Deep Beams MCQ with answer and solution

Concept

Internal Behaviour of Deep Beams

Formula

N/A

Step-by-step solution

1. Review the given question about the internal behaviour of a Deep Beam according to IS 456:2000. 2. Recall that deep beams carry loads through an internal "arch and tie" mechanism, keeping the lever arm nearly constant. 3. Compare with the given options and select Option (c) as the correct choice.

Explanation

In a deep beam, the internal load is carried directly from the loading point to the supports through diagonal concrete compression struts and a main tension tie (an "arch and tie" action). Because of this arching behavior, the lever arm between the compression and tension zones stays nearly constant throughout the span instead of varying like in ordinary shallow beams.

Shortcut

To remember Deep Beam behavior, use the memory rule "Deep Beam = Arch & Tie": - Arch & Tie Action: Deep beams act as an internal tied arch, transferring loads directly to supports through diagonal concrete struts and main tension steel. - Constant Lever Arm: Due to this arching action, the internal lever arm stays nearly constant. - Non-Linear Strain: Unlike shallow beams, plane sections do NOT remain plane due to significant shear deformation.

Common mistake

A common mistake is selecting Option A or Option B by incorrectly applying standard shallow beam theory (Bernoulli's hypothesis) to deep beams, assuming that plane sections remain plane and strain distribution is linear. In reality, deep beams experience significant shear deformation, causing non-linear strain and stress distribution. Another frequent mistake is choosing Option D under the false assumption that deep beams do not require shear reinforcement, whereas IS 456:2000 explicitly specifies nominal web reinforcement to control cracking and carry shear forces.