International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 11 Issue: 06 | Jun 2024 www.irjet.net p-ISSN: 2395-0072
COMPARATIVE STUDY OF BRACED STEEL STRUCTURE WITH UNBRACED STEEL STRUCTURE
Uzair Yaseen1 , Misbah Danish Sabri2
1Department of Civil Engineering, Al-Falah University, Faridabad India
2Assistant Professor Department of Civil Engineering, Al-Falah University, Faridabad India
Abstract - In modern construction, steel structures are used for almost every type of structure including heavy industrial building, high-rise building, equipment support systems, infrastructure, bridges, towers, heavy industrial plant, etc. This study investigates as well as compares the performances of braced steel system & unbraced steel system. To perform the analysis ETABS is used to get the output using dynamic analysis (Response Spectrum). The performances ofstructures are evaluated withthehelp of base shear, deflection, story drift, story displacement, natural time period, Structure is stabilized by providing braceframeinbothlongitudinalandtransversedirection, SemiRigiddiaphragmofconcretemetaldeckisconsidered in each story is provided to ensure proper lateral load transfer to vertical brace hence providing stability and controllingthedeflectionwhileanalysinganddesigningthe structures.Byconsideringvariousparameterssuchasstorey displacement,drift,stiffness,lateral force,and base shear, you'reabletocomprehensivelyassesstheeffectivenessof bracing in resisting seismic forces. Using two different models, we can compare how buildings with different structureshandleearthquakes.
Key Words: Baseshear, Time period,storey drift, Storey displacement,Bracing,Responsespectrum.
1. INTRODUCTION
A steel structure is a metal structure which is made of structuralsteelcomponentsconnectedtoeachothertocarry loadsandproviderigidity.Becauseofthehighstrengthof steel, these structures are reliable and require less raw material than some other types of structure such as concrete. Braced frames are known for their ability to provide efficient lateral stiffness. It's now widely acknowledgedthatbracingsystemscanofferthenecessary stiffness to withstand moderate earthquakes and similar dynamic forces, while also serving as a source of energy dissipation through post-buckling hysteresis behaviour of braces
Bracingsystemsarebroadlyclassifiedintotwocategories: concentric bracing and eccentric bracing. In eccentric schemes, preventing brace bucklingiscrucial to confining inelasticdeformationtoashortsegmentofthegirdersacting as shear hinges bracing systems, braces undergo cyclic deformations beyond buckling and yielding due to severe
dynamic excitation. Understanding the cyclic inelastic behaviourofbracingmembersisessentialfor.Inconcentric evaluating the dynamic response of concentrically braced structures. Previous researchers have developed several analyticalmodelstorepresentthecyclicbehaviourofsteel braces. These models incorporate important phenomena observedduringinelasticcyclicloading,suchascompression strengthdeterioration,residualelongationduetoplasticity, andlocalbuckling.
1.1 MODEL CONFIGURATION
The general software E-TABS has been used for the modelling. It is more user friendly and versatile program thatoffersawidescopeoffeatureslikestaticanddynamic analysis,non-lineardynamicanalysisandnon-linearstatic pushoveranalysis,responsespectrumanalysis,timehistory analysisetc.ETAB.Softwareisusedinmodellingofbuilding framesanditisgeneralpurposesoftwareforperformingthe analysis and design of a wide variety of structures G+ 7 story two regular steel building are considered, one with vertical bracing and the other without bracing. The beam lengthin(x)transversedirectionandlongitudinaldirection isshownintheFigurehaving12baysinx-directionand5 baysiny-direction.Storyheightofeachbuildingisassumed 4.5m.Figure1.2showsthe3Dframebuildingofunbraced building and figure 1.3 shows the 3D frame of braced building.
Fig:1.1PLANOFBOTHBUILDING.
