Working stress method of design of reinforced concrete structures is also known as

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UKPSC JE Civil 8 May 2022 Official Paper-I

Answer 1

The working stress or elastic method, assumes that the material (both steel and concrete) remains elastic i.e., obeys Hooke's Law until failure. Essentially, it's a method where the concrete structure is designed considering a certain allowable or working stress level that does not exceed the elastic limit of the material.
The modular ratio method term comes from the fact that it uses a "modular ratio," which is the ratio of modulus of elasticity of steel to that of concrete. This method, therefore, involves the transformation of a cross section to an equivalent cross section consisting of one material (either steel or concrete). This transformation uses the modular ratio (denoted often as m or n) to convert areas of one material into equivalent areas of another.
Yield stress method, is more closely aligned with Limit State Design methods which allow for plastic or non-linear behavior beyond the yield stress. Instead of the concrete structure being designed so that the stresses should never exceed the elastic limit, it is instead designed with knowledge that limited non-linear or plastic behavior can be accepted in some circumstances.