Tension Only Bracing Cables In Sap2000 ???

[TekEngr]

how can we assign tension only cable bracing in sap2000? When i assign cross cable bracing in PEB roof, both of cables start taking roof DL and Roof LL..... i want only cable bracing work in tension only under the wind load.

 

[LQQD]

Hi, you should model elements as frames and then go to assign-->frame---->Tension/Cmpression Limits... and assign 0 in compression. Load cases must be nonliear, you may choose the geometric nonlinearity as you wish, any of the available options will give you tension only elements.

good luck

 

[TekEngr]

Thx for you reply….please suggest the below procedure is correct as per you above suggestions.
(if you say I can attached the SAP model here...)
I define the solid circular shape of 12 mm dia in section designer and assign the material A416G270.
After draw the cable I assign the compression value as zero
And then changed my analysis linear to nonlinear (in load cases dialogue box I simple checked the nonlinear analysis option).
But still I have following doubt after analysis.
Does this define section will give accurate result as cable?
After providing the roof cross cable bracing the base moment of column reduced 20 percent in wind condition does this change in reactions correct?
And the roof cable also effecting the ridge vertical deflection (before it was 65 mm vertically and now it is 58 mm ) does the roof cable bracing reduced the vertical deflection a little bit at ridge point ?
Please clarify the above point….
Thx in advance

 

[LQQD]

The above description is exacltly what i suggested. You won´t get cable behaviour this way. In order to make your element work as a cable you can either draw it as a cable, in which case you should also define the load case as nonlinear using setting "geometric nonlinearity parameters" as "none". An alternative approach giving the same results is using frame alements and definig the load case as nonlinear an setting "geometric nonlinearity parameters" as "P-Delta plus Large Displacements and, of course, assigning compression only. Using this approach take into account this is a second order analysis as convergence is reached when equilibrium is satisfied on the deformed geometry of the structure. In either of both types of analysis, as you wish to model cable behaviour, you will have to define an installation tension or sag as a cable will always have certain tension; unless it's lying on the floor. For a better understandin of cables in sap and for some tips on how you could define the tension in the cable modeling it as a cable element please refer to the following video:

https://www.youtube.com/watch?v=xXZ77VoCZO8

In order to define the installation tension in the cable using the second method you can assigne a temperature drop o the cable or an initial strain.

Anyway, i don't really know which is the objective of modeling it as a cable, i think you could get reasonable results modeling the cable as i mentioned in previous post. You could assign property modifier assigning 0 weight. In this case you will get similar results as a taut cable, if you are making a dynamic analysis consider setting mass modifier to 0 also. You may need to consider an initial instalation force depending on the impact this load may have on the structure, as it is not being modeled in this approach. I personally model cable bracings using frame alements with 0 initial forces!

I hope i was clear!!!