A shell is a thin-structural element used in a building composed of curved sheets of materials dividing the interior space of the structure from its exterior. The shell elements are typically curved and assembled into a large structure. It is made of reinforced concrete and serves both as a structure and covering. Shell structures are self-supporting and used to cover a large area of span without any supports of beams, columns, and walls. Its efficiency is based on its curvature (single or double), which allows different stress paths and gives the optimum form for transmission of many different load types. A single curvature shell is monoclastic, which can be curved in one direction and comes in the form of barrel vaults or conoid shells. Double curvature is synclastic and anticlastic which comes in the form of a sphere or hyperboloid.
Components of a shell structure;
- The structural skeleton and foundation
- Base plant
- Building cladding
- The building envelope
- Fire barriers
- Fire detection system
- Electrical and plumbing systems
- Pathways, boundary walls,
- Pavement, and fencing
- Landscaping
- Signage
The main purpose of constructing the shell structure is that it will cover a larger area of the building.
Advantages of Shell structures
- A light form of construction
- Faster construction
- An easy method of fabrication
- Waste reduction as no requirement of fittings
- Covers a large area
- Aesthetic in appearance
- Energy efficient
- Lesser material usage
Types of Shell Structure
Cylindrical Shell
These shells are the primary structural component of both aquatic and airborne systems. Frames or ribs are also used to stiffen these structures. Some examples of typical cylindrical shells include the :
- Semi-ellipse.
- Arch circle.
- Cycloid catenary.
- Horseshoe form.
Multiple Cylindrical Shells
Thes cylindrical shells comprise a of cylindrical shells that are parallel and transversely continuous.
North Light Shells
This shell construction is used to provide vast areas of north light windows for factories that need good natural lighting. This kind of shell is typically used as a roof in the case of factories.
Asymmetrical Cylindrical Shells
This shell arrangement is asymmetrical across the crown.
Barrel Shells:
A barrel shell is a collection of very thin arches that have the same compressive power. It can withstand very large quantities of weight as long as the weight is spread proportionally.
Barrel Vaults
A barrel vault is a continuous vaulted form that could be semi-circular in shape, resembling the roof of a cave, or pointing at the apex. It is usually built by a sequence of edge arches or vaults.
Short Shells and Long Shells
Short shells are those with a short period of length and long shells Where the period length is greater than the width, the shell shape is referred to as a long shell.
Domes
A dome is a structured framework that occupies an area that is somewhat square or circular. The domes are connected to a surface formed by some curve rotating around a vertical line.
Intersection Shell Structure
The structural effects of the intersection shell are dependent upon the angle of intersection of the surface
Shell Arches
Small shell thicknesses can be rendered much smaller than an arc if the stresses are mostly compressive. Shells are not a very effective framework for high bending moment values.
Translation Shells
A translation shell is created by moving a vertical curve over another vertical curve.
Combination Shells
It is a combination of shell, solid, and frame construction. A sturdy foundation beneath a home supports the weight of the structure. A brick, concrete, or other material shell is supported by a wood or metal frame. The frame is the skeleton of the house. It provides stability and support for the walls and roof.
Applications of shell structures
The shell structure is typically found in nature as well as in classical architecture.
- Industrial structures: – silos, tanks, cooling towers, reactor vessels etc.
- Auditoriums and food courts
- Architectural special structures
Examples of shell structures in India;
Apart from Lotus temple in India, shell structure has been used across the country, few of them are given below.
Conclusion
Discussed above are different types of shell structures, advantages and applications. With the growing modernisation of building design, these structures are being used across India. In an upcoming series of articles, we will analyse different types of materials, forms and their design adaptability across India.
Analysis of shell structures
Advantages of Shell structures
Asymmetrical Cylindrical Shells