1)
Above two identical beams are subjected to either 3pt bending (top) or 4pt bending
(bottom). Both beams are subjected to a net load of 2P. To the right is a cross section of
the beam. It is a hollow beam with a wall thickness of b and h as shown. Compare the
two bending schemes. Derive expressions for the internal shear force and bending
moment in these two cases, and draw shear and bending moment diagrams. Determine
the locations (x and y) of the maximum tensile and compressive stresses and derive the
equations that describe these stresses at the maximum locations.
These bending tests are frequently used to characterize the material properties and/or
mechanical response of materials, such as in the bone bending lab in the BME
curriculum. Which test (3 or 4pt bending) do you think provides a better, more
straightforward means of testing materials? Explain.
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2)
A paraplegic patient weighing 70kg is performing a pushup in the prone position
(below).
The lower legs and hands are supported by the floor.
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 Fall '11
 JosephFreeman
 Force, Second moment of area, Fundamental physics concepts

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