Which term describes the bending effect due to a transverse load on a bridge member?

• A. Shear
• B. Axial force
• C. Torsion
• D. Moment

Answer: (D)

Bending moment describes the bending effect produced by a transverse load on a bridge member. When a load acts across the member, it creates a turning tendency about each cross-section; the internal force that resists that tendency is the bending moment. It’s what causes the beam to curve: the top fibers tend to be compressed while the bottom fibers tend to be stretched, producing curvature. This is different from shear, which is the internal force that would slide one part of the cross-section past another; axial force, which acts along the length and causes tension or compression without bending; and torsion, which twists the member around its longitudinal axis. So the term that best describes the bending effect from a transverse load is the bending moment.