I'm not familiar with the software, but if you model the RC beam as a line element for uniaxial test, you could model it as a parallel spring model, with the components being the concrete and reinforcements.

If you are modelling a beam as a unidimensional element you can just define a homogenized young modulus as well as the different stress limit (elastic and maximal) and you'll be fine. You will probably also have to define the second moment of area but that's jsut plain geometry and has nothing to do with material.

I gues you can use this paper for values: 

https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CC4QFjAB&url=http%3A%2F%2Fwww.springer.com%2Fcda%2Fcontent%2Fdocument%2Fcda_downloaddocument%2F9789400779075-c1.pdf%3FSGWID%3D0-0-45-1431211-p176308691&ei=aqlUVemAKYmgNp24gEg&usg=AFQjCNGIf6nxBhKysGpvtoJMWQIQDbkhaw&sig2=RfN21eveCxAtfiFb98Pj2Q&bvm=bv.93112503,d.ZGU&cad=rja

Hope this is what you're looking for... Bye

thank you @thanh and @arthur ... i will try and update you...