Limit State

(redirected from Limit state design)
Also found in: Wikipedia.

limit state

[′lim·ət ‚stāt]
(civil engineering)
The condition beyond which a structure or a structural member is deemed unsafe due to one or more loads or load effects.

Limit State

in civil engineering, the point at which a structure or a foundation no longer meets the service requirements. The concept of limit state is employed in the design method that was developed in the USSR and introduced into the Construction Code in 1955. Compared to the methods previously used, with respect to working stresses and breaking loads, the limit state design is more accurate. It offers a complete evaluation of the bearing capacity and reliability of structures through consideration of the probability characteristics of the loads acting on the structures and the resistances to these loads. It also evaluates the specific performance of various types of structures and the plastic properties of the materials used.

Instead of the single safety factor used heretofore, several independent factors are used in the limit state design, each of which plays a particular role to ensure the reliability of the structure and the guarantee against the occurrence of a limit state. These factors include the safety factor for a material and the soil, which takes into account the statistical variability of the strength properties for materials and the soil. It also takes into account certain other factors for which statistical evaluation is either ruled out or is very difficult, such as the difference between the strength of a material in a structure and that determined by sample tests.

The load factor takes into account the possible deviation of the actual loads from the design (standard) values owing to the variability of loading and departures from normal service conditions. The factor for the operating conditions accounts for those aspects of the actual performance of the structural elements, the foundations, and the buildings and structures as a whole that are not directly built into the calculations. There is also a reliability factor that takes acount of the endurance limit of a structure and the comparative importance of the limit state of various parts of the structure.

A distinction is made between the limit state at which a structure becomes unfit for normal service and that at which it completely loses its bearing capacity. For normal service, a structure usually requires adequate rigidity, limited settling, and a certain degree of crack resistance. The loss of bearing capability may become evident in a change in the structural configuration or in the form of brittle, ductile, and fatigue failure of the material. The basic objective of the limit state design is to prevent such failure throughout the serviceable life of a building or structure.

Limit state design has been used extensively in the USSR and in member countries of the Council for Mutual Economic Assistance, the European Organization on Standardization, and the European Committee for Concrete. In the USSR, the limit state is calculated in the design of such mechanical-engineering structures as the metal framework of bridge cranes, overhead cranes, and tower cranes.

REFERENCES

Stroitel’nye normy i pravila, part 2, section A, ch. 10. Stroitel’nye kon struktsii i osnovaniia. Osnovnye polozheniia proektirovaniia. Moscow, 1972.
Baldin, V. A. (et al.). “K vykhodu SNiP II-A. 10–71.” Stroitel’naia mekhanika i raschet sooruzhenii, no. 4, 1972.

A. A. BAT’ and V. A. OTSTAVNOV

limit state

A condition beyond which a structure is unfit to perform its intended function.
References in periodicals archive ?
Ng, "Probabilistic limiting tolerable displacements for serviceability limit state design of foundations," Geotechnique, vol.
The load and resistance of a pipeline may be defined considering limit state design (LSD) or load- and resistance-factored design (LRFD) (Figure 2).
The estimations can be subsequently used to predict failure pressures and life times in the context of limit state design guidelines.
The main aim of this paper is to compare objectively the limit state design results based on the partial safety factors design (PSFD) and the load and resistance factors design (LRFD) suggested in Europe and the USA, respectively, using the load combinations recommended by EN 1990 and ASCE/SEI 7-05.
According to both limit state design methods, the analysed columns are suitable in service.
continues in the tradition of keeping ahead of new techniques and theories by being the first to cover the fundamental changes in the ethos of geotechnical design in Eurocode 7, which will be fully adopted across Europe by 2010, with the effect being a radical shift to limit state design.
This approach also enables us to develop "deterministically looking" design codes that deliver design outcomes with approximately consistent [beta] (Lo et al 1992, 1994), ie having RBD as the theoretical basis for deriving partial factors of limit state design codes.