Seismic Performance of Regular and Irregular Buildings with Fixed Base and Lead Rubber Bearing Base

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

Volume: 13 Issue: 04 | Apr 2026 www.irjet.net p-ISSN: 2395-0072

Seismic Performance of Regular and Irregular Buildings with Fixed Base and Lead Rubber Bearing Base Isolator

Ashwini Madke1 , Dr. Sarika Modak2

1 PG Student, Priydarshini College of Engineering, Nagpur, India.

2Assistant Professor, Priydarshini College of Engineering, Nagpur, India.

Abstract - The implementation of Lead Rubber Bearing (LRB) base isolation systems significantly optimizes the seismic performance of multistory reinforced concrete moment-resisting frames, particularly for G+10 structures whereplanirregularities suchasL-shapedconfigurations induce complex torsional effects and non-uniform stiffness distribution. While fixed-base irregular structures exhibit amplified inter-story drift demands and localized force concentrations under seismic excitation, the integration of LRB isolators serves as an advanced passive control strategy that extends the fundamental natural period and enhances energydissipation.ResponseSpectrumAnalysisdemonstrates that base isolation effectively decouples the superstructure from ground-induced inertiaforces,resulting inasubstantial reduction in base shear and lateral displacement profiles comparedtoconventionalfixed-basesystems.Ultimately,this seismic isolation technique mitigates the adverse dynamic response associated with structural asymmetry, ensuring superior structural integrity and serviceability in high-risk seismic zones.

Key Words: Lead Rubber Bearing (LRB), Structural Plan Irregularity, Seismic Base Isolation, Response Spectrum Analysis,Inter-storeyDriftRatio,TorsionalEffectMitigation

1.INTRODUCTION

Base isolation represents a paradigm shift in performance-basedseismicengineering,evolvingfromearly patentedconceptsintoaprimarystrategyforensuringthe operational continuity of critical infrastructure. While conventional seismic design relies on the ductility of structuralmemberstopreventcollapse oftenresultingin significant residual damage base isolation prioritizes the protection of both structural integrity and sensitive nonstructural components, such as medical equipment and electricalsystems.ByintegratingflexibleinterfaceslikeLead RubberBearings(LRB)orFrictionPendulumSystemsatthe foundation,thesuperstructureiseffectivelydecoupledfrom horizontalgroundmotion.

Thisdecouplingshiftsthebuilding'sfundamentalnatural period away from the high-energy range of earthquake ground motions, leading to a marked reduction in transmittedflooraccelerations,baseshear,andinter-storey drift.Unlikeinternaldampingsystemsthatmanageenergy within the building frame, base isolation mitigates seismic

demandatthesource.Thisensuresthatregularandirregular reinforced concrete structures remain not only stable but fully functional, preserving safety and serviceability in the immediateaftermathofmajorseismicevents.

1.1 Concept of Base isolation system

Base isolation is a sophisticated structural control strategy that introduces a flexible or sliding interface between a building's superstructure and its foundation to decoupleitfromhorizontalgroundmotion.Byextendingthe fundamentalnaturalperiod,thissystemsignificantlylimits the transmission of earthquake-induced inertia forces, protecting both the structural frame and sensitive nonstructuralcomponents.

To be effective, isolation devices must maintain high vertical load-bearing capacity and service-level lateral stiffness(forwindandminortremors)whileexhibitinghigh lateralflexibilityandenergydissipationduringmajorseismic events. Furthermore, an ideal system incorporates selfcentringcapabilitiestominimizeresidualdisplacementpostearthquake.Thisapproachisparticularlycriticalforfacilities requiringimmediateoccupancy suchashospitalsanddata centers asitprioritizesoperationalcontinuityandreduces long-termlife-cyclecostsbyminimizingstructuraldamage andrepairrequirements.

1.2 Lead Rubber Bearing system

Lead Rubber Bearings (LRBs) have become a predominantsolutioninseismic-resistantdesignduetotheir integrated mechanical efficiency. Structurally, an LRB consistsofalternatinglayersofvulcanizedrubberandsteel reinforcement shims, which provide high vertical axial stiffness to support gravity loads while preventing lateral bulging.

Thedefiningcomponentisthecentrallylocatedleadplug, whichundergoesplasticsheardeformationduringseismic events. This creates a stable bilinear hysteretic response, providingthenecessaryenergydissipationanddampingto control the building's lateral excursions. Because lead recrystallizes at room temperature, it exhibits excellent fatigue resistance and microstructural recovery, ensuring consistentperformanceovermultiplecycles.Bycombining verticalloadsupport,service-levelwindresistance,andhigh seismicflexibilitywithinasinglecompactunit,LRBsoffera technicallyrobustandcost-effectivemethodfordecoupling structuresfromdamaginggroundmotions.

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

Volume: 13 Issue: 04 | Apr 2026 www.irjet.net p-ISSN: 2395-0072

2. AIM AND OBJECTIVE

2.1 Aim:

The primary aim of this research is to investigate and compare the seismic performance of regular and irregular multistoreyreinforcedconcretebuildingsunderfixed-base andLeadRubberBearingbase-isolatedconditions,inorder to evaluate the effectiveness of base isolation in reducing earthquake-induced forces, controlling structural deformations, and improving overall safety and functional performanceofbuildingssubjectedtoseismicexcitation.

