# Question of Precomp

**URL:** <https://forums.nlr.gov/t/question-of-precomp/83>\
**Category:** Computer-Aided Engineering Software Tools\
**Created:** [March 9, 2006, 7:04am UTC](https://forums.nlr.gov/t/question-of-precomp/83 "2006-03-09T07:04:51Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![zzz.ytsunsh](https://avatars.discourse-cdn.com/v4/letter/z/e68b1a/32.png) [@zzz.ytsunsh](https://forums.nlr.gov/u/zzz.ytsunsh)\
**Post date:** [March 9, 2006, 7:04am UTC](https://forums.nlr.gov/t/question-of-precomp/83/1 "2006-03-09T07:04:51Z")

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the shear center result of precomp doesn’t match with my experience,  
plz see my file on [ytsun.go1.icpcn.com/work/](http://ytsun.go1.icpcn.com/work/)  
thank you  
_🙂_

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**Author:** ![Gunjit.Bir](https://avatars.discourse-cdn.com/v4/letter/g/5f9b8f/32.png) [@Gunjit.Bir](https://forums.nlr.gov/u/Gunjit.Bir)\
**Post date:** [March 24, 2006, 3:10pm UTC](https://forums.nlr.gov/t/question-of-precomp/83/2 "2006-03-24T15:10:10Z")

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I ran a few more verification cases and got good agreement for all results except the shear center location.

You are right in your observation that PreComp does not provide the shear center location accurately. In fact, I am going to update our user’s guide to caution users about this.

You must get close agreement for all other properties though. I will wait for your confirmation.

I did not go for a rigorous calculation of the shear center for two reasons:

1. We will not require explicit location of shear center when we integrate PreComp with FAST. All properties will eventually be referenced to the reference center.

2. Definition of shear center for a composite section can be ambigous. As you probably know, warping and shearing effects can substantially effect its location and in fact its very interpretation.

Even if I ignore warping and shear effects, its computation will require extensive computational effort involving partial area moments and imposition of closed section requirement. It is doable. However, our management is unwilling to allow me to put the extra effort unless a majority of users feel that it its accurate computation would benefit them.

Look forward to your comments.

Gunjit

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**Author:** ![zzz.ytsunsh](https://avatars.discourse-cdn.com/v4/letter/z/e68b1a/32.png) [@zzz.ytsunsh](https://forums.nlr.gov/u/zzz.ytsunsh)\
**Post date:** [April 24, 2006, 6:26am UTC](https://forums.nlr.gov/t/question-of-precomp/83/3 "2006-04-24T06:26:37Z")

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Table 7. Ouput Parameters in the user’s guide says  
EI\_flap --Section flap bending stiffness about the YE axis  
EI\_lag --Section lag (edgewise) bending stiffness about the XE axis.

And Figure 13 shows the XE-YE coordinate 's origin is on the shear center.

If the location of shear center is not right,is EI\_flap & EI\_lag result believable?

THX.

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╰───┬Ｏ────Ｏ┬──╯  
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**Author:** ![Gunjit.Bir](https://avatars.discourse-cdn.com/v4/letter/g/5f9b8f/32.png) [@Gunjit.Bir](https://forums.nlr.gov/u/Gunjit.Bir)\
**Post date:** [April 24, 2006, 4:34pm UTC](https://forums.nlr.gov/t/question-of-precomp/83/4 "2006-04-24T16:34:46Z")

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I have already made a few minor changes in PreComp. As per these changes, the bending stiffnesses wil be referred to the tension center (elastc centriod) and not the shear center. This should remove any ambiguity resulting from an approximate estimate of the shear center.

Also, I am coordinating with GEC and Sandia to test PreComp agaianst Ansys. Once verification studies are completed, I’'ll post the modified PreComp on our website.

Thanks for your very useful input.

Gunjit

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**Author:** ![zzz.ytsunsh](https://avatars.discourse-cdn.com/v4/letter/z/e68b1a/32.png) [@zzz.ytsunsh](https://forums.nlr.gov/u/zzz.ytsunsh)\
**Post date:** [May 30, 2006, 2:16am UTC](https://forums.nlr.gov/t/question-of-precomp/83/5 "2006-05-30T02:16:04Z")

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how long would this change take? 😮