Need a book? Engineering books recommendations...

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

RE: FOS for von-Mises stress criteria

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I would disagree.  When the Code says that I have to have a safety
factor of 1.5 for overturning of a footing then I know that my
overturning resistance must be 1.5 the actual overturning forces, both
of which can be calculated for any given footing.

Maybe your comment is applicable to Geotechnical Engineers who apply a
SF of 2 to 3 to capacities that are derived from a combination of lab
tests and experience.

Matthew Stuart 
Structural Department
Manalapan
Extension 1283


-----Original Message-----
From: Christopher Wright [mailto:chrisw(--nospam--at)skypoint.com] 
Sent: Friday, January 13, 2006 1:23 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: FOS for von-Mises stress criteria


On Jan 13, 2006, at 7:04 AM, Arun Sarkar wrote:

> can anyone suggest what factor of safety (for structural steel) should

> be used when the checking criteria is von-Mises stress ?
You're playing with fire. Sounds like you have some FEA results you're 
trying to apply to something like ASD rules.  Von Mises stress _If_ 
you're considering working stress design and _if_ there are no stabiity 
issues, and _if_ there are no fatigue issues and _if_ you're talking 
about primary stress only and if the material is structural steel where 
the ultimate stress doesn't govern the allowables, the margin against 
first yield is about 1.6. So keep your von Mises stress to about 60% of 
the minimum specified yield value. If any of the foregoing ifs aren't 
met you're out of luck with simple-minded rules of thumb, particularly 
if you're trying to apply limit analysis procedures. You need to 
understand what the basis of your particular design code actually is, 
and match your FEA results to it.

'Factor of safety' is a silly phrase. It's a number that you only need 
because you don't know what it is.

Christopher Wright P.E.    |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com       | this distance"   (last words of Gen.
____________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw


******* ****** ******* ******** ******* ******* ******* ***
*   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) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions 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) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions 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 
******* ****** ****** ****** ******* ****** ****** ********