Twin Box culvert - 2 D analysis

Hello,

I am using STAAD PRO to model 2 D twin Box culvert. I also have beam elements (Grout) as a connection between two box culverts. I am wondering what type of the spec, I should apply to release the Moments and forces. I am thinking releasing all the moments and axial force and force in direction.

I am wondering if I am going in the right direction?

Thanks