Differential soil settlement

[Juhiimi]

Hello,


Our design software recently introduced the option to define soil parameters at the foundation level. As a result, the entire building now experiences additional stresses, especially in concrete beams and slabs — and the effect is quite significant.


Should we consider this additional stress in the superstructure, or is it sufficient to account for it only in the substructure?
Also, if we do take it into account, should we apply the standard safety factors for loads, or is it acceptable to use reduced values in this case?

 

[HTURKAK]

the option to define soil parameters at the foundation level. As a result, the entire building now experiences additional stresses, especially in concrete beams and slabs

Lets make clear in this context , I imagine you provide WINKLER spring constants and the software calculates the settlement and differential settlement as per the load experienced by the footing.
The settlement calculation ( say predicition) is not so simple.

Your internet country code implies that the Eurocodes are applicable. The differential settlements should be considered for the design of foundation and superstructure.
Pls look Basis of structural design EN 1990 for detail and combinations.

 

[Cleilson Bernardino]

Greetings!
It is likely that your design software has introduced soil-structure interaction through winkler springs or similar. However, it is important to interpret these additional stresses with caution.

If the beams and slabs showing significant additional stresses are those located at the ground level, in direct contact with the soil, this may be a consequence of an unrealistic modeling effect — something like a parachute effect. In this situation, the slab-beam system is artificially restraining the settlement of the columns supported by the foundations. In practice, this restraint is unlikely to occur because during construction, the soil layer beneath these slabs and beams will naturally be mobilized by construction teamwork. There will be a natural accommodation and the rigid restraint implied by the model will not materialize. Therefore, the significant additional stresses predicted in the superstructure due to this soil interaction may not be realistic. Moreover, this modeling approach will also tend to underestimate the reactions transferred from the columns to the foundations.

For this reason, I would generally recommend not modeling a direct connection (i.e., springs) between ground-level beams and slabs with the soil, unless this is explicitly desired and you are ensuring that the soil layer below the slab is properly compacted and prepared to act as a structural support element.