• Author / Uploaded
• nandu shah

Citation preview

SHELL STRUCTURES • 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. • LATTICE AND PORTAL FRAME BUILDINGS CONSIST OF A STRUCTURAL FRAME WHICH SUPPORTS SLAB, ROOF AND WALL COVERING. THIS FRAME SERVES PURELY AS THE STRUCTURAL SUPPORT AND PROVIDES PROTECTION AGAINST WEATHER. • THE ROOF AND WALL COVERING ADD NOTHING TO THE STRENGTH AND THE RIGIDITY OF STRUCTURAL FRAME.

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.

CONOID BARREL VAULT

• 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 AND SO IS A DOME. • THE TERMS SINGLE AND DOUBLE CURVATURE ARE USED TO DISTINGUISH THE COMPARITIVE RIGIDITY OF THE TWO FORMS AND COMPLEXITY OF CENTERING NECESSARY TO CONSTRUCT THE SHELL FORM.

HYPERBOLOID PARABOLOID

DOME

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. • 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.

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

COOLING TOWER, GENERATED BY STRAIGHT LINES GOULD 1988

FORMS OF CURVATURE SPACES OF TRANSLATION : • 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. • IF TWO PARABOLAS ARE SIMILAR, THE SURFACE BECOMES A SURFACE OF REVOLUTION, CALLED PARABOLOID OF REVOLUTION.

TYPES OF SHELL STRUCTURE FOLDED PLATE SHELLS: • THE DISTINGUISHING FEATURE OF THE FOLDED PLATE IS THE EASE IN FORMING PLANE SURFACES. A FOLDED PLATE MAY BE FORMED FOR ABOUT THE SAME COST AS A HORIZONTAL SLAB AND HAS MUCH LESS STEEL AND CONCRETE FOR THE SAME SPANS. • 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.

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. ESTHETICALLY 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

CASE STUDY- SYDNEY OPERA HOUSE: SYSTEM SPANS AND EFFECTIVE SPANS: • 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 OF 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. • CABLE BEAMS WERE BUILT AND REINFORCED BY STEEL CABLES TO RELEASE THE STRESS OF THE WEIGHT. THE STRENGTH OF THE CABLES WAS TESTED BY LOADING ADDITIONAL WEIGHTS. WHEN THE BUILDERS WERE SATISFIED THAT THE CABLES WOULD SUPPORT, THE BEAMS WERE MADE EXTENDABLE BY OTHER BEAMS.

• THE "SHELLS" WERE PERCEIVED AS A SERIES OF PARABOLAS SUPPORTED BY PRECAST CONCRETE RIBS. • THE FORMWORK FOR USING IN-SITU CONCRETE WOULD HAVE BEEN PROHIBITIVELY EXPENSIVE, BUT, BECAUSE THERE WAS NO REPETITION IN ANY OF THE ROOF FORMS, THE CONSTRUCTION OF PRE-CAST CONCRETE FOR EACH INDIVIDUAL SECTION WOULD POSSIBLY HAVE BEEN EVEN MORE EXPENSIVE. • THE DESIGN TEAM WENT THROUGH AT LEAST 12 ITERATIONS OF THE FORM OF THE SHELLS TRYING TO FIND AN ECONOMICALLY ACCEPTABLE FORM (INCLUDING SCHEMES WITH PARABOLAS, CIRCULAR RIBS AND ELLIPSOIDS) BEFORE A WORKABLE SOLUTION WAS COMPLETED.

• IN MID-1961, THE DESIGN TEAM FOUND A SOLUTION TO THE PROBLEM: THE SHELLS ALL BEING CREATED AS SECTIONS FROM A SPHERE. • THIS SOLUTION ALLOWS ARCHES OF VARYING LENGTH TO BE CAST IN A COMMON MOULD, AND A NUMBER OF ARCH SEGMENTS OF COMMON LENGTH TO BE PLACED ADJACENT TO ONE ANOTHER, TO FORM A SPHERICAL SECTION.

CONSTRUCTION

SYDNEY OPERA HOUSE STEEL REINFORCING

SYDNEY OPERA HOUSE ON COMPLETION OF PODIUM 2

2. SYDNEY OPERA HOUSE ON COMPLETION OF PODIUM 1

FINISHES: • ACTUAL CLAY, BRICK, AND STONE VENEER

• GRANITE OR MARBLE CLADDING • EXPOSED AGGREGATE FINISH • SAND BLASTED FINISH • FORM LINER PATTERNS • THE SYDNEY OPERA HOUSE USES WHITE GLAZED GRANITE TILES. • 1,056,000 TILES WERE USED TO COVER THE MASSIVE STRUCTURE.