What is the difference between EN-ULS (STR/GEO) Set B and Set C combinations?
The user can choose between two sets of EN-ULS combinations Set B and Set C (figure 1).
Figure 1: EN-ULS Set B and Set C combinations.
- Set B should be used for the design of structural members where geotechnical actions are NOT involved.
Depending on the chosen approach, Set B may also have to be used for the design of structural members involving geotechnical actions and the resistance of the ground.
In versions before SCIA Engineer 2010.0, only Set B is implemented.
- Set C only has to be used for the design of structural members (footings, piles, basement walls, etc.) involving geotechnical actions and the resistance of the ground, depending on the chosen approach.
Starting from SCIA Engineer 2010.0, Set C has been added to the Combination Types, because of the new module Pad foundations.
For more detailed information, reference is made to some articles from “EN 1990 - Basis of structural design”.
EN 1990 - §6.4.1:
The following ultimate limit states shall be verified:
EQU: Loss of static equilibrium of the structure or any part of it considered as a rigid body, where:
- minor variations in the value or the spatial distribution of actions from a single source are significant, and
- the strengths of construction materials or ground are generally not governing.
- STR: Internal failure or excessive deformation of the structure or structural members, including footings, piles, basement walls, etc., where the strength of construction materials of the structure governs.
- GEO: Failure or excessive deformation of the ground where the strengths of soil or rock are significant in providing resistance.
- FAT: Fatigue failure of the structure or structural members.
The design values of actions have to be in accordance with EN 1990 - Annex A.
EN 1990 - §A1.3.1:
- Design of structural members (STR) not involving geotechnical actions should be verified using the design values of actions from Table A1.2(B) - Design values of actions (STR/GEO) (Set B).
- Design of structural members (footings, piles, basement walls, etc.) (STR) involving geotechnical actions and the resistance of the ground (GEO) should be verified using one of the three approaches supplemented by EN 1997, for geotechnical actions and resistances. The use of approaches 1, 2 or 3 is chosen in the National Annex, and defines if Set B and/or Set C have to be used for the design.