ASCE 7-10 Wind Loads
ASCE 7-10 Wind Loads
(OP)
What was the purpose of switching the wind provisions from ASCE7-05 from allowable to strength methods in ASCE 7-10? IBC requires you to calculate wind loads in accordance with ASCE 7-10 but then requires you to calculate a Vasd?????? and Vasd is the determining factor when you get into the Structural Observations for Wind Requirements of chapter 17. Not to mention that now all of my allowable wind drift and deflection limits (H/400 under allowable loads ect.) are all different because of the increase in the wind speed.
Very frustrating.
Very frustrating.






RE: ASCE 7-10 Wind Loads
Anyway, I've attached a slick website (for all of you not familiar with it) that gives site specific wind speeds. You can even show that you're at the right site if you magnify the little map on the pdf.
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
This ain't gonna go away anytime soon folks!
Mike McCann
MMC Engineering
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
My real point, and perhaps yours as well, is that I have trouble keeping up with all the modifications, refinements, complications, and multiple disparate requirements from various sources. Further, it seems to me that said complexities have long since passed the point of diminishing returns and are now well into the realm of being a hindrance, rather than an aid, to good design.
And believe me, I abbreviated and tempered my thoughts on this topic in both of my posts. To call it a source of frustration would be an understatement.
RE: ASCE 7-10 Wind Loads
However, I do like to look at my building drift under the pure wind load case.... which is now amplified. I also find it funny that IBC has you calculate Vasd and uses this figure for a few different bits in the code.
RE: ASCE 7-10 Wind Loads
Not yet, the 2014 NCEES Exams are still based on the 2009 IBC and subsequently ACSE 7-05, ACI 318-08, AISC 360-05, NDS 05, etc. I checked, just in case I didn't pass this October, I'd get another two shots at my current codes.
RE: ASCE 7-10 Wind Loads
Well, my son will be taking the structural test within the next year or so, and he is tearing that code apart right now, I assume for a logical reason.
Mike McCann
MMC Engineering
RE: ASCE 7-10 Wind Loads
FWIW, there is an old timer engineer around here who still just uses 15 psf for the MWFRS, 20 psf for C&C and .05w for seismic.
RE: ASCE 7-10 Wind Loads
Excel,
I can assure you that there are a lot of engineers who do that, or a variation thereof. But your example might be a tad complicated; I've heard of 20 psf for wind and .1w for seismic.
Isn't it interesting that first year engineering students have the concept of significant digits battered into their heads only to have the codes impose absurdly "refined" design parameters that completely fly in the face of that?
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
Hull speeds are "im'm'aginary" too, right? I always exceeded mine.
Mike McCann
MMC Engineering
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
Again, I find it frustrating...... and I haven't even expressed my frustration with the fact that I will need to update my software soon. Kind up puts some pressure on the small shops like myself who don't have the resources larger companies do.
Excel,
I find it interesting what you see with older engineers. I find many large engineering shops will have people go out for the AISC and give lectures on how to go about engineering. Then I get a set of drawings in from them to do some connection design and I find that they are not even following their own guidelines. I seem to remember on lecturer saying that he only does modal analysis... only to find out a few weeks later that they design most of their systems using the equivalent lateral force procedure using R=3. Then there was the large engineering shop that doesn't even remotely follow the guidelines of IBC Chapter 17.
RE: ASCE 7-10 Wind Loads
Just like tax codes, the wind loads need to be simplified. It shouldn't take twice as long just to determine your load magnitude versus your static analysis of the loading applied!!
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
2 I like that the IBC has added the subscripts for Vult and Vasd. That way there is no confusion on the construction documents during the transition period.
3. For those that have trouble calculating Vasd = Vult sqrt(0.6), the IBC has table 1609.3.1.
4. For drift, I prefer to scale the design loads with the wind speeds in the ASCE 7 commentary to appendix C. [pdrift = pdesign x Vdrift2 / Vdesign2].
5. For deflection, IBC table 1604.3 changed footnote f from 0.7 times the C&C wind load to 0.42 times the C&C wind load for the deflection limits.
6. The IBC requires the design wind pressure on CDs for the components and cladding not designed by a "registered design professional". The design load, "W", in the 2012 IBC is at ultimate not ASD. Until the components, cladding, and equipment manufactures get up to speed with the changes, it may be a good idea to provide both ASD and ultimate design pressures. However, I think the manufacture may figure it out quickly once the start seeing huge design pressures.
RE: ASCE 7-10 Wind Loads
I actually do change the spacing or gage of the studs at corners if the building is big enough to make it economical.
The metal stud subs I do engineering for always underbid these things so I have to find them some money where I can without making things too complicated in the process.
But I agree, it is a pain - though not as much as dealing with parapets!
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
Is that a joke.... because I don't get jokes.
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
What is the reasoning behind the switch?
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
Mike McCann
MMC Engineering
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
Mike McCann
MMC Engineering
RE: ASCE 7-10 Wind Loads
I don't like it and I think it is a huge complicating waste of time and money, but I can see where those folks are coming from. I also think it is a bit of earthquake envy.
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
wind pressures were based on NYC 1968 Building Code which was used until 2008.
The new NYCBC 2008 is based on IBC 2003 / ASCE 7 -05. Those simplifications were thrown to the winds.
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
So, if the numbers at the same........ why switch?????????? Oh, and I know all the numbers end up being the same in the end.
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
...and the academics or scientific community who justify their existence by promoting these changes.
RE: ASCE 7-10 Wind Loads
I would love for them to simplify the codes for basic structures, but we all know that's not going to happen. While the wind load chapters have grown in size, I find ASCE 7-10 actually easier to use. I know I'm in the minority though.
RE: ASCE 7-10 Wind Loads
RE: ASCE 7-10 Wind Loads
I actually don't mind the whole concept and having site unique site specific wind speeds is pretty awesome. And it's not any harder to use than ASCE 7-05. I just have a problem with the fact that just because we have bigger computers that we need to add several layers of complications to the code that was OK. I'm carrying wind pressures to three figures for pity's sake. Does the wind know that?
RE: ASCE 7-10 Wind Loads
It must. It seems to know what category the building is.
RE: ASCE 7-10 Wind Loads