Elastic Flexure Example - Doubly Symmetric I-shape

In this example a doubly symmetric I-shaped steel beam section is analyzed. The section is constructed by welding 8”x1” flanges to a 20”x1/2” web using steel with a yield stress of 50 ksi. Due to the section's symmetry, the centroid - and thus the neutral axis - is located at its geometric center, 11” from both the top and bottom. The analysis includes calculation of the section's moment of inertia as 2,099 in^4 and its elastic section modulus as 190.8 in^3. Under an applied bending moment of 600 k-ft, the normal stresses at the extreme fibers are 37.74 ksi, acting in compression at the top and tension at the bottom. Finally, the yield moment - the bending moment that causes first yielding in the extreme fibers - is determined to be 795.0 k-ft. 0:00 - Introduction 0:45 - Centroid Location 5:08 - Calculation of Moment of Inertia 6:15 - Parallel Axis Theorem 10:41 - Calculation of Bending Stress 13:06 - Elastic Section Modulus 14:56 - Calculation of Yield Moment