comparison of soil load and equivalent beam load

Question:

hi!
with reference to the horizontal beam element in the attached 2D model, we are trying to compare between 2 analysis cases:
results forces from a case analysis of soil load, and results forces for equivalent beam load (you can see the way of calculation by the attached file). 
the results are very differ (for example the bending moment in the middle of the beam is 4 times greater for the second case).

the model is built according to the suggestion of Midas support:
- plane strain model for 1 m
- soil load with no reference to constructive element dimension.
- equivalent beam load that reference to the dimension of our element.

other numerical calculations with GEN software and also schematic manual calculation are closer to the soil load analysis case rather then to the equivalent beam load analysis case.

we will be glad for your assistance to understand these differences and the correct way of modelling.
thank in advanced,
David.


Answer:

Hi Sir,

Apologies for not responding to you via globalsupport.midasuser.com. I was in business trips, so couldn't able to reply. But I was discussing about this issue with Mr. David via Skype.

There will always be a difference between the results obtained from soil load and equivalent beam load. This is due to the elastic modulus that we define for the soil. I made a trail model  which is as follows,

  


 Direct Soil Load:
 In this case soil is modeled instead of equivalent beam load. The results of the bending moment are as follows,



Equivalent Beam Load:
In this model soil is not modeled and equivalent beam is calculated and applied on the beam. The results of the bending moment are as follows,

So the results are almost two times in the "Equivalent Beam Load" when compared with "Direct Soil Load". This is Due to the Elastic modulus defined by us. Because of the elastic modulus the soil is able to resists some amount of load by itself. So I made a third model in which soil is modeled but the elastic modulus is kept as 1 kN/m2 so that the internal load resistance of the soil is almost neglected. Then the results of bending moment are as follows,


So we can observe that the results of second model ("Equivalent Beam Load model") and third model ("Direct Soil Load with E=1kN/m2") are matching.

Hence we need choose among three types of models while proceeding for the real project. But to be on conservative side most of engineers go for "equivalent beam load" type of modelling.

Regards,
Harsha

Creation date: 7/22/2021 11:21 AM (Harsha)      Updated: 7/22/2021 11:23 AM (Harsha)
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2D AM250 Frame_SOIL@266 ver05.gts
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DataImage32.png
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menual load calculation.PNG
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