Hello everyone,
I have downloaded the Dlubal example model of a 4-point sail 10,000 × 5,000 × 10,000 m.
In the original model, the prestress of the membrane is 1 kN/m and the prestress of the edge cables is 10 kN.
For my model, I applied a snow load of 0.68 kN/m² and increased the prestress to 4 kN/m in the membrane and 40 kN in the edge cables.
In the calculation, under the snow load case, the stress σx is almost zero over the entire membrane area, while σy shows normal values. I have already tried applying different prestresses in the x and y directions, but without success.
How can I ensure that the prestress remains throughout the entire membrane under snow load and that σx does not drop to zero?
Thank you very much for your help!
Segel Kopie.rf6 (13.7 MB)
Dear neje1011,
Welcome to the community!
This behavior is normal for four point canopies with two highpoints and two low points.
Between the highpoints (local y-direction in your case), the membrane acts like a catenary cable and is under tension for snow load.
Between the low points (local x-direction in your case), the membrane acts theoretically as a compression arc for snow load. Since the membrane cannot bear compression forces, the stress sigma_x drops to zero and the membrane gets wrinkled in this area.
If this zero-stress situation for snow loads is a problem for any reasons (for example risk of snow or water ponding in the middle of the canopy), you can insert a cable between the highpoints. In this way you create a ridge and force the membrane to "hang" from the ridge for snow loads (similar to a duo-pitch roof).
Depending on the snow load intensity and the visual appearance of the canopy, you can adjust the prestress/shape of the ridge cable to make it higher (more straight) or lower (more soft and curved). In this way you can play with the shape until the zero-stresses for snow load disappear.
I hope I could help you. If you have any other questions, please feel free to reach out again.
Best regards,
Hrvoje Petrovic
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