Communication Cable and STAAD 1

[Egnorant]

I am trying to model a communication (Telephone cable), in STAAD, strung between to points which are not at the same elevation. I know the properties of the cable (Area, Density, Modulus of Elasticity and initial tension at two ends under the self loading) but I don't know the sag and the cable length . I have used the "CABLE" element in the STAAD and was expecting that the cable will sag under its own weight and then I'll be able to get the maximum sag, but it seems that the "cable" element is not any different from truss element and it does not give any deflection under the self weight. Could somebody advise if there is any other way of modelling the cable and to find out the resultant sag, or could somebody suggest a good literature for hand calculations. I can only find literature for cables without initial tension and with ends at same elevations. Could somebody help. Thanks

 

[TLHS]

Have you tried breaking your cable into a series of elements so that it reports the deflection at those intermediate locations to you?

 

[Egnorant]

Yes I have and it still does not give any deflection.

 

[TLHS]

Are you using the advanced analysis enginer and non-linear cable analysis? Some of the cable stuff doesn't work without it, notably I believe that setting an initial length won't work. I think it's in the help file. Also take a look at your output file for warnings about that sort of thing.

 

[Lomarandil]

If your sag is less than 8-10% of the span length, you can use parabolic equations to hand calculate the tension/sag.

The basic equation is T=w*l^2/(8*d) where T is horizontal tension, w is self weight, l is horizontal span length, d is sag at midspan.

I don't have my reference in front of me to find the equation for inclined cables or total cable length, but you should be able to find it with a quick google search.

It's overkill for this, but having an old copy of an EE handbook around (

https://www.amazon.com/gp/product/007020974X/ref=oh_aui_search_detailpage?ie=UTF8&psc=1)

is handy.

 

[jayrod12]

I don't know if staad is the same. But in RISA, you have to take a guess (rough calculation) at the initial final sag under self weight full loading and model it along that curve. Take a look at the sagging cable section 1/3 of the way down the page RISA Modelling Tips

 

[SlideRuleEra]

The parabolic equations that Lomarandil mentioned can be found in the "US Steel Wire Rope Engineering Handbook". It can be downloaded from the middle of this page of my website: Miscellaneous

Page 50 shows what I understand to be the conditions you are interested in:

Page 50 refers to equations on Page 43:

The section of the book concerning the diagrams shown above begins on Page 38.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[gravityandinertia]

I haven't used this particular software much, but can you not apply a distributed loading to cable elements representing it's weight. F (lb/ft) = density*cross sectional area?

 

[Denial]

Apologies for the late reply, but I somehow missed this post when it was current.[ ] If you a looking for a tool to analyse an inclined cable under self weight, with or without a single point load somewhere along its length, I have developed a spreadsheet for the task.[ ] See

http://rmniall.com/downloads/software-downloads/#LoadedCable

 

[Sye123]

Here are a couple of suggestions

First ensure that you have the license for the Advanced Analysis Plus Engine. Secondly you should be using the advanced nonlinear cable analysis ( PERFORM CABLE ANALYSIS ) which is only available if you have the license mentioned above.4

If you have the license and you are using the advanced non linear cable analysis and still not getting any deflection, please upload your .std file and I will take a look.