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EC8: P delta Verification

12 REPLIES 12
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Message 1 of 13
35058535
1315 Views, 12 Replies

EC8: P delta Verification

Hi,

 

How can I make appear Ptot (total gravity load above the level n) and Vtot (seismic story shear) in order to know if I have to check the P-delta effect. (4.4.2.2 (2)).

 

 

Thank you in advance for your answer.

 

 

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12 REPLIES 12
Message 2 of 13
Artur.Kosakowski
in reply to: 35058535

You may try to define the load case with the gravity load above the given story (or delete the part below and replace it with supports) and check the value of the reactions for Ptot and check the values of horizontal forces for seismic case in the stories table for Vtot.

 

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.

 

 



Artur Kosakowski
Message 3 of 13
Tuctas
in reply to: 35058535

  In my opinion, the very important value of "θ" should be automatically calculated and displayed in the table of stories. This value is a similar one to that of EC3 in chapter 5.2 that is called "αcr" for which i have already post in the wish list:  

http://forums.autodesk.com/t5/Robot-Structural-Analysis/Coefficient-%CE%B1cr-Alpha-critical-accordin...

 

 Artur:

 The corresponding to the proper load case value of Fz in Reduced forces that is displayed in the the table of stories (or viewed in Diagrams for buildings) isn't wat we need about Ptot in order to calculate "θ"? Why should we do that kind of approach that you mentioned ? 

  Are the values of displacements (U or dr) in the table of stories properly calculated for seismic load cases (i.e the calculated value obtained from elastic analysis multiplied with the defined value q)? 

 

Message 4 of 13
35058535
in reply to: Tuctas

I asked, in aprevious post (in french), if the displacements calculated were taking in accoubnt the behavior factor.
The answer is "The behavior factor is included" according to Artur Kosakowski.
You don't have to multiply your calculated value with "q".
Message 5 of 13
Tuctas
in reply to: 35058535

  35058355, that is true in many cases (i suppose) but not in all Seismic codes (e.g in the Greek code: EAK2000/2003 this multiplication unfortunatelly isn't implemented in Robot for the dicplacements so i have it in mind in my calculations). It is o.k, for instance, when using EN1998-1-1:2004 ...

Message 6 of 13
Artur.Kosakowski
in reply to: Tuctas

 The corresponding to the proper load case value of Fz in Reduced forces that is displayed in the the table of stories (or viewed in Diagrams for buildings) isn't wat we need about Ptot in order to calculate "θ"? Why should we do that kind of approach that you mentioned ? 

Simply I didn't think about  such possibility writing the answer Smiley Happy Thank you for finding the easier way.

 

  Are the values of displacements (U or dr) in the table of stories properly calculated for seismic load cases (i.e the calculated value obtained from elastic analysis multiplied with the defined value q)? 

 

These results are based on displacements of nodes. When q is included in the values of nodal displacements it is also included in this table.

 



Artur Kosakowski
Message 7 of 13
Artur.Kosakowski
in reply to: Tuctas

 in the Greek code: EAK2000/2003 this multiplication unfortunatelly isn't implemented in Robot for the dicplacements so i have it in mind in my calculations).

What is the way EAK code scales the displacements depending on the value of the behavior factor?



Artur Kosakowski
Message 8 of 13
Tuctas
in reply to: Artur.Kosakowski

  It is the same way that EN1998-1 does Smiley Happy

Message 9 of 13
Artur.Kosakowski
in reply to: Tuctas

In principle of course yes but my understanding was the exact formulas are a bit different. Thank you for your answer.



Artur Kosakowski
Message 10 of 13
Tuctas
in reply to: Artur.Kosakowski

  Dear Artur,

 

  The formulas used in EAK and EN1998-1 are exactly the same. It means that after the elastic analysis is perfomed by deviding the seismic forces with the factor q, the final and real (i.e inelastic) displacements obtained from elastic analysis must be multiplied with the same factor. In EN1998-1, there is a note that mentions the cases when the funtamental period is less that Tc where the multiplication factor should be slightly bigger than q. In EAK, the case of T<Tc is covered without changing the multiplication factor because the effect of it is already accounted in the responce spectrum.

  In Robot when EAK is used, the values of final displacements are changing with the change of "q" but they should remain the same. In EN1998-1 the displacements are indeed the same after changing the q value.   

Message 11 of 13
Artur.Kosakowski
in reply to: Tuctas

Thank you for the clarification.  I have added the request for EAK behavior factor being taken into account for displacements to the wish list.



Artur Kosakowski
Message 12 of 13

Thank you for the clarification.  I have added the request for EAK behavior factor being taken into account for displacements to the wish list.

 

Implemented in Robot 2015.

 

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.



Artur Kosakowski
Message 13 of 13
Tuctas
in reply to: Artur.Kosakowski

That's nice...Smiley Happy

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