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RE: 2013 Codes

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Last year, I did a project in Odessa, TX, where they had already adopted 
IBC 2012, and hence, ASCE 7-10.  At the time, RAM Structural System hadn't 
incorporated the new wind provisions, so I did a little exercise to compare 
 the results of the new method -- with wind pressures calculated at 
ultimate levels, then used in load combinations with a factor of 1.0 for 
LRFD or 0.6 for ASD -- versus the old method.  In the end, the new method 
resulted in forces about 4% lower than the old method for my particular 
case.  In other words, you wind up at essentially the same place, but take 
a completely different path to get there.  I used the software-generated 
wind forces, based on ASCE 7-05 and went about my business.

It sure threw off the curtain wall manufacturer, though.  Their engineer 
was making a fuss about how my general notes required them to design for 
120 mph, when they've been using 90 mph for years.  I had to explain that 
he needs to use the new code, that 120 mph produces an ULTIMATE-level wind 
pressure, and that in the end, their design should come out about the same 
as what they've done in the past.  I think it took him a while to get his 
head wrapped around it.

I'm not sure what the impetus was for the changes in the wind code, but I'm 
 SURE it represents a giant leap forward in engineering knowledge (that was 
 typed in "sarcasm mode", if you couldn't sense the tone).

-- Joel

the structural alliance
Joel Adair, PE, LEED AP

-----Original Message-----
From: seaint-seaosc(--nospam--at) [mailto:seaint-seaosc(--nospam--at)] On 
Behalf Of Polhemus, William Sent: Wednesday, November 06, 2013 12:58 PM
To: seaint-seaosc(--nospam--at)
Subject: RE: [SEAINT-SEAOSC] 2013 Codes

It's actually (IMO and that of many others) more complicated. I'm not sure 
why they chose to do it as they did, but they decided to remove the 
"Importance Factor" and instead provide THREE wind speed maps.

The wind speeds are "higher," but so as to induce forces at the "factored"
level such that they've reduced the load factors in those combinations that 
 include wind.

Puff, puff.

And other stuff...

And spread things out over several chapters...


Well, the point is, it may be BETTER but it's not what I think ANYONE would 
 call "simpler."

-----Original Message-----

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