Allowable stress in axial compression in reinforced concrete

The allowable stress in axial compression in reinforced concrete is an important factor to consider in the design process. It is the maximum stress that a concrete member can withstand without experiencing failure. The allowable stress depends on several factors, including the grade of concrete and the reinforcement used.

Factors affecting allowable stress in axial compression

1. Grade of concrete

The grade of concrete used in the construction of a member affects the allowable stress in axial compression. The higher the grade of concrete, the higher the allowable stress. The allowable stress is usually expressed as a fraction of the characteristic compressive strength of the concrete (fck).

2. Reinforcement

The amount of reinforcement used in a concrete member also affects the allowable stress in axial compression. The greater the amount of reinforcement, the higher the allowable stress.

Approximate allowable stress

The approximate allowable stress in axial compression in reinforced concrete is given by the following formula:

fcd = 0.25fck / γc

where fcd is the design compressive strength of concrete, fck is the characteristic compressive strength of concrete, and γc is the partial safety factor for concrete. The value of γc is usually taken as 1.5.

Using the formula, the approximate allowable stress in axial compression for different grades of concrete can be calculated as follows:

1. For M15 grade concrete, the approximate allowable stress is 0.25 x 15 / 1.5 = 2.5 N/mm2
2. For M20 grade concrete, the approximate allowable stress is 0.25 x 20 / 1.5 = 3.33 N/mm2
3. For M25 grade concrete, the approximate allowable stress is 0.25 x 25 / 1.5 = 4.17 N/mm2
4. For M30 grade concrete, the approximate allowable stress is 0.25 x 30 / 1.5 = 5 N/mm2

Conclusion

The allowable stress in axial compression in reinforced concrete depends on the grade of concrete and the amount of reinforcement used. The approximate allowable stress can be calculated using the formula fcd = 0.25fck / γc, where fck is the characteristic compressive strength of concrete and γc is the partial safety factor for concrete.

0.44fck