Shear Stress Distribution in Reinforced Concrete Section

When a reinforced concrete section is subjected to shear forces, the distribution of shear stress is not uniform. The shape of the shear stress diagram depends on the shape of the section, the amount and arrangement of reinforcement, and the magnitude and distribution of the shear force.

Parabolic above Neutral Axis

Above the neutral axis, the shear stress distribution is parabolic. This means that the shear stress is maximum at the top of the section and decreases towards the neutral axis.

This is because the concrete is assumed to be a homogeneous material and hence the shear stress distribution is similar to that of a beam made of a homogeneous material like steel or timber.

Rectangular below Neutral Axis

Below the neutral axis, the shear stress distribution is rectangular. This means that the shear stress is constant and equal to the average shear stress over the depth of the section.

This is because the concrete in the compression zone is cracked due to the combined action of shear and bending. The cracks are assumed to be vertical and hence the shear stress is assumed to be constant and equal to the average shear stress over the depth of the compression zone.

Combined Shear Stress Distribution

The overall shear stress distribution is a combination of the parabolic distribution above the neutral axis and the rectangular distribution below the neutral axis.

The shear stress is maximum at the top of the section and decreases towards the neutral axis. Below the neutral axis, the shear stress is constant and equal to the average shear stress over the depth of the compression zone.

Conclusion

In a reinforced concrete section, the shape of the shear stress diagram is parabolic above the neutral axis and rectangular below the neutral axis. This distribution of shear stress is due to the combined action of shear and bending in the section. The shear stress is maximum at the top of the section and decreases towards the neutral axis. Below the neutral axis, the shear stress is constant and equal to the average shear stress over the depth of the compression zone.