Trellising high-value crops or adding superstructure to existing trellises should not be left to guesswork.
The engineering principles applied to trellises are proven equations used in everything from agricultural buildings to bridges, tractors to helicopters.
Minimizing economic risk by employing sound engineering principles to support your horticulture is a “best practice” for modern fruit production.
Trellis engineering considers the environmental loads associated with a region, such as wind and soil.
Countless data have been collected from across the U.S. to predict probabilistic numbers that engineers use to design structures against wind.
A trellis design is a combination of geotechnical, structural, agricultural and biological engineering disciplines.
This past year, I had the privilege to lead a team project — integrating private and public sectors — to analyze trellis systems from an engineering standpoint.
Here are some take homes from Trellising 101:
—Design the trellis to protect your capital investment.
—Design the trellis to your horticulture preference.
—Use the TrellX model to estimate wind loads.
—Soil tests uniquely describe locations in orchards for foundation optimization.
—Increase embedment depth for angled trellis with intra-row braces.
—Minimize twisting (torsion) when using nonsymmetric metal shapes.
—Use restraints in shallow soils.
—Use the TrellX model to estimate trellis span between posts.
—Consider unexpected loads and use a factor of safety to reduce risk of failure.
—Add secondary trellises for any horticulture above the current trellis.
—Do not pre-stress trellis members by over-tightening row and anchor wires.
—Leaning posts indicate inadequate foundation (soil) support.
—Consult an expert.
The design process for a trellis should follow these steps: consider the horticulture, determine soil structure(s), account for environmental variation, select desired material and develop an installation plan.
Neglecting any individual step compounds the potential for risk and subsequent loss. Vertical, lateral and longitudinal loads require quantified reasoning when planning a site-specific trellis.
The trellis span will vary based on wind loads and trellis material. Each trellis is as unique as the orchard where it will be located. There are as many correct styles of trellises as there are varieties of apples. It is important to understand your trellis system’s structural integrity and potential areas of weakness. It is there where confidence can be built upon to support the best fruit in the world.
Resources are available at www.trellx.com, through the Washington Tree Fruit Research Commission and Washington State University. •
An infamous failure
“Nobody wants Galloping Gertie in the orchard,” says Mark De Kleine, referring to an engineering disaster. Construction workers building a suspension bridge over Washington’s Tacoma Narrows, south of Seattle, nicknamed it Galloping Gertie, because the bridge danced up and down in windy conditions.
The bridge, at the time the third-longest suspension bridge in the world, opened to traffic on July 1, 1940, and collapsed in 40 mph winds just four months later, Nov. 7, 1940. Its failure boosted research in the field of bridge aerodynamics.
– by Mark De Kleine, a researcher and project engineer for his own company, De Kleine Machine Co. For more information about the company and its trellis research, visit www.mdekleine.com or trellx.com.