Warping in Beams

Hi,

I am looking for a way to define warping for an open cross-section beam using Abaqus, what is the your recommendations. 

In fact, I found that the open cross-section beam element type B310S has a 7th degree of freedom representing warping amplitude, but I am not able to find that additional degree of freedom among the boundary conditions to apply warping constraint when needed, and the results show zero warping moment.