Can I count on shear-friction capacity of the reinforcement? 3

[RobertEIT]

I have checked an existing concrete beam, Its shear capacity is not enough, and there is no shear reinforcement(i.e. no tie rebar), But its flexural capacity is over kill and it has an extra layer of longitudinal rebar, Can I take this extra layer of rebar as shear-friction rebar and caculate its shear-friction capacity to compensate the lack portion of the shear capacity?

Thanks a lot.

 

[JAE]

mhijazi - please start a new thread.

 

[Gumpmaster]

The shear concepts in ACI 318 are practical in most cases, but I think they're a little dated.

Modified compression field theory, as developed by Vecchio and Collins at the University of Toronto tends to predict shear behavior a little (or a lot in some cases) more accurately. AASHTO shear calculations implement MCFT. You can download a free program (Response 2000) that will run a quick shear calc for you with MCFT.

I've retrofitted beams with external FRP stirrups before. FRP reinforcement is gaining popularity with departments of transportation. ACI 440 will tell you how to design it.