This document discusses different types of shell structures used in building construction. It describes shells as thin, curved structures that can span large areas without internal supports. Various shell forms are outlined, including barrel vaults, domes, hyperbolic shells, folded plate structures, and cylindrical shells. Advantages of shells include their lightweight and cost-effective nature, while accurate formwork and prevention of moisture penetration can be challenges. Specific examples like the British Museum roof and Lotus Temple dome are also examined.

1. Spring-2020
Course Code: ARC 2143
Mid-term Examination (Online)
Course Title: Building Technology
DATE: 15-11-2020
NAME: JANNATUL NAIEM
ID-201932030022
SHELL STRUCTURE

2. SHELL STRUCTURE
Shell: Shell structures are also called plate
structures. They are lightweight constructions
using shell elements. These elements, typically
curved, are assembled to make large structures.
Typical applications include aircraft fuselages, boat
hulls, and the roofs of large buildings. A thin shell
is defined as a shell with a thickness which is small
compared to its other dimensions and in which
deformations are not large compared to thickness.
A primary difference between a shell structure and
a plate structure is that, in the unstressed state,
the shell structure has curvature as opposed to the
plates structure which is flat. Membrane action in a
shell is primarily caused by in-plane forces (plane
stress), but there may be secondary forces
resulting from flexural deformations. Where a flat
plate acts similar to a beam with bending and
shear stresses, shells are analogous to a cable
which resists loads through tensile stresses. The
ideal thin shell must be capable of developing both
tension and compression.

3. SHELL STRUCTURES

4. • Thin shells-types
1. Concrete shells- monolithic dome or stressed ribbon bridge
or saddle roof.
2. Lattice shell structures(grid shell)-geodesic dome or
hyperboloid structure. 3.
3. Membrane structures- fabric structures, other tensile
structures, cable domes, pneumatic structures.
• Types and Forms of Shell Structure
1. Folded Plates
2. Barrel Vaults
3. Short Shells
4. Domes of Revolution
5. Folded Plate
6. Domes Intersection
7. Shells Warped
8. Surfaces Combinations
9. Shell Arches

5. CONCREATE SHELL
The most popular types of thin-shell structures are:
Concrete shell structures, often cast as a monolithic
dome or stressed ribbon bridge or saddle roof. The
thin concrete shell structures are a lightweight
construction composed of a relatively thin shell made
of reinforced concrete, usually without the use of
internal supports giving an open unobstructed interior.
The shells are most commonly domes and flat plates,
but may also take the form of ellipsoids or cylindrical
sections, or some combination thereof. Most concrete
shell structures are commercial and sports buildings
or storage facilities. There are two important factors
in the development of the thin concrete shell
structures: The first factor is the shape which was
developed along the history of these constructions.
Some shapes were resistant and can be erected
easily. However, the designer’s incessant desire for
more ambitious structures did not stop and new
shapes were designed. The second factor to be
considered in the thin concrete shell structures is the
thickness, which is usually less than 10 centimeters.
For example, the thickness of the Hayden planetarium
was 7.6 centimeters

6. Versatility inform
While air form thin-shell
concrete construction is
versatile and varied, it is
limited toshapes that can
be inflated. There seem
to be no limits on the
designs.

7. Versatility inform

8. • Marine park
Largest in Europe
Over 1,000,000 sq ftsurface
Over 11,000,000 galcapacity
Valencia,Spain
Thesite/project

9. The structural strength is derived from the hyperbolic
shape which evenlydistributes and directs loads
downwardall in a compressivemanner
• 6 cm thick concrete shell
• 40 meter span
• Steel fiberreinforced
Structure andform

10. • Advantages and Disadvantages of Concrete Shells
The curved shapes often used for concrete shells are naturally
strong structures.
Advantages
 Shell allowing wide areas to be spanned without the use of
internal supports, giving an open, unobstructed interior.
 The use of concrete as a building material reduces both
materials cost and the construction cost
.  As concrete is relatively inexpensive and easily cast into
compound curves.
Disadvantages of Concrete Shells
 Since concrete is porous material, concrete domes often have
issues with sealing. If not treated, rainwater can seep through the
roof and leak into the interior of the building. On the other hand,
the seamless construction of concrete domes prevents air from
escaping, and can lead to buildup of condensation on the inside
of the shell. Shingling or sealants are common solutions to the
problem of exterior moisture, and ventilation can address
condensation

