HigherEd 2.0

The Facts

We had a small discussion in class the other day about the graphical method for shear and moment diagram construction. In particular, we had some difficulty with determining whether a particular quadratic-or-higher-order curve was concave up or concave down. For instance, we had a case of a linear shear, and the question was: does the moment (2nd order curve) get drawn concave up or concave down?

Well, one can think of this by asking the question of the slope of the moment curve, which is the shear value at a particular point. In the case we did in class, the shear went to zero at the boundary, so that meant that the moment slope went to zero as well. The only way it could do that was if the moment curve was concave up.

You can also have a look at this, a guideline sheet from another university. Or you can look at this very instructive page, especially bullet item #5 and item #1D. This Cal State page neatly summarizes the math and the visual/graphic nature of the diagrams, with useful guidelines.

“There is nothing either good or bad, but thinking makes it so.”

Hamlet’s wisdom could be applied to shear and moment diagrams, but we can also seek the advice of a modern HAMLET, which is actually a really slick web-based shear and moment diagram tool. You can control the boundary conditions, loading, etc. and it automatically calculates the shear and moment diagrams (and bending deflections too) for you.