Comparative Analysis of an RC framed building under Seismic Conditions

International Research Journal of Engineering and Technology (IRJET)

Volume: 09 Issue: 04 | Apr 2022 www.irjet.net

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Comparative Analysis of an RC framed building under Seismic Conditions.

1,2,3B.Tech Student, Dept. of Civil Engineering, Delhi Technological University, Delhi, India 4Professor, Dept. of Civil Engineering, Delhi Technological University, Delhi, India

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Abstract India has suffered four great earthquakes of magnitudes 8.5 and greater, in the past hundred years yet human memory being short, it is generallynot recognizedthat we continue to live under the long shadow of such future calamities. Due to Improper design of the structure without seismic resistance many buildings have collapsed and lives have lost during earthquakes. . Different shapes andmaterials of buildings have been used to achievethestrengthrequired to withstand the earthquake. In modern era, lots of seismic force resisting techniques are being used to make a structure/building earthquake resistant. These techniques include introducing Shear walls, Bracings, base isolation, column jacketing etc. to enhance the structure. We discussthe work done by various authors on Different typeofFailuresdue to Earthquake along with the Design andAnalysisofStructure in Earthquake prone Area and present a Comparativeanalysis of earthquake resisting techniques on a G+10 story building with the help of different types of Shear walls & Bracings, using software. The comparison is done between: an un Resisting structure, parallel shear walls, corner shear wall, X shaped bracing at bracings at middle bays, X shaped bracings at corners and X shaped bracings in whole structure. The use of shear walls and bracings helps to strengthen the structure to make it more Earthquake resistant. The analysis in done on a G+10 building for Delhi region as per IS 1893:2016 provisions. The software that we have used to carry out this analysis is Staad pro v8.

Key Words: Static Analysis, Comparative Analysis, STAAD pro, Shear Wall, Bracing, Seismic Conditions, Earthquake.

1. INTRODUCTION

Fromthehistoryofearth,Earthquakeissuddenviolent shakingorVibrationsoftheground.Earthquakecausedby tectonicmovementinearthCrustandalsocausedbysudden sliponafaultorruptureofgeologicalfaults,Butalsobyother events(natural&artificialcauses)suchasvolcanicactivity, Landslides,mineblastsandnuclear tests.Inrecentstudies geologistclaimthatglobalwarmingisoneoftheReasonfor seismicactivity.Accordingtothesestudiesmeltingglaciers andRisingsealeveldisturbthebalanceofpressureonearth tectonic plates thus causing increase in frequency and intensity ofearthquakes results in Damages structure & propertyofnation. Hence, earthquake is amajorproblem

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by development of nation & great Challenge for structural engineer to construct building in seismic region (Zones). Hence,structureshouldbeanalyzedforearthquakeforcesto avoidthedamages.GenerallyStructurehavingtwotypesof loadingthatisstaticloadinganddynamicloading.Staticloads are Constant and dynamic loads are change with time. In maximumcivilbuildingsorstructuresonlystaticloadsare consideredanddynamicloads are not calculated because of more complications in calculation. In Indiavarious previousexamplescanbenotedincludingBhuj2005where thousandsoflivesgotsufferedandthousandsofstructures gotdestroyedbecauseofearthquake.Hencetherewasaneed to make the structure earthquake resistant in order to minimize the destruction of structures and human life these various techniques are being implemented on structuretomakethemseismicallyresistantorearthquake resistant. These techniques include addition of various structuralelementslikesharewalls,bracings,baseisolation dampersetc.InthispaperIamdiscussingthecomparative analysisofvariousearthquakeresistanttechniquesona10 story buildingusingsoftware. Inthispapercompletestatic analysisisperformedbyusingSTAAD Prosoftware.

1.1 SEISMIC RESISTANCE TECHNIQUES

Addition of Shear walls: Shear wall isa seismic restraint member used to oppose lateral forces parallel to the wall. Shear wall opposes the loads due to CantileverAction. So, Shear walls are vertical components of the horizontal or lateralforceresisting

Addition of Bracing: Abracedframeisaframeworkusedin structurestoresisthorizontalloads,forexample,windand seismic pressure. They are commonly made ofbasic steel, which when exposed both tension and compression, work efficiently.Thebeamsandcolumnsthatformtheframecarry vertical loads, and the bracing system carries the lateral loads.Theshaftsandsectionsthatstructuretheframeconvey verticalburdens,andthepropping frameworkconveysthe sidelongloads.

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2. METHEDOLOGY

The methodology worked out to achieve the mentioned objectivesisasfollows:

1. ModelingoftheselectedbuildinginStaadpro.V8i Software.

2. Five models as per the Indian code specification wereprepared.ModelsincludingBareframe,frames withshearwallsandframeswithbracings.

3. Load combinations as per IS 875 part 1 and IS 1893 2016(part10wereappliedandallthemodels analyzed for axial forces, moments, lateral displacements, max shear, storey displacement, storeydriftandgraphicalandtabularrepresentation ofthedataispresented

3. ANALYSIS TECHNIQUES USED ON STAAD PRO.

1. Maxdeflection:Maxdeflectioncanalsobecalledthe Top deflection of the structure. It is themaximum extent to which the structure displaces in X & Z direction under earthquake loads in both perpendiculardirections.

