Open wind area and shielding 1

[haynewp]

I have this open little farm shed. After adding up all the areas of all the 2x10 roof joists at 16" o.c., I of course have a whole lot of area and therefore a whole lot of force. At what spacing could you consider a joist shielding the wind from the adjacent joist thereby taking only one area into account instead of two? Any references/tests on this?

 

[austim]

Hi, Haynewp.

If your 'little shed' were subject to the Australian Wind Loading code, then you would take 100%* load on the first joist, and 20% on ALL OTHERS.

AS 1170.2 refers to a study by Georgiou and Vickery, "Wind Loads on Building Frames", Proceedings of 5th. Conference on Wind Engineering, Fort Collins, 1979, pp 405 - 420

 

[haynewp]

I am in U.S., 20% sounds pretty reasonable.

 

[ishvaaag]

NBE AE 88 says only a 25 reduction. Furthermore it instructs to use +10 and -10 deg inclination to the horizontal wind cases, so not even this reduction must be allowable from such code.

IAP 1998 that rules bridge construction gives a table that gives the factor to consider multiplying the basic unreduced wind pressure of the element. Since for solid webs is only a column, I quote

Relative distance Coeff x to use
(times the depth)

0.5 0.06
1 0.10
2 0.20
3 0.31
4 0.46
5 0.69
6 1.00

So from this table your 16/10 relative distance would mean to use 0.16 times the exposed face; hence the 20% is safe.

 

[haynewp]

What does NBE AE stand for?

 

[ishvaaag]

NBE AE 88 is the code that rules the loads to use for buildings in Spain. It has then 14 years standing, and more since almost exact transcription of even older code MV-101.

NBE AE 88 stands in spanish as
Norma Básica de la Edificación Acciones en la Edificación and 88 is the year in which it was issued. A set of NBEs constitute the more important codes to consider when dealing with buildings.

Just as another example NBE EA 95 is the Norma Básica de la Edificación Estructuras de Acero, rules Steel Construction in Buildings and was issued in 1995.