRV FRUCHTMAN <ifaeng@yahoo.com> wrote:
Joe,
I'd assume 2-d flow and calc the force per ft, on each column and for each direction as: = Cd x q x S,
where
Cd =1.2 for round column; = 2 for square column
q = dynamic pressure @ 110 mph
S = Frontal Area

Irv

--- On Fri, 9/30/11, nma <nma@nma-se.com> wrote:

From: nma <nma@nma-se.com>
Subject: Re: Wind forces on the columns of open structure
To: seaint@seaint.org
Date: Friday, September 30, 2011, 1:59 PM


Joe:

How big are the columns?  I would load up all the columns and ignore any shielding effects.  One of the things I've seen in this kind of a structure is vibration - i.e. small shaking of the whole thing.  It may also makes a small difference in the shape of the columns - round or rectangular?  You didn't say what the wind speed or exposure factor is or where the structure is located - i.e. on a hill or in the middle of a city. 

For the flying bit - I've have been criticized for larger footings than the city inspector thinks the footings should be.  But I signed for the structure and not him.   I've also seen the result of a roof flying off its supports - had my back turned with it happened.

Neil


On 9/30/2011 10:47 AM, Joseph Grill wrote:

Neil,
Thanks, I understand the flying bit.  But there is going to be a lateral wind load on the columns themselves. I am looking for the criteria to determine the horizontal load to the columns.

On Sep 30, 2011 1:38 PM, "nma" <nma@nma-se.com> wrote:
> Joe:
>
> Just figure it is going to try to fly.
>
> Neil
>
>
> On 9/30/2011 10:16 AM, Joseph Grill wrote:
>>
>> I tried to send a message yesterday on this subject. But with new
>> phones, new wireless providers, a move across country etc i'm not sure
>> it went through.
>>
>> Anyway I am designing an outdoor picnic pavilion. The plan dimensions
>> are about 60' x 30'. It will have monoslope roof supported by 4 bays
>> of 3 columns. I have calculated the wind loads for the MWFRS at the
>> roof. I can't decide on what ASCE requirements/equations to use for
>> the MWFRS loads to the columns and if that load should be applied to
>> each column in each row parallel to the load direction. In another
>> words if there are 4 columns in line parallel to the wind load would
>> all 4 columns be loaded?
>>
>> I have considered using loads calculated from section 6.5.15 "Design
>> Wind Loads on Other Structures". Am I wrong? If so can anyone suggest
>> what i should be doing?
>>
>> Thanks,
>> Joseph R. Grill, PE
>>
>
>
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David Topete, SE
at