Return to index: [Subject] [Thread] [Date] [Author]

RE: Non Linear Dynamic Analysis and the number of records

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Adolfo-
Don't lose sight of the fact that any earthquake records are simply a given
earthquake recorded at a specific location in a specific direction at a
specific time.  Using substantially more records than recommended in the
Blue Book will not give you a much more accurate answer.  Focus rather on
the behavior of the structure you are analyzing.  

Be sure it has ductile details and ensure that the structure has clear,
simple and understandable load paths to resist the seismic forces.  Over
reliance on analysis with out exercising good engineering judgement will not
make your structure safer.  Remember that the dispersion of the records
reflects how imprecisely we know the basic input motions.  Don't try to
analyze more precisely than your input information.  Remember the old
computer saying: "Garbage in, garbage out."

Regards,
Bill Cain, S.E.
Oakland  CA


	-----Original Message-----
	From:	Adolfo Galvez [SMTP:agv(--nospam--at)amauta.rcp.net.pe]
	Sent:	Wednesday, August 02, 2000 10:34 AM
	To:	seaint(--nospam--at)seaint.org
	Subject:	Non Linear Dynamic Analysis and the number of
records

	For those of you who are NDP experts, or have had experience in this
field,
	here is a question:

	In non linear time-history analysis, we face, amongst others, the
following
	problems:

	1.- The selection of the records
	2.- The number of records to use, or
	3.- The allowed  one-sigma confidence bandwidth in the mean response
of the
	structure

	SEAOC Blue book and FEMA 273 suggested the use between 3 to 7
records;
	using the maximum structural response if you use 3 as the sample
size, or
	the mean response for 7 or more records.

	As everyone knows, the results are very scattered, even if two
records have
	almost the same Response Spectrum they would yield very different
	structural responses.

	The dispersion for the intensity ,Sa[fo] (Response Spectrum
Acceleration
	at the fundamental structural period ), is on the 50%-90% range,
depending
	on [fo]. If we need a 95% confidence level, and a +o- 10% bandwidth,
means
	use a very large number of records, if my figures are accurate,
between 100
	to 324, being a function of dispersion.

	The use of SEAOC Blue book or FEMA 273 Guidelines (3 to 7 records),
implies
	a one-sigma confidence band of 30% or more.

	So, this  question arises: How many records to use? Or, in other
words,
	which bandwidth should be used in the mean structural response and
at which
	confidence level?

	Also, if any, please feel free to comment on the normalization
procedure or
	the scaling parameter to be used on the record's sample.

	TIA for your answers.

	Adolfo Galvez, MSc.
	Lima - PERU

	******* ****** ******* ******** ******* ******* ******* *** 
	*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp 
	*   This email was sent to you via Structural Engineers 
	*   Association of Southern California (SEAOSC) server. To 
	*   subscribe (no fee) to the list, send email to 
	*   admin(--nospam--at)seaint.org and in the body of the message type 
	*   "join seaint" (no quotes). To Unsubscribe, send email 
	*   to admin(--nospam--at)seaint.org and in the body of the message 
	*   type "leave seaint" (no quotes). For questions, send 
	*   email to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
	*   send to the list is public domain and may be re-posted 
	*   without your permission. Make sure you visit our web 
	*   site at: http://www.seaint.org 
	******* ****** ****** ****** ******* ****** ****** ********

******* ****** ******* ******** ******* ******* ******* *** 
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) to the list, send email to 
*   admin(--nospam--at)seaint.org and in the body of the message type 
*   "join seaint" (no quotes). To Unsubscribe, send email 
*   to admin(--nospam--at)seaint.org and in the body of the message 
*   type "leave seaint" (no quotes). For questions, send 
*   email to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********