SHELL STRUCTURES

SUBMITTED BY –

AMRUTHA U S MADHURI A R MEGHA K POOJA W PUSHKAR P K SHUBADHA N SOUJANYA V VINAY K G YASHASHWINI K P YOSHITHA VK

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CONTENTS

• INTRODUCTION

• PHENOMENA – STRUCTURAL BEHAVIOUR

• FORMS OF CURVATURE

• TYPES OF FORCES

• SHELLS – CLASSIFICATION

• TYPES OF SHELLS

• SUITABILITY

• PROS AND CONS

• EXAMPLES

• CONCLUSION

INTRODUCTION

• A SHELL STRUCTURE IS A THIN CURVED MEMBRANE OR SLAB USUALLY OF REINFORCED CONCRETE THAT FUNCTIONS BOTH AS STRUCTURE AND COVERING.

THE TERM “SHELL” IS USED TO DESCRIBE THE STRUCTURES WHICH POSSESS STRENGTH AND RIGIDITY DUE TO ITS THIN, NATURAL AND CURVED FORM SUCH AS SHELL OF EGG, A NUT, HUMAN SKULL, AND SHELL OF TORTISE.

SHELLS OCCURING IN NATURE

PRINCIPAL SHELL PHENOMENA

An extreme load carrying capacity can be achieved when the design allows the shell to be in a membrane state where every fiber in the body is equally strained (and in the elastic regime also equally stressed).

Form finding of 4-point supported shellCompression and bending behavior

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 AND DOULBE CURVATURE ARE USED TO DISTINGUISH THE COMPARITIVE RIGIDITY OF THE TWO FORMS AND COMPLEXITY OF CENTRING NECESSARY TO CONSTRUCT THE SHELL FORM.

FORMS OF CURVATURE:SURFACES OF REVOLUTION:

SURFACES OF REVOLUTION ARE GENERATED BY THE REVOLUTION OF A PLANE CURVE, CALLED THE MERIDIONAL CURVE, ABOUT AN AXIS, CALLED THE AXIS OF REVOLUTION.

IN THE SPECIAL CASE OF CYLINDRICAL AND CONICAL SURFACES, THE MERIDIONAL CURVE CONSISTS OF A LINE SEGMENT.

E.G. : CYLINDERS, CONES,SPHERICAL OR ELLIPTICAL DOMES,HYPERBOLOIDS OF REVOLUTION, TOROIDS.

FORMS OF CURVATURE: -

SURFACES OF TRANSLATION ARE GENERATED BY SLIDING A PLANE CURVE ALONG ANOTHER PLANE CURVE, WHILE KEEPING THE ORIENTATION OF THE SLIDING CURVE CONSTANT. THE LATTER CURVE, ON WHICH THE ORIGINAL CURVE SLIDES, IS CALLED THE GENERATOR OF THE SURFACE.

IN THE SPECIAL CASE IN WHICH THE GENERATOR IS A STRAIGHT LINE, THE RESULTING SURFACE IS CALLED A CYLINDRICAL SURFACE.

FORMS OF CURVATURE:

SURFACES OF TRANSLATION IF TWO PARABOLAS ARE SIMILAR, THE SURFACE BECOMES A SURFACE OF REVOLUTION, CALLED PARABOLOID OF REVOLUTION.

FORMS OF CURVATURE: RULED SURFACES RULED SURFACES ARE GENERATED BY SLIDING EACH END OF A STRAIGHT LINE ON THEIR OWN GENERATING CURVE. THESE LINES ARE NOT NECESSARILY AT RIGHT ANGLE TO THE PLANES CONTAINING THE END CURVES.

COOLING TOWER, GENERATED BY STRAIGHT LINES GOULD 1988

CONOID, GENERATED BY STRAIGHT LINE TRAVELING ALONG ANOTHER STRAIGHT LINE AT ONE END AND CURVED LINE AT OTHER END. JOEDICKE 1963

FORMS OF CURVATURE: SURFACES WITH DOUBLE CURVATURE CANNOT BE DEVELOPED, WHILE THOSE WITH SINGLE CURVATURE CAN BE DEVELOPED. DEVELOPABLE AND NONDEVELOPABLE SURFACES :

IN OTHER WORDS, SURFACES WITH POSITIVE AND NEGATIVE GAUSSIAN CURVATURE (I.E. SYNCLASTIC AND ANTICLASTIC SURFACES) CANNOT BE DEVELOPED, WHILE THOSE WITH ZERO GAUSSIAN CURVATURE CAN BE DEVELOPED.

DEVELOPED NONDEVELOPED

TYPES OF GAUSSIAN CURVATURE.

