“A Study of Affordable Roofing System with Rectangular Pyramidal Panels”

American Journal of Engineering Research (AJER) 2016 American Journal of Engineering Research (AJER) e-ISSN: 2320-0847 p-ISSN : 2320-0936 Volume-5, Issue-10, pp-121-128 www.ajer.org Research Paper Open Access

“A Study of Affordable Roofing System with Rectangular Pyramidal Panels” Ravindra R1, Subramanya K.G2, Tejus V3 1AssociateProfessor,Dept.of CivilEngineering,R.V. College of Engineering, VTU,India 2AssistantProfessor,Dept.of CivilEngineering,GSKSJTI, VTU,India.

3Post Gradute student,Dept.of CivilEngineering,GSKSJTI, VTU,India.

ABSTRACT:affordablehousingisatermusedtodescribedwellingunitswhosecostsaredeemed“affordable”toagrou pofpeoplewithinaspecifiedincomerange.Structuralfloors/roofsaccountforsubstantialcostofbuildinginnormalsituat ion.ThereforeanysavingsachievedintheroofingSystemsconsiderablyreducethecostofthebuildingunit.Afocusedinve stigationistobemadetocheckwhethertheprefabricatedroofingwouldreplacethenormalroofingprocess. In the study undertaken,Pre-cast RCC roof infill elements are supported on precast RCCj oist System.The rectangular pyramidal panels consideredhavealeastsizeof0.5mand0.75mwiththeaspectratiovaryingfrom1.25to2withariseof60mmatthecenter.Th eanalysisoftheroofSystemismadebyusingSTAADPROsoftwareandlaterdesignedusingM20gradeconcreteandsteelc orrespondingto415N/mm2.Thecostanalysismadeforthe affordable roofingSystemproposedindicatesacostreductionbetween0.4%to34.7%whencomparedtotheconventionalRCCslab of same size.The panels weighless errand can easily be handled by three to five masons. It proves to bea strong alternative to the conventional RCC roofing System.

Keywords –Affordable Roofing, Precast Concrete, CostEconomics of Roofing System, Aspect Ratio.

Affordable housing

I. INTRODUCTION Housingaffordabilityhasalwaysbeenaworldwideconcern.Roofsarethecomponentsinstalledatthetopofthebuildingsto protecttheoccupantsagainstadverseweatherconditionssuchastemperaturechanges,solarradiation,rain,snow,andwin d.So,anykindsofsavingattainedintheconstructionofroofingSystemsubstantiallyreducesthecostofthebuildingunit.

Asotheressentialpartsofbuildings,roofscorrespondtoabout811%ofthetotalprojectcost[1].InIndiaaccordingtotheWorldBankestimatesof2013,around23.6%oftheresidentsareres idingunderthelowerpovertylineandtheshortageintheurbandwellingunitswasassessedas17millionunits.

Inviewofsearchofalternateroofingtechnology,thepresentworkundertakenhasprecast RCCroofinfillelementswhicharesupportedonagridworkofprecastRCCjoistSystemandwithanoverlayofinsituconcrete.The components of roofing Systema r e (i).Roofinfillelementofrectangularpanelswithpyramidal shapeofsmaller thicknesstohavemembraneactionaswellasarchingaction. (ii).PrimaryandsecondaryRCCprecastbeamslikegridSystem.

Thenecessityinthereductionofthecostinconstructionledtothedevelopmentofalternativeroofingtechnologies.Fillersla bisonesuchtechnology,whichisbasedontheprinciplethatconcretecantakeupcompressionbutisweakintension.Thusint heconventionalRCCslab,bottomportionofthe concreteissubstitutedwith acheaperandlighterfillermaterialforcosteffectiveadvantageoverRCCslab[2].PrecastRCCplanksandjoistSystemisanotheralternativeroofingtechnology.Her e,precastplanksaresupportedabovethepartiallyprecastjoistSystemacrossandarethenlinkedtogetherbyinsituconcretepouredoverfullroofingareaandreinforcedhooksprojectoutfromthejoistSystemstohavemonolithicaction[ 3].

