civil engg/bridge design/solidworks

Need three changes to the beam(s) on my bridge (not the cables or trusses) and calculations showing their improvement. bridge is to be strong and light weight

the 3 pics (pic1,2n3) show my preliminary design. I am to model 3 new designs changing things like height or width of I beam or putting in more smaller I beams

in the project files is the description of all project but we are only on phase 2. If you use solid works that is good and you can use it to calculate the stresses (bending and shear) and the deflection, but must show how the calculations are done

I need your help in determining which changes to the I-beam would be most effective and weigh the least. I could just change the height of the beam without changing the placement. I could cut into 3 Ibeams- two on the edges and a larger one in the center (decreases weight but what's effect on strength?) Could the i-beam width be reduced so it is just in the center where the load is borne?...would this work if the edges of the bridge are stabilized by the cables on the sides the "costs" i was referring to are not in $ it is just the allowable shear bending etc for wood as a material, so the design can't exceed those stresses. I need designs that determine the best way to use the I-beam in the bridge design to reduce weight but leave a bridge that can bear the load and then looking at those three designs and calculate the stresses and deflection

3 designs of beams only (no truss , cable etc) so basically 3x3 calculations ( bending, shear , deflection for each design of beam)

More explanation

It is a wood bridge. There is an i-beam supporting the bridge. I am to manipulate the I-beam portion to see how to best minimize weight while improving ability to maintain the load. In the documents I sent you can see how the load will be placed. What i need is to vary the I-beam