wind on inverted umbrella structure? 2

[IJR]

Pals

I am interested in wind load distribution on inverted umbrella type structures

Any input will be highly appreciated

respects
ijr

 

[ishvaaag]

I did one of this in my previous jobs. The "umbrella" was made of small wood members, so aerodynamic effects were lessened and in fact disregarded. All steel but that wood. Since small scale (just about 2,50 m tall or so) and followed a brute force approach by scaling wind forces upwards.

For perforated cases like mine, a 25% void ratio lessens 50% the wind forces. 50 % void ratio gets around 25% wind forces respect when no holes.

For a blind umbrella aerodynamic forces are present, and for weak structures may require proper attention. For building structures it will depend on the slenderness and ability to vibrate etc.

Spain's no longer current loads code NBE AE-88 gave wind push coefficients for 2D "umbrella" structures in wind current, that should be conservative for your case, wind vortex shedding effectsx apart. If you place your case I may give you the wind forces for the angles. Likely now it would get in more bigger factors for small areas.

Better, the current code I see still preserves the case and you can download it from

http://www.codigotecnico.org/fileadmin/Ficheros_CTE/Documentos/CTEabr09/DB SE-AE abril 2009.pdf

page 37.

There's a certain trend to involve structural building designers with aerodynamics. Maybe we must resist that trend in reasonable terms (for some cases it wouldn't be reasonable). CFD is not perfectly sanctioned as a source of loads, and planes use to be more dear to acquire than buildings, in proportion; except they want the buildings cost more.

 

[csd72]

IJR,

Dont forget to allow for ponding if the drains block up. This is a classic failure case.