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Re[4]: Plastic moment capacity of concrete filled steel

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     Anand,

     Based on review of section I4, including equation C-I4-1 of the
     commentary (LRFD blue edition), it appears that you are correct.
     Without reinforcement and shear connectors, the plastic moment
     capacity is limited to that provided only by the pipe without
     consideration of the concrete.  It is inferred, however, that with an
     axial load greater than 30% of the axial capacity, the bond is not
     lost and therefore the combined moment capacity can be considered.  It
     sounds like that for your application there wouldn't be enough axial
     load though.

     John Hubert


______________________________ Reply Separator _________________________________
Subject: Re: Re[2]: Plastic moment capacity of concrete filled steel
Author:  AnandNene(--nospam--at)aol.com at Internet
Date:    3/16/98 5:41


Thank you, John Hubert, for your response.  I have the blue colored edition
and section I3.2 gives criteria for plastic capacity of beams WITH shear
connectors.  I am particularly concerned with Steel pipes with infill concrete
WITHOUT shear connectors.  As I see it, the capacity is essentially that of
the steel pipe if no connectors are provided.  Could you or someone provide
more information?

Thanks.

Anand Nene, S. E.

In a message dated 98-03-12 16:23:30 EST, you write:

<< Anand,

      See section I2-2 of the LRFD Manual of Steel Construction (this is for
      the edition which is silver colored).  Essentially, a modified yield
      stress and modulus are calculated.  These are then used to determine
      the ultimate compression and bending strength, which are then used in
      an interaction equation.

      John Hubert


 ______________________________ Reply Separator
_________________________________
 Subject: Re:Plastic moment capacity of concrete filled steel pipes
 Author:  AnandNene(--nospam--at)aol.com at Internet
 Date:    3/12/98 7:24


 I would like to know a reliable reference to estimate plastic moment capacity
 of concrete filled steel pipe and detailing requirements.

 I am reviewing a sope stabilization design where 8" dia. steel pipes
 (Fy=50ksi) filled with f'c=5000 psi concrete are proposed.  There is no
 reinforcing inside the pipe nor any provision for shear transfer.  The
 designer used capacity of both cocnrete and steel to estimate total plastic
 moment capacity claiming that for small diameter pipes this is the way things
 are done - on Caltrans projects.  I do not do work for Caltrans and not too
 familiar with bridge projects.

 I would appreciate comments and references on this subject.
  >>