STABILITY ISSUES IN TRUSS MEMBER

[Anonymous]

KINDLY HELP ON THIS. THANKS

[DennisVDijk · Accepted solution]

Hello,

[1] Truss members only take axial forces;

[2] Your member is under tension, so no buckling check is needed and only the section check is aplied.

See screen below:

hope this will help you 🙂

[Anonymous]

However, I think there is a check for tension resistance. How can we check for tension members stability in robot? Does it mean Robot lacks this???

[DennisVDijk · Accepted solution]

Members under tension have no stabily issues. Buckling is a compression fail meganism.

[Anonymous]

solved, thanks so much for this. 

[Anonymous]

HI Dennisveendam,

I discovered Robot assigned tension members as negative and compression members as positive, whereas the reverse ought to be the case. Are there any means I can change this?

Also kindly check the top chord in my model, I was expecting compression all through in the member, (from my hand calculations, only the top chord results disagreed with my hand calculation result)

[Romanich]

Not possible to change.This is a sign convention for bar elements: positive - compression, negative - tension.

[Anonymous]

KINDLY CHECK THE TOP CHORD, WHY IS THERE COMPRESSION AND TENSION?

[Artur.Kosakowski]

Hi @Anonymous

Try to select only the top chord and open it in a new window and then display the axial force diagram. It is not clear what values are for what element on the picture you attached. 

[Anonymous]

[Artur.Kosakowski]

Hi @Anonymous

Could you attach both the model and your hand calculations (indicate the part for the top chord)?

[DennisVDijk · Accepted solution]

Your support on ax 7 must be free in x direction, only support vertical. If both support on ax 1 and 7 are fixed horizontaly, tension force will built in the top cord due to bending. 

[Anonymous]

Thanks man, you are good.

[jayvans]

Change the supports to pinned and roller