Abaqus: Modelling of Reinforced Concrete Slab

Dear all,

Iam modelling a simply supported RC slab subjected to uniformly distributed loading at the top surface of the slab using Abaqus. I've chosen element type of C3D8R to model concrete slab and truss elements for steel bars reinforcement which are embedded into the concrete slab.

After running the model, I found that the load against central deflection curve at linear region, i.e from zero load to yield load is very much stiffer compare to the experimental test result. My question is that how to lower down this elastic curve so that it would closely match to the experimental test result.

 Please let me know and thank you.