Dynamic Response Of Hybrid Slab Configurations Under Seismic Loading

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056

Volume: 13 Issue: 03 | Mar 2026 www.irjet.net p-ISSN: 2395-0072

Dynamic Response Of Hybrid Slab Configurations Under Seismic Loading

Arjun Tilak C R1 , Dr Chethan K2

1P.G. Student, department of Civil Engg. , Major: Earthquake Engineering, University of Visvesvaraya College of engineering, Karnataka, India, 2Associate professor, department of Civil Engg. , University of Visvesvaraya College of engineering, Karnataka, India

Abstract- This study evaluates the seismic performance of a 15-storey (G+15) reinforced concrete building using finite element analysis (FEA) in accordance with IS 1893:2016 provisions. The structure was analysed through Modal analysis and Response Spectrum analysis to assess parameters such as natural period, storey displacement, and drift. Results show that the hybrid slab system incorporating core walls and drop panels exhibits superior seismic performance, achieving lower displacement and greater stiffness compared to the conventional flat slab system. The inclusion of core walls and drop panels provides an effective balance between flexibility, stability, and economy, making the hybrid slab configuration suitable for mid-rise buildings in seismic-prone regions.

Keywords: Seismic performance, flat slab, hybrid slab, dynamic analysis, storey drift, base shear, core wall, drop panel

1. INTRODUCTION

Thisprojectinvolvesthedesignandanalysisofa15-storey (G+15)reinforcedconcretebuildingwithdifferentstructural systems, including RC beam–slab, flat slab, and hybrid configurations.Themodelsincorporatecorewallsanddrop panelsandarecomparedintermsofstructuralperformance, cost-effectiveness, and constructability to assess the influence of various slab systems on overall building behavior

1.1 Classification of structural system

Three structural systems were considered to evaluate the seismic performance of a 15-storey (G+15) reinforced concrete building designed as per IS 1893:2016. Type 1 representstheconventionalRCbeam–slabsystem,offering highstiffnessandmomentresistancebutwithgreaterweight andlongerconstructiontime.Type2isahybridsystemwith RCbeam–slabconstructioninthelowerfloorsandflatslabs above,aimingtoreduceself-weightandimproveefficiency. Type3adoptsflatslabsinthelowerfloorsandRCbeam–slab construction above to study the effect of flexible lower storeysonseismicresponse.Allmodelshavea32m×32m baseplanwith4×4baysandareanalyzedunderidentical loadingandseismicconditions.

1.2 Objective of the study

Thestudyevaluatestheseismicperformanceofflatslaband hybrid slab systems under dynamic loading using finite elementanalysis(FEA).ConventionalRCbeam–slabandflat slabsystems,withandwithoutdroppanelsandcorewalls, arecomparedtoassesstheireffectiveness.Theinfluenceof structuralconfigurationandbuildingheightonkeyseismic parameters such as time period, displacement, and storey drift is examined. The effect of drop panels on enhancing stiffnessandreducingseismicvulnerabilityisalsoanalyzed to identify the most efficient slab system with improved seismicresistanceandoverallstability

2.PRELIMINARY DATA CONSIDERED FORANALYSIS

Building Models and Geometry

Sixreinforcedconcretebuildingmodelsweredevelopedfor the15-storey(G+15)structure,incorporatingconventional RCbeam–slab,flatslab,andhybridslabsystemswithand without core walls and drop panels to assess seismic performance.:

Table -1: 6 STRUCTURAL SYSTEMS NOMENCLATURE

Structural System Nomenclat-ure

Firsthalfportionofbuilding floorwithRCbeamslaband abovehalffloorswithFlatslabs 8B8F

Firsthalfportionofbuilding floorwithRCbeamslaband abovehalffloorswithFlatslabs withCore,Drop 8B8FWCD

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056

Volume: 13 Issue: 03 | Mar 2026 www.irjet.net p-ISSN: 2395-0072

5 Firsthalfportionofbuilding floorwithFlatslabandabove floorwithRCBeamslab 8F8B

6 Firsthalfportionofbuilding floorwithFlatslabandabove floorwithRCBeamslabwith Core,Drop 8F8BWCD

Building Dimensions:

•TotalHeight:45m(15storeys)

•StoreyHeight:3m

•PlanDimension:32m×32m(square)

•BayWidth:8m

Material Properties and Sections

ConcreteandSteelProperties:

