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[SEAOC] Seismic Evaluation and Rehabilitation, FEMA 178, FEMA 172 and FEMA 273.

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Dear Colleagues,                                                    December
2, 1996
After reading my reply to Dave Evans concerning the subject matter, I though
you might also be interested in the discussion.  Please refer to my previous
email message to Dave Evans, which was also posted on the SEAOC List Server,
which explained how to obtain copies of FEMA 178 and  FEMA 172, and the lack
of easy availability of FEMA 273. 

Dave Evans,                                                              December 1, 1996
Save your money.  Stay with FEMA 178 for your evaluation of an existing building.
FEMA 178 has gone through the Building Seismic Safety Council (BSSC) review and  BSSC member voting approval process.  Although the American Society of Civil Engineers does not recognize the BSSC review and voting process as a "consensus" process leading to establishment of a "standard" , it could be argued that FEMA 178 does represent the "standard of practice and care" for the evaluation of existing buildings and has been endorsed by the Interagency Committee on Seismic Safety in Construction for the seismic evaluation of existing federal buildings.  ASCE FEMA 178 Update Project will update FEMA 178 using all or portions of FEMA 273 and make FEMA 178 a "consensus standard" by going through a very rigorous comments, review and voting process which should be completed by the end of 1997.
FEMA 273, September 1996 Ballot version is going through a BSSC Balloting procedure with ballot comments due on December 15, 1996.  There have been many questions raised about the September 1996 Ballot Version of FEMA 273 that it is reasonable to assume that it will go through a second ballot procedure before FEMA 273 is approved by the BSSC Board of Directors, etc.  Save your money and wait for the final FEMA 273 version that has been approved by BSSC and accepted by FEMA by the end of  1997.

FEMA 172 is a "how to do it" handbook with detail drawings and instructions.  FEMA 172 should be used with FEMA 178.   If you do not have a copy of FEMA 172, you should get a copy so you can see for yourself what I am trying to explain.

FEMA 273 is a very complex document which attempts to go back to the basics of the actual elastic and inelastic seismic response of buildings.  FEMA 273 attempts to use Linear Static Procedures and Linear Dynamic Procedures as well as Nonlinear Static Procedures (Pushover Analysis, etc.),  but not Nonlinear Dynamic Procedures, to predict the actual seismic response of buildings when subject to various levels of earthquake ground motions.  FEMA 273 has varying Seismic Performance Objectives which are a combination of various seismic hazard levels and seismic performance levels or damage states.  It is complex. 

FEMA  178 is simplier and more straight forward and you can explain to your client what is wrong with the building you are evaluating in simple terms.  In fact, in FEMA 273 is a "simplified procedure" that says that if a buildings passes FEMA 178 or is rehabilitated to meet all the True or False test questions in FEMA 178, then, for certain limited height and types of structural systems, the building meets one of  FEMA 273 Seismic Performance Objectives.  You will have to get a copy of the Ballot Version of FEMA 273 to better understand what I have attempted to explain.
  
FEMA 273 attempts to use base shear values, based on unreduced base shear equations that have no reduction factors like "R" for strength design,  like  V = C1*C2*C3*SaW in an attempt to predict the nonlinear displacement of the building under assumed levels of ground shaking.  For example, this equation for V results for
buildings in high seismic zones that the building is subjected to base shear values equal to 100% W  or the total weight of the building and then you looking at the "yield" or "ultimate" strength capacity of various components or elements of the building to determine if these components or elements can resist the high forces that result from 100% W.  In some cases, particularly for low period buildings with T less than 0.40 seconds, the V (base shear) can be greater than 100% W.
The application of some of the provisions of  FEMA 273 to seismic evaluate existing buildings and provide Guidelines for the seismic rehabilitation - retrofit - of  existing buildings, according to some structural engineers, are more restrictive than evaluating and/or rehabilitating the existing building to comply with the 1994 NEHRP Provisions and/or 1994 Uniform Building Code.

The "Bottom Line Question" is : Is it GOOD PUBLIC POLICY for the application of the FEMA 273 provisions for any material for the evaluation (ASCE FEMA 278 Proposed Update) and Guidelines for rehabilitation of existing buildings to be more severe or restrictive than the provisions of the 1994 NEHRP Recommended Provisons for Seismic Regulations for New Buildings and/or the 1994 Uniform Building Code provisions for the design of new buildings?

What you do think should be the answer to the above question?

Save your money.  Attempt to limit your professional liability by following FEMA 178. Wait until the smoke clears concerning FEMA 273.
 
I apologize for the long response, but this is not simple stuff.

Frank McClure   FEMCCLURE(--nospam--at)aol.com