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RE: Upgrade Fatigue?

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In Florida we've already adopted ASCE 7-10.  The revised wind provisions 
with its different wind speeds have been a real hassle to explain to 
architects.

Architect:  "What's the wind speed in that location?"  Us:  "It depends. 
The wind blows harder on a hospital than it does on an office building."

In order to save us the trouble of multiplying by 1.15 they increased the 
physical size of the code and opened a can of worms.  Ever try to explain 
mean recurrence intervals to an architect?

Having said that, it's not within our power to refuse to go along.  All we 
can do is kvetch.

Though Florida doesn't have seismic problems (by legislative fiat) we also 
design in other locations.  Here's a dramatically oversimplified 
illustration of a AISC 341 catch-22:

In an ordinary concentric braced frame, you’re (theoretically) allowed to 
 use K-braces.  In order to make sure you don’t have buckling in the 
braces, AISC 341 8.2b makes you select a seismically compact section. 
Under that provision, an HSS 3x3 brace chosen for capacity gets bumped to a 
 much heavier HSS 5x5.

So, good, right?  No worries about buckling because your section is 
seismically compact, right?

Not so fast.  Go to section 14.3.  That makes you introduce an unbalanced 
force into the column at the connection.  There are a bunch of  calcs to go 
 through, but you essentially check the tensile CAPACITY of the brace.  Not 
 the actual load, the capacity.  And since they just made you dramatically 
upsize the member, there’s a lot of capacity.  Then you compare it to 30% 
 of the capacity of the compression brace.  The remainder goes into the 
column.

So now, in this example, you have almost 15 times the horizontal load going 
 into the column than you’d have if there wasn’t any compression brace 
at all.  You say “the heck with it” and change to x-bracing.

Same rules, by the way, for V-type and inverted V bracing.  AISC 341 
provisions apply for all building with R > 3, which is pretty much 
everything made out of steel.  (With some impractical exceptions.)  AISC's 
passive-aggressive way of saying not to use those systems?

Fun with constant code improvements.

Regards,
Carl W. Jenne, P.E.
Allan and Conrad, Inc.
Consulting Structural Engineers
Ring 407.628.5282 x 102
www.acstructural.com


.

-----Original Message-----
From: seaint-seaosc(--nospam--at)mail-list.com [mailto:seaint-seaosc(--nospam--at)mail-list.com] On 
Behalf Of Bill Polhemus Sent: Wednesday, April 10, 2013 11:10 AM
To: seaint-seaosc(--nospam--at)mail-list.com
Subject: [SEAINT-SEAOSC] Upgrade Fatigue?

Just an observation, eliciting response.

I've noticed in particular with respect to ACI 318-11 and ASCE 7-10, there 
seems to be real pushback on their adoption in practice.

I've noticed this in such things as design software, erection drawings for 
steel buildings, and even examples of university engineering coursework 
found online.

For whatever reason, with the introduction of the "International" codes in 
the U.S. and the ICC decision to pursue a thee-year code update cycle, 
coupled with their incorporating material design standards by reference, 
the old five- or six-year update development cycle was of course abandoned 
by the material design standard bodies in order to keep pace with the ICC. 
Not sure why but there it is.

ASCE 7 has followed suit as well.

Now, I think perhaps the practicing community has simply grown tired of it, 
 and at least in practice they're refusing to go along.

Truncated 451 characters in the previous message to save energy.

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