Limit State Theory

The limit state theory is a design philosophy used in structural engineering to ensure the safety and serviceability of structures. It involves determining the maximum loads or actions that a structure can safely withstand without experiencing failure or excessive deformation.

In the context of concrete structures under axial compression, the limit state theory considers the ultimate limit state and the serviceability limit state.

Ultimate Limit State

The ultimate limit state refers to the condition where the structure is on the verge of failure. In the case of concrete under axial compression, this would correspond to the concrete reaching its maximum compressive strain.

Maximum Compressive Strain in Concrete

The maximum compressive strain in concrete is a parameter that determines the behavior of the material under compression. It is an important consideration in the design of concrete structures, as excessive strains can lead to structural failure.

According to IS 456, which is the Indian Standard Code of Practice for Plain and Reinforced Concrete, the maximum compressive strain in concrete in axial compression is taken as 0.002.

Reasoning behind the Answer

The choice of 0.002 as the maximum compressive strain in concrete is based on empirical studies and experimental data. It represents a conservative estimate to ensure the safety and serviceability of concrete structures.

The value of 0.002 is considered appropriate because it allows for a certain amount of deformation in the concrete before reaching failure. It takes into account factors such as material variability, workmanship, and loadings.

By limiting the maximum compressive strain to 0.002, designers can ensure that the concrete will not undergo excessive deformation or failure under normal operating conditions.

Conclusion

In summary, the maximum compressive strain in concrete in axial compression is taken as 0.002 according to the limit state theory and IS 456. This value ensures the safety and serviceability of concrete structures by limiting the deformation of the material under compression.