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Re: Fracture in concrete

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The only work I have seen used nonlinear finite element computer programs
that changed the section properties of the concrete sections as the strain
in the concrete increased to the point were the concrete was considered to
be cracked.    Most of the work in that area is in the research field.  I
have never seen a actual design that used the nonlinear software.  Most of
the time, analysis in concrete assumes either uncracked gross section
properties or the "cracked section properties" (the section properties when
the reinforcing steel is at or close to yield).    The Commentary to ACI
318 has a short discussion of this topic in Section 8.6.



                                                                                                                                       
                      Christopher                                                                                                      
                      Wright                   To:       "SEAOC Newsletter" <seaint(--nospam--at)seaint.org>                                        
                      <chrisw@skypoint.        cc:                                                                                     
                      com>                     Fax to:                                                                                 
                                               Subject:  Fracture in concrete                                                          
                      11/25/2002 08:31                                                                                                 
                      AM                                                                                                               
                      Please respond to                                                                                                
                      seaint                                                                                                           
                                                                                                                                       
                                                                                                                                       




This is a curiosity question for any concrete guru with a few minutes to
kill. . I don't do structural concrete and I'm enough ignorant on the
topic so I still use 'pour' for 'place' and 'cement mixer' for 'concrete
hauler.'

There are inquiries from time to time on a FEA list I frequent from
people looking to do cracked sections with FEA, and I got curious whether
these guys are just student newbies in a FEA course or whether there's
active research in fracture mechanics of concrete.

What's the current practice on figuring the strength and ultimate
capacity of cracked beams?

 Is fracture mechanics used? (I was taught to use the uncracked section
in my only exposure to design in concrete, but that doesn't square with
what I know (a fair amount) about fracture propagation and critical crack
length.)

Is reinforcing considered to arrest cracks? (Pretensioning probably will,
but what happens to cracks in non pretensioned structures.)

How is fatigue cracking or propagation of shrinkage cracks considered?

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


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