Shade-cloth Structure Design

Several forms of shade cloth structures are available including span structures, peaked sail structures, cantilever structures as pictured below and tent like structures with large central supports.

Shade structure in field

Stresses on shade cloth structures

 
Loading Problem Design Solution
Wind Loads

 

Ripples or waves may lead to premature failure 

Ensure the shade cloth is adequately tensioned.

Horizontal winds generating lift (like an aeroplane)

Flatten to between 10 and 14° or install it with an inclination in excess of 20° . Roof angles of 15 to 18° should be avoided. 

Poor materials selection, proneness to ripping in high wind loads.

Choose adequate fabric strength, lack of structural reinforcement and excessive spans which can lead to billowing.  

Dead Loads 

 

 Gravity

Brace frames or cables supporting shade cloth are usually used to ‘stay’ or brace posts.  

 Poorly distributed loads

 Angled posts provide tension to evenly distribute dead loads but this can also contribute to instability when the cable support is removed.

 Cloth impregnated with dust or supporting leaves, twigs, hail, ponded water or wetted from beneath

Lighter connections and structural system such as cabling  

 Live loads

 

 Hailstones or rainfall cascading down a roof, water pooling on the canopy or being shed through or from shade cloth.

 Regular cleaning and maintenance. Inclusion in maintenance and operational schedules

Human traffic on roof

Prohibited under OHS regulations for shade cloth roof structures.  

 Clogging from water pools

Regular cleaning and maintenance. Inclusion in maintenance and operational schedules.  

 
If you intend to install a shade structure, consult a registered builder or structural engineer.

Alternatively, if you are buying a package shade cloth structure ensure that structural computations are supplied, the installers are experienced and local building regulations are met.

Design considerations for maximum effectiveness and useful life

Materials selection

Cloth performance requirements to consider:

  • blocks at least 80% of sunlight
  • minimum 300 grams / sqm (GSM)
  • Green or black coloured material
  • 10 years age-life, and
  • Higher quality and tighter weave fabrics will last longer.

Stressors to consider:

  • exposure to sunlight
  • dust
  • accumulated debris
  • water
  • flexing, and
  • failure or loosening connections.

Tension system and maintenance considerations

 

Tension System

Failure/maintenance considerations

Load-carrying straps

Regular checks for durability or damage due to loading.

Chains and U-bolts

Chain connections should be avoided.  In the event of over-stress, breakage of a link can lead to the launch of a projectile whereas a cable will fray or unravel, allowing time for repair, replacement or escape from injury.

Adjustable cables and turnbuckles

Turnbuckles for tensioning cable supported shade cloth structures are prone to loosening or failure through repetitive loading so they should be inspected regularly and tightened or replaced.

Design note

  • Cows resist being moved from bright areas to dark areas and prefer dappled shaded spaces so they tend to get used to a shade cloth structure more quickly than a solid roofed structure, provided the cloth is not billowing or flapping noisily.

  • Shade cloth is also prone to bird, insect and rodent attack and areas not able to be hosed down or easily inspected for maintenance are particularly prone.

Support posts and foundations

When installing footings, they should be:

  • deep and concreted into the ground
  • left to cure for 2 weeks before bearing any load
  • free from collisions from animals and vehicles, and
  • rigidly attached to a wide steel plate which is mounted on the foundation using bolted connections.

Design notes:

  • Galvanised and threaded starter bars extending from the footing reinforcement are better for holding the plate than dynabolts.

  • Apart from central supports these posts usually lean against the applied horizontal load to maintain the tension rather than being vertically upright. They need to be free standing in a farm situation. Guy cables must be avoided.

  • If possible, position posts outside the animal traffic area so they are not in contact with manure and water or interfere with washing. If are located in the yard, place a raised concrete or PVC sleeve around the pipe to reduce corrosion potential.

Fastening fabric to posts

Prevent cloth damage by:

  • Applying sufficient tension using flexible and adjustable connections to prevent tearing in the wind.
  • Reinforcing cables and seams to distribute the point load at the stanchion to the fabric. This reduces the chance of rips and damage.

If shade cloth fastening is too loose:

  • Flapping causes excessive flexing and can generate noise during wind events which can disturb cows and irritate people.

If shade cloth fastening is too tight:

  • If a cable or cable connector fails due to over-tensioning, it can cause instantaneous and catastrophic structural failure.
  • Shade cloth structures can become a hazard if damaged by storms. Blown cladding can provide serious injuries whilst broken cables and unsecured shade cloth can whip.

Fastening shade

IChain connections shade

Different fastening methods.

Design elements

Height

A minimum height of 4.0 m is recommended to ensure:

If it’s too low;

  • Cows might hesitate when entering the area

  • Reduces effectiveness and installation of sprinklers and fans

If it’s too high:

  • limits the area of shaded footprint

  • Maintenance becomes difficult, especially if you’re running machinery under the shade cloth, it can become damage from the exhaust

Location

The height of the structure, the angle of winter and summer sun and the required area of shaded footprint govern the orientation of the shade structure – north-south or east-west.

If the structure is aligned east west the passage of the sun will generally ensure that the northern side of the structure is more exposed to sunlight than the southern.

If the paving is earthen and subject to animal traffic, drainage should be directed to formed drains.

If well designed, installed and maintained there is no greater risk of failure of these structures compared with other farm buildings.

 

WEAKNESSES in shade cloth structures are usually associated with:

  • lack of fabric strength
  • inadequate fabric reinforcement or degradation at connections
  • poor choice of connection
  • loose posts and failure in footings
  • billowing in spans
  • corrosion, and
  • rain, hail or debris accumulating on top of the shade cloth.

ADVANTAGES of a shade cloth structure over a solid-roofed shade structure:

  • more than 50% cheaper than solid-roofed structures
  • easy to remove if not needed in cooler months or during a storm (store it away from vermin)
  • easy to upgrade and maintain in responses to farm’s changing needs
  • if well made, the posts and foundations are long lasting, and
  • has fewer drainage considerations.