Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: Wind Loads

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Not just coastal areas.  A lot of "near miss" tornado events cause failures in
the midwest.  Such wind loads are no different from coastal wind loads, both
being essentially horizontal for low-rise buildings.  Like ice loads, it's a
rarely considered load condition, but no less common in the midwest than an
earthquake.

I'd like to see more in the wind code.  At the same time, it'd be nice if it
didn't become the headache seismic has become.

As to the question, I use a MWFRS load for the lateral design.  I'm very
conservative with uplift, and usually include some kind of load to simulate
suction on the underside.  If I have no reason to do otherwise, I'll use the
same load underneath the canopy as above.  For MWFRS, I check uplift and
downward suction as separate load cases, as well as in combination.

-Keith Fix, PE

--- "Kestner, James W." <jkestner(--nospam--at)somervilleinc.com> wrote:
> Andrew:
> 
> If you look up "canopy" in the index of "Guide to the use of the Wind Load
> Provisions of ASCE 7-98" it refers you to page 124, which is a blank page.
> Also on page 122, question 123 states that coefficients for canopies are not
> given in ASCE 7-98 but you can use coefficients from published literature
> provided they are used with care. It refers you to references listed in
> Section 1.4.
> 
> Would coefficients based on roof overhangs be similar to canopies? Probably
> not. I agree that coefficients for canopies need to be included in ASCE 7-98.
> This is common construction all over the country but the design becomes very
> critical in coastal areas. 
> 
> Jim K.
> -----Original Message-----
> From: Andrew D. Kester [mailto:andrew(--nospam--at)baeonline.com]
> Sent: Thursday, February 20, 2003 7:54 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Wind Loads
> 
> 
> This is an age old questions in our office, and I have asked professors and
> lecturers and many others this question, with no definitive response.
> 
> According to FL Building Code 2001 / IBC/ ASCE  (you pick), how would you
> model a canopy structure? What we have always done is model it as an "open
> building", then check loads according to ASCE. Then we have compared those
> results with overhang loads (when the canopy is attached directly to a
> building) according to the FBC. Well, FBC overhang loads always govern, and
> seem plenty high and thus conservative. It usually does not matter too much
> because canopies are a small component, so if we are overdesigning a bit it
> does not make much of a difference in cost. It seems justifiable to use an
> overhang load when the canopy is directly connected to the main structure
> because the way the wind is hitting the structure and loading the canopy,
> with pressure building up underneath and suction forces on the top, should
> be like that of an overhang. This type of structure, at least in FL (it
> rains a lot) and most places come think of it, are outside almost every
> building entrance, especially long ones outside of shopping plazas, grocery
> stores, hospital and hotel entrances, and in FL, there are lots of these at
> schools connecting outside classrooms. In residences, these are carports and
> porches.
> 
> PROBLEM- how should you model a freestanding canopy, that is either far away
> from the main structure, or not connected at all? For example, I am thinking
> first of gas station canopies because of their prevalance. But our specific
> issue is that of a toll plaza canopy. This has a depth of 10' and a length
> of over 120'. It stands around 20' off of the ground. It is completely
> seperate from any structure. Unlike the shallow depth of a gas station type
> canopy, with little issue with lateral loading, this has 10' of fascia that
> is exposed to lateral loads. Should you model this as a MWFRS, as an
> enclosed building? It has a ceiling, walls, and roof, but it is 20ft off the
> ground. It is not pressurized inside the canopy. Or as a partially enclosed
> or open building? We thought of even using AASHTO sign loads or ASCE sign
> loads, but then again, this is not really a sign at all. Component and
> cladding loading is a seperate issue.
> 
> Any insight or "what I do"'s would be more then welcome. Basically, my
> answer from "wind experts" is that they are doing testing, and more testing
> needs to be done, and they need to add this to the building codes or ref
> docs like ASCE. I see this as a major gap in the code as most buildings have
> this type of structure, it is extremely prevalent and common. Also, if you
> look at historical storm damage, these types of structures seem to be the
> first or only part of the structure to fail or sustain the most damage.
> These lightweight structures can also become flying debris. So I see them as
> a very succeptible part of a structure in wind loading. This should be in
> the codes specifically if you ask me.
> 
> 
> Thanks,
> 
> Andrew Kester, EI
> Longwood, FL
> 
> 
> 
> 
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> * 
> *   This email was sent to you via Structural Engineers 
> *   Association of Southern California (SEAOSC) server. To 
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
> *   send to the list is public domain and may be re-posted 
> *   without your permission. Make sure you visit our web 
> *   site at: http://www.seaint.org 
> ******* ****** ****** ****** ******* ****** ****** ******** 
> 
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org
> ******* ****** ****** ****** ******* ****** ****** ******** 


__________________________________________________
Do you Yahoo!?
Yahoo! Tax Center - forms, calculators, tips, more
http://taxes.yahoo.com/

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********