Porosity of shade cloth 1

[letrab]

I am looking at shaded car ports. The structure comprises a rigid metal frame with a fabric roof. the fabric roof is considered a tensile structure and connected to the steel frame at discrete points.
The designer claims the wind force coefficient can be reduced due to the openings in the weave of the fabric. The proposed reduction is 50 %.
We cannot accept this large reduction and consider the factors should remain as stated in the code, especially when one considers the fabric when wet
Has anyone come across any literature or research dealing specifically with wind action on fabric

 

[tolchijb]

I do not know of any specific research but I would be inclined not to reduce the load. If the fabric is truely porous, then in a snow/ice event the pores would no longer be open.

 

[JAE]

Don't reduce the load. Over time the fabric can become clogged with dust/dirt. In actuality, the wind pressure is not linear with the open areas. Wind must change from laminar flow to turbulent flow over and around each fiber of the fabric, which creates pressure.

I had an Aerospace Engineer once state that a single wire cable on an old biplane produces as much drag as a full wing.

 

[RacingAZ]

I'm not sure where your project is located but for non-snow regions, LL for fabric shade per IBC is only 5 PSF. Regarding the reduction, it really depends on the type of the fabric. There are some netting / mesh type shades and some others are made of solid fabric, completely water resistant, made to shed water.

I've done some designs where I was able to justify reducing the calculated wind load by 50% for mesh type fabric shade. You have to find out what the actual fabric shade will be to make an engineering decision if a reduction is appropriate or not.

 

[letrab]

Thanks for the replies Gents,

It would seem that the prudent approach would be to reject the reduction in load unless it can be substantiated with reviewed published research

 

[Ron]

As with most structures, check the connections of the fabric to the structure. I agree that the load should not be reduced, but it is also likely that the fabric will fail in pullover strength at the fastener head prior to transferring full load to the structure.