I am building a bridge out of 3/32'' cross sectional area basswood. The minimum dimension is 300mm long. Maximum dimensions are 400mm long, 80mm wide and 50mm tall.

I would like to know what is the most efficient bridge design to support a load on the center or 50mm away form the center on the x axis. The loads start with 2kg and escalate form that. Good bridges are known to stand 70lbs. The thing is that the winner is the one who has the best efficiency coefficient E. E=(mass supported)/(mass of bridge). The maximum mass of the bridge is 28g. Thanks in advance, GO ENGINEERING!