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steel and concrete composite section

steel and concrete composite section

steel and concrete composite section

(OP)
Hi, all. I am doing a dynamic modelling of a building. SOme of the beams are made up with 2 W-sections side by side encased in concrete. ANy suggestion on how to model the equivalent section? I suppose the total area of section can be calc by Ac+As(Es/Ec), but what E do you use? Ec or an equivalent E? how would you calculate the equivalent E?

Thanks in advance for all suggestion.

Peter Lee
www.neillandgunter.com

Peter Lee
www.neillandgunter.com

RE: steel and concrete composite section

Hi n9yz

Correct me if I am wrong as I am no civil or structural engineer but for a beam of two materials I would proceed as
follows:- Assuming that the steel and concrete are connected
ridgidly together the bending moment:-


      M=Mc + Ms

      M= Ec*Ic/(R) + Es*Is/(R)

      but Es/Ec = m = modular ratio

      M= (Ic/(R) + m*Is/(R))*Ec

      divide thru by R
      
       M=(Ic+m*Is)*Ec/R   and Ec/R= fc/y

      : M=(Ic+m*Is)*(fc/y)

      where fc=stress
            Is,Ic= second moments of area for steel
                   and concrete beam.
        
             R = radius of curvature of beam

             Ec,Es = modulus of elasticity of materials

              y = distance to neutral axis


     By using this method I have found the equivalent    
     second moment of area of a complete concrete beam by
     using the modular ratio and converting the steel part
     into a equivalent concrete part.So you can now
     calculate stress using Ec only. Alternatively you can
     turn the concrete portion into an equivalent steel beam
     if you desire again using m however the formula would
     look like this:-

       M=(Ic/(m))+Is)*(fs/y)

     hope this helps

     regards desertfox

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