Beam Element to represent Uncracked Transformed Section of Concrete Element

Hi all,

I am trying to model a reinforced concrete structure. As the structure is large, our intention is only to model the detail reinforced concrete elements for a small area of interest. For other portion of the structure, our intention is to model the reinforced concrete element by beam elements. I converted the reinfored concrete section to a uncracked transformed section, where the reinforcement has been converted to concrete. Then I used beam elements to model the uncracked transformed section, connect them to the detail reinforced concrete portion being modeled and run the simulation. 

The error I got from Abaqus are:
Error in job Trial: BEAM SECTION DATA IS UNREALISTIC. I(11)*I(22)-I(12)**2 MUST BE POSITIVE.
Error in job Trial: BENDING STIFFNESS I(22) OF BEAM  SECTION IS ZERO; CHECK INPUT DATA.

However, I checked my uncracked section properties and I got my centroid and other calculations correct.

I modeled the uncracked concrete sections as 3D beam elements, with an arbitary profile. Attached a schematic of the uncracked transformed section.

Can anyone advise me whether the way I modeled my beam elements is correct? All suggestions and help are greatly appreciated.

Thank you.

Rgds,

Joseph