Question about Balsa Wood Bridges?

I'm currently building a balsa wood bridge for a high school physics cl and would like some help. Most of my clmates are copying other designs or randomly going for them ,but I want to try mathematically approach.(My partner though, is skeptical). Can somebody either tell me the equations and formulas I would need or direct me to the location I should go to learn all of this? I have knowledge of force problems and the sort, so I should be able to understand them. Thanks!