Shell Structure

In building construction, a shell structure is a thin, curved plate structure shaped to transmit applied forces by compressive, tensile, and shear stresses that act in the plane of the surface. They are usually constructed of concrete reinforced with steel mesh.

This structure maintains its size and support load, even without a frame or solid mass material inside.

A shell is a building that is empty from inside, these shell elements are typically curved and assembled into a large structure, they are lightweight constructions using shell elements.

Here we will learn about shell structure, types of shell structures & much more.

Introduction to shell structure:

In the shell structure, a thin shell is defined as a shell with a thickness that is smaller than its other dimensions.

In the thin-shell structure, the deformation is not as large compared to the thickness.

The main difference between shell structures and plate structures is that within the unstable state, the shell structures have curvature, unlike the plate structures which can be flat.

Membrane action in a shell structures are mainly due to plane stress, although flexural deformation may result in secondary forces.

Types of Shell Structure:

1.Cylindrical shell:

This cylindrical shells in which stationary cure called as directrix or moving curve called generatrix is a straight line.

Semi ellipse, parabola, arch circle, cycloid catenary, horse-shoe shape are the example of some common cylindrical shells.

2.Multiple cylindrical shells:

Multiple cylindrical shells is a series of cylindrical shells that are parallel and transversely continuous.

3.North light shells:

The north light shell in which two springing are provided at different levels is called the north light shell.

The provision of curves at different levels towards the north gives maximum north-light, this type of shell is usually provided as a roof in case of factories.

4.Asymmetrical cylindrical shells:

This asymmetrical cylindrical shell structure is not symmetrical about the crown.

5.Barrel shells:

This barrel shells is symmetrical about the crown.

6.Barrel vaults:

Barrel vaults are most useful for shell structures because of the greater span capacity of up to 50 m with minimal material.

They are very efficient structures because the arch form is used to reduce stress and thickness in the transverse direction.

7.Short shells and long Shells:

The number of terms has been developed to describe cylindrical shells depending upon its span short or long.

Short shells: If the span length is short, then it is termed as short shells.

Long shells: If the span length is large in comparison with its width, the shell form is termed as long shell.

8.Domes:

A dome is a space structure that covers a more or less square or circular area.

The domes are attached to a surface generated by a curve of any form revolving about a vertical line.

When the surface has a double curvature that gives rise to a hard and strong shell structure of snoring rather than a curved surface.

9.Intersection shell structure:

The structural effectively of the intersection shell is dependent upon the angle of intersection of the surface.

If the angle is small, a rib fanned by adjacent elements of the original shell is much larger than the adjacent shell on each side.

And if the angle of intersection is too large, it is called a shallow intersection, if the angle of intersection is 90, it gives a rigid rib.

10.Shell arches:

Shell arches are in the same category as small shells.

If the stresses are mainly compressive, all thicknesses can be made much smaller than an arc.

Shells are not a very efficient structure for the high value of bending moment.

11.Translation shells:

A translation shell is generated by a vertical curve sliding along another vertical curve.

Curves have different shapes such as circles, ellipse, and parabola therefore vertical segments are all the same as opposed to a round dome in which all vertical segments differ in height.

In short, translation shell is simply a square dome in which the shape is generated by curve moving along another curve.

https://youtu.be/2PNcJ3m0KXk

Applications of shell structure:

(1) Fuselages of aero planes.

(2) Boat halls.

(3) Roof structures in some buildings.

Also read: RCC Framed Structure, Prefabricated Structure & Space Frame Structure

Shell structure examples:

These types of structures provide fantastic architectural views, Opera house in Sydney is the world-famous thin-shell structure.

In India, the Lotus temple at Delhi is, also a good example of shell structure and various shell structures bring out the miracle in building construction history.

Also read: Grain storage structures,  Pneumatic Structures & Folded plate structures

Conclusion:

Shell structure also called plate structures are lightweight constructions using shell elements.

Usually these curved elements are assembled to form a large structure.