Question

Which of the following statements best explains why shear reinforcement (stirrups) is provided in reinforced concrete beams?

• A. To resist bending moment
• B. To increase the ductility of the beam
• C. To resist diagonal tensile stresses caused by shear
• D. To reduce deflection under service loads

Hint:

Stirrups in beams prevent brittle shear failure and enhance the ductility and safety of the structure.

Answer 1

The Correct Option is C

Step 1: Understand the function of shear reinforcement
In reinforced concrete beams, shear reinforcement (usually vertical or inclined stirrups) is not meant to carry bending loads.
Step 2: Recognize the failure mode in shear
Shear cracks develop at an angle due to diagonal tensile stresses, especially near the supports where shear is maximum.
Step 3: Role of stirrups
Stirrups help in resisting these diagonal tensile stresses and prevent shear failure, which is often sudden and brittle in nature.
Step 4: Evaluate the options
(1) Resisting bending moment is the job of longitudinal reinforcement — Incorrect
(2) Ductility is enhanced by other reinforcement detailing — Incorrect
(3) Correct purpose of shear reinforcement — Correct
(4) Deflection control relates more to flexural stiffness — Incorrect
Step 5: Conclusion
Hence, shear reinforcement is provided to resist diagonal tensile stresses caused by shear.