•GradeofConcrete:M30

•CompressiveStrengthofConcrete:30N/mm²

•ModulusofElasticity(Concrete):27,32N/mm²

•GradeofSteel(Reinforcement):Fe550

•RebarStrength:550N/mm²

SectionDimensions(Commonforallsystems):

•Beam:600mm×600mm(RectangularRCCsection)

•Column:1000mm×1000mm(RectangularRCCsection)

•Slab:220mmthickness,FlatSlab:400mmthickness

•Core(Centralshearwall):300mmthickness,thickness ofdrop100mmand4mx4m(square)

SpecialElements:

•Diagrid(DG):CHS1000×40mm

•Outrigger(OT):600mmthicknesswall

•BeltTrussSystem(BTS):RHS600×1000×30mm

Loading Conditions

GravityLoads(asperIS875-1987PartI&II):

•SuperImposedDeadLoad:1.5kN/m²

•LiveLoad:4.0kN/m²

•MassSource:100%deadload+25%liveload

SeismicLoadParameters(asperIS1893-2016):

•SeismicZone:ZoneV

•ZoneFactor(Z):0.36

•SoilType:mediumSoil

•ImportanceFactor(I):1.2

•ResponseReductionFactor(R):5

•DampingRatio:5%

MODELS USED FOR FE ANALYSIS

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3DViewandElevationG+15[8B8F]

3DViewandElevationG+15[8B8FWDC]

3DViewandElevationG+15[8F8B]

3DViewandElevationG+15[8F8BWDC]

3. RESULTS AND DISCUSSION

3.1 Modal Analysis

Table-2: MODE 1 TIME PERIOD OF ALL STRUCTURES

Chart -1:Modaltimeperiodofallstructure

3.2 Base Shear from Time History Analysis

Table-3: Corrected Dynamic Base shear for all models (106) IN kN

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3.4 Inter Storey Drift Ratio

Table-5: MAX INTER STOREY DRIFT RATIO (10-3)

3.3 Storey Displacement

Table-4: MAX STOREY DISPLACEMENT IN (mm)

Chart -3: MaxDisplacementofAllStructure

4. CONCLUSIONS

Modal Analysis

Modelswithcorewallsanddroppanelsshowbetterseismic performance, with 1B15FWCD, 8B8FWCD, and 8F8BWCD increasing base shear by 68.4%, 98.5%, and 54.9%, respectively. Among base systems, 8F8B performs best, offeringbalancedstiffnessandimprovedseismicresistance.

Base Shear Response

The introduction of core walls and drop panels greatly enhances the lateral load resistance of all models. The 1B15FWCD,8B8FWCD,and8F8BWCDsystemsexhibitbase shear improvements of 68.4%, 98.5%, and 54.9%, respectively, compared to their non-core counterparts. Among the original configurations, the 8F8B model demonstrates the highest base shear, indicating superior performanceinresistingseismicforces

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Lateral Displacement

Incorporatingcorewallsanddroppanelsleadstoamarked reduction in lateral displacement. The 1B15FWCD, 8B8FWCD, and 8F8BWCD models show displacement reductions of 51.9%, 35.1%, and 20.5%, respectively, compared to their non-core versions. Among the basic configurations, the 8F8B model exhibits the least displacement,indicatinggreaterstiffnessandbetterseismic control.

Drift Ratio and Damage Control

The integration of core walls and drop panels effectively minimizesinter-storeydrift,enhancingoverallrigidity.The 1B15FWCD, 8B8FWCD, and 8F8BWCD models show drift reductions of 54.2%, 30.8%, and 40%, respectively, compared to their non-core systems. Among the base configurations,8B8Frecordsthelowestdrift,demonstrating bettercontroloflateraldeformation.

System Ranking & Performance

Models with core walls and drop panels perform much betterinearthquakesbyincreasingstrengthandreducing movement. The 1B15FWCD, 8B8FWCD, and 8F8BWCD modelsshowhigherbaseshearby68.4%,98.5%,and54.9%, alongwithreduceddisplacementanddriftcomparedtotheir normal versions. Among the three main configurations (1B15F,8B8F,and8F8B),the8F8Bsystemperformsbest,as itshowshigherbaseshear,lowerdisplacement,andbetter overallstability.Overall,the8B8FWCDmodelgivesthebest seismic performance, proving that core walls and drop panels greatly improve stiffness and safety during earthquakes.

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Structure under Seismic Load. International Research JournalofEngineeringandTechnology(IRJET),Volume 7,Issue9,September2020.

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