B.V.VenkataramanaReddy,JagadishKSet.al[4]havehighlighted someissuesrelatingtotheenvironment,energyeffectsofalternativebuilding techniquesintheresearchwork.Alternatebuildingtechniquesdevelopedwereenergyefficientandtheembodiedenergyo fthehousingunitsconstructedusingtheseskillsarefoundtoconsumelessenergythanhalfoftheenergyutilizedbyconventi

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onalhousingunits.HiraBNandNegiSK[5]havefoundoutanumberofaspectsofprefabricatedbuildingpracticesforlowc osthousingbyhighlightingthevariousprefabricationtechniques,andtheeconomicbenefitsattainedbyitsadoption.Adla khaPKandPuriHC[6]havesuggestedtheuseofthePrecastRCPlanks and joists, PrecastRC Channel Roofing,PrecastConcretePanels,PrefabricatedBrickPanels,Precast RBCurvedPanels, andPrecast HollowSlabs etc.asroofelements.ResearchworkscarriedbyAdlakhaPK[8],VivianW.Y [9],TiwariP [10],and IanHolton[11]givesthecosteffectiveconstructionandsustainableenergy,anditisfoundthatthereisaneedof environment-friendlyand innovativehousingtechniquesforthedevelopmentofhousesandstructureswithsubstantialreductioninthecost.

WilliamG.Davids[12],hasgivenastudywhichmainlyemphasizesonthein-planeloaddeflectionsaswellasbucklingresponseofthepressurizedprefabricatedarchesof continuouscircularcrosssection.ImmanuelGandKharthiK[13],havefoundoutbehaviourofvarioustypesofshelleleme ntsinroofslabsorinanyotherstructure.Researchworkswerecarriedoutontheoptimizationmethodsforroofslabsforthele astpossiblecost.RichardJ.BallingandXiaopingYao.,BoozWet.al[14],havementionedofoptimizationmethodforthree -dimensionalreinforcedconcreteframedstructuresandotherfloor/roofstructures.

ItisnotedthatconventionalroofinginahousingSystemisoneofthemostcostlycomponentsandalsocontributeshugelytot heembodiedenergyofthebuildingsasawhole.Hence,itisnecessarytofindasuitablecosteffectivealternativeroofingtech nologybyusingprecastingtechniques.Byusingthistechnology,formworkcost,Labourcharges,castinsituworktobecarr iedoutetc.canbeavoided.Thisprojectaimsatdevelopinga costeffectiveroofingtechnologywhichiseconomical,lesstimeconsumingforconstructionandaestheticallypleasing roofingSystem.ItalsoaimsatdevelopingatechnologyofprovidingroofingSystemwithprecastpanelssupportedonpreca stbeams.

II. SCOPE AND OBJECTIVE OF THE STUDY Themainobjectiveofthisanalyticalinvestigationundertakenistoexaminethebehaviourandperformance ofthe precast joistsandpanel roofingSystem.ItalsoaimsatdevelopingatechnologyofprovidingroofingSystemwithprecastpanelssupportedonprec astbeams.Rectangularprecastpanelshavingshortersideoflength0.5mand0.75mareconsideredinthestudy.Theaspectr atioofthepanelisvariedfrom1.25to2withariseof60mm atthecentre.Table1showsthedetailsoftheproposedslabSystemundertakenforstudy.AtypicallayoutoftheroofingSyste misshowninFig1.

ARS refers to affordable roofing system Table 1 Parameters Undertaken For the Present Study SL NO 1 2 3 4 5 6 7 8

Rectangular panel Dimension in (m) 0.5 X 0.625 0.5 X 0.75 0.5 X 0.875 0.5 X 1.0 0.75 X 0.9375 0.75 X 1.125 0.75 X 1.3125 0.75 X 1.5

Aspect Ratio 1.25 1.50 1.75 2.00 1.25 1.50 1.75 2.00

No. of Panels Along shorter span 5 5 5 4 4 4 4 4

Along span 4 4 4 3 4 3 3 3

longer

Total Size of the ARS Slab 2.50 X 2.50 2.5 X 3.0 2.5 X 3.5 2.0 X 3.0 3.0 X 3.75 3.0 X 3.375 3.0 X 3.94 3.0 X 4.5

Fig1.Typical Layout of the Roofing System

III. LOADS CONSIDERED  

Aliveload (LL)of 1.5KN/m2isconsidered,inaccordancetoIS875:1987 (Part2).

