Wind loads for decorative awnings?? 8

[YukonOne]

I'm trying to get my arms around a reasonable wind load to use for an architectural feature (an awning ? 140 sf) on a building I'm working on. It will be a fabric, to be determined later, it will have an irregular shape oriented in an irregular manner supported by a steel/aluminum framework spaced about 20' apart.

My first thought was to use component/cladding loads, but after pushing numbers I can't imagine an awning like this anywhere designed for these load magnitudes.

Anybody have any thoughts or experience with this type of beast?

 

[gwynn]

The couple projects I've seen involving similar structures have found it more econmical to design the frame based on the fabric breaking strength and replace the fabric after significant events.

 

[archeng59]

Where do you get the info about fabric breaking strength?

 

[spats]

Tyically, fabric awnings should be closed during a design wind event. In any case, it's not a life safety issue if it fails, unless the flying debris hits somebody... but then again, there's all other kinds of debris flying around anyway. I doubt seriously if awning manufacturers design their fabric awnings for 100-year wind loads.

 

[archeng59]

I am working on a project where the owner wants to add fabric awnings to an existing multi-story building in a downtown area. There are no structural drawings for the building and the owner will not allow any demo to expose the existing structure for field measurements. The owner wants to attach the awnings to precast concrete veneer panels. The owner wants me to say the awnings and connections to the veneer panels meets code so he can get a city permit. So far, I have found no reasonable way to help him.

 

[SgherPE]

Search

http://www.spacegass.com.There

is this program use to complete a combined fabric/ steel analysis called Spacegass. Alternately you can search "fabric tensile structure" and may return list of specialty contractors (design-build). They have the complete package from designing, engineering and installation on this line.

 

[csd72]

Are you designing it for catenary loads from the fabric? The reaction perpendicular to the wind can often be only one fifth(or less) of the total tension in the fabric.

The edge members need to be able to take this tension reaction. Look up roarks for a simple formula.

 

[plasgears]

Sunsetter is a supplier of power operated awnings. This version is cantilevered off the wall. It would be worth looking into their catalog and discussing your concerns with their people. I have seen them, and they give a good impression. Naturally, it should be retracted in a strong wind.

 

[gwynn]

Are you designing it for catenary loads from the fabric? The reaction perpendicular to the wind can often be only one fifth(or less) of the total tension in the fabric.

This is one of the main reasons behind designing for the fabric breaking strength, not the actual loading. It is also generally easier to get a hold of breaking strengths than elasticity values from my experience. As far as I've seen elasticity is not a common testing criterium.

Other posters have pointed to some sites/companies for material information, but a canvas of local suppliers would also get you the relevant information.

As for structural impact on the building, it's worth taking a look at what the loads actually are. Chances are the wind loading on the awning adds almost no net load to the building, as it shields surfaces behind it, and the overall weight of the structure may be insignificant. Generally the main concern when adding this sort of structure is the anchorage. If you cannot determine what you are anchoring to then you are in trouble.

 

[csd72]

gwyn,

I understand what you are getting at, but what if your fabric breaking strength is much graeter than it needs to be? Even if it is not then you have no guarantee that your individual piece is not 20% stronger!

We get this issue with mesh banners and signs so in this case we have to design it for the full catenary action. The elasticity is hard to come by but we have usually found that the test data sheets show elongation at various stages during the testing which can be used to estimate EA.

 

[OzEng80]

I have designed similar structures based on the breaking strength of the clasp/careens. A recent project had stainless steel M12 bolts with a specified breaking strength of 1.2t. This is below the calculated force based on catenary loading and is certainly easier to justify and resolve. (I put a 1.5 S.F to get over the hump in the bell curve).

Perhaps you could specify a frangible fixing yourself - just be sure you aren’t around when the magic load is reached - your could lose an eye... or a limb