Designing / CAD Modeling a Balsa Bridge and Assembly Drawing in Onshape from Start to Finish

The specifications that my 9th grade Engineering class will be using for this build are as follows:

All balsa sticks are 1/8 inch by 1/8 inch. Laminations are not allowed.
Maximum of 16 linear feet of balsa to be used in the design.
Maximum overall length -- 12 inches
Maximum overall height -- 4 inches
Width must be between 2 - 4 inches
Clear Span -- 9 inches
Bridge should securely cross the span and be freestanding during testing.
Testing block is 1.75 x 4 x 0.5 inches, with a 0.5 inch hole in the middle to mount an eye bolt or similar apparatus to connect to chain holding the bucket for testing.
To be able to support this testing block, the balsa beams used for the "vehicular roadway" should be at least 0.5 inches apart in the center of the structure, and may not be laminated anywhere along the length of the bridge.
Testing goal will be for bridge to hold 15 pounds, while ultimately aiming to be the most efficient bridge. Efficiency is determined by the mass of the load at failure / mass of the bridge.
Substructure is not required, but if used, maximum length is 8 inches with at least 1/2 inch away from the abutments on either side of the span.

The individual sections of the bridges will be printed in 1:1 scale to used as a guide for construction.

The Assembly Drawing should show all relevant views, fully dimensioned, in either 1:1 or 1:2 scale, and the Design goal is for the bridge to be sturdy and symmetrical, while aiming to match the CAD drawing after construction, including the lateral bracing and plan for the roadway.