04-01-2010, 08:46 AM
Ssamis, you're right, but only for homogeneous material of the beam. So if you have steel T-beam, then it doesn't matter if it is inverted or not, because the Inertial moment is the same if you rotate the section at 180 degrees, because you will have the same axis. That means that for steel beam the deflection will be the same. We will have different stability, but this is another topic.
Let's see for reinforced-concrete where we have changeable stressed cross section, because the concrete cracks when it is in tension (and the steel bars are take this tension).
In the reversed T the concrete is not used optimally, because the centroid of the compressed concrete goes much more (actually with the ration of the top to bottom width of the T) closely to the centroid of the steel bars. So for RC beam you will have different stiffness, depending on the width-distribution of the concrete.
Let's see for reinforced-concrete where we have changeable stressed cross section, because the concrete cracks when it is in tension (and the steel bars are take this tension).
In the reversed T the concrete is not used optimally, because the centroid of the compressed concrete goes much more (actually with the ration of the top to bottom width of the T) closely to the centroid of the steel bars. So for RC beam you will have different stiffness, depending on the width-distribution of the concrete.