Dead load is considered to be the self-weight of beams and panels. The Density is taken as

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25KN/m3.InaccordancetoIS875:1987 (Part 1).   

Screed Concrete isassumedasfloorfinishing.Densityofscreed concreteisassumedas20KN/m3, thethicknessofscreed concreteiscalculated based on rise. Fig2showsthecrosssectionaldetails.

Water proofing coat: The Density of WPC is taken as 20.40KN/m3 inaccordancetoIS875:1987 (Part 1)and the Thickness of WPC is taken as 50mm fig 2 gives the details of panel thickness and WPC thickness.

Theanalysisiscarriedfora loadcombinationof1.5(DL+LL)asperIS456:2000

Fig 2 Panel Thickness and Floor Finishes Considered For Slab

IV. ANALYSIS AND DESIGN RectangularPanels ThesizingofthemainbeamandthesecondarybeamismadebypreliminaryanalysisoftheroofingSystemproposed.Thesi zeofthebeamof150mmwidthand150mmdepthwassufficientforallthetypesoftheslabsconsidered.Thedetailed analysisoftheroofingSystemismadeusingSTAADPROsoftware.Therectangularpanelsarediscretisedintothreenod edandfournodedelements.Atypicaldiscretised modelofarectangularpanelisshowninFig3(a) and 3(b).T heslabthicknessoftherectangularpanelsareassumedtobe 75mm in the initial phase of analysis which was later revised based on analysis results.Thesecondarybeamsaresupportedonthebracketprovidedon themain beam asshown inFig4.The analysisof the roofing System using thesoftwareyieldedthecriticalvaluesofbendingmoment(MxandMy),shearstress(SqxandSqy),andinplanestresses(SxandSy).ThenotationsforthecriticalvaluesforbendingmomentshearstressandinplanestressesarethesameasusedintheSTAADPROsoftware.

Thetypicalstresscontoursofarectangularpanelmeasuring 0.5mx 0.625misshown inFig5(a),5( b),and 5(c).TherectangularpanelsaredesignedbylimitstatemethodinaccordancetoIS456:2000.Therectangularpanelsared esignedforBendingMoment,Shearandalsoforthecombinedactionofbendingmomentandinplanestresses.Atypicalreinforcementdetails in 2 therectangularpanelisshowninFig6.M20gradeofconcreteandreinforcementhavingyieldstrengthof415N/mm isass umedinthedesign.

Fig 3(a) Top view of Discretised Slab panel

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Fig 3(b) Front view of Discretised Slab panel

Fig 4 ConnectionbetweenBracketandSecondaryBeam

Fig 5(a) MxLocalStresses (for0.5mx0.625mPanel)

e Fig 5(b) SxLocalStresses(for0.5mx0.625mPanel)

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Fig 5(c) SqxLocalStresses(for0.5mx0.625mPanel)

Fig6ReinforcementLayout(forPanelofSize0.5mX0.625m)

Fig7 SlabofSize2.5mx2.5m(For0.5mx0.625mPanel) PrimaryandSecondaryBeam Theanalyticalmodeldevelopedforaroofofsize2.5mx2.5mis showninFig7.Theprimarybeamandthesecondarybeamofsize150mmx150mmaredesignedbylimitstate

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methodusingM20gradeconcreteandsteelhavingyieldstrength415N/mm2.Thesecondarybeamsareassumedtobesi mplysupportedattheends.Theassumeddimensionofthebeamsof150mmx150mmisfoundtobeadequateforthecritic al values ofbendingmoment andshearobtainedfromthedetailedanalysisusingthesoftware.

