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RE: ASD vs. LRFD

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	Nicely said. "Understanding either
> is not the point, understanding how the structure behaves and providing
> acceptable behavior in our designs is what it is all about." 
	When I structure fails for whatever reason, we cannot reason out
that LRFD, ASD, WSD, USD or LSD was used as a specification for the design.
Sometimes we get so attached to the provisions of the any code that we tend
to forget the way a structure would behave. 



> ----------
> From: 	Cain, William[SMTP:bcain(--nospam--at)ebmud.com]
> Reply To: 	seaint(--nospam--at)seaint.org
> Sent: 	Tuesday, June 22, 1999 1:08 AM
> To: 	'seaint(--nospam--at)seaint.org'
> Subject: 	RE: ASD vs. LRFD
> 
> Jake-
> 
> Remember that code requirements are MINIMUM requirements.  Procedure
> shopping for a way to "make them work" is frequently done.  Is it good
> engineering?  IMHO not by itself, particularly with wind and seismic
> loadings.  I hope you tried to understand the real loadings and what they
> mean to the REAL behavior of the structure before you accepted the LRFD
> analysis at face value.  The structure could care less which method you
> used.  It may result in a "more economical design" or it may result in one
> that falls down in the next earthquake or windstorm because the design was
> cut too fine.  In the latter case, the owner may have though it was
> economical until it fell down, then he'll feel it is disastrous.
> 
> Both ASD and LRFD are simply tools to help us make design decisions.  They
> both need to be used with good engineering judgement.  Understanding
> either
> is not the point, understanding how the structure behaves and providing
> acceptable behavior in our designs is what it is all about.
> 
> Bill Cain, SE
> Oakland, CA
> 
> 
> 	Jake wrote:
> 	<snip>
> 
> 		I am currently working on a major retail remodel in Salt
> Lake.  A
> 	co-worker of mine did a preliminary column capacity check using ASD.
> 
> 	Many of the columns failed, but only slightly.  After verifing his
> 	loading conditions, I did and LRFD check and many of the columns
> will
> 	now work.  Continuing even further, his original checks on footings
> used
> 	ACI 381-95 load factors for strength and nearly every footing
> failed.  I
> 	then checked them using ASCE-7 load combinations (with reduced phi
> 	factors) and made many (not all) of them work.  It helped in this
> 	particular case because ACI demands a full 1.7 on snow and live load
> at
> 	the same time.  Meanwhile, ASCE lets you reduce one of the load
> factors
> 	to 0.70 and the other to 1.6.  This created a dramatic decrease in
> 	loading.
> 
> 		The point: Yes ASD works, but when designing columns in
> particular -
> 	LRFD will give you a more economicle design.  And with additional
> 	research, even the current load factors will change with time.  I
> 	believe ACI in the procedure of adopting the ASCE-7 factors. <snip>
> 
> 	
> 
>