Basic differences among working stress and limit state method

WORKING STRESS METHOD: It's a conventional method that is effective for reinforced concrete design where concrete is supposed to be elastic. Steel and concrete function together elastically where the connection among loads and stresses is linear.

Limit state design (LSD) alias load and resistance factor design (LRFD), stands for a design method that is employed in structural engineering. A limit state is a condition of a structure across which it no more meets the applicable design criteria.

Given below, the points of differences among working stress method and limit state method.

This method is created on the basis of the elastic theory that suspects that concrete and steel are elastic and the stress strain curve is linear for both.
This method is developed on the basis of the actual stress-strain curves of steel and concrete. For concrete, the stress strain curve is nonlinear.

In this method the factor of safety are employed to the yield stresses to obtain permissible stresses.
In this method, Partial safety factors are employed to obtain the design values of stresses.

No factor of safety is applied for loads.
Design loads are obtained by multiplying partial safety factors of load to the working loads.

Proper margin of safety is unidentified.
Proper margin of safety is recognized.

This method provides deeper sections, so it is not cost-effective.
This method is cost-effective because it provides thinner sections.

This method supposes that the actual loads, allowable stresses and factors of safety are recognized. So it is known as deterministic method.
This method is developed on the basis of the probabilistic approach which depends upon the actual data or experience, hence it is known as non-deterministic method.