topic Can we use temperature variation for pretension in cables in Robot Structural Analysis Forum

Can we use temperature variation for pretension in cables

Anonymous — Tue, 31 Jan 2017 10:58:31 GMT

Hello, I've read somewhere that for the pretensioned cables, we can use the temperature variation in stead of pretension. Is this true?

I also join here a file comparing two models of a prestressed cable truss: 1st one using cable elements, 2nd one using bar elements. I found some differences in internal forces and deformation, can we accept these difference.

Another question concerning the alert: " Matrix is not positive definite - the critical load may have been exceeded". In fact, i have to model the cable truss with 20kN of pretension in these cables (according to the initial design). But when i use option "Force Fo = 20KN", this alert appear and ask me to continue or not, can i click on "yes"? I tried to use "elongation" but the forces in cables are so low (1-2KN) even when relative elongation = 0.

I'll appreciate a lot if some one can give me some ideas. Thanks a lot!

Re: Can we use temperature variation for pretension in cables

Artur.Kosakowski — Tue, 31 Jan 2017 14:21:35 GMT

Hello, I've read somewhere that for the pretensioned cables, we can use the temperature variation in stead of pretension. Is this true?

You can apply (additional) temperature load for cables but not as a cable definition in the assembly load case.

I also join here a file comparing two models of a prestressed cable truss: 1st one using cable elements, 2nd one using bar elements. I found some differences in internal forces and deformation, can we accept these difference.

IMHO the bar model cannot be used for this kind of structure.

Another question concerning the alert: " Matrix is not positive definite - the critical load may have been exceeded". In fact, i have to model the cable truss with 20kN of pretension in these cables (according to the initial design). But when i use option "Force Fo = 20KN", this alert appear and ask me to continue or not, can i click on "yes"? I tried to use "elongation" but the forces in cables are so low (1-2KN) even when relative elongation = 0.

You cannot ignore it but defining the cables by -0.001 relative elongation should be just what you need

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Re: Can we use temperature variation for pretension in cables

Anonymous — Wed, 08 Feb 2017 10:46:18 GMT

Thanks a lot Artur, your answers are very clear and help me a lot

Re: Can we use temperature variation for pretension in cables

Artur.Kosakowski — Wed, 08 Feb 2017 10:49:38 GMT

I'm glad I was able to help.