Design of Columns MCQ with answer and solution

Concept

Load transfer between concrete members of different casting stages using dowel bars to prevent bearing failure.

Step-by-step solution

1. Understand that columns are usually cast after the footing concrete has set. 2. To ensure proper load transfer of axial forces from the column longitudinal reinforcement to the footing without exceeding the permissible bearing stress of concrete, dowel bars are embedded into the footing and extend into the column. 3. This prevents bearing failure at the interface of the column and footing.

Explanation

Dowel bars are short lengths of steel bars provided at the base of columns to transfer loads (specifically compressive forces and moments) from the column down into the footing safely, preventing bearing failure at the column-footing interface.

Why the other options are wrong

A: Punching failure in footings is resisted by adequate footing thickness and two-way shear reinforcement. B: One-way shear failure is resisted by the concrete shear strength and transverse shear reinforcement in beams/slabs. C: Flexural failure is resisted by main longitudinal reinforcement.

Shortcut

Remember: Dowel bars = Bearing failure prevention at joints.

Common mistake

Confusing dowel bars in columns with dowel bars in pavement slabs (which are for load transfer across joints) or mistaking them for shear reinforcement against punching shear (which is usually provided as stirrups or shear heads).