Autodesk Robot Structural Analysis

[#1]

Hi All

Robot help says:

"If properties of materials used during design are identical to those used in a model, then the value of the coefficient D / B > 1.0. This coefficient can be interpreted (mainly for slabs subjected to unidirectional bending) as an elastic deflection multiplier. If different materials are used in a model and calculations (for example, with different classes such as concretes with different Young's modulus or Poisson's ratio), the coefficient value is corrected automatically. It may result in disturbing the the earlier mentioned inequality."

Please, may have more information about following assertion ?

1) This coefficient can be interpreted (mainly for slabs subjected to unidirectional bending) as an elastic deflection multiplier:

• Which is the meaning of "elastic" in this context ?   The coefficient D/B take in account of "element cracking, rheological effects, adherence of calculated reinforcement, etc. and averaged for both directions"  so it is, The intent is to simulate a inherently inelastic situation
• "rheological effects" means long term delayed strain estimation as in UNI EN 1992-2 5.8.4 -  Creep Annex KK ?
• "mainly for slabs subjected to unidirectional bending" I think that  for bidirectional slabs should be the same thing

2) it may result in disturbing the the earlier mentioned inequality. Which is the meaning ?. If in the model I am using i.e.. RCK 25 and in RCK 35 for the calculation off shell deflection D/B may be less than 1 ?

3) If I am using reduced stiffness of elements like http://forums.autodesk.com/t5/Autodesk-Robot-Structural/EC8-4-3-1-7-Reduced-moment-of-Inertia/td-p/3... the D/B calculation uses reduced or full inertia of elements ?

Thanks in advance 

 

[#2]

1) This coefficient can be interpreted (mainly for slabs subjected to unidirectional bending) as an elastic deflection multiplier:

• Which is the meaning of "elastic" in this context ? 

The one you get after running the static analysis of the model.

•   The coefficient D/B take in account of "element cracking, rheological effects, adherence of calculated reinforcement, etc. and averaged for both directions"  so it is, The intent is to simulate a inherently inelastic situation?

Correct.

• "rheological effects" means long term delayed strain estimation as in UNI EN 1992-2 5.8.4 -  Creep Annex KK ?

I'm not sure which effects you mean as I'm don't have what is included in the UNI EN 1992-2 5.8.4 -  Creep Annex KK provisions

• "mainly for slabs subjected to unidirectional bending" I think that  for bidirectional slabs should be the same thing

Yes, the scaling as described in the description of the method you refer to is done for all shapes of panels. The main intention of this statement is to inform that the influence of in-plane forces is disregarded.

2) it may result in disturbing the the earlier mentioned inequality. Which is the meaning ?. If in the model I am using i.e.. RCK 25 and in RCK 35 for the calculation off shell deflection D/B may be less than 1 ?

I'm not sure if more or larger than 1 for this particular case but theoretically you can use 10MPa concrete in the model and decide on setting e.g. 50MPa concrete with creep coefficient set as 0 in the panel design parameters

3) If I am using reduced stiffness of elements like http://forums.autodesk.com/t5/Autodesk-Robot-Structural/EC8-4-3-1-7-Reduced-moment-of-Inertia/td-p/3... the D/B calculation uses reduced or full inertia of elements ?

Reduced (for the value of D)

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[#3]

Hi Artur,

You are right. "UNI EN 1992-2 5.8.4 -  Creep Annex KK provisions" is related to bridges instead of buildings.

Anyway I am looking for a detailed description of the method used by Robot to take into account the concrete creep in the D/B coefficient calculation.

Thanks

[#4 · Accepted solution]

Robot uses the formula 7.20 from 7.4.3.(5) of EC2.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[#5]

Thanks Artur