11. SINGLE OR DOUBLE CURVATURE SHELLS
• Single Curvature Shell: Are Curved On One Linear Axis And Are A Part Of A Cylinder Or Cone In The
Form Of Barrel Vaults And Conoid Shells.
• Double Curvature Shell: Are Either Part Of A Sphere, Or A Hyperboloid Of Revolution.
• The Terms Single Curvature And Double Curvature Do Not Provide A Precise Geometric Distinction
Between The Form Of Shell Because A Barrel Vault Is Single Curvature But So Is A Dome.
• The Terms Single And Double Curvature Are Used To Distinguish The Comparative Rigidity Of The
Two Forms And Complexity Of Centering Necessary To Construct The Shell Form. Barrel Vault Canoid
Dome Hyperboloid Paraboloid

12. CYLINDERICAL SHELLS
CYLINDERICAL SHELLS __
Doubly curved surface- shape of a saddle.
I. It has a convex form along one axis and concave form
on along the other.
II. Easy to construct using a series of straight structural
members
III. Constructed using concrete.
IV. The curvature reduces its tendency to buckle in
compression and achieves stiffness.

13. BRITISH MUSEUM , LONDON
• Designed by Foster and Partners, the Queen Elizabeth II Great Court transformed the Museum’s
inner courtyard into the largest covered public square in Europe. It is a two- acre space enclosed by a
spectacular glass roof with the world-famous Reading Room at its centre. • The court has a
tessellated glass roof designed by Buro Happold and executed by Waagner-Biro, covering the entire
court and surrounds the original circular British Museum Reading Room in the centre, now a
museum.
• It is the largest covered square in Europe.
• Since the circular structure is not set precisely in the middle of the courtyard, the glass roof has a
complex geometric form.
• The double-curved steel framework was delivered in segments and welded together on site.
• To avoid applying any sideways load to the quadrangle buildings, the roof is supported on sliding
bearings. These allow the structure to move naturally.
• The glass and steel roof is made up of 4,878 unique steel members connected at 1,566 unique
nodes and 1,656 pairs of glass windowpanes making up 6,100m2 of glazing; each of a unique shape
because of the undulating nature of the roof.
• A slightly unearthly quality of light comes from the mass of green ceramic dots covering the outer
panes of glass to limit the amount of sunlight entering the court.

14. British Museum

15. Parabolic shells
I. Parabolic shells Series of parabolas stung
together.
II. The use of reinforcing steel in the upward
curvature of the parabola allows for the
tensile forces to flow into first the neutral
sag, or catenary then the thrust of the forces
flow into the compression on the downward
parabola.
III. Both the axial parabolas are compressed
and in tension.
IV. examples
Saddle dome in Calgary, Alberta
Lee valley velopark, Londan

16. Model of the Lotus temple
• Interior dome is 28 m in height and 34m in diameter • Inner leaves
are of 200 mm thick and of 33.6 m in height
• Outer leaves are of 135 mm from their cusps to the line of glazing,
beyond which they thicken to 250 mm and of 22.5 m in height
• Entrance leaves are of 150 mm at center to 300 mm thick at their
edges and of 7.8 m in height
• Shells within the interior dome: 60mm thick Analysis & Design of
Structural components:
• Spherical surfaces for the Entrance & Outer leaves
• Arch soffits have a Parabolic cone shape
• Spheres, cylinders, toroids & cones for Inner leaves
• Nine intersecting spheres form interior dome
• Final geometrically converted shapes were so complex that it took
the designers over two & a half years to complete the detailed
drawings of the temple.
• In-situ Reinforced Concrete construction
Lotus temple

17. Hyperbolic shell
Hyperbolic:
A saddle-shaped quadric surface whose
sections by planes parallel to one
coordinate plane are hyperbolas while
those sections by planes parallel to the
other two are parabolas if proper
orientation of the coordinate axes is
assumed In simple words, I is a
combination of hyperbolae and parabola
within a single entity.
Examples:
•Lee Valley Velo Park •House by James
R. Mowry
•Scotiabank Saddle dome, Canada
Hyperbolic shells

18. Folded Plate
Structures
Folded Plate Structures Folded plates are flat plate
assemblies connected together rigidly over their edges
in a manner that the structural system is able of holding
loads without the need for extra supporting beams
along ridge edges. Some of them have constant
thicknesses and the other ones have variable
thicknesses according to the nature of the structure
and the applied loads as shown in figure1. The
application of folded structures is experienced in
several types such as roofs, wall structures, steel sheet
piles and floor structures …etc.

