Regarding modelling of Tension rod system of Skylight in STAAD

[Arbu]

Dear All,

I am trying to analyse and design a Tension rod system for horizontal skylight with tension rod at top and bottom. The concept is given by consultant. But I am getting difficulty in analysis and design. My question is which element I have to consider Either tension or cable while analyzing. If I am considering cable i cannot provide Pretension as it is tension rod only. If I am considering tension rod then deflection is infinity. I posted same question in STAAD forum but didn't got reply. Please reply if any one is having Idea. Drawing has been attached.

 

[ldeem]

It appears Architects are the bane of structural engineers the world over.

My background is heavy industrial and I have no experience with this sort of tension rod system. Personally I don't really see how it could work but that opinion is mainly based on the fact I have never done something like this.

I would suggest asking the architect to provide some examples of a similar design. At least than you could have a level of comfort that such a system is feasible.

In your STAAD model I tried changing to P-delta analysis and still have all but the temperature load cases showing instabilities.

You have quite a big challenge here.

 

[WARose]

Something else that is jumping out at me as I look at this model: your tension trusses do not appear (to me) to be put together correctly. Every member in it (except for the vertical member) appears to be a tension member. Based on their configuration, I don't think that is right.

You either have to have 2 parabolas (inverted to each other) as your top & bottom "chords".....i.e. something like this:

https://images.search.yahoo.com/search/images?p=cable+truss&fr=mcafee&imgurl=http://

http://www.strudyna.com/images/defa...truss/2-cable-truss.jpg?sfvrsn=0&action=click

Or you'd have to have a top chord be a continuous, non-tension member.....i.e. something like this:

https://images.search.yahoo.com/sea...sion+cable+truss&fr=mcafee#id=60&iurl=http://

http://www.kevinludlow.com/files/photos/Thumbs/249/76903_311703_1376973087_00604.jpg&action=click

The dark line being the cable. This is a lot closer to what I have seen and it internalizes the force.

Speaking of that, with your tension truss......I'm not sure you'd ever get it to work because as you tighten that thing, the perimeter columns likely move in and relieve it. (That's probably why it won't converge.)

 

[klaus.]

As I said before...designing a structure like that you need a good knowledge and experience on cable structures.... otherwise you will not be able to get results ....

 

[Arbu]

Dear All ,

thanks for the suggestion and response. The system with truss and tension rod was working manually but there are again some doubt.
Now our management agreed to change the system now top tension rod is a Pipe and one profiled tension rod at bottom. SO Pipe will carry compression and tension rod will carry tension.