it is a method of design in rcc structures, in which stresses of materials is calculated by using working load and compared with allowable stress by considering a linear stress strain relation ship.
1-(k/3)
The methods depend based on the type of structures. for eg. for water Retaining structures the Working stress method gives good life and for other structures which is not exposed to water, mostly limit state design works.
limit state method
i think , because water tanks are more vulnerable structures and plus the tank is sometime overfilled and sometime empty, the pressure inside is so varying, its needs more safety precautions and as we all know working stress method assumes more safety factor than limit state design, which is an economical design, we prefer to use working stress method...
factor of safety
This is the method in which the structure is analyzed by elastic theory i.e. theory of simple bending in which materials obey the Hook's law.
working stress: in this a structure is designed by considering the stresses in its working condition..Limit state: In this the structure is designed by considering the stresses at different limit states. there are two limit states. ultimate limit state (situation in which structure collapse) and servicability limit state (situation in which cracks etc appears.)
for concrete a F.O.S. upto 3 is used . and for steel 1.75 to 1.85 .. is used.
Working stress method of design based on the elastic theory in which materials, concrete and steel are assumed to be stressed well below their elastic limit under the design loads. Working stressess (permissible stress) for the materials are determined by dividing the ultimate or yield stressess by suitable factor of safety values. Limit state method of design based on limit state concept, te structure shall be designed to withstand safely all loads liable to act on it throughout its life;It shall also satisfy the serviceability requirements, such as limitations on deflection and cracking. The acceptable limit for the safety and serviceability requirements before failure occurs is called a "limit state". The aim of design is to achieve acceptable probabilities that the structure will not become unfit for the use for which is intended, that is that it will not reach a limit state...
line stress controllers in new Austrian tunnelling method
allowable stress design-2/3rd of yield working stress design is process yield
In ultimate load method, the working loads are increased by suitable factors to obtain ultimate loads. These factors are called load factors. The structure is then designed to resist the desired ultimate loads. This structure is then designed to resist the desired ultimate loads. This method takes into account the non-linear stress-strain behavior of concrete. The term safety factor has been used in the working stress method to denote the ratio between the yield stress and the permissible stress. It had little meaning as far as the ratio between collapse loads and working load was concerned. The team load factor has been traditionally used to denote the ratio between the collapse or ultimate load to the working load. The knowledge of load factor is more important than the knowledge of factor of safety. Several ultimate load theories have been proposed in the past. In each of these theories and idealized stress-strain curve has been adopted for concrete which is the only difference among them. This theory is based on the assumption that ultimate strain in concrete is 0.3% and the compressive stress at the extreme edge of the section corresponds to this strain. Whitney replaced the actual parabolic stress diagram by a rectangular stress diagram such that the centre of gravity of both diagrams lies lat the same point and their areas are also equal.