I have build my own bridge from paper and i want to know the elastic module for the bridge, my bridge is flat all over the way and cylindrical from the sides.

  • 2
    $\begingroup$ Do you mean elastic modulus? Scaled drawings and photos? Hit the edit link below your question ... $\endgroup$
    – Transistor
    Nov 13 '19 at 16:45

Elastic Modulus is a property of material, not the shape of the structure.

In your case it depends on the type of the paper you used and also weather the bridge walls are parallel to the paper fiber grain or perpendicular, or angled, because paper is not an isotropic material.

Most likely the paper you have used is composed of randomly mixed fibers, which means it does not have a consistent modulus of elasticity regardless of the direction of stress.

You can test the modulus of elasticity of you paper by hanging a weight at the end of a narrow strip of the paper say 1/4 inch wide by 3 feet long and measure how much it elongates; then edit your question with these results. we can then help with an estimate of the E. If you detect a grain repeat the test for strip parallel and perpendicular to that. you need to be judicial and careful in setup and measuring, may be first let the weight hang for few minutes and use a vernier.

  • $\begingroup$ Relevant: en.wikipedia.org/wiki/Section_modulus#Elastic_section_modulus $\endgroup$ Nov 13 '19 at 19:46
  • $\begingroup$ The OP may also be interested in the elastic modulus of his bridge as a beam analog. Some truss manufacturers will post the effective E*I of their truss for designers to perform deflection analysis. Would be pretty simple to load the bridge midspan and measure deflection in order to assign it effective EI. Just a though. $\endgroup$
    – ShadowMan
    Nov 14 '19 at 18:50
  • $\begingroup$ @ShadowMan, then he needs to draw a section as to how the slab and walls go together and how it is being supported at the ends. and then he should ask for section modulus not elastic modulus. $\endgroup$
    – kamran
    Nov 14 '19 at 18:59
  • $\begingroup$ @kamran yes in order to calculate it from section properties I agree. But you can experimentally obtain EI effective by force vs deflection data. Anyway I would love to see the paper bridge! $\endgroup$
    – ShadowMan
    Nov 14 '19 at 19:02
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    $\begingroup$ @ShadowMan, i agree it can be measured by load versus deflection. Funny thing i have a Cessna 172 which i fly with the other friends and many of the wings and flaps surfaces feel as thin as paper, but they do the job. $\endgroup$
    – kamran
    Nov 14 '19 at 19:09

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