Shell structure.pdf

Complex structures in architecture 'SHELL STRUCTURE'

1. SHELL STRUCTURES

2. 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 STRENGHT AND RIGIDITY DUE TO ITS
THIN,
NATURAL AND CURVED FORM SUCH AS SHELL OF EGG, A NUT, HUMAN SKULL, AND SHELL OF TORTISE.

3. TYPES OF CURVES

4. APPLICATIONS
Architectureandbuilding.
ThedevelopmentofmasonrydomesandvaultsintheMiddleAgesmade
possibletheconstructionofmorespatiousbuildings.Inmorerecenttimesthe
availabilityofreinforced
concretehasstimulatedinterestintheuseofshellsforroofingpurposes.
Powerandchemicalengineering.
constructionofsuitableboilers.Thesethinshellswereconstructedfromplates
suitableformedandjoinedbyriveting.
Structuralengineering.
Animportantproblemintheearlydevelopmentofsteelforstructuralpurposes
wastodesigncompressionmembersagainstbuckling.Astrikingadvancewas
theuseoftubularmembersintheconstructionoftheForthrailwaybridgein1889:
steelplateswererivetedtogethertoformreinforcedtubesaslargeas12feetin
diameter,andhavingaradius/thicknessratioofbetween60and180.
Vehiclebodystructures.
Theconstructionofvehiclebodiesintheearlydaysofroadtransportinvolveda
systemofstructuralribsandnon-structuralpanelingorsheeting.Themodern
formofvehicleconstruction,inwhichtheskinplaysanimportatntstructural
part,followedtheintroductionofsheet-metalcomponents,preformedintothin
doublycurvedshellsbylargepowerpresses,andfirmlyconnectedtoeachotherby
weldsalongtheboundaries.Theuseofthecurvedskinofvehiclesasaloadbearing
memberhassimilarlyrevolutionizedtheconstructionofrailwaycarriagesandaircraft.
Intheconstruction
Compositeconstruction.
Theintroductionoffiberglassandsimilarlightweightcompositematerialshas
impactedtheconstructionofvehiclesrangingfromboats,racingcars,fighterand
stealthaircraft,andoon.Theexteriorskincanbeusedasastrongstructuralshell.
MiscellaneousExamples.
Otherexamplesoftheimpactofshellstructuresincludewatercoolingtowersfor
powerstations,grainsilos,armour,archdams,tunnels,submarines,andsoforth.

5. SINGLE OR DOUBLE CURVATURE SHELLS
SINGLECURVATURESHELL:ARECURVEDONONELINEARAXISANDAREAPARTOFACYLINDEROR
CONEINTHEFORMOFBARRELVAULTSANDCONOIDSHELLS.
DOUBLECURVATURESHELL:AREEITHERPARTOFASPHERE,ORAHYPERBOLOID OFREVOLUTION.
THETERMSSINGLECURVATUREANDDOUBLECURVATUREDONOTPROVIDEAPRECISEGEMOETRIC
DISTINCTIONBETWEENTHEFORMOFSHELLBECAUSEABARRELVAULTISSINGLECURVATUREBUTSO
ISADOME.
THETERMSSINGLEANDDOULBECURVATUREAREUSEDTODISTINGUISHTHECOMPARITIVERIGIDITY
OFTHETWOFORMSANDCOMPLEXITYOFCENTRINGNECESSARYTOCONSTRUCT THESHELLFORM.
CONOID
DOME
HYPERBOLOID
PARABOLOID
BARREL VAULT

6. TYPES OF SHELL STRUCTURES:
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.
THE PRINCIPLE COMPONENTS IN A FOLDED PLATE STRUCTURE CONSIST OF :
1) THE INCLINED PLATES
2) EDGE PLATES WHICH MUST BE USED TO STIFFEN THE WIDE PLATES
3) STIFFENERS TO CARRY THE LOADS TO THE SUPPORTS AND TO HOLD THE PLATES IN LIN
4) COLUMNS TO SUPPORT THE STRUCTURE IN THE AIR.
FOLDED PLATE TRUSS
Z SHELL
TAPERED FOLDED PLATES
CANOPIES
THREE SEGMENT FOLDED PLATE

