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truss design

17 REPLIES 17
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Message 1 of 18
CKDDIZ
5701 Views, 17 Replies

truss design

hello,

my question is related to truss design,when the moment release is applied to the truss member during calculations the instability window appears!!! Why does this happen?

 

Thanks

17 REPLIES 17
Message 2 of 18
Rafacascudo
in reply to: CKDDIZ

You shouldn´t apply releases to the members that have a pinned support as one of their nodes.

Also ,Instead of using releases you can use "truss bars  only" through geometry/additonal atributes/advanced properties

 

 



Rafael Medeiros
Robot Structural Analysis

Message 3 of 18
CKDDIZ
in reply to: Rafacascudo

I tryed to model an example from the truss database selection on two fixed columns, the truss members are moment realesed from the truss table option.

Still got the stability window during calcs!! 

Message 4 of 18
Artur.Kosakowski
in reply to: CKDDIZ

Delete the side posts and replace them with the columns.



Artur Kosakowski
Message 5 of 18
CKDDIZ
in reply to: Artur.Kosakowski

Hi,

calculated a truss in 2D in truss structure type (pic 1), exporting it in 3D ( pic 2) getting instability in Y dir.

 

Suggestions please!

 

Thank you

Message 6 of 18
Artur.Kosakowski
in reply to: CKDDIZ

If you have out of truss plane releases nothing prevent horizontal movement of its elements in this direction. I think you should add some boundary conditions (or redefine the releases) to prevent this from happening.



Artur Kosakowski
Message 7 of 18
CKDDIZ
in reply to: Artur.Kosakowski

1) using the truss bar option without any bar release, getting the same instability type.

2) using bar release in X,Z direction only , same instability.

 

Trying to solve the roof structure in 3D, how important is the bar offset of the transversal beams (purlins) in this case?

Do you recommend roof as cladding, and wind load applied on it?

 

Thanks

Message 8 of 18
Artur.Kosakowski
in reply to: CKDDIZ



1) using the truss bar option without any bar release, getting the same instability type.

 

Truss bars are similar to bars with pinned end connections.

 

2) using bar release in X,Z direction only , same instability.

 

For a 3D structural roof you should keep the chords as continuous (see the attached model). Otherwise you can consider use of partial releases.

 

partial releases.PNG

 

Trying to solve the roof structure in 3D, how important is the bar offset of the transversal beams (purlins) in this case?

 

 Personally I would not define any offsets.

 

Do you recommend roof as cladding, and wind load applied on it?

 

This is one of the options but this is going to be your decision Smiley Happy

 

P.S. I have corrected the error of not applying truss bar attribute to one line of posts in the attached model too.


 



Artur Kosakowski
Message 9 of 18
CKDDIZ
in reply to: Artur.Kosakowski

Thanks Smiley Wink

Message 10 of 18
CKDDIZ
in reply to: CKDDIZ

Is there an option in RSA, example 2 bars to be connected as 1?

Message 11 of 18
Rafal.Gaweda
in reply to: CKDDIZ

Is there an option in RSA, example 2 bars to be connected as 1?

Vote here : http://forums.autodesk.com/t5/Robot-Structural-Analysis/Merging-two-bars-into-one-bar/idi-p/3701596

 



Rafal Gaweda
Message 12 of 18
Artur.Kosakowski
in reply to: CKDDIZ
Message 13 of 18
CKDDIZ
in reply to: Artur.Kosakowski

the first one, got the answer 🙂

 

thanks

Message 14 of 18
CKDDIZ
in reply to: CKDDIZ

Can you please show step by step what changes did you do to the 3d model, 😞

I see, you applied pinned-pinned releases to the purlins, what else?

The chords must be continuous or use partial releases, but I don't see in the model you applied partial releases to the chords!!

Message 15 of 18
Artur.Kosakowski
in reply to: CKDDIZ

Can you please show step by step what changes did you do to the 3d model, 😞

I see, you applied pinned-pinned releases to the purlins, what else?

 

No, actually they were already defined in the model you sent Smiley Happy

 

The chords must be continuous

 

therefore I deleted truss bar attribute from them

 

or use partial releases, but I don't see in the model you applied partial releases to the chords!!

 

That was just the suggestion which you can take or reject. This depends on the expected behavior of the truss node connections and  the final decision is in your hand.

 



Artur Kosakowski
Message 16 of 18
CKDDIZ
in reply to: Artur.Kosakowski

Smiley Embarassed got it

 

Message 17 of 18
CKDDIZ
in reply to: CKDDIZ

Trying to apply the wind load on a 3D model, getting the following problem

 

Thanks

Message 18 of 18
Artur.Kosakowski
in reply to: CKDDIZ

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