Mdeling 3/4" rods with turnbuckles 2

[maneesha0702]

How do I model the above in Risa. I modeled them as eyebars and they are not failing or bearing any load. However they are showing huge deflections of the order of 80 inches for a length of 25 ft.

 

[msquared48]

Did you model them as tension only members?

What kind of deflections are you getting? Elongation, compression, lateral buckling? What's happening?

Have you looked at a moving model to see what's happening?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[JoshPlumSE]

When you are modeling Rods or Cables, it is generally a good idea to first go to your materials spreadsheet and create a material that has zero density. Assign this to your rod or cable and you should get rid of those crazy looking deflections.

FWIW, those deflections are caused by the members self weight. The 1st order bending stiffness of those rods and cables is virtually nothing. Therefore, even the small amoutn of self weight is enough to cause them to deflect wildly. It doesn't happen in reality because the tension in the member creates a second order stiffness which will resist the deflection. But, that is not accounted for in the RISA analysis.

Also, you can use thermal loads to add some pre-tension that you would get from your turnbuckles.

 

[msquared48]

Also... Check your EI units for the rod. This could be a simple as a dimensional error.

And don't try to model the turnbuckle - just show the rod as continuus.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[maneesha0702]

Thanks to JoshPlum & msquared48. I corrected it by creating a material with Zero density. I did model them as continous and Tension only memebers originally.