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 11 Issue: 06 | Jun 2024 www.irjet.net p-ISSN: 2395-0072
1.2 STRUCTURE MODEL DATA
The G+7 story steel building was analysed for gravity, seismicandwindloadsinEtabs.Forthecomparativestudy, beam and column dimensions are kept same in both the buildings. Height of the story is 4.5 m and beam length in longitudinalandtransversedirectionisshowninFig:1.2.1 andFig:1.2.2
No.ofStories G+7
StoryHeight 4.5m
Gradeofconcrete M30
Gradeofsteel Fe345
Width of building in Xdirection
Width
Table:1.2.1
Structural Element Crosssection Length(m)
Beam in (x) direction. W24x94 W24x104
W24X117 W24X131 7,8,9,9.5,10 7,8,9,9.5,10
Table:1.2.2
2. RESULTS
TIME PERIOD: -Timeperiodofabuildingisthedurationit takes for one complete cycle of vibration. Bracing can significantlyaffectthebuilding'sstiffness,therebyaltering itsnaturalfrequency&hencethetimeperiodofvibration.
The decrease in the natural period of a structure with bracingcomparedtoonewithoutindicatesthatthepresence ofbracingmodifiesthestructuraldynamics.Whenbracings areintegratedintothestructuralsystem,theyenhancethe overallstiffnessofthebuildingandestablishamoreefficient pathforlateralloads.Consequently,thestructuretendsto respond more swiftly to dynamic loading, resulting in a shorternaturalperiodandtypicallyastiffersystem.
BASE SHEAR: - Baseshearisthetotallateralforceactingat the base of the structure due to seismic or wind loads. Bracingsplayacrucialroleindeterminingthedistributionof thisbaseshearthroughoutthestructure.
Fig:1.23DVIEWOFUNBRACEDBUILDING
Fig:1.33DVIEWOFBRACEDBUILDING
Fig2a
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 11 Issue: 06 | Jun 2024 www.irjet.net p-ISSN: 2395-0072
Fig2b
Ifstructurewithoutbracinghaslessbaseshearcomparedto structurewithbracing,itsuggeststhatpresenceofbracing redistributeslateralforcewithinstructure.
STOREY DRIFT: - Storey drift is defined as the relative displacementbetweenthetopandbottomofanystorey.Itis calculated by considering the difference in displacements between the top and bottom of each storey due to lateral forces. According to IS 1893-2016, clause 7.11.1.1 Storey drift in any story shall not exceed 0.004 times the storey height,undertheactionofdesignbaseshearwithnoload factors mentioned in 6.3 of Is 1893-2016, story drift is a critical parameter that governs the design and seismic performance of buildings. Engineers adhere to stringent guidelines to ensure that structures can withstand lateral forces while maintaining safety and functionality during seismicevents.
COMPARISONOFSTOREYDRIFTSOFTWOBUILDINGS
Bracings significantly reduce peak earthquake & wind displacements in both X & Y directions, as well as peak earthquake story drifts, highlighting their effectiveness in enhancinglateralstiffness&structuralstabilityunderlateral force
STOREY DISPLACEMENT: - Storeydisplacement"refers totheverticaldisplacementormovementofeachfloorlevel inabuildingstructure.Whenanalysingthebehaviourofa building under various loads such as gravity loads, wind loads, or seismic forces, engineers often calculate the displacementateachstoreytounderstandhowthebuilding respondstotheseloads
COMPARISON OF STOREY DISPLACEMENT OF TWO BUILDINGS
SPECX
MAX.STOREYDRIFT(X-Dir)
MAX.STOREYDRIFT(Y-Dir)
MAX.STOREYDISPLACEMENT(X-Dir)
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 11 Issue: 06 | Jun 2024 www.irjet.net p-ISSN: 2395-0072
MAX.STOREYDISPLACEMENT(X-Dir)WINDX
MAX.STOREYDISPLACEMENT(Y-Dir)SPECY
MAX.STOREYDISPLACEMENT(Y-Dir)WINDY
3. CONCLUSIONS
Economic Efficiency: Bracing structures with vertical geometricregularityexperienceminimallateraldeformation duringseismicevents,makingthemeconomicallyfavorable duetoreducedmaterialusage&constructioncosts.
LateralStabilityEnhancement: Theuseofslenderbracings enhancesthe lateral stabilityofthestructure,leading toa significant reductioninself-weight.Thisreductioninload contributes to more efficient seismic analysis & overall structuraldesign.
Deformation&Drift: Themax.storeydeformation&drift duetoearthquakeforcearewithinsafelimitsaccordingtoIS guidelines,indicatingstructuralstability&safetyofbuilding underseismicloading.