19. Folding Systems in Nature
The principle of folding as a tool to develop a general structural shape has been known for a
long time. Folded structure systems which are analogous to several biological systems such as
found at broadleaf-tree leaves, petals and foldable insect wings, are adopted to be employed in
a new, technical way. Leaf of Palm Tree Beetle Insect With Foldable Wings Seashell.

20. The Principle of Folding The
structural characteristics of
folding structures depend on-
I. The pattern of the folding.
II. Their geometrical basic shape.
III. Its material.
IV. The connection of the different folding planes.
The design of the bearings

21.  Types of Folded Structure Based on geometric shape folded
structures can be divided into:
1. Folded plate surfaces structures
2. Folded plate frames structures
3. Spatial folded plate structures
 Types of Folded Structure Classification of folded structures
based on the material they are made of:
1. Folded structures made of reinforced concrete
2. Metal folded structures
3. Folded structures of wood
4. Folded structures of glass
5. Folded structures of plastic materials
6. Folded constructions made in combination of different
material
CLASSIFICATION OF FOLDED PLATE

22. 1. As Roof Structure
2. As Wall Structure
3. As Steel Sheet Piles
4. Floor Structure
The Application of Folded Structures

23. Advantages:
I. Very light form of construction. To span 30 m shell
thickness required is 60 mm only.
II. The use of concrete as a building material reduces
both materials cost and a construction cost.
III. Longer span can be provided.
IV. Flat shapes by choosing certain arched shapes.
Esthetically it looks good over other forms of
construction
Disadvantages:
I. Shuttering is difficult.
II. Greater accuracy in formwork is required.
III. Good labor and supervision necessary.
IV. Rise of roof may be a disadvantage.
Advantages and Disadvantages of
Folded-Plate Structure

24. CYLINDRICAL BARREL VAULTS
Barrel vaults are perhaps the most useful of
the shell structures because they can span
upt o 150 feet with a minimum of material.
They are very efficient structures because the
use the arch form to reduce stresses and
thicknesses in the transverse direction. Barrel
vaults are essentially deep concrete beams
with very thin web members and may be
designed as such by the ordinary methods of
reinforced concrete. The curve of the cross
section of the barrel is usually a circle.
However, any other form maybe used, such
as the ellipse, a parabola, or a funicular curve
which fits the thrust line of the applied load.
Each curve has its particular structural and
esthetic qualities.A number of terms have
been developed to describe cylindrical shells.
If the span is large in comparison to the width,
the form is called a long shell. If the length is
short, it is called a short shell. An arbitrary
ratio for long shells is a span/radius ratio of 5.

25. DOMES OF REVOLUTION
A dome is a space structure covering a more or
less square or circular area. The best known
example is the dome of revolution, and it is one of
the earliest of the shell structures. Excellent
examples are still in existence that were built in
Roman times. They are formed by a surface
generated by a curve of any form revolving about a
vertical line. This surface has double curvature and
the resulting structure is much stiffer and stronger
than a single curved surface, such as a cylindrical
shell. The simples dome of revolution is a portion
of a sphere. However, other curves are also
satisfactory, such as the ellipse, the parabola, other
conic sections, or random curves.Typical profiles
for domes are shown later in the chapter and there
are an infinite variety of possible shapes, each
suitable for a particular purpose. Parts of domes of
revolution, square or polygonal in plan with
portions of the shell removed, are also considered
in this chapter as domes of revolution. Their
structural action is much more complex than the
dome circular in plan

26. System SpansAnd Effective Spans Of
Shell
• Spanisthe distance between two
intermediate supports for a structure.
• Thin shellStructure which couldbe flat but
in many casesisdome take the form of
ellipsoidsor cylindrical sections, or some
combination thereof
• Spansdistance in athin shell structure
isin between 40 –300 and muchlarger.