2.2 Objective:

1. To evaluate the seismic performance of multistorey reinforcedconcretebuildingswithregularandirregular planconfigurations.

2. To investigate the influence of plan irregularity on dynamicresponseparameterssuchasfundamentaltime period, base shear, storey displacement, inter-storey drift,andflooracceleration.

3. Toanalyseandcomparetheseismicbehaviouroffixedbasestructureswithbase-isolatedstructuresusingLead RubberBearing(LRB)isolators.

4. TostudytheeffectivenessofLeadRubberBearingbase isolationsysteminreducingseismicforcetransmission andenhancingoverallstructuralresponse.

5. To determine the improvement in global seismic performanceandstructuralsafetyachievedthroughthe adoptionofbaseisolationtechnique.

3. METHODOLOGY

Forthisresearchwork,ETABSsoftwarewasused.ETABSisa structuralengineeringsoftwareusedformodelling,analysis, anddesignofmultistorybuildingsundergravityandlateral loads such as wind and earthquake. It provides advanced analysis features including response spectrum and time historyanalysis,makingitsuitableforevaluatingtheseismic behaviorandperformanceofregularandirregularbuilding systems.

Building shape Ordinary (Regular) & L-Shaped (Irregular )

BuildingHeight 33m

OverallStory’s G+10

FloorHeight 3m

LineloadConsidered 6.9kN/m,9.0kN/m,3.0kN/m

ArealoadConsidered LL=3.0kN/m2

SDL=1.5kN/m2

BeasSizeassumed 300x500

ColumnSizeassumed 450x50

Slabthickness 125

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

Volume: 13 Issue: 04 | Apr 2026 www.irjet.net p-ISSN: 2395-0072

Fig -4:RegularBuildingwithLRB

Table -2: Seismicdataconsideration

Seismiczone III

ZoneFactor 0.16

ImportanceFactor,I 1.2

LineloadConsidered 6.9kN/m,9.0kN/m,3.0kN/m

Soiltype II

ResponseReduction factor,R 5

Fig -5:IrregularBuildingwithLRB

Table -3: LRB(LeadRubberBase)Dataconsideration

Fig -5:ExternalLRBused

Fig -6:InternalLRBused

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

Volume: 13 Issue: 04 | Apr 2026 www.irjet.net p-ISSN: 2395-0072

4. RESULTS

4.1 Modal Participation

Table -4: ModalParticipatingMassRatio(RegularBuilding)

Table -5: ModalParticipatingMassRatio(RegularLRB)

Chart -1:ModalBehaviorregularvsregularLRB

Table -6: ModalParticipatingMassRatio(IrregularBuilding)

Table -7: ModalParticipatingMassRatio(IrregularLRB)

Chart -2:ModalBehaviorirregularvsirregularLRB

4.2 Story Drift

Table -8: StoryDriftregularvsregularLRBbuilding

Chart -3:StoryDriftregularvsregularLRB

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

Table -9: StoryDriftirregularvsirregularLRBbuilding

Chart -4:StoryDriftirregularvsirregularLRB

4.3 Story Displacement

Table -10: StorydisplacementregularvsregularLRB building

Chart -5:StorydisplacementregularvsregularLRB

Table -11: StorydisplacementirregularvsirregularLRB building

Chart -6:StorydisplacementirregularvsirregularLRB

3. CONCLUSIONS

1.The integrationofLeadRubberBearing(LRB)isolators significantly optimizes the seismic performance of G+10 reinforced concrete frames by mitigating the complex torsional effects and non-uniform stiffness distribution associatedwithplanirregularities.

2. Base isolation effectively decouples the superstructure fromground-inducedinertiaforces,resultinginamarked extension of the fundamental natural period and a substantial reduction in base shear and lateral displacement.

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

Volume: 13 Issue: 04 | Apr 2026 www.irjet.net p-ISSN: 2395-0072

3. The bilinear hysteretic response provided by the LRB’s leadcoreenablesstableenergydissipationanddamping, which limits the transfer of seismic forces and protects bothstructuralandsensitivenon-structuralcomponents.

4.ComparativeanalysisusingResponseSpectrumAnalysisin ETABSconfirmsthatisolatedirregularstructuresexhibit significantly lower inter-storey drift demands and floor accelerationsthantheirfixed-basecounterparts.

5.The system's self-centring capability and the microstructuralrecoveryoftheleadplugensureconsistent mechanical performance and minimal residual displacementacrossmultipleseismiccycles.

6.Byreducingseismicdemandatthesource,baseisolation ensuresthatregularandirregularbuildingsremainfully functional,prioritizingoperationalcontinuityandreducing long-termrepaircosts.

REFERENCES

[1] NafisaAnjum,“SeismicPerformanceEvaluationofa10storyRCBuildingUsingPushoverAnalysis&Response SpectrumAnalysis”,January2026.

[2] Md. Saniul Haque Mahi, “Seismic Performance AssessmentofRegularandIrregularRCBuildingsUnder BNBC2020UsingETABS”,July2025.

[3] Vinod vawadra,“ Pushover analysis of G+20 RCC StructurewithHorizontalIrregularity”,June2024.

[4] Walid A. Al-Kutti, “Potential Design of Seismic Vulnerable Buildings Incorporating Lead Rubber Bearing”,February2019.