Trapezoid pleating

Some photographs illustrate the pattern:

Trapezoid pleating - 6-sided tube

Trapezoid pleating - 4-sided tube

Trapezoid pleating - 3-sided tube

Trapezoid pleating - tunnel structure

Front of 6-sided tube

Front of 3-sided tube

The resulting tubular structures tend to be somewhat flexible.

The flexibility can be controlled by altering the depth of the pleats.

The structures can easily be made with spiral ridges - allowing reinforcement with long, continuous strands of wire - as is commonly done with existing duct technology:

Wire-reinforced spiral ducting

This appears to be a pattern with considerable industrial potential.

The main advantages of the structure over existing technologies are:

• Fabrication can be done from sheet material;
• The material folds neatly - instead of crumpling.

The main disadvantages are:

• There are exposed corners;
• Use of a polygon (rather than a circle) results in some of the advantages of an arch being lost;
• Flexibility of the resulting structure is limited;
• Construction can be more complex.

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