Which railing features an additional corrugation or wave pattern on the top surface to enhance rigidity?

• A. Box beam guardrails
• B. Cable railings
• C. Thrie beam railings
• D. Steel tube railings

Answer: (C)

A corrugation or wave pattern on the top surface increases stiffness by adding extra resisting area to bending, so the railing behaves more rigidly under load. In thrie-beam guardrails, the top surface is formed with this shallow wave, which acts like a ribbed panel and raises the section’s moment of inertia. That extra stiffness helps distribute impact loads across the rails and posts more effectively, reducing deflection and improving overall rigidity. Other railing types—box beam, cable, or steel tube—rely on different geometries and do not employ a top-surface corrugation to boost rigidity, so they don’t gain that same resistance to bending from a corrugated top.