Covers of containers, silos and tanks

A variety of roof constructions are available to close containers, silos or tanks upwards for various reasons. SKI Ingenieurges. mbH offers the possibility to carry out a dimensioning or assessment of different roof variants in existing buildings or in the planning of construction projects.

View of tanks with different roof constructions
View of tanks with different roof constructions

Tent roof (foil cover) with center support

The simplest form of tank cover is the tent roof or foil cover, which can be designed with or without a central support. The tent roof is stretched over the edge of the container with straps fastened to the central support. It reduces emissions (odour reduction) and prevents contamination of the storage liquid (e. g. leaves). In the case of a tent roof, the roof shape may not be dimensionally stable in extreme events, such as extreme snow or storm events. 

View of a tent roof with center support
View of a tent roof with center support

Double membrane roof (wearing air) with/without central pillar

Double-membrane roofs, also known as air-supported roofs, are often used for fermentation residue storage tanks in biogas plants. A double membrane roof usually consists of two different membranes. The outer membrane is referred to as weather protection film and the inner membrane as gas storage film. The cavity between the two foils is pressurized by a backup air blower and keeps the roof in shape. Depending on the design of the support pressure, the double membrane roof may not remain dimensionally stable in extreme events such as extreme snow or storm events. First and foremost, a double membrane roof serves as weather protection or thermal insulation. There are versions with and without central support. In the case of double-diaphragm roofs with central supports, straps are tensioned radially between the central support and the container edge. This prevents the gas storage foil from depositing on the filling medium, e. g. in the state of maintenance.

Double membrane roof for a biogas plant (without central pillar)
Double membrane roof for a biogas plant (without central pillar)
State of stress of weather protection foil membrane theory
State of stress of weather protection foil membrane theory

Rafter roof with crown ring

In the case of containers, tanks or silos with accessible roofs as well as higher loads due to pressure conditions, traffic loads and agitators, rafter roofs are generally used. In the centre of the roof is a crown ring, which serves as a connection for the rafters running to the edge of the vessel and for receiving an agitator. Rafters are self-supporting roofs and central supports, which transfer the roof loads via a shell support structure into the wall of the circular cylinder shell. These roofs are usually designed with a low roof pitch of < 20°. 

View of a rafter roof with agitator
View of a rafter roof with agitator

Folded zinc

For smaller cylinder diameters, it is possible to form a rafter roof instead of a rafter roof. The rafters consisting of folded profiles (e. g. Z-profiles) are manufactured together with the roof cladding. The joints are then screwed together, which reduces the number of joints and fasteners compared to the rafter roof. Seam roofs are usually made of stainless steel.

Floors and hoods of puncture fixed tanks / silos

Pressure shock resistant tanks or silos are usually equipped with round or conical roof covers. In addition, there are also multiple applications for bobbin or arched bottom plates, which can also be used as bottoms or boundaries of horizontal tanks. The dimensioning of these shell support structures for pressure impact-resistant tanks / silos is determined in accordance with the relevant regulations for pressure equipment (AD 2000, EN 13445).

GfK segment roof

If a container cover with low dead weight and high resistance to chemically aggressive media is required, (glass) fibre-reinforced plastics are the material of choice. The roof shapes range from flat roofs to stiffened spherical shells and domes made of tonnage segments. The direction-dependent material properties for GfK roofs can be determined on the basis of DIN 18820 or the manufacturer's specifications. 

Model of a segment roof
Stresses due to loads
Stresses due to loads
Deformations of a segment roof
Deformations of a segment roof

Cone and roof of frustum of cone

Cylindrical silos often end up with a bowl in the shape of a cone or truncated cone. For larger diameters, the roof segments are provided with a stiffening upstand in the radial direction or spherical roofs are constructed. 

View of a truncated cone roof ©Farmatic
View of a truncated cone roof ©Farmatic

Services

SKI Ingenieurges. offers the following services within the scope of dimensioning and design of roofs or covers for containers, silos and tanks: 

  • Analytical or numercal calculations in the ultimate limit state and servicebilits limit state for all named types of roofs
  • Checks by the membrane theory (flexural strength of the shell is very small)
  • Determination of the branch oads
  • Detail checks for bolted or welded connections
  • Stability analsysis for roofs and covers
  • Monitoring and evaluation of component tests
  • Assessment of replacement or retrofitting of a tank covers 
  • Design taking into account the regulations for pressure equipment (AD 2000, EN 13445) 
  • Expert reports in the event of damage to roofs or tank covers