How is the design shear strength of concrete (c ) influenced by the percentage (p_t ) of tensile reinforcement in a beam?

Explanation:

In reinforced concrete design, the design shear strength of concrete increases with the percentage of tensile reinforcement (pt). Here's the reasoning behind it:

1. Tensile Reinforcement in Shear Resistance:

   • The primary function of tensile reinforcement in a beam is to resist bending, but it also helps in resisting shear forces.

   • When tensile reinforcement increases, it helps to improve the overall shear strength of the beam because it contributes to the beam's ability to resist shear stresses, particularly in preventing diagonal tension cracks.

2. Concrete and Reinforcement Interaction:

   • Concrete alone has limited shear strength, but with increased tensile reinforcement (especially in cases of high shear demand), the interaction between the concrete and reinforcement improves.

   • This interaction helps in better resisting shear forces, thus increasing the overall shear strength of the beam.

3. Increasing Tensile Reinforcement:

   • When the tensile reinforcement percentage increases, it provides more resistance to the formation of shear cracks and helps in carrying more shear force.

   • This results in a direct increase in the shear strength of the concrete beam.

Thus, the shear strength of concrete increases with an increase in the percentage of tensile reinforcement, and this is why the correct answer is 3.

 Additional Information

• The percentage of tensile reinforcement should not be excessive, as other factors such as ductility and the potential for early cracking come into play. But up to a certain limit, increasing the reinforcement enhances the beam’s shear strength.