TECHNIQUES FOR MITIGATION OF SOFT STORY ON TALL BUILDINGS UNDER LATERAL LOADS

TECHNIQUES FOR MITIGATION OF SOFT STORY ON TALL BUILDINGS UNDER LATERAL LOADS

ABSTRACT

Thesoftstoryplaysasignificantroleinitsseismicsuccess in high rise construction. The framework's uniformity is discontinuous at the soft story level because of no infill wallsordifferencesinfloorheight Thisconsistencycauses thestructural collapse ofmulti stored buildingsunderthe burdens of the earthquake. Severe structural damage sustained in recent earthquakes by many modern buildings highlights the significance of preventing sudden shifts in lateral rigidity and strength in this project with seismiczoneV,andthestructuralStoryisG+26.Thestudy iscarriedoutbyconsideringearthquakeswithasoft story effect and mitigation techniques like BRB brace, crescent brace, and combination to prevent soft story. Moreover, the displacement, story drift, and time period are compared after examining the above structure. There is alsoastudyofdifferentdesignparameters,andsignificant results have been obtained. Keywords: BRB brace, crescent brace,earthquake,soft story

Keywords:softstory,BRB,andcrescentbrace.

1. Introduction

Inotherwords,"softstories"refertostoriesinastructure with a lower level of stiffness or inadequate energy absorption(ductility).Abuildingonasoft storyhasa70% less stiff floor than the floor above it. There's a lot of potential for damage in an earthquake because of this unstablefloor.Softstoriestendtobeonthebottomfloors for commercial and garage spaces. If one falls, the whole structure would be destroyed, resulting in substantial structuraldamagethatmightrenderthestructureentirely useless.

Researchers at the University of Bologna have recently suggested using the Crescent Shaped Braces (CSB) as an improved diagonal brace in framed buildings, following the Performance Based Seismic Design framework. Concentric stiff diagonal braces are often used as lateral resisting systems. However, CSBs enable practical designers to select between several levelsof side stiffness without compromising device yield strength, thanks to theirunique,ad hocstructure.

A concrete housing supports the slender steel core, which holds restrained bracelets (BRBs). The center and the casing are detached to avoid contact. The problems of standard braced frames may be avoided by adopting buckling reinforced braces, which prevent buckling in the theme brace during compression (BRBs). Buckling limits the appealing brace's energy dissipation capability, reducing steepness and strength. Inversely, buckling restrained braces have high stable hysteretic dissipation. Restraint buckling braces can be used in damage controlledstructures.

Literature Review

Niloufar Mashhadiali (Journal of Constructional Steel Research Volume 181, June 2021): Buildings often use steel concentricbraced frames(CBFs).Alarge earthquake generatesdamageconcentrationinoneorfewstories due to the high nonlinear behavior of CBFs. Improved structural behavior and reduced soft story processes are proposedinthisarticle.Thesuggestedsystemcombinesa restrained buckling brace (BRB) with a strong brace (SB). The robust braces are intended to flex during an earthquake. Tale by the story, BRB and SB zigzag in opposite directions. This design results in both stiffness and ductility. This enhances CBFs' soft narrative mechanisms and buckling capability. The nonlinear static (pushover) and dynamic studies of a series