The steel structure of a Dutch Venlo greenhouse consists out of the following primary construction elements: columns, trusses, beams, purlins and braces. Together, these elements deal with the forces applied to them by means of the weight of the greenhouse, wind, snow, the crop and the installation loads. Due to the importance of light in the greenhouse, all steel structural elements are carried out as light as possible whilst complying with the constructual regulations.
The columns of the greenhouses are put under pressure in three different ways. Firstly, they carry the weight of the glass and 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. Lastly, 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 is dependent of the type of crop and cultivation method applied within. Also, if grow lights are installed, the greenhouse is often carried out higher.
Together with the columns, the trusses form the skeleton of the Venlo greenhouse and have the important duty to transfer all loads to the foundation. The steel trusses don’t 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.
Braces and Beams
With only columns and trusses, the greenhouse structure is strong enough to tackle loads at a 90 degrees angle. To ensure the strength of the steel structure for forces applied from any other angle, braces are applied. The main function of cross braces is to transfer the horizontal loads in the gutter direction to the foundation. To prevent the foundation from tilting, a bridging beam is mounted to the pre-fabricated dollies and also to the columns.
All steel elements are always galvanized to prevent oxidation. This gives the steel structure a grey exterior. To improve the light characteristics of the greenhouse, the columns and tellis are often coated white for less light absorbance within the greenhouse.