Learn : Limit state concept,Limit State of Collapse,Limit State of Serviceability Limit state is the acceptable limit of safety,serviceability requ.before failure.
Limit state concept
The aim of this method is that the structure should be able to withstand safely all the load that are liable to act on it throughout its life and it should also satisfy the serviceability requirements of limiting deflection and cracking. Limit state is defined as the acceptable limit of safety and serviceability requirements before failure. The most important limit states which are considered in design as are follows:
(i) Limit state of collapse.
(ii) Limit state of serviceability
Limit State of Collapse
This limit state is also called as strength limit state as it corresponds to the maximum load carrying capacity i.e., the safety requirements of the structure. The limit state of collapse is assessed from collapse of the whole or part of the structure. As per this limit state, the resistance to bending, shear, torsion and axial loads at every section shall not be less than that produced by the most unfavorable combination of loads on that structure. The following limit states of collapse are considered in design:
(i) Limit state of collapse in flexure (bending)
(ii) Limit state of collapse in compression
(iii) Limit state of collapse in shear
(iv) Limit state of collapse in torsion.
Limit State of Serviceability
A structure is of no use if it is not serviceable. Thus, this limit state is introduced to prevent excessive deflection and cracking. It ensure the satisfactory performance of the structure at working loads. It is estimated on the basis of elastic theory or working stress method because deformation is of significance under working load and not at collapse. Limit state of serviceability of following limit states:
(i) Limit state of deflection
(ii) Limit state of cracking
(iii) Limit state of vibration
The structure should be designed which considering all the appropriate limit state of safety and serviceability and on the basis of most critical limit state and then checked for all other limit states.