As an agricultural building, greenhouses are designed to be as lightweight as possible. Fine-tuning the structural calculations can lead to significant differences in the amount of steel needed for a similar building.
Steel grade and profiles
The steel grade typically used for Dutch greenhouses is S235 (a readily weldable low carbon manganese steel with good impact resistance). Posts, trusses and foundation posts are fabricated from hot rolled hollow steel profiles. These S235 profiles provide structural strength, do not distort through galvanisation and allow flexibility for welding and cutting.
Columns & Posts
The columns or posts of the greenhouses are put under pressure in three different ways. Firstly, they carry the weight of the glass, the aluminium roof system and the installations within the greenhouse. Secondly, the greenhouse columns are subjected to an upward vertical load, under influence of wind-suction. Finally, the steel columns are pressured by horizontal forces; they are pulled on by the trusses and are subjected to wind pressure.
Columns determine the height of the greenhouse, the post height. The optimal height of the greenhouse depends on the type of crop and cultivation method applied within. A higher greenhouse has a larger climate buffer above the crop than compared to lower greenhouse, which creates a more stable climate. Additionally, if grow lights are installed or ducts are installed in a semi-closed greenhouse, the greenhouse is often carried out higher. The modern Dutch greenhouses have a post height of around six meters, or twenty feet.
Together with the columns, the trusses form the skeleton of the Dutch greenhouse and have the important duty to transfer all loads to the foundation. The steel trusses do not only fulfill this duty, they also take care of the suspension of all technical installations. The ventilation mechanism, screening system, hanging gutters, heating systems, crop wires and more, dependent of the type of crop cultivated within the greenhouse. The trusses themselves consist out of four elements; the top and bottom box-profile, the diagonals and the end-plates.