What is the primary action of beams in resisting loads?

• A. Tension
• B. Compression
• C. Shear
• D. Bending

Answer: (D)

Beams resist loads mainly through bending (flexure). When a beam spans between supports and carries a transverse load, it develops bending moments that cause the beam to curve. This curvature produces tensile stresses on one side and compressive stresses on the opposite side, described by sigma = M*y/I, with M the bending moment and y the distance from the neutral axis. Shear exists and is important for overall strength, but the dominant response of a beam to typical transverse loads is bending, not pure tension or compression. If a member were to carry loads only in tension, it would be a tie, and if only in compression, a column—neither is a beam’s primary action.