Flexure Formula  
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The diagram on the left shows an “I” bar consisting of three sections, 1, 2 and 3. The section 1 on top is horizontal with a length of 3.0 inches. The section 2 has a thickness of 0.5 inches and is between the sections 1 and 3. The section 3 is horizontal and has a length of 6.0 inches. The centroid is at the origin of the x y axes on the vertical section 2 at a height of 2.645 inches from the bottom edge of the horizontal section 3 and at a distance 5.355 below the top edge of the section 1. The diagram to the right shows a bent “I” bar with the moment M applied in the clockwise direction on the left end and the moment M is applied in the counterclockwise direction on the right end.

A positive bending moment creates compression stresses above the neutral axis. The stresses increase in magnitude as the distance from the neutral axis increases. Therefore, the maximum compression stress occurs at the top of the beam. Similarly, the maximum tension stress occurs at the bottom of the beam for a positive bending moment.