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Active Contributor
kope
Posts: 49
Registered: ‎10-27-2010

Hx (Rx) Elastic Ground Reaction

297 Views, 15 Replies
03-03-2014 06:10 AM

Hi there. How can I check the Hx (Rx) Elastic Ground Reactions for a bar on elastic ground? (I found out the Ky and Kz in the diagrams for bars dialog but there's no Hx)

thanks. 

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Product Support
Rafal.Gaweda
Posts: 5,189
Registered: ‎04-26-2010

Re: Hx (Rx) Elastic Ground Reaction

03-03-2014 06:19 AM in reply to: kope
I am afraid it is not possible.
Option is registered for implementation.


Rafal Gaweda
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Active Contributor
kope
Posts: 49
Registered: ‎10-27-2010

Re: Hx (Rx) Elastic Ground Reaction

03-03-2014 06:50 AM in reply to: Rafal.Gaweda

Once the bar on elastic ground is transfered to the continous footing module, it seems that the calculations are done using only the Kz (vertical) related forces, is that correct? In this case, i cat set to none the Hx rotation on bar on the elastic ground dialog and use a regular linear suport with the same elastic stiffness. I think I'll get tjhe same results, right?

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Active Contributor
kope
Posts: 49
Registered: ‎10-27-2010

Re: Hx (Rx) Elastic Ground Reaction

03-03-2014 07:12 AM in reply to: kope
seems that cannot be done if the bar elastic ground extends beyond the supported wall. The linear support may be applied only to the panel's edge...
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Product Support
Rafal.Gaweda
Posts: 5,189
Registered: ‎04-26-2010

Re: Hx (Rx) Elastic Ground Reaction

03-03-2014 08:12 AM in reply to: kope

kope wrote:

Once the bar on elastic ground is transfered to the continous footing module, it seems that the calculations are done using only the Kz (vertical) related forces, is that correct? In this case, i cat set to none the Hx rotation on bar on the elastic ground dialog and use a regular linear suport with the same elastic stiffness. I think I'll get tjhe same results, right?

RC contitnus footing design moduel calculates element on imported internal forces so depending on elasticity defined in FEM model these forces may vary.
Then design is made basing on imported vertical forces and soil layer defined by user in footing module.

 



Rafal Gaweda
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Active Contributor
kope
Posts: 49
Registered: ‎10-27-2010

Re: Hx (Rx) Elastic Ground Reaction

03-04-2014 09:50 AM in reply to: Rafal.Gaweda

Right. The internal forces should be compatible with the various boundary condiitions set for the FEM model. Then the beam
design is conducted as for any other beam, irrespective of its type (continuous footing or RC beam)

But, I was reffering to the soil pressure diagram for the continuous footing - my understanding is that only vertical forces are considered,
meaning no eccentricity along Y-direction and no out-of-plane bending (such as that imposed by some supported wall) are included.

(the pressure diagram looks uniform along y direction - i.e. transversally - no matter the rotation around its own centerline
due to any side loading).

Is this correct?

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Distinguished Contributor
Tuctas
Posts: 183
Registered: ‎10-10-2012

Re: Hx (Rx) Elastic Ground Reaction

03-04-2014 12:55 PM in reply to: kope
That's true Kope, unfortunately the diagram of soil pressure under the foot is always uniform... :-(
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Active Contributor
kope
Posts: 49
Registered: ‎10-27-2010

Re: Hx (Rx) Elastic Ground Reaction

03-05-2014 08:01 AM in reply to: kope

The deflections calculated by the continuous footing module shouldn't be compatible with those provided by the FEM model assuming both are using the same KZ stiffness?

 

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Distinguished Contributor
Tuctas
Posts: 183
Registered: ‎10-10-2012

Re: Hx (Rx) Elastic Ground Reaction

03-05-2014 01:04 PM in reply to: kope

 I suppose they are the same...

 I was talking about the fact that Robot doesn't take into account column’s base moments about longitudinal axis of the footing and ignores torsional/rotation interactions between footing and soil (that would result in non-uniform soil stress distribution in the direction perpendicular to the axis of continuous footing) in the Continuous Footing Design module. If you are interested, take a look at an older post of mine: 

http://forums.autodesk.com/t5/Robot-Structural-Analysis/Spread-footing-vs-Continuous-footing/m-p/394...

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Active Contributor
kope
Posts: 49
Registered: ‎10-27-2010

Re: Hx (Rx) Elastic Ground Reaction

03-06-2014 01:04 AM in reply to: Tuctas

yes Tuctas, I was refering to the same issue - that the program disregards pressure modification due to Hx rotations.

 

The deflection is another story :-) Meanwhile I found out some other things that i don't understand. Let me summarize

all of them for other readers convenience; they are related more ore less to the elastic ground beam

 

  1. The Hx rotations are disregarded when calculating the soil pressure
  2. The deflection calculated by the module is not the same with the FEM model (see the attachement) 
  3. Mx diagram is null in case you're assigning any value to the Hx stiffness (see attachement)
  4. The question mark appearing nearby the element name within the RC Component inspector remains intact even if you're using the RC element update (such as for instance after adjusting the loading and running the analysis again). You have to add again the member in order to get rid of the question mark.

 

The displacement calculated by the FEM model - 2cm

 

 

Deflection - FEM Model

 

The deflection calculated by the RC module -  6cm

Deflection - RC Module

 

 

 

Null Mx diagram along the bar in case that HX elastic stiffness is assigned

 

Null Mx

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