2. Storydrift:Storydisplacementistheabsolutevalue of displacement of the storey underaction of the lateralforces

3. Storyshear:Thedesignseismicforcetobeappliedat eachfloorleveliscalledstoreyshear.

4. MaximumAxialforce:TheAxialForceisgenerally defined as the Force acting along the axis of a member. The maximum axial force is mostly experienced at the base of the structure, at the bottommostcolumns.

4. BUILDING MODELLING.

4.1 General

InthisprojectwemodelledaG+10storeybuildingwith samefloorplanwith4bayshavingsamelengthsof3malong the longitudinal and the transverse directionas shown in figure.Thebuildingsaremodelledusingsoftware STAAD PROV8i.

4.2 Input Data

4.3 Loading Details

Dead Load Slab: Thickness assume = 150 mm FloorFinish=75mm

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Wallloadsexternalwall:230mmthickwallfor 3.0heightsThicknessofwall‘b’ 0.23mHeightof walls‘h’ 3.0m

Unitweightofbrick masonryγ 19.2kN/m3= 0.23 x 3.0 x 19.2 Total load h*b* γ = 13.248 kN/m3

Internalorpartitionwalls:150mmthickwallfor height3.0mThicknessofwall‘b’ 0.12mHeight ofwalls‘h’ 3.0m

Unitweightofbrickmasonry‘γ’ 19.2kN/m3= 0.12 x 3.0 x 19.2 Total load h*b* γ = 6.912 kN/m3

Typeofstructure: multi storey fixed jointed planeframe.

Numberofstories 11(G+10).

Floorheight 3m

Seismiczone IV(DELHI region) (IS 1893 (part1):2016).

MaterialsConcrete (M35)

Reinforcement (Fe415).

Bay sizes in the X direction 3m,3m,3m&3m 4bays

Bay sizes in the Z direction 3m,3m,3m&3m3bays.

Thickness of Wall Externalwall 230mm

Thickness of Internal wall 150mm

Column 450 x 450 mm (for all columns)

Beam 300x300mm(forallbeams).

Typeofsoil mediumsoil

4.4 Load Combination

Theanalysishas beendoneforthedeadload(DL),live load (IL), & earthquakeload(EL) in all the directions i.e. swaytoleft( EL)andswaytoright(EL)byusingsoftware Staadpro.Thecombinationofloadshasbeenmadeaccording tocl6.3ofIS1893(Part1)LoadCombinationforEarthquake Design

Load combinations that are to be used for Limit state Designofreinforcedconcretestructurearelistedbelow.(1) 1.5(DL+LL),(2)1.2(DL+LL±EQ X),(3)1.2(DL+LL±EQ Y),(4)1.5(DL±EQ X),(5)1.5(DL±EQ Y),(6)0.9DL±1.5EQ X,(7)0.9DL±1.5EQ Y.

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LiveLoadAllFloor=2kN/m2

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International Research Journal of Engineering and Technology (IRJET)

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4.5 Earthquake Loads

LoadsarecalculatedasperIS1893:2016(Part1)Seismic parametersconsideredforanalysisareTable 2:

Table 1: Earthquakeloadtable

Seismic Intensity ZoneIV Zonefactor(Z) 0.24

Response Reduction Factor(R) 5

Importancefactor SoiltypeMediumsoil Damping5%

Thedesignhorizontalseismic coefficient Ah for the structure shall be calculated as follows, (IS:1893 2002,Cl.6.4.2)

5. ANALYSIS

AnalysisofbuildingisoneusingSTAADPro.Themodels werepreparedintheSTADDPro.Softwarebyusingdifferent typesofRCshearwallviz.ParallelShearwallandCornered shearwallandthesearelocatedatdifferentlocationsuchas alongperipheryandatcorner.Andalso,analysisisdoneby modellingstructurewithDiagonalandCrosstypeBracings.

1. BaseStructure(withoutseismicrestraints)Abase structureismodelledonlywiththeuseofcolumns andbeams,andnoadditionalseismicrestraintsare used. This the plain or base structure that will be furtherusedforcomparisonwithothermodelswith additional seismic restraints. The following structureisaG+10storybuildingdesignedonstaad prohavingnoseismicrestraints.

2. ParallelShearWallsModelispreparedusingstaad pro software where the high rise structure is embedded&supportedwithshearwallonallfour sides.Theplandimensionstheshearwallisgivenas (8mx0.200m)fromthebasetotheroofi.e.33m.As theShearwallsareinparalleldirectionwithrespect tothetwodirectionsofearthquakeEQX&EQZ,itis namesasParallelShearwalls.

3. CornerShearWallsModelispreparedusingstaad pro software where the high rise structure is embedded&supportedwithshearwallonallfour Cornersofthebuilding.Theshearwallinstalledhere isaL Shapedshearwallwithplandimensionsgiven as(4mx0.200m)+(4mx0.200m)fromthebaseto theroofi.e.33m.

