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[SEAOC] Proposed Modifications to ASTM Spec's for Struc. Steel in Seis. Applications

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TEXT FILE ATTACHED

December 17, 1996

Dear Colleagues: 

Attached herewith is a copy of the letter from the SEAOC Seismology Committee
which was recently forwarded to Mr. Iwankiw, Vice President of Technology &
Research with the American Institute of Steel Construction.  In this letter,
the Committee has suggested certain improvements to the current ASTM
Specifications for enabling design professionals to specify a readily
available structural steel with highly predictable properties that is
adequately ductile and weldable for applications in seismic force resisting
systems.  These areas include Chemistry, Tensile/ Elongation Properties,
Toughness Properties, Dimensional Tolerances and Rejection Criteria.  

A critical part of this dialogue with the AISC & Steel Industry
representatives is the effective participation and input from our membership.
 The Committee will attempt to provide periodic updates and keep everyone
abreast of any progress being made.  

If you have difficulty downloading this file and are interested in receiving
a faxed copy please do not hesitate to contact me.

Ali Sadre, Chairman
SEAOC Seismology Committee

c/o EsGil Corp.
9320 Chesapeake Dr., # 208, 
San Diego, CA 
Tel: (619) 560-1468
Fax: (619) 560-1576 
Dec. 17, 1996

Mr. Nestor Iwankiw                                                                        
Vice President of Technology & Research                                      
American Institute of Steel Construction, Inc.
400 North Michigan Avenue
Chicago, Illinois 60611
 
SUBJECT:  PROPOSED MODIFICATIONS TO ASTM SPECIFICATIONS
FOR STRUCTURAL STEEL IN SEISMIC APPLICATIONS

Dear Mr. Iwankiw:

Over the past several months, our Structural Steel Ad Hoc Committee of the SEAOC Seismology Committee has discussed ways to improve the material aspects of structural steel, while preserving the many good qualities which already exist.  Simply stated, our goal is to be able to specify a readily available structural steel with highly predictable properties in at least two grades which is suitably ductile and weldable for application in earthquake-resisting systems.  Following are the areas where, in our opinion, current ASTM specifications require improvement if that goal is to be realized.  It is no coincidence that some of the items included herein are also contained in the SAC Interim Guidelines.

CHEMISTRY:
1)  Place control on trace elements.
2)  Include analysis and reporting of an expanded set of elements in the mill test report.
 
TENSILE/ELONGATION PROPERTIES:
1)  Make available at least two grades with a suitable difference between their respective yield strengths, such as 36 ksi and 50 ksi.
2)  Set requirements on both minimum and maximum yield values for all grades.  Ideally there would be a sufficient spread between the yields of any two grades of material such that the probability of yield for a lower grade exceeding that for a higher grade would be appropriately small.
3)  Set maximum limits on the yield ratio (ratio between the maximum yield strength and the minimum ultimate tensile strength).  Studies show that the plastic deformation capacity decreases substantially with an increase in yield ratio (Kato 1991).  Thus, we recommend the yield ratio not to exceed 0.75 for the current code R-factors.  In addition, a long strain plateau length between yield and tensile failure is necessary to achieve an adequate displacement ductility capacity.  A minimum plateau-length ratio, ep/ey, of 9 to 10 is recommended until further studies indicate otherwise.
4)  When reporting yield strength, report both the yield point (first yield) and the 0.2% offset strength (second yield or plateau) for flanges and, where requested, for the web.  In addition, make submission of standardized stress(strain or load(deformation plots available as a supplemental requirement.
5)  Establish requirements for through-thickness (z-direction) strengths and develop relevant test procedures to determine conformance.
6)  Set property requirements on a Group basis where appropriate.

TOUGHNESS PROPERTIES:
1)  Set requirements for toughness and require their reporting.  Consider relating these requirements to the lowest anticipated service temperature.
2)  The required toughness requirements shall apply anywhere within the shape cross-section.
3)  Tests should be conducted by the producer on material selected from standardized critical locations with appropriate frequency.

DIMENSIONAL TOLERANCE:
1)  Set suitable tolerance limits on flange and web thickness for wide flange shapes in addition to the cross-sectional area restrictions already specified.

QUALITY/REJECTION:
1)  Include clear and comprehensive language regarding rejection of material.
2)  Include lack of weldability with conventional methods as a just cause for rejection.
3)  Achieve Level I acceptance standards (per ASTM A 898-91) as a minimum for internal discontinuities (e.g. laminations) as determined by ultrasonic examination, where such testing is requested for critical connection regions.

While we considered unilaterally recommending specific values for many of the above items, in the end we felt it more appropriate to establish them in concert with the steel industry via subsequent discussions and correspondences.  We acknowledge that some improvements to material property specifications have already been made by virtue of the new 50 ksi single grade specification and the recent ASTM A 913 specification; however, it is apparent that even more progress is required if we are to achieve our stated goal.

I welcome the opportunity to work with you and the steel community in the months ahead.  On behalf of the Committee, I would like to acknowledge the efforts of Mr. Peter C. Revelli for preparing the draft of the Committee's consensus. 


Sincerely, 
 


Ali Sadre, Chairman

SEAOC Seismology Committee

cc: 	Mr. Karl K. Frank
 



Proposed Modifications to ASTM Specifications for Structural Steel in Seismic Applications		 
Page 2, December 17, 1996