Non linear Lateral soil Spring

[stan123lee]

I have a probolem in modelling the lateral soil spring.

To cater the yielding of soil (An upper bound of spring capacity), i believe i have to model the lateral soil spring with two bi-linear curves, is there any way i can make it in etabs?

Maany Thanks.

 

[ge0san]

You stated that you need a bilinear behavior of the soil. I believe that this can be achieved using two very close springs instead of one. On the first domain, the sum of springs should give the first linear behavior and on the second domain (after the first spring fails) only the second would react.
I never tried this, but by the principle of superposition of actions (therefore reactions) and starting from the hypothesis that the behavior has two linear domains, I find is reasonable to make the above assumption. If you get acceptable results, please let me know about this.

 

[stan123lee]

Thanks for ge0san reply first.

May I know what the commands for the following steps

(i) how to define a spring with an upper limit of capacity?

(ii)when the first spring fail, and further the 2nd springs will become active?

I am a new user for ETABS. I may be not fully know every single command in ETABS.

Please advise

Thanks.

 

[ge0san]

stan123lee,
I don't know how to define the upper limit of spring capacity either. For that, it would be needed a limit for displacement, upto which the law of variation applies and I don't know where can that be input (or if).
But, I thought of another way. It is not sophisticated, instead it may take some aditional time to model and analyze: use nonlinear hinge. This is what I thought of:
- define supports, like columns, with a separate material and input there elasticity modulus and strength of soil. Put dimension of supports such as to cover the full supported area
- go to define > frame nonlinear hinge properties and define a nonlinear hinge for AxialP (instead of using the default generated by ETABS, you can Modify/show for P the bilinear variation there)
- assign > frame line > frame nonlinear hinges > TheHinge to the supports (the columns defined as supports)
- define > static nonlinear/pushover case and add a case using your loads and afferent coefficients. Monitor on UZ a relevant point (like the location of a support)
- run the elastic analysis, then the static nonlinear analysis and Display > show static pushover curve for a graphically display of the effect of increasing load on the nonlinear behaving soil.

I advise to ask for a second opinion on this procedure. I have never verified its validity, but I hope it is useful for you. Please let me know if this works.