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Both USD and WSD were taught in my concrete design class in 1973.  In the mid 1970's the practice was to do small structures, foundations, and water retaining structures in WSD.  Multi level commercial structures were using USD regularly by the late 1970's.  Water retaining structures were done in USD beginning in the mid 1980's although there are some engineers today that still use WSD.

The ACI 318-63 code had only 18 pages dedicated to USD.  

Keep in mind that WSD was killed.  It did not just die out.  The 318-77 put WSD in the appendix and required USD for the design of columns. 

Left to normal evolution it took 30 years for all structures.  Forced by ACI 318-77, it took about 15 years.

The same process is happening in AISC.  ASD will be killed with the new seismic building code.  Try doing a seismic design using ASD and the new AISC Seismic Provisions. The first LRFD came out in 1986.  In the land of high and intermediate seismic and BOCA and SBC the conversion was forced in 1992 following the AISC Seismic Design Provisions.  BOCA and SBC do not have the ASD seismic provisions that are contained in the UBC.

Right or wrong, I think it is time to get the shovel and bury our old ASD friend.  This is as painful for me as anyone.

In the land of BOCA and SBC seismic, the conversion took a little over 6 years for commercial structures.  In the land of UBC the death will come in the form of the 2000 IBC or about 14 years for UBC.  So steel and concrete are on about the same time frame for UBC jurisdictions.

Harold Sprague, PE
Krawinkler, Luth & Assoc.

-----Original Message-----
From:	CarlS95(--nospam--at) [SMTP:CarlS95(--nospam--at)]
Sent:	Tuesday, July 28, 1998 11:07 PM
To:	seaint(--nospam--at)
Subject:	More ASD, LRFD, USD

Question No. 2 for the oldtimers:

How long did it take for concrete Ultimate Strength Design to take hold once
it was codified?  Are we ahead or behind that schedule with LRFD?