Designing a shade sail. Help with load analysis.

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Discussion Overview

The discussion revolves around the load analysis for designing a tensioning mechanism for shade sails, specifically focusing on calculating the peak tension experienced by the sail during installation. The scope includes theoretical modeling and practical application in engineering design.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes the setup of the shade sail, noting its dimensions and material density, and seeks help in calculating the peak tension for selecting appropriate steel for the mechanism.
  • Another participant suggests approximating the sail as a point mass on two strings to calculate tension, asserting that this would be an over approximation due to the angle of elevation in the model.
  • Another response proposes modeling the situation as a uniform weight suspended cable problem, providing a link for further reference.
  • A different participant challenges the uniform weight model, arguing that the load is variable along the sail and may not be accurately represented by that approximation, mentioning a quadratic or linear distribution of load.
  • One participant shares their success in a related design assignment, indicating satisfaction with their work despite the lack of assistance from the forum.

Areas of Agreement / Disagreement

Participants express differing views on the appropriate modeling approach for calculating peak tension, with no consensus reached on the best method. Some participants agree on the need for approximations, while others contest the validity of those approximations.

Contextual Notes

There are unresolved assumptions regarding the load distribution on the shade sail and the implications of different modeling approaches on the accuracy of tension calculations.

rieuk
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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.
 
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*chirp chirp* ... damn crickets.
 
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.
 
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...
 
Last edited:
rieuk said:
No thanks to anyone here...

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

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