Seismic Performance: Bracing buildings demonstrate the capability to absorb max. lateral force from earthquake events,resultinginamoreeconomicaldesigncomparedto other building types. The addition of bracings increases stiffness of building, leading to reductions in peak earthquake displacements & story drifts in both X & Y directions,enhancingoverallseismicperformance.
Impact on Time Period & Base Shear: Introduction of bracings decreases time period of building by 22% but increases the base shear by 20% to 26% compared to buildings without bracings, reflecting the influence of bracingsonbuildingstiffness&responsetoseismicforce.
ReductioninDisplacements&Drifts: Bracingssignificantly reducepeakearthquake&winddisplacementsinbothX&Y directions, as well as peak earthquake story drifts, highlightingtheireffectivenessinenhancinglateralstiffness &structuralstabilityunderlateralforce.
Increased Stiffness: Bracing contribute significant lateral stiffnesstothestructure,enhancingitsresistancetolateral loads. This increased stiffness leads to a shorter natural periodofvibration,therebyreducingtheoveralltimeperiod
Stiffness&Resistance:Bracingincreaseoverallstiffnessof structure,makingitmoreresistanttolateralmovement.This increasedresistancemeansthatmoreofthelateralforceis resisteddirectlybythebracing,leadingtohigherbaseshear values.
Restriction of Lateral Deformation: Bracing restrict the lateral deformation of the building, thereby reducing its flexibility.Thisrestrictioninflexibilityresultsinashorter timeperiodforthestructure'svibrationalresponse
Lateral Force Distribution: Bracing are designed to resist lateralforcesuchasthosefromseismicorWL.Whenthese forceactonthebuilding,bracinghelpdistributethemmore efficientlythroughoutthestructure.Asaresult,theoverall baseshearislikelytobehigherinbuildingswithbracing
Overall,thefindingssuggestthatincorporatingbracingsin building design improves seismic performance, reduces deformations & drifts, & enhances structural stability, ultimatelyleadingtomoreeconomical&resilientstructures inseismic-proneregions.
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 11 Issue: 06 | Jun 2024 www.irjet.net p-ISSN: 2395-0072
REFERENCES
[1] IndianNationalCodes(IS-875,IS800-2007,IS-456,IS1893-2016)
[2] Rakib Al Mahmood, Amit C. Barman2, Md. Hasnain Hossain3,S.Khusru41,2,3GraduateStudent,4Assistant Professor,DepartmentofCivilEngineering,Ehsanullah University of Science and Technology, Dhaka-1208, Bangladesh.(2020)
[3] Department of Civil Engineering, Hasan Kalyoncu University, Gaziantep, Turkey Faculty of Civil Engineering, Gaziantep University, Gaziantep, Turkey Received1July2016,Revised13April2017,Accepted 16June2017,Availableonline17June2017,Versionof Record21June2017
[4] ShaikMohammadB.TechStudent,DepartmentofCivil Engineering,PaceInstituteofTechnologyandSciences, Ongole. 523001, India. N. Raja Nikhil Reddy B. Tech Student,DepartmentofCivilEngineering,PaceInstitute ofTechnologyandSciences,Ongole.523001,IndiaCh. SaipraveenProfessorDepartmentofCivilEngineering, Pace Institute of Technology and Sciences, Ongole. 523001, India. Vankayalapati Raghu Professor Department of Civil Engineering , Pace Institute of TechnologyandSciences,Ongole.523001.
[5] MadhusudanG.Kalibhat1,KiranKamath2,PrasadS.K. 3,RamyaR.Pai41(AssistantProfessor,Departmentof Civil Engineering, Manipal Institute of Technology, Manipal, INDIA) 2 (Professor, Department of Civil Engineering,ManipalInstituteofTechnology,Manipal, INDIA)3(Professor,DepartmentofCivilEngineering,S. J. College of Engineering, Mysore, INDIA) 4 (Post Graduate Student, Department of Civil Engineering, ManipalInstituteofTechnology,Manipal,INDIA)
[6] Osama Mohamed * and Rania Khattab College of Engineering,AbuDhabiUniversity,AbuDhabi59911.
[7] ETABSVERSION21.0
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