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RE: 2006 IBC Wind Load question[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: 2006 IBC Wind Load question
- From: "Dennis Wish" <dennis.wish(--nospam--at)verizon.net>
- Date: Wed, 29 Aug 2007 23:01:05 -0700
I can understand the need for rocket science in really high wind regions where there is a lot of noted damage to traditional light framing, but in most areas of the country the problem appears to be the uplift on eaves where the roof is not adequately tied to the wall but my real question is how much damage to wood residences in the 85 mph zones has occurred on record other than to manufactured homes set on raised foundations. I haven’t seen the amount of damage that would justify such a complicated design method in most of California or the US other than in Hurricane regions.
Maybe I’m not seeing something, but in 21 years of private practice I’ve yet to see wind damage in a residential home in California that was not caused by poor construction or a basic wind load that was rated for 70 mph exposure C when it probably should have been in a 90MPH region such as I north Palm Springs area.
“At any rate – we gotta do what we gotta do so what are we gonna do?”
P.S. (and to think I spent ten years fighting rigid diaphragm analysis for light-frame residential structures only to have it finally changed in the 2006 IBC). So why is Conventional Construction not required to be designed to the complicated ASCE 7-05 or is it somehow simplified in the International Residential Code – putting all of us out of business :>)
I went to a 2006 IBC Wind Design Seminar by Dr. Ghosh yesterday. Of course, the IBC references ASCE 7-05 for wind design. And the simplified method isn't really simple. I concur with another on the list that it's probably best to learn the so-called analytic method. It seems more simplified than the simplified method and covers any building configuration except those than must be done by wind tunnel. Basic wind speeds are set by ASCE 7 Figure 6-1 and are 85 mph on the west coast. There are a couple special wind regions in the west and wind speeds in those areas would have to come from local AHJ's. I think your greatest joy will be experienced when you calculate the gust effect factor - this is rocket science here!
Bob Garner, S.E.
From: Dennis Wish
I’ve discussed the design of wind loads for the next generation of IBC codes that California will adopt in 2008 to replace the 97 UBC. As most of you who use the UBC or California building code are aware, the 97 UBC is a fairly straight forward method to determine wind design.
Most of the engineers I’ve spoken to who are in IBC country have mentioned that they rarely use more than the windward side of loading and have not used the more extensive load design methods that check windward, leeward, uplift on eaves and on interior roof areas (where there is a percentage of space exposed to consistent wind loads). I do check uplift on the eaves but only if the uplift occurs on a very light roof such as asphalt shingle or metal. When clay tile is use and the exterior dead load exceeds a lightweight tile then I find that the roof weight rarely shows that uplift occurs. Of course I do not live in a high wind area that exceeds 90-psf wind gust.
My concern is that I have to add the wind design into the next version of MultiLat and as many of you know I have been suffering with the learning process based on the latest ASCE wind load design methods.
My question is whether or not you think that the values we need to design to will be provided by the local municipality in which you will design your structure or if you will be required to work everything out by maps and government references. Currently the building department sets the limits we design to and I’ve never had to rely on reference maps from government references.
Have any of you worked up a worksheet design method of the simplified wind load conditions to be used with the 2006 IBC and are willing to share it with me to help me understand the steps. I’ve been told that the design wind loads can be designed more like the 97 UBC if the design values are supplied by the building official. I wish to add this to MultiLat, but would prefer to use a method based on inputting local conditions provided by the building department your structure is designed for.
I would like some advices as to how many of you plan to design wind loads in the 2006 IBC and what you have done in the past AND what you expect to do in the next code cycle. If you are willing to share your ideas with me, I would be greatly appreciative. However, remember that I am in the mindset that whatever I create is submitted for public domain so that others can save a bit of time.
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