(A) POSITIVE GAUSSIAN (B) ZERO GAUSSIAN (C) NEGATIVE GAUSSIAN

TYPES OF FORCES IN SPHERICAL SHELLS

• The existence of two sets of forces in separate directions within the surface of a spherical shell tends to make the shell act in a fashion similar to that of a two-way plate structures.

• In an arch, no bending is present if the arch is funicularly shaped for the applied full- loading condition. If the loading is changed, however to partial loading, substantial bending is developed in the arch.

HOOP FORCES IN SPHERICAL SHELLSHoop forces that act in the circumferential or latitudinal direction.

The distribution of meridonal and hoop forces can be found simply by plotting the equation for the two forces,as is evident,meridonal forces are always in compression,while the hoop forces undergo a transition at an angle of 51°49‘,as measured from the perpendicular.

• A tension ring is simply a planar ring against which the outward thrusts push,

Causing tension to develop in the ring.. The horizontal components of the meridional forces act outwardly along the circumferential length of the ring.

SUPPORT CONDITIONS:TENSION AND COMPRESSION RINGS

CLASSIFICATION OF SHELLS• There are many different ways to classify shell structures

but two ways are common:

1. The material which the shell is made of: like reinforced concrete, plywood or steel, because each one has different properties that can determine the shape of the building and therefore, these characteristics have to be considered in the design.

2. The shell thickness: shells can be thick or thin.

Types of shell structure

Types of shell structure and reinforcement details

THIN SHELL STRUCTURES

CONNECTION DETAILS

SUITABILITY OF SHELL STRUCTURE

• Storage facilities

• Commercial buildings

• Residential homes.

• Concrete shell construction techniques are well suited for

complex curves and are also used to build boat hulls.

ADVANTAGES AND DIS-ADVANTAGES OF SHELLS:

ADVANTAGES:

• 1. VERY LIGHT FORM OF CONSTRUCTION. TO SPAN 30.0 M SHELL THICKNESS REQUIRED IS 60MM

• 2. DEAD LOAD CAN BE REDUCED ECONOMIZING FOUNDATION AND SUPPORTING SYSTEM

• 3. THEY FURTHER TAKE ADVANTAGE OF THE FACT THAT ARCH SHAPES CAN SPAN LONGER

• 4. FLAT SHAPES BY CHOOSING CERTAIN ARCHED SHAPES • 5. AESTHETICALLY IT LOOKS GOOD OVER OTHER FORMS OF CONSTRUCTION

DIS-ADVANTAGES:

• 1. SHUTTERING PROBLEM • 2. GREATER ACCURACY IN FORMWORK IS REQUIRED • 3. GOOD LABOUR AND SUPERVISION NECESSARY • 4. RISE OF ROOF MAY BE A DISADVANTAGE

Shell structures rely upon their three-dimensional curved geometry and

correct orientation and placement of supports for their adequate

structural performance.Palazzetto dello Sport, Rome, Italy, Pier Luigi Nervi withA Vitellozzi, 1957. Inclined struts support the shell roof. At the Palazzett dello Sport, Rome,

the shell surface does not meetthe foundations directly but ends at the eaves level where inclinedstruts resist the outward thrusts.

Interlacing ribs that evidence itsprecast concrete formwork segments both increase shell stability andachieve a much admired structural texture.

Hexagons are the building blocks ofthese shells, or biomes as they are called. Due to the long spans of upto 124 m, the outer primary hexagonal steel structure is supplementedby a secondary inner layer of tension rods .

Biome interior structure consisting of outer primaryhexagons and an inner layer of braced rods.

SYDNEY OPERA HOUSE, AUSTRALIA NAGOYA DOME , JAPAN

KRESGE AUDITORIUM, CAMBRIDGE MCDONNELL-PLANETARIUM , USA

Felix candela “los manantiales”

John F. Kennedy International Airport, New York

The UAE pavilion at shanghai expo  Shell in the middle of the woods in Karuizawa. 

CONCLUSION• Modern concrete shells, are made from thin steel reinforced concrete,

and in many cases lack any ribs or additional reinforcing structures, relying wholly on the shell structure itself.

• Shells may be cast in place, or pre-cast off site and moved into place and assembled.

• Shells may be constructed from concrete sections, or may be constructed of a lightweight foam with a layer of concrete applied over the top.

• Monolithic domes are cast in one piece out of reinforced concrete

• These shells are considered to be cost-effective and durable structures • Especially suitable for areas prone to natural disasters. They also point

out the ease of maintenance of these buildings. Shells can be built as homes, office buildings, or for other purposes.