# Homework Help: Flexural rigidity, what does high flexural rigidity mean?

1. Jun 4, 2012

### chris_usyd

1. The problem statement, all variables and given/known data
simply put, i got 2.1E+10 N.mm^5 for my steel beam experiment?
but i am wonder, what conclusions can i make?

2. The attempt at a solution
from online resouce, flexural rigidity is defined as the force couple required to bend a rigid structure to a unit curvature.
so , the higher EI, the better?

2. Jun 5, 2012

### PhanthomJay

Not necessarily better, but the higher the EI, the stiffer the beam, and the harder it will be to bend. Actually, definition not withstanding, the stiffness depends not only on EI, but also the length of the beam and its end conditions. What was your experiment? The units don't make sense.

3. Jun 5, 2012

### chris_usyd

units?
yeah, i am confused as well.
isnt N.mm^2? since E(N/mm^2) I(mm^4)
the experiment is to examining the stiffness of a steel beam through 2 types of deformation-deflection and curvature..
now i am writing the discussion part, but not many things to be mentioned.

4. Jun 5, 2012

### chris_usyd

but i got different values..
so also need some comparisons.

5. Jun 5, 2012

### chris_usyd

by the way, jay, "what are the assumptions in calculating EI that may not be strictly true??"
i cant even find one
you know, by deflection, i plotted the mid-span moment(M) against the curvature(K). because M=EIk, the slope is the value of EI.
i think it is perfect..

6. Jun 5, 2012

### PhanthomJay

EI has units (N/mm^2)(mm^4) = N*mm^2

Curvature k is EI/M and has units of mm.

I am not surewhat you are measuring in your experiment...deflection, stress, curvature?...and what you are trying to calculate.

If you have a simply supported beam of length L with a concentrated load P at L/2, then M_max = PL/4 at midpoint, and max deflection is PL^3/48EI at that point, in theory.