Permissible Bond Stress for Deformed Bars in Tension as per IS 456: 2000

Permissible bond stress for deformed bars in tension is defined as the maximum stress that can be applied to the surface of the reinforcement without causing slip between the reinforcement and surrounding concrete.

Formula for Permissible Bond Stress for Deformed Bars in Tension

As per IS 456: 2000, the formula for permissible bond stress for deformed bars in tension is given as:

𝜏_bd = (0.87fy)/(1.5√fck)

where,

𝜏_bd = permissible bond stress for deformed bars in tension (in N/mm^2)
fy = characteristic strength of deformed reinforcement bars (in N/mm^2)
fck = characteristic compressive strength of concrete (in N/mm^2)

Comparison with Permissible Bond Stress for Plain Bars in Tension

The permissible bond stress for plain bars in tension is 0.9 N/mm^2, which is much lower than the permissible bond stress for deformed bars in tension as per IS 456: 2000.

Reason for Higher Permissible Bond Stress for Deformed Bars in Tension

Deformed bars have a higher surface area than plain bars, which results in better adhesion between the reinforcement and surrounding concrete. This leads to a higher permissible bond stress for deformed bars in tension as compared to plain bars.

Benefits of Higher Permissible Bond Stress for Deformed Bars in Tension

The higher permissible bond stress for deformed bars in tension results in better utilization of the strength of reinforcement bars, which leads to more economical design of reinforced concrete structures. Additionally, it ensures that the reinforcement bars do not slip under the applied loads, which results in more reliable and safer structures.

Conclusion

As per IS 456: 2000, the permissible bond stress for deformed bars in tension is given by the formula 𝜏_bd = (0.87fy)/(1.5√fck). The higher permissible bond stress for deformed bars in tension is due to their higher surface area, which results in better adhesion between the reinforcement and surrounding concrete. This leads to more economical and reliable design of reinforced concrete structures.

For deformed bar having grips on it permissible bond is increased by 60% -
= 0.9*1.6 = 1.44N/mm^2