What happens when horizontal restraints are added to a thin column?

• A. Increase bending stress
• B. Decrease stiffness
• C. Stiffen the column
• D. Do nothing

Answer: (C)

Horizontal restraints provide lateral support to the column, which cuts down its tendency to bow under axial load. That lateral support raises the column’s resistance to buckling, effectively increasing its stiffness. In Euler buckling terms, the critical load grows when the column is laterally restrained because the system behaves as if it has a shorter unsupported length or reduced effective length, so it can carry more load before buckling. So the column behaves stiffer after adding these restraints. This isn’t about increasing bending stress; it’s about reducing lateral deflection and increasing the load the column can carry before instability occurs. It certainly isn’t doing nothing.