Brackets ThearrangementofabracketSystemisshowninFig4.Thebracketsizeismadeconsideringthemaximumshearingforcetr ansmittedbythesecondarybeam.Basedonthisconditionthewidthofthebracketiskeptsameasthewidthofthebeams,wh ileabearinglengthof80mm wassufficientto ensurethebearingstresseswithinthepermissiblelimits (0.45fck).Depthofthebracketof 50mmissufficienttotakecareofthebendingmomentgeneratedduetotheeccentricityofthereactionsofthesecondarybe am.Limit state adoptedforthedesignofthebrackets [18].Thecentralbeamisaprimarybeamwhichsupportstwosecondarybeamsoneitherside.Secondarybeamtransfersar eactionontheprimarybeamwhichinturninducesamomentcausingtheupperfaceofthebrackettoactasatensionregiona ndthebottomregionasa compression. Thebracketisdesigned asper the guidelines ofIS456:2000.Fig8 showsaprimarybeamwithbracketconnectiononboththesideofitandsecondarybeamsrestingoverit.Atypicalreinforce mentofsecondarybeamrestingoverthebracketsoftheprimarybeamisshowninFig8.Slotisprovidedinthebracketandth esecondarybeamforplacinga10mmbarandgroutedwiththecementmortarforadepthof25mm.The slot is grouted with cement slurry for better connectivity.

Fig8 TypicalReinforcementofSecondaryBeamRestingovertheBracketsofthePrimaryBeam

V. COST ANANLYSIS Economy in the construction industry is one of the prime factors apart from safety and durability. Cost analysis is made for proposed affordable roofing System and conventional RCC slab. For a conventional RCC slab System concreting, shuttering and bar bending is done in-situ, where as in case of the proposed Affordable roofing System it is done in the casting yard. Hence same rate cannot be considered for both Conventional RCC slab and Affordable roofing System (ARS) slab, Rate analysis is done for the above said items and the respective rates are considered for cost analysis.

Cost ratio is the ratio of cost of ARS slab to cost of conventional RCC slab per Sqm in Rupees (Rs) Table 2 Cost Comparison of ARS and Conventional RCC Roof (Rise 60mm) SL NO

SizeofSlab in m

1 2 3

2.5 2.5 2.5

X X X

2.5 3.0 3.5

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Rise mm 60 60 60

in

Conventional slab

ARS slab

Total Cost in Rs 14460.12 17093.63 21428.18

Total Cost in Rs 13193.54 15493.87 20628.69

Cost Per Sqm in Rs 2313.62 2279.15 2448.94

Cost Per Sqm in Rs

Cost Ratio

2110.97 2065.85 2357.56

0.912 0.906 0.963

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2.0 3.0 3.0 3.0 3.8

X X X X X

3.0 3.75 3.38 3.94 4.5

60 60 60 60 60

13979.66 25996.53 23591.83 27463.86 43033.79

2329.94 2310.80 2330.06 2324.98 2550.15

13923.87 19623.45 18934.42 21966.41 28109.10

2016 2320.65 1744.31 1870.07 1859.59 1665.72

0.996 0.755 0.803 0.800 0.653

Table3 WeightsofPanel,PrimaryBeamandSecondaryBeam

VI. CONCLUSION Based on all the analytical investigations carried out in the project the following conclusions may be drawn.  The precast beam and panel roofing System designed in the work proves to be a strong alternative to the conventional RCC roofing System.  There is 0.4%-34.7% of cost reduction in the precast roofing Systems when compared to the RCC roofing System, which advocates the adoption of this technology in low cost housing projects.  The alternative roofing System proposed has a pleasing aesthetic appearance in the soffit of the pyramid portion. It requires no plastering work and false roofing work can be avoided which reduces the cost of the roofing unit.  The roofing Systems proposed in the current project is designed to take the factored load of 1.5 times the dead load and live load.  The important factor during the construction is the total time consumed for construction. The kind of roofing System adopted in the project would reduce the time of construction as the panels and joists are readily available precast and can be just placed avoiding the cast in-situ construction.  The panel weighs lesser and can easily be handled by three to five masons. Thus reduces the cost in using Labour for construction and can be erected in a very short period of time.

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