Dear Researchers,
The modulus of subgrade reaction is widely used in the Winkler beam method on an elastic foundation. The most reliable estimation is given by Bowles [1996] as it takes into account the dimensions of the foundation as 40*qu (for around 2.5cm). This subgrade modulus value is it the same for static and seismic conditions?
As far as I understand, since qu is the ultimate bearing capacity, the subgrade value is equal in both states (static and seismic).
What are your views regarding these?
Seismic loading requires consideration of small-strain behavior and degradation of soil stiffness, hence an approach allowing for updating of Winkler spring stiffness based on ground deformation is more appropriate. A constant value such as 40qu is not good enough for static analysis either. The assumed soil deformation of 2.5cm will be different based on your ground profile and geotechnical parameters. Winkler spring averages the behavior of the whole ground profile you have underneath your foundation hence provides a very crude analysis for the ground behavior.
Totally agreed with @Eris Uygar view.
Modulus of subgrade reaction also increases with depth. If you are using Winkler spring model you can use variable springs using shear beam model.
The elastic media of the soil is represented by a mechanical model, a mathematical model, and a numerical model. The Winkler model is a mechanical model that uses a system of multiple independent linear springs to model the soil. Nevertheless, the Winkler limitations are as follows:
1-the springs are not connected, lack of continuity between the springs, therefore we get no deformation beyond the loading regions.
2- The spring are considered as linear, but the bearing soils is not linear
3- the equal amount of settlement.
It will be better to use non-linear models: Chandra (1979), Boussineq (1985), or an Orthotropic Elastic continuum model (Vlazov model).
Thank you all for your replies. I was wondering the coeffiecients mentioned by this author, "Estimation of the vertical subgrade reaction modulus ks from CPT for shallow foundations on cohesionless soils" N. Barouni 2017.
"Then, by applying numerous dynamic modification factors to the static spring stiffness (ASCE, 41-13 or Gazetas, 1991), the dynamic spring stiffness can be evaluated. Dynamic modification factors are applied to account for the frequency of the excitation force, the embedment of the foundation and the foundation shape"
Thanks.
Spring constants for dynamic analysis can be obtained from low strain shear modulus.
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