bridge question?

I want to build a bridge that will provide the best weight to mass ratio.A brick will be placed on the very top of the bridge (not on the bottom platform) and a machine will apply certain pressure to the brick.Sosay the bridge has a mass of 50 grams, and will hold a weight of 150 pounds, then the ratio would be 3, which is good.I am currently considering building a pratt, howe, warren, or warren (w/ verticals) bridgeI do not knwo which one will be best for this projectPlease help and give any tipsThanks and happy holidays!also, i do not know for the trusses, what angles i should use (for the triangles).specifications: gt;30cm long6cm-6.5cm wide Please help and give any tipsThanks and happy holidays!


Any of those types can be made to workYour most likely failure modes are going to be joint failure and Euler bucklingYou will want your joints to be so strong that the truss members break before the joints breakEuler buckling is going to be where the strength to weight tradeoff takes placeIf your truss members are slender, they will need flanges creating that I shaped cross sectionThis will add weight, howeverYou will have to decide if the added weight is worth the additional strengthIf a truss member breaks before the other modes of failure, then you have utilized the maximum capacity of your structureIf buckling or joint failure occurs, then you have not utilized the full strength of your truss members.

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