1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: How do I estimate stress in a non-prismatic shape?

  1. Apr 9, 2016 #1
    1. The problem statement, all variables and given/known data
    In a mathematics-based investigation, I am trying to estimate the stress through a voussoir (member) of an arch bridge. However, these members have non-uniform cross-sections. I don't need to know how to exactly calculate the stress in each part of the member, only the total stress (unless there is an easy way to do so, but judging from my research, there won't be) The force through it is known, it is just the cross-section that I need to get a reasonable estimate of. A visualisation of the problem is attached here: http://imgur.com/ZiX8JR9

    2. Relevant equations
    Stress = Force/(cross-sectional area)

    3. The attempt at a solution
    My idea was to take the volume of the member, and divide it by the length of the object in the direction of the force, to provide an estimate of the cross-sectional area.
  2. jcsd
  3. Apr 9, 2016 #2


    User Avatar
    Science Advisor
    Gold Member

    The applied down force is reacted by components of the contact forces between the block in question and the adjacent blocks to left and right .

    Have a think about this and try to draw the free body diagram for the block .
    Last edited: Apr 9, 2016
  4. Apr 9, 2016 #3
    I see what you mean, thanks. However, the components of the contact forces don't act perpendicular to any uniform cross-section either, so my question remains. Is there any good way to estimate the stress you could propose (e.g. finding the average stress).
  5. Apr 10, 2016 #4


    User Avatar
    Science Advisor
    Gold Member

    For basic estimate of stress assume that the contact forces act in a direction normal to the contact surfaces and that contact stress = contact force / contact area .

    There is section in one of those papers that I gave a link to in your previous thread that tells you in detail how to calculate all the forces and stresses in an arch bridge .
    Last edited: Apr 10, 2016
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted