Designing a shade sail. Help with load analysis.

[rieuk]

I have to develop a mechanism with which to tension shade sails (its basically material tensioned between four posts to provide shade). I've got the mechanism going, but for the failure analysis, I need to calculate the peak tension in the shade sail. This is my information:

1. Largest shade sail is 8m x 8m. Heaviest sail material has density of 0.5 kg/m^2
2. During installation, one corner of the sail will be attached to its support pole, and the diagonal corner will be tensioned so that the whole sail is supported with a 250mm sag in the middle.

I just need the peak tension to find out what steel to use in my mechanism to withstand it. The mechanism essentially 'grabs' one end of the sail, and the post, and brings them together so that a shackle can be insterted.

I'm not sure if the teacher gave us fact 2 hinting that the peak tension the mechanism will experience is when only two corners are attached, and that we can use a rope simplification. Anyone who can suggest a good method of approximating the maximum load on the mechanism (peak tension) would receive a great many thanks.

 

[rieuk]

*chirp chirp* ... damn crickets.

 

[rieuk]

To anyone who's interested, I approximated the sail to be a point mass on two strings and then calculated the tension in those strings. I asserted that this tension will be an over approximation to the actual tension because the angle of elevation of the tension force in the approximation model is lower than in actuality.

 

[haynewp]

It sounds like you can approximate it as a uniform weight suspended cable problem.

http://tinyurl.com/rmv6w

 

[rieuk]

No haynewp, in case you did not notice, it is a SHADE SAIL (square shaped piece of fabric/whatever material used for sail) held up by two corners. It clearly can not be modeled as a uniform weight (it is a variable load as you go along the sail - quadratically if I remember correctly..or maybe linear). If I approximated it by this model, it would be hard to tell whether it was an over/under approximation.
In any case, I got 18/20 for this design assignment, so I'm pretty happy with that. No thanks to anyone here...

 

[FrogPad]

No thanks to anyone here...

People will help if they can, no reason to be snobby about it. Good job on the project.