4. Bracing CrossedModelispreparedusingstaadpro softwarewherethehighrisestructureframeworkis embedded & supported with steel bracings. The

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steel bracing used is an angle section having dimensions ISA 100x100x12. The bracings are connected diagonally throughout the framework fromonecolumnbeamjointtoanother.

5. Bracing CrossedModelispreparedusingstaadpro softwarewherethehighrisestructureframeworkis embedded & supported with steel bracings. The steel bracing used is an angle section having dimensions ISA 100x100x12. The bracings are connected diagonally at middle portion of the frameworkfromatallsidesoftheframe.

6. Bracing CrossedModelispreparedusingstaadpro softwarewherethehighrisestructureframeworkis embedded & supported with steel bracings. The steel bracing used is an angle section having dimensions ISA 100x100x12. The bracings are connectedatallcornersoftheframework.

7. Combination of bracing and shear wall is used to preparetwomodelsas perconfigurations givenin diagram.

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Significantreductioninshearforceisobservedincaseof structureswithXbracingsascomparedtothosewithshear walls. In structures with X bracing the best placement of bracingsamongcornerandmiddleismiddleoftheframeas observedformthegraphabove.CombinationofXbracingat cornerwithshearwallalsoreducestheshearforcebylarge amounts.

5.3 Axial Force

Fig 3:MaxbendingmomentinZ

Themaximumreductioninbendingmomentisincaseof bracingandleastincaseofshearwall.Thiscanbeexplained form the fact that shear walls reduce the lateral displacements more as compared to the corresponding bracing structuresasa result larger overturning moments develop in them as compared to structures with bracing. Overallthereisreductioninbendingmomentswithrespect tobareframebutthebestseismicrestraintsinthecaseisX bracing.

5.2 Max Shear Force

Fig 6:Axialforce

Maxaxialforcerepresenttheaxialforcethroughcolumnsat thebaseofthestructure.. Themaxaxialforceisobservedin themodelwithXbracingsandleastisobservedintheModel withshearwallsignifyingimplyingshearwallsarecapableof reducingaxialforces.

5.4 Base Shear

Fig 7:Baseshear

Baseshearisdependentupontheweightofstructurethatis more the weight more is the value of base shear. The minimum value is obtained in case of bear frame while maximumvalueincaseofX bracingatcorner withshear wall.Thetrendshowsthatstructureswithshearwallhave higherbaseshearascomparedtothosewithbracingsdueto moreweightincaseofshearwall.

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5.5 Weight of Structure

Fig 8:Weightofstructure

Themaximumincreaseinweightofstructureisobserved incaseofshearwallswhereasincaseofbracingsthereisno significantincreaseinweightofstructurethatagainsignifies that bracing are better seismic restraintsas the give more stabilitywithoutsignificantincreaseinweightofstructure.

6. CONCLUSIONS

1. Eight RC framed models have been observed and analyzed by introducing various earthquake resistingmembers,like:Parallelshearwalls,Corner Shear walls, & Cross Bracings in various configurations.

2. Byprovidingshearwallsandbracingstothehigh risestructure,seismicbehaviourwillbeaffectedtoa greatextentandalsothestiffnessandthestrengthof thebuildingsisincreased.

3. It is found out that shear walls and bracing contribute largely in reducing the deflection by increasingthestrengthandstiffnessofthebuilding. The results of thisproject can further be used to enhance the seismic strength of buildings using combinationofseismicresistancetechniques.

4. It is observed from the above analysis that the displacement observed in the models, which are withoutshearwalls&bracingsismoreascompared to themodels having shear walls and bracings at differentlocations.

5. It has been observed that the Max deflection is significantlyreducedafterprovidingtheshearwalls orbracingsintheRCframeinX directionaswellas inZdirection.

6. The best location of shear wall in multi storey buildingisparallelshearwallsAndthebesttypeof bracingsthatcanbeusediscrossbracingonwhole structure.

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7. The lateral deflection of column for building with cross bracing on whole structure is reduced maximum followed by those with shear walls as comparedtoallmodels.

8. Finally,itisconcludedthat,optimizationusingcross bracingsisthebestprocedure,inpresentworkmode formaximumearthquakeresistance

9. Shear wall elements are very much efficient in reducinglateraldisplacementofframeasdriftand horizontaldeflectioninducedinshearwallframeare much less than that induced in corresponding braced frame(i.e comparing shear wall at middle with X bracingat middleand shearwall atcorner withXbracingatcorner)andplaneframe.

10. Thecombinationofbareframewithcoupledshear wall in combination with x bracing also provides goodresultaboutreducingthestressesandlateral forcesoverthestructure.Thisimpliesthatthesetype of structure provide better stability during the seismicactivity.

11. Overalltheframescanbearrangedinorderoftheir seismicstability(consideringmoments,storeydrift, storeydisplacementsanddeflections)as

X bracing on whole structure> X bracing at middle with shear wall> X bracing atcorner with shear wall> Shear wall at middle>Shear wall at corner> X bracing at middle> X bracing at corner> Bare frame

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