AISC Seismic Provisions
AISC Seismic Provisions
(OP)
Do the AISC Seismic Provisions allow an Ordinary Moment Frame of steel to be taller than one story?
The building in question is in Charleston, SC and is a two story commercial/office use building with every beam to column connection Fully Restrained as part of the Lateral (Seismic) Force Resisting System.
The Fabricator says it must be a Special Moment Frame, but cannot provide a rationale other than the AISC provisions, but we can't find any stipulations in the Provisions either.
The building in question is in Charleston, SC and is a two story commercial/office use building with every beam to column connection Fully Restrained as part of the Lateral (Seismic) Force Resisting System.
The Fabricator says it must be a Special Moment Frame, but cannot provide a rationale other than the AISC provisions, but we can't find any stipulations in the Provisions either.






RE: AISC Seismic Provisions
ht
(free .pdf download)
refers to "...siginicant height and other limitations..." placed on ordinary moment frames by ASCE 7-02.
I have not followed this lead to ASCE 7-02, but since Charleston has stringent seismic design criteria, the fabricator is probably correct.
Also, IBC 2003 may have language on this issue.
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RE: AISC Seismic Provisions
Two story would violate footnote "h". An office building would likely have floor dead loads and roof dead loads bigger than 15 psf and thus violate footnote "i".
You probably need SMRF's if you are SDC D is or worse.
Out of curiosity, does wind or seismic govern? Charlestown, SC is unique in that it has seismic and hurricane issues.
RE: AISC Seismic Provisions
The worst seismic is about 25 miles inland - dropping as you approach the city (near the coastline).
The worst wind is on the coast, dropping as you go inland.
With so many variables, you have to put the ASCE 7 maps "under a magnifying glass" (almost literally) to find what conditions apply.
For waterfront structures you also have the possibility of major ship collisions. This whole combination was quite a consideration for the recently completed cable stay bridge
http://www.cooperriverbridge.org/
www.SlideRuleEra.net
RE: AISC Seismic Provisions
I agree that the maps they give you are typically far too small a scale to make any interpolation meaningful.
It would be nice if they gave you more printed maps at a smaller scale or a web site or something like that. I did find a website once that had Ss and S1 by zip code, but it said it was "not approved for design purposes"...
The contour lines are pretty close for the accelerations and wind speeds there.
RE: AISC Seismic Provisions
For IBC2000/2003:
Map for spectral response acceleration of 0.2 sec:
http
For 1.0 sec:
http
For seismic lookup by zipcode for IBC2000/2003:
http://eqint.cr.usgs.gov/eq/html/zipcode.html
For IBC2006:
http:/
Regards,
-Mike
RE: AISC Seismic Provisions
Thanks for the warning about checking the zip code accelerations.
RE: AISC Seismic Provisions
www.SlideRuleEra.net