SHELL STRUCTURES

DHRUV KOHLI 642

APRAJITA GUPTA 643

SHIV DAYAL 644

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.

SINGLE CURVATURE SHELL 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 DOUBLE CURVATURE SHELL: ARE EITHER PART OF A

SPHERE,AS A DOME OR A HYPERBOLOID OF REVOLUTION.

DEVELOPABLE SURFACES (SINGLY CURVED) DEVELOPABLE SURFACE IS A SURFACE THAT CAN BE

UNROLLED ONTO A FLAT PLANE WITHOUT TEARING OR STRETCHING IT.

IT IS FORMED BY BENDING A FLAT PLANE, THE MOST TYPICAL SHAPE OF A DEVELOPABLE SHELL IS A BARREL.

BARREL SHELL IS CURVED ONLY IN ONE DIRECTION

NON-DEVELOPABLE SURFACES (DOUBLY CURVED) :

Most smooth surfaces (and most surfaces in general) are not developable surfaces. Non-developable surfaces are variously referred to as having "double curvature", "doubly curved“ etc

Spheres are not developable surfaces under any metric as they cannot be unrolled onto a plane.

Some other examples includes Helicoid, Hyperbolic Paraboloid and Hyperboloid.

CONSTRUCTION MATERIAL THE MATERIAL MOST SUITED FOR CONSTRUCTION OF

SHELL STRUCTURE IS CONCRETE BECAUSE IT IS A HIGHLY PLASTIC MATERIAL. WHEN FIRST MIXED WITH WATER THAT CAN TAKE UP ANY SHAPE ON CENTERING OR INSIDE FORMWORK. SMALL SECTIONS OF REINFORCING BARS CAN READILY BE BENT TO FOLLOW THE CURVATURE OF SHELLS.

ONCE THE CEMENT HAS SET AND THE CONCERETE HAS HARDENED THE R.C.C MEMBRANE OR SLAB ACTS AS A STRONG, RIGID SHELL WHICH SERVES AS BOTH STRUCTURE AND COVERING TO THE BUILDING.

ADVANTAGES VERY LIGHT FORM OF CONSTRUCTION TO SPAN 30m SHELL THICKNESS REQUIRED IS .6m DEAD LOAD CAN BE REDUCED ECONOMIZING

FOUNDATION AND SUPPORTING SYSTEM THEY FURTHER TAKE ADVANTAGE OF THE FACT THAT

ARCH SHAPES CAN SPAN LONGER THAN FLAT SHAPES BY CHOOSING CERTAIN CURVILINEAR PLANE

AESTHETICALLY IT LOOKS GOOD OVER OTHER FORMS OF CONSTRUCTION

DISADVANTAGES SHUTTERING PROBLEM GREATER ACCURACY IN FORMWORK IS REQUIRED GOOD LABOUR AND SUPERVISION IS NECESSARY RISE OF ROOF MIGHT BE A DISADVANTAGE AS PER

THE REQUIREMENTS

CASE STUDY SYDNEY OPERA HOUSEAR. JOHN ULTZON

THE SYDNEY OPERA HOUSE SPANS UP TO 164 FEET THE ARCHES ARE SUPPORTED BY OVER 350KM OF

TENSIONED STEEL CABLE. THE SHELL THICKNESS GOES FROM 3 TO 4 INCHES ALL SHELLS WEIGHT A TOTAL OF 15 TONS THIS INVOLVED LAYING THE FOUNDATIONS AND

BUILDING A PODIUM 82 FEET (25 M) ABOVE SEA LEVEL. MORE THAN 39,239 CUBIC FEET (30,000 M3) OF ROCK AND SOIL WERE REMOVED BY EXCAVATORS.

THE FOUNDATION WAS BUILT ATOP A LARGE ROCK THAT SAT IN SYDNEY HARBOUR. THE SECOND STAGE SAW THE BUILDING OF THE SHELLS, THE PODIUM STRUCTURE, THE STAGE TOWER, AND THE NECESSARY MACHINERY.

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