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Re: Precomposite Stresses in Reinforced Steel Sections

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I would have taken your approach; your collegue's
method seems accurate to me if the member is jacked to
horizontal before reinforcing.

John Riley

--- Matt & Priscilla Muhlenkamp
<muhlenkamp(--nospam--at)mindspring.com> wrote:

> When strengthening a steel section (an open-web
> joist, beam, or girder in my
> most recent case), I always did the following (ASD):
> 1. assume a more or less permanent load (mainly the
> DL taken by the member),
> and compute the stresses and deflection due to this
> load on the original
> section.
> 2. compute the additional stresses and deflection
> based on the reinforced
> section (due mainly to LL and any additional DL -
> like permanent mechanical
> equipment)
> 3. add the two together (at appropriate points on
> the section) to determine
> the total stress, and compare with allowable.  If
> the section is
> overstressed, then require some load removal prior
> to reinforcing (e.g.
> jacking to remove some DL).
>  
> Recently, an engineer in my office told me he only
> checks the 1st condition.
> In step 2, he puts the entire DL + LL on the new
> reinforced (i.e. increased)
> section, and doesn't consider the locked in stresses
> due to the permanent
> load on the original section.
>  
> While I know AISC ASD allows this for composite
> beams, it seems this is
> based on certain approximations and simplifications.
>  I just think that it
> cannot be correct in an elastic approach to the
> problem, especially when
> considering things like coverplating, etc.   (I know
> using a plastic section
> approach would make a big difference, but I only
> talking elastic in this
> case)
>  
> Any thoughts?
>   
> Thanks,
>  
> Matt
> 



		
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