Analysis According to the Theory of Limit States (LSD)
The verification methodology based on the theory of "Limit states" proves the safety by comparing a resisting variable (resisting force, strength, bearing capacity) and a variable causing failure (sliding force, stress).
where: | Xpas | - | A variable resisting the failure (resisting force, strength, capacity) |
Xact | - | A variable causing the failure (sliding force, stress) |
Xact is in general determined from the design parameters of soils and load:
- soil parameters are reduced by corresponding coefficients
- load (its action) is increased by corresponding coefficients
Xpas is determined based on the following assumptions:
- soil parameters are reduced by corresponding coefficients
- the calculated structure resistance is reduced by a corresponding coefficient
In general, it can be stated that the verification based on "Limit states" is more modern and apt approach in comparing to the "Safety factor". However, it is less lucid.
Modern standars used for verification of structure safety (EN 1997, LRFD) arise from the concept of limit states. In addition, they introduce various values for the coefficients of partial factors for favorably and unfavorably acting loads.
Detailed description for individual programs and types of structures can be found in the following chapters (Walls and retaining structures, Slope Stability, Spread Footing, Pile, Rock Stability, Micropile, Pile CPT, Pile Group).