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Re: EBF's

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     Bruce, I am glad to here your positive experiences using EBF's. I am 
     curious though as to how using a different type of bracing system 
     influences metal deck diaphragm design?
     
     Thanks, Ghassem Khosrownia.


______________________________ Reply Separator _________________________________
Subject: EBF's
Author:  Bruce(--nospam--at)uskh.com at Internet
Date:    9/3/97 4:35 PM


We just designed a facility in Anchorage (zone 4), single story, with an EBF. 
This facility is 580' x 220' x 41' with moment frames in the north/south 
direction (220 foot direction) and two EBF's in each of the north and south 
walls (parallel to the 580 foot dimension).
     
We looked at using concentrically braced frames first, but the size of the steel
and foundations became prohibitive.  Using EBF's allowed us to reduce costs in 
terms of reduced steel sizes and significantly reduced foundation sizes.
     
We were able to reduce the steel deck from 16 gage to 20 gage  on 130,000 square
feet of structure.  Significant savings alone.
     
The design includes two EBF's in each of the long walls.  The two frames are 
adjacent, sharing the intermediate column.  Steel sizes were drastically reduced
in the EBF's over the concentrically braced at the expense of more detailing and
field welding.  Overall, we saved money again.
     
The greatest savings was in the foundation work.  The entire site was excavated 
to 20+ feet and backfilled.  Overturning was a significant problem which 
resulted in large footings, very deep.  Using EBF's allowed us to minimize the 
foundations and place them much nearer the surface, significantly reducing 
costs.
     
Word of caution, if you intend to use LRFD design, second edition (silver book),
you must use the 97 UBC seismic loads (1991 NEHRP) to be compatible with the 1.0
Earthquake factor.  Read the preface on page 6-303 in the AISC LRFD Manual, 
Second Edition.
     
Bruce Hopper, P.E.
     
USKH, Inc.
2515 A Street
Anchorage, AK  99503
     
907.343.5231
     
bruce(--nospam--at)uskh.com