If the frame is to be analyzed as a truss (i.e. members are pinned together instead of being regarded as fixed to each other) you can add releases to the rotational DOFs specifying 'uplift - none'.
The members with the uplift none rotational releases will be analyzed as two-force members, where they cannot hold a moment load (unless you apply gravity, then there will be bending moment loads within the beam).
I hope this helps...
Simulation QA Engineer
DLS (Simulation and Material Sciences)