TECHNICAL 11 · LOADS

Crop support: the load nobody puts on the drawing.

A high-wire tomato crop puts several tonnes of fruit and wire tension into the structure, added to wind and snow. It is usually the last load to be quantified and the first to cause a sagging rail.

Where crop load goes
System	Load path	Governing member
High wire (tomato, cucumber)	Wire → rail → post / truss	Rail and its fixing
Trellis net	Net → posts and wires	Post and wire tension
Table-top benches	Bench → feet → floor	Floor and stand, not the arch
Racks / shelving	Rack → floor and wall	Floor load per m²
Hanging gutters	Gutter → structure	Purlin and hanger

Bench and rack systems usually load the floor; wire systems load the frame. They are different problems.

Estimating wire load without inventing a number

Wire load is the crop's fresh weight per metre of row, plus the tension the wire is pulled to, plus dynamic load when workers lean on it. A grower usually knows the first figure from last season's yield; the second is set by the installer; the third is why rails are specified with margin.

What to send

Row spacing, wire height, kg per metre of row at peak, and whether picking platforms or trolleys hang from the wire. That is enough to size the rail and its fixing.

The cheap failure

Rails are often installed at 2 m spacing to save tube. At 3 m the rail sags under wire tension, the wire loses height, the crop leans and the pickers slow down. The saving is a few hundred dollars; the cost is a season of labour.

A second cheap failure: rails fixed with self-tapping screws into a 1.5 mm post. The screw pulls out under tension, and the rail drops. Use a clamp, or specify a thicker post where the rail lands.

Open selection list

Turn this into a quoted frame list

If this page answered the technical question, the next step is a number. Send the parameters and we will price the tube, profiles, gutters and fittings as one package.

Get a frame quotation Ask a follow-up