Defining Support conditions

HI...

I'm modelling composite concrete bridge deck over longitudinal steel I girders. I'm defining deck as Area objects and define Steel I girders in same plane. I move steel beams to bottom of the slab by varing cardinal points and joint offsets. Now I want to add supports at each girder locations. When I try to do that by means of joint restraint, It allways add support at slab mid depth. Actually I want to move the Supports to the bottom of the beams. How can I do that? I'm not using BRIDGE MODELER. I also want to know that how above setup (i.e.without moving the support to the bottom)will affect my analysis. Pls help if sombody knows how to do this.

Thanks..