Eccentric Braced Frame EBF or Not EBF (IBC 2000)
Eccentric Braced Frame EBF or Not EBF (IBC 2000)
(OP)
Please could I ask for an opinion.
IBC 2000 1602 Defines an EBF as
"A diagonally braced frame in which at least one end of each brace frames into a beam a short distance from a beam-column or from another diagonal brace".
If a brace was eccentric at both ends, would it still be classed as an EBF as defined by IBC 2000. ie. framed into a column at a distance above / below the nearest beam / column connection.
To stick my head on the block, I would say a braced frame with braces eccentric at both ends is not an IBC 2000 EBF thus "Design Coefficients" listed in Table 1617.6 and others parts of are not relevant and thus cannot be used to support the design. (The column "links" in this "design" are not specially strengthened or modified).
I would value your views.
IBC 2000 1602 Defines an EBF as
"A diagonally braced frame in which at least one end of each brace frames into a beam a short distance from a beam-column or from another diagonal brace".
If a brace was eccentric at both ends, would it still be classed as an EBF as defined by IBC 2000. ie. framed into a column at a distance above / below the nearest beam / column connection.
To stick my head on the block, I would say a braced frame with braces eccentric at both ends is not an IBC 2000 EBF thus "Design Coefficients" listed in Table 1617.6 and others parts of are not relevant and thus cannot be used to support the design. (The column "links" in this "design" are not specially strengthened or modified).
I would value your views.





RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
Eccentricity in the brace beam connection should effect the structural damping. The deliberate working of the structural system is done in the beam, being less critical to failure than the column.
If the diagonal were eccentrically connected to a beam above and below, it would still be an EBF. Or if diagonals were specifically designed to load each other like the diagonal beam connection, it too would be an EBF.
I think the system if it were designed to "work" the columns, would not be allowed.
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
Regards
VOD
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
Uniform Building Code (UBC) - Everything west of the Mississippi River
Building Officials Code Association (BOCA) - Northeast US
Standard Building Code (SBC) - Southeast US
These three merged in recent years to form the ICC (International Code Council) which produced the International Codes (IBC, IPC, etc.) This was an attempt to create a singular model code for all of the US.
Unfortunately, the NFPA (National Fire Protection Association) did not like certain portions of the International Codes that pertained to their areas. They decided to create their own code and this is the NFPA building codes.
Right now, most of the US is going to the IBC but some areas (such as the State of California - not necessarily the cities) have adopted the NFPA - but its all a very political struggle.
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
Thanks for your response. In this thread I have noticed from Taro and yourself that K frames or chevrons are now "outlawed" in most American codes. Is this true?
I had noticed that the UBC '94 allowed EBF K frames (eccentric on the top horizontal beam only) for seismic loads as can be seen at www.aisc.org under Steel Tips.
Regards
VOD
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
Regards
VOD
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
EBF's in the IBC aren't restricted except without dual system moment frame detailing in high seismic areas. Even then most buildings are still allowed.
Neither Chevron nor K braces are EBF's.
EBF's introduce bending in the link beam by offsetting the connection from the beam column joint.
My IBC refers to a section 2212 for seismic rules, but there is no 2212 in my book!! AISC is referenced. LRFD is referenced.
So it's obvious, High seismic zones can't adopt the IBC. Gotta stay with the UBC.
And K braces are specifically outlawed there.
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
The AISC Seismic Provisions aren't really new. They were first published in 1990 and have been updated about 5 times since then.
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
The code treatment of steel is altogether different. IBC basically says see AISC. The UBC on the other hand assumed to codify the design standards especially in seismic issues. The AISC was just not the adapted reference standard for seismic issues. However, the UBC published basic steel design criteria, but truthfully, I used the AISC reference first for basic steel design.
I'm glad to see AISC take a better practical role in seismic issues, but I still see the UBC just too vested in their knowledge and responsible administration of seismic design to see it yet anytime soon relinquish authority to a lesser responsible authority. And the IBC assumes no authority whatsoever in this steel design issue.
RE: Eccentric Braced Frame EBF or Not EBF (IBC 2000)
The UBC is now a code that will not be renewed as the IBC is intended to replace it in the future. The intent of the ICC committees was to begin to develop model codes that would (properly in my mind) reference OUT to more established bodies such as the ACI, AISC, etc. instead of manhandling all the provisions coming out of those specialized material bodies.
So the UBC (ICBO)has essentially "relinquished their authority" already by signing on to create the IBC.