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LRFD-ASD & USD-WSD

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Sprague's postmortem of ASD is good and accurate, as is Turk's nostalgic
review of WSD (nostalgia is not what it used to be); both posts are
interesting and should be very informative to those who were not in the
business during the WSD to USD years.  As for LRFD, the inexorable movement
to strength design for steel is just the same as it was for concrete, but
comparing the advancing fronts, the transition toward LRFD is more powerful
than that was toward USD.  Anyone who doubts that ASD is dead does not know
about, or does not recall, the transition for concrete design, and has been
out of touch as well.  Step back and look at the process that has occurred
over the last 15 years.

All research in steel design is in LRFD; nothing has been done in ASD for
years nor will there be.  Education (with exception, at smaller colleges
without graduate programs) is all LRFD.  All research-endowed universities
have dropped ASD from their undergraduate programs (1990 was the last year
of ASD at UC Berkeley) and the only financial support given or even
available for graduate work is in LRFD and this has been so for 10 years.
Look at a major indicator of trends, the quintessential text book on a
subject, which for steel design is  "Steel Structures - Design and
Behavior", Salmon & Johnson.  Starting with the Third Edition (1990) the
title was enlarged to include "Emphasizing Load and Resistance Factor
Design" and the Fourth Edition (1996) has all but relegated ASD to history.
 As for seismic design, the 1992 AISC Seismic Provisions, issued as a
supplement to both the 1986 LRFD and 1989 ASD manuals, was authored by AISC
Specification Task Committee 113 chaired by Prof. Egor Popov, UC Berkeley.  

The codes are all heading for strength design, but they move glacially
because they have to follow collection and digestion of input, and deal
with politics and challenges.  The AISC 1990 LRFD Seismic Provisions
followed 1988 NEHRP and the AISC 1992 LRFD Seismic Provisions, which also
gave ASD as "Alternate", were delayed because 1991 NEHRP was not issued
until January 1992.  However, ICBO relatively quickly adopted retroactively
the 1992 LRFD Seismic Provisions, as an "appropriate new standard", into
1991 UBC Sec. 2702.  The 1993 LRFD Specifications and the 1994 LRFD Manual
incorporate the 1992 AISC Seismic Provisions, and Chapter 22 of the 1994
and 1997 UBC is also based on the 1992 AISC Seismic Provisions. 

The implication that LRFD is not adopted into the Appendix of the
California Building Code (1995 CBC 2203A.1, which applies "only" to
buildings regulated by DSA & OSHPD) is validation of the uselessness of
LRFD ignores the fact that 1995 CBC "State" (Appendix) Chapters 16A, 17A,
18A, 19A, 20A, 21A, 22A & 23A all include serious modifications and contain
many restrictions that are applicable only to buildings regulated by the
"enforcing agency" (the phrase in the CBC Appendix which replaces "building
official" in the UBC).  Therefore if the philosophy expressed by DSA/OSHPD
towards LRFD, and other DSA/OSHPD restrictions, were to apply to
occupancies under local jurisdictions, most design and construction in
California would grind to a halt.  


Incidentally, adding to posts by others, the 1998 CBC, based on the 1997
UBC, was adopted a week ago (July 21, 1998).  USD made its first UBC
appearance in 1964 UBC Sec. 2611(b), and 1964 UBC Standard 261264, which
was based on ACI 318-63.  Cost of the 1964 UBC (503 pages):  $8.60
(hardcover).  For the textbook parallel to Salmon & Johnson (of UW Madison)
noted above for steel, the bible for concrete design (at the time) was
"Design of Concrete Structures", now known as Winter & Nilsen but
originally known as Urquhart & O'Rourke and later Urquhart, O'Rourke &
Winter (all of Cornell).  The first coverage of USD is in the Fifth Edition
(1954), 514 pages, and the dust jacket heralds "A new chapter on Modern
Development has been added, covering plastic (ultimate) design and
prestressed concrete".  Cost: $7.50.  The almost apologetic introduction
picks up a bit with "In fact, A. N. Talbot, one of the pioneers in this
field (RC research and design; behavior of stresses and strains in concrete
being proportional only at relatively low stresses but that at higher
stresses the strain increases at a faster rate than the stress) pointed out
as early as 1905 that a curved stress strain relationship must be used for
an accurate determination of strength of RC members", and that "this method
(later RC theory based exclusively on the assumption of elastic behavior)
in many cases led to uneconomical design".  As Sprague summarized, "this
discrepancy became so glaring in column design that it finally led to
abandoning the concept of elasticity for such members".

For those who can overcome the loathing of LRFD associated with the fear of
learning something new, and are also willing to risk being progressive in
their chosen profession, read "Essentials of LRFD" published in Modern
Steel Construction, in 3 parts (June, July, August 1995).  Work your way
through the logic of, for example, beam column design using LRFD, and then
track development of the ASD counterpart by thumbing through the Fifth to
Ninth Editions of the AISC Manual.

The ASD Ninth Edition is 10 years old, and there will not be another.
Browse through an AISC LRFD CD ROM (you will not find one for ASD).  As for
progress of this forum, unfortunately, it looks like Charlie Carter is
gone; his low key protest of nontechnical content was trampled.  An
absolutely invaluable resource for a forum such as this, lost.  For those
who are interested in an authoritative and succinct eulogy for ASD,
attached is an electronic version of AISC's "Final Resolution on future of
AISC Specifications".  For those of you who believe ASD has a viable
future, note the bottom line, which was the change in the draft that
resulted in the final resolution, almost 4 years ago. 
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{\plain Date:\tab March 8, 1995\par
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{\plain To:\tab Distribution below\par
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{\plain From:\tab Charlie Carter\par
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{\plain RE:\tab Final Resolution on future of AISC Specifications\par
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{\plain ________________________________________________________________________\par
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{\plain   \par
}{\plain For your information, the draft resolution, which resulted from our \'93Summit\'94 meeting on 
February 1, 1995, has been reviewed and approved by the AISC Board of Directors as 
follows:\par
}{\plain \par
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{\plain Based on expert input from its Committee on Specifications, the Board of Directors 
of AISC affirms that the 1993 }{\plain \i Load and Resistance Factor Design (LRFD) 
Specification for Structural Steel Buildings}{\plain  is the preferred Specification for the 
fabricated steel industry.  LRFD is a modern and technologically superior steel 
design specification.  Its direct representation of ultimate structural behavior is 
especially relevant for seismic design, design of frames with partially restrained 
connections, and composite systems design.  It offers engineers the opportunity to 
innovate in the analysis and design of highly reliable and competitive steel 
structures by encouraging the consideration of strength and serviceability criteria 
under appropriate combinations of gravity and lateral loads.  In this way, LRFD is 
consistent with the prevailing trend toward limit-states design in all structural 
materials, both domestically and internationally.\par
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{\plain \par
}{\plain This approved final statement differs from the draft resolution in two ways: (1) it was 
editorially reorganized, and (2) the sentence indicating the maintenance of ASD as an 
alternative was eliminated.\par
}{\plain \par
}{\plain \ul Distribution}{\plain \par
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{\plain F. Wylie\tab \tab \tab B. Ellingwood\par
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{\plain R. Owen\tab \tab \tab D. Sherman\par
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{\plain R. Freeland\tab \tab \tab T. Winneberger\par
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{\plain R. Abramson\tab \tab \tab W. Thornton\par
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{\plain L. Gurthet\tab \tab \tab J. Fisher\par
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{\plain S. Lindsey\tab \tab \tab AISC Staff\par
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{\plain T. Galambos\tab \tab \tab AISCM Staff\par
}}

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