7. TYPES OF SHELL STRUCTURES:
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.
MULTIPLE BARRELS -
CORRUGATED CURVES UNSTIFFENED EDGES OUTSIDE STIFFENERS THE LAZY S

9. TYPES OF SHELL STRUCTURES:
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.
HALF SPHERE
SPHERE SEGMENT
DOMES -SQUARE IN PLAN

10. MOSTSUITABLEMATERIAL
THEMATERIALMOSTSUITEDFORCONSTRUCTIONOFSHELLSTRUCTUREISCONCRETEBECAUSEITISAHIGHLY
PLASTICMATERIALWHENFIRSTMIXEDWITHWATERTHATCANTAKEUPANYSHAPEONCENTERINGORINSIDE
FORMWORK.
SMALLSECTIONSOFREINFORCINGBARSCANREADILYBEBENTTOFOLLOWTHECURVATUREOFSHELLS.
ONCETHECEMENTHASSETANDTHECONCERETEHASHARDENEDTHER.C.CMEMBRANEORSLABACTSASA
STRONG,RIGIDSHELLWHICHSERVESASBOTHSTRUCTUREANDCOVERINGTOTHEBUILDING.

11. TYPICAL SHELL ROOF FORM
L<S/2
=S/6
=S/9

12. TYPICAL SHELL ROOF FORM
W/8
W/5
R=W S/20
S/7

13. CONTINUOUS CONOID ROOF

14. CONSTRUCTIONOFBARRELVAULT
THEBARRELVAULTISTHEMOSTSTRAIGHTFORWARDSINGLECURVATURESHELLCONSTRUCTION.ITISTHEPART
OFACYLINDERORBARRELWITHSAMECURVATUREALONG
ITSLENGTH.
ANYNUMBEROFCONTINUOUSBARRELSORCONTINUOUSSPANSAREPOSSIBLEEXCEPTTHATEVENTUALLY
PROVISIONISMADEFORTHEEXPANSIONOFTHEJOINTSINALARGESTRUCTURES.
THEBARRELVAULTSAREUSEDASPARKING,MARKETPLACE,ASSEMBLYHALL,ETC.
TYPESOFBARRELVAULTS
1.SHORTSPANBARRELVAULTS
2.LONGSPANBARRELVAULTS

15. BARREL VAULT SHELL ROOF
SHORT SPAN BARREL VAULT
SHORT SPAN BARREL VAULTS ARE THOSE IN WHICH SPAN IS SHORTER THAN ITS WIDTH. IT IS USED FOR THE WIDTH
OF THE ARCH RIBS BETWEEN WHICH THE BARREL VAULT SPAN.
LONG SPAN BARREL VAULT
LONG SPAN BARREL VAULTS ARE THOSE IN WHICH SPAN IS LARGER THAN ITS WIDTH.
STRENGTH OF THE STRUCTURE LIES AT THE RIGHT ANGLES TO THE CURVATURE TO THAT SPAN IS LONGITUDINAL TO
THE CURVATURE.
USUAL SPAN OF THE LONGITUDINAL BARREL VAULT IS FROM 12-30 M WITH ITS WIDTH BEING ABOUT 1/2 THE SPAN
AND RISE IS 1/5 OF THE WIDTH.
TO COVER LARGER AREAS MULTIBAY ,MULTI SPAN ROOFS CAN BE USED WHERE THE ROOF IS EXTENDED ACROSS THE
WIDTH OF THE VAULT AS A MULTIBAY .

