The Structures 2.0 application no longer allows a bridge design with a combined side and deck truss (see attachment). In a combined configuration, the deck trusses are either attached to the underside of the floor, or they are attached directly beneath the side trusses. Both of these designs - while prevalent - are in our opinion poor designs from a STEM learning perspective.
In an earlier version of Structures 2.0, students could attach a deck truss to the underside of the floor. In this type of configuration, the purpose of the deck truss is simply to support the floor as opposed to carrying load directly out to the abutments. We found this to be a very inefficient design, and perhaps more importantly a very confusing and complicated design from STEM learning perspective. The new floor system in Structures 2.0, which is comprised of stringers and floor beams, is a far better way to support a load applied to the floor. It is representative of how "real" bridges work and ensures that any load applied to the floor is properly carried to the truss joints. For more information on this, please see the attached PDF document.
When the deck truss is directly attached to the side trusses (as shown in the attachment), the bridge is statically indeterminate. Structures 2.0 does not allow statically indeterminate trusses because students simply would not have any understanding of why their bridge behaves as it does. The application would be a "black box" with little learning value. For more information on this subject, see the following article on truss sketches: