4. SHELL STRCTURES
Definition:
A Shell is a thin structure composed of curved sheets of
material,so that the curvature plays an important role in the
structuralbehavior, realizing a spatial form.
A shell is the most efficient way of using the material, and can
bevery useful in case o storage of fluids and solids (uniform
loads)
5. The curved form may lead to different failure modes and often
unexpected behavior occurs
The analytical formulas are very complex and complicated in
comparison with all the other structural forms
Shell structures are very attractive light weight structures which are
especially suited to building as well as industrial applications.
6. • The shell structure is typically found
• in nature
• as well as in classical architecture.
7. • There are two principal uses of shells in civil engineering:
• industrial structures:
• – silos, tanks, cooling towers, reactor vessels etc.
• aesthetic and architectural special structures
9. • Eurocode on strength and stability of Steel Shell
• Structures – EN1993 Part 1.6 (2007)
• • Generic normative standard on shells for
• chimneys, towers, masts, silos, tanks, pipelines
• • Buckling of Steel Shells European Design
• Recommendations 5th Edition (ECCS – 2008)
10. Structural typologies
• Shells are the most difficult form of structure to analyse and the form
with the most complex behaviour. As a result, all but the simplest
conditions must be analysed using computers.
11.
12. Examples – Steel reticulated dome
• US pavilion Expo 67 Montreal
Architect: Buckminster Fuller & Shoji Sadao
The 250ft diameter by 200ft high dome roughly
presents a three-quarter sphere, while geodesic
domes before 1967 were hemispherical. The dome
consists of steel pipes and 1,900 acrylic panels. To keep the indoor
temperature acceptable, the design included mobile triangular panels
that would move over the inner surface following the sun. Although
brilliant on paper, this feature was too advanced for its time and never
worked.
14. Aluminium alloy reticulated dome
Spruce Goose dome, Long Beach, USA
Architect: R. Duell and Associates
Engineer/builder: Temcor
• A - Aluminum cover plate with silicone seal
• B - Aluminum gusset plates, bolted to struts
• C - Aluminum batten secure silicone gaskets
• D - Triangular aluminum panels
• E - Wide-flange aluminum struts
• F - Stainless steel bolts
15.
16. – Timber-steel free form grid shell
Architect: Thomas Herzog
Engineer: Julius Natterer
• Wood grid shell with PTFE
membrane
• The theme pavilion advanced the
philosophy:
• Wood is the only renewable material
• Requires the least energy for
production
• Use of wood maintains healthy
forests
17. Shell Design
• Resistance
• Stability
• Highly sensitive to imperfections
• Buckling is a process by which a structure cannot withstand loads with its
original
• shape, so that it changes this shape in order to find a new equilibrium
• configuration. This is an undesired process (from the point of view of the
• engineer), and occurs for a well–defined value of the load.
18. The consequences of buckling are
basically geometric:
• The are large displacements in
the structure
• There may also be
consequences for the material, in
the sense that
deflections may induce plasticity
in the walls of the structure
Local buckling
of a tank
Global buckling
of a wind
turbine tower
20. • CONCRETE SHELL ARCHITECTURE IN HISTORY
• Today’s concrete shell architecture is an evolution of structural
concepts and construction techniques used in Egyptian, Assyrian, and
Roman civilizations, in which arched and vaulted structures were
erected, using stone masonry and rudimentary types of concrete as
primary building materials.
• The Pantheon in Rome and the Hagia Sophia in Istanbul are the more
ancient spectacular examples of Concrete Architecture.
• The Pantheon, in particular, is the oldest known shell structure:
completed in 125 C.E., is constructed of Roman Concrete which was
typically at the time faced with stone or brick. Roman concrete was
composed of cement, similar to modern concrete, and aggregate,
typically far larger than in modern concrete, often amounting to
rubble. As a result, Roman concrete was laid rather than poured.
21. A concrete shell, also called a “thin
shell” concrete structure, is
composed of a thin shell of concrete
formed in such a way as to be self-
supporting, often with no
interior columns or
exterior buttresses. The shells are
most commonly flat plates
and domes. They can also take the
form of ellipsoids
or cylindrical sections. The first
concrete shell dates back to the 2nd
century.
22. • These concrete shapes are usually strong
structures, allowing clear spans without
the use of internal supports, giving an
open, unobstructed interior. The use of
concrete as both the form and structure
can reduce both material cost and
construction cost over other approaches
to design and construction, as concrete is
relatively inexpensive and plastic to
conform to compound curves. The
resulting structure may be immensely
strong and safe; modern monolithic
dome houses, for example, have
resisted hurricanes and fires, and are
widely considered to be strong enough to
withstand even F5 tornadoes.
• These concrete shapes are usually strong
structures, allowing clear spans without
the use of internal supports, giving an
open, unobstructed interior. The use of
concrete as both the form and structure
can reduce both material cost and
construction cost over other approaches to
design and construction, as concrete is
relatively inexpensive and plastic to
conform to compound curves. The
resulting structure may be immensely
strong and safe; modern monolithic
dome houses, for example, have
resisted hurricanes and fires, and are
widely considered to be strong enough to
withstand even F5 tornadoes.
23. These concrete shapes are usually strong structures, allowing
clear spans without the use of internal supports, giving an open,
unobstructed interior. The use of concrete as both the form and
structure can reduce both material cost and construction cost over
other approaches to design and construction, as concrete is
relatively inexpensive and plastic to conform to compound
curves. The resulting structure may be immensely strong and safe;
modern monolithic dome houses, for example, have
resisted hurricanes and fires, and are widely considered to be
strong enough to withstand even F5 tornadoes.
25. • Gridshells are today not the most
common type of structure but
increasingly finds its use in buildings
focusing on the architectural shape
in addition to good performance,
efficiency and cost. Spectacular
shapes may be constructed, as there
is lot of flexibility concerning the
form finding, as long as it has its
basis in structural considerations.
That is, to be fruitful there is a clear
benefit, even a clear demand,
regarding understanding and
collaboration between the architect
and structural engineer.
Trondheim gridshell (2015)
26. • A gridshell structure is a shell
construction divided in a grid of smaller
elements where loads are carried ideally
through membrane forces, in-plane
forces, rather than bending and transvers
shear forces. Gridshells can be
constructed using a kinematic
construction process, by first building a
flat grid that is later formed by gravity
into its final shape, possible by some
additional final pulling or lifting of
sections and/or boundaries of the grid.
Many different materials can be used,
where also wood is considered an
appropriate material, not at least due to
its good bending attributes
28. GRID SHELLS ARE AN EFFICIENT MEANS OF SPANNING SPACE. THEY HAVE BEEN USED TO COVER BOTH
EXISTING SPACES SUCH AS THE CABOT CIRCUS.
THE BENEFIT OF USING A GRID SHELL COMPARED TO EITHER THE CONVENTIONAL SLAB AND FRAME SYSTEM
OR THE CONTINUOUS SHELL ARE BOTH AESTHETICAL AND STRUCTURAL.
GRID SHELLS CREATE DRAMATIC SPACES BY PULLING THE EYE TO HEIGHTS HIGHER THAT THE BUILDING TOP,
AND BY ARTICULATING THE SPACE WITH ITS DISCRETIZED TOPOLOGY
THEY CREATE BEAUTIFUL SPACES BECAUSE THEY ARE LIGHT AND AIRY DUE TO THEIR EFFICIENT USE OF
MATERIAL, SINGLE-LAYER MEMBERS, AND OPENINGS.
THEIR FAIRLY SIMPLE CONSTRUCTION OF MEMBERS AND NODES CREATES SHELL-LIKE STRUCTURES WITHOUT
THE ARDUOUS PROCESS OF FORMWORK AND POURING.
GRID SHELLS ALSO DIFFER FROM CONVENTIONAL FRAME SYSTEMS AND CONTINUOUS SHELLS IN THAT THEY
CAN CREATE MORE SUSTAINABLE DESIGNS BY LOWERING EMBODIED ENERGY AND BY REDUCING OPERATING
ENERGY.
30. A structural membrane or shell is a
curved surface structure. Usually, it is
capable of transmitting loads in more
than two directions to supports. It is
highly efficient structurally when it is
so shaped, proportioned, and
supported that it transmits the loads
without bending or twisting.
A membrane or a shell is defined by its middle
surface, halfway between its extrados, or outer
surface and intrados, or inner surface. Thus,
depending on the geometry of the middle
surface, it might be a type of dome, barrel
arch, cone, or hyperbolic paraboloid. Its
thickness is the distance, normal to the middle
surface, between extrados and intrados.
32. In construction, the monocoque is the method of using the
external structure to support the load. The name literally means
“single shell" and refers to fabricating an external frame into a
single unit. Alternative names for this method include unibody,
unitary construction, and structural skin. It is useful for
significantly reducing an object's weight while maintaining its
strength.
Monocoques were first used in automobiles but were
developed extensively by the aeronautics industry.
Prior to the 1930s, most airplanes were built with a
full internal frame. This resulted in a heavy fuselage.
Advancements in technology allowed the use of
lighter and stronger materials for the aircraft's
surface that could still carry the majority of cargo.
The more durable exterior eventually replaced the
heavy frame.
34. Steel frame construction involves assembling steel
columns and beams to support floors, roofs,
cladding, internal fixtures, and finishing. Thanks
to the material's distinctive qualities, steel frame
construction has been the ideal construction method
for many architects and contractors
Steel framing is a building technique with a
"skeleton frame" of vertical steel columns and
horizontal I-beams, constructed in a
rectangular grid to support the floors, roof, and
walls of a building which are all attached to the
frame. The development of this technique
made the construction of the skyscraper
possible.
36. A Geodesic structure is a spherical or partial-spherical
shell structure constructed from a network of triangular
elements. The triangular elements (typically made from
metal or wood) are interconnected so that they can distribute
loads evenly across the dome's surface. Aside from its
inherently beautiful form, the spherical shape of a geodesic
dome is particularly efficient in terms of strength and
stability which makes it an ideal structure for enclosing
large spaces.
The design and building of geodesic domes hold
special significance within the field of architecture for
a few different reasons. First, geodesic domes are
incredibly energy efficient. The spherical shape of the
dome allows it to enclose a large amount of space with
a minimal amount of material. This means that
geodesic domes require less energy to heat and cool
than traditional rectangular structures. Additionally, the
interlocking triangular elements of a geodesic dome
create a sturdy and stable structure. This makes
geodesic domes resistant to high winds and
earthquakes, which is an important consideration in
areas where natural disasters are common. A final
reason for their significance worth noting is their
striking and unique appearance.