16. ROOFLIGHTS:
TOPLIGHTCANBEPROVIDEDBYDECKLIGHT
FORMEDINTHECROWNOFVAULTORBYDOME
LIGHT.THEDECKLIGHTCANBECONTINUOUSOR
FORMEDASINDIVIDUALLIGHTS.ROOFLIGHTS
AREFIXEDTOANUPSTANDCURBCAST
INTEGRALLYWITHTHESHELL.
ADVANTAGEOFTHESHELLISTHATITSCONCAVE
SOFFITREFELECTSANDHELPSTODISPERSE
LIGHTOVERAREABELOW.DISADVANTAGEIS
THATTOPLIGHTMAYCAUSEOVERHEATINGAND
GLARE.
ROOFCOVERING:
SHELLSMAYBECOVEREDWITHNON-FERROUS
SHEETMETAL,ASPHALT,BITUMENFELT,A
PLASTICMEMBRANEORALIQUIDRUBBERBASE
COATING.
ROOFINSULATION:
THETHINSHELLOFFERSPOORRESISTANCETO
TRANSFEROFHEAT.THENEEDTOADDSOME
FORM OFINSULATINGLININGADDS
CONSIDERABLYTOCOSTOFSHELL.THEMOST
SATISFACTORYMETHODOFINSULATIONISTO
SPREADALIGHTWEIGHTSCREEDOVERTHE
SHELL.
DIFFICULTIESOFPROVIDINGINSULATIONAND
MAINTINGTHEELEGANCEOFCURVEDSHAPE
MAKESTHESESTRUCTURESLARGELYUNSUITED
TOHEATEDBUILDINGSINTEMPERATECLIMATE.

17. STIFFENINGBEAMSANDARCHES:
UNDERLOCALLOADSTHETHINSHELLOFTHE
BARRELVAULTWILLTENDTODISTORTANDLOSE
SHAPEANDEVENCOLLAPSEIFTHERESULTANT
STRESSESWEREMORE.TOSTRENGTHEN THE
SHELLAGAINSTTHISPOSSIBILITY,STIFFENING
BEAMSORARCHESARECASTINTEGRALLYWITH
THESHELL.
THECOMMON PRACTICE ISTOPROVIDE A
STIFFENING MEMBER BETWEEN THECOLUMN
SUPPORTINGTHESHELL.
DOWNSTAND STIFFENINGRCCBEAMISMOST
EFFICIENTBECAUSE OFITSDEPTH,BUTTHIS
INTERRUPTSTHELINEOFSOFFITOFVAULTS,FOR
THISUPSTANDSTIFFENINGBEAMISUSED.
THEDISADVANTAGE OFUPSTANDBEAMISTHATIT
BREAKS
UPTHELINEOFROOFANDNEEDPROTECTIONS
AGAINST
WEATHER.

18. EDGEANDVALLEYBEAMS:
DUETOSELFWEIGHTANDIMPOSEDLOADTHETHIN
SHELLWILLTENDTOSPREADANDITSCURVATURE
FLATTENOUT.TORESISTTHISRCCEDGEBEAMS
ARECASTBETWEENCOLUMNS.
EDGEBEAMSMAYBECASTASDROPPEDBEAMSOR
UPSTANDBEAMSORPARTIALLYASBOTH.INHOT
CLIMATETHEDROPPEDBEAMISUSEDWHEREASIN
TEMPERATE CLIMATEUPSTANDBEAMISUSEDTO
FORMDRAINAGECHANNELFORRAINWATER.
INMULTI-BAYSTRUCTURES, SPREADING OFTHE
VAULTSISLARGELY TRANSMITTED TOTHE
ADJACENTSHELLS,SODOWNSTANDANDFEATHER
VALLEYBEAMISUSED.

19. EXPANSIONJOINTS:
THECHANGEINTEMPERATURE
CAUSESTHEEXPANSION AND
CONTRACTION INCONCRETE
STRUCTURES,WHICHCAUSES
THESTRUCTURES TODEFORM
ORCOLLAPSE.
TOLIMITTHISCONTINUOUS
EXPANSION JOINTS ARE
FORMEDATTHEINTERVALOF
ABOUT30M,ALONGTHESPAN
ANDACROSSTHEWIDTHOFTHE
MULTI-BAYAND MULTI-SPAN
BARREL VAULT ROOFS.
LONGITUDINAL EXPANSION
JOINTSAREFORMED INAUP
STANDVALLEY.

28. CATENARY SHELL
•Cheeseclothandplastershells
weredriedupsidedown
creatingformsinpuretension.
Whenflipped,shellsrestinpure
compression,resultingin
lightweightformsthatcouldbe
builtfromthinconcrete.

33. 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

34. NUBIAN VAULT

36. GUNA TUBE VAULT