Friction Drag on Industrial Single Story? 3

[IJR]

Pals

Do we have to take into consideration friction drag forces coming from walls and roofs when we design the frame for a single story industrial building long or short?

respects
ijr

 

[csd72]

I have always checked the drag across the ribs but not usually along them as the coefficient is much smaller and the width is usually much smaller.

 

[ishvaaag]

In Spain, till the current code in a legal setup, I would be doubtful on the legal need of enforcement of such loads. CTE now even provides a "how to".

"The action of wind also generates tangential forces to the surface. They are calculated as the product of the external pressure by the friction coefficient, of value similar to 0,01 if the surface is very flat, for example of steel or aluminum, 0,02 if it is rough as in the case of concrete, and 0,04 if it is very rough, like in the case of existence of waves, protrusions or pleats. In the surfaces to windward and leeward won't be necessary to keep in mind the action of the friction if its value doesn't overcome 10% from the due perpendicular force to the action of the wind."

 

[csd72]

Yes the 0.04 applies across the ribs and the 0.01 along the ribs.

 

[jhardy1]

Table D3 of the Australian Standard AS 1170.2 specifies:

Cf = 0.04 for ribs across the wind direction
= 0.02 for corrugations across the wind direction
= 0.01 for smooth surfaces, or for corrugations or ribs parallel to the wind direction

Hope this helps!

 

[IJR]

Do you check drag for multiple pitch roofs in the direction perpendicular to ridges? I mean you have wind forced to go over roof slopes there

respects
ijr

 

[csd72]

I have said this before but...

You should check everything until you have the confidence to judge that it is not critical.h

 

[ishvaaag]

Yes, for that the need to check was already standing by the sixties. The MV 101-1962 code indicated ...

"In the surfaces located inside the projection, in the direction of the wind, of another element, such for example, in sheds, the eolic coefficient can be reduced in 25%"

That's not much allowed reduction. It may be kept in mind however all along this problem that rythmically repeated elements are prone to develop resonance for some particular wind speed. This might still not be of relevance to the main structural members yet it being the case for secondary structural elements or non-structural insets like glazing.

More precise indication about wind loads in structures sheltered from wind is given in the code IAP-98 that rules the construction of road bridges in Spain. You can find there also other interesting technical wind and not wind information. I enclose a pdf of the same, where you can find at page 7470 and around (Table 2 mainly) how shaded elements can be thought to be loaded.

 

[IJR]

Thanks ishvaaag

nice to have you around here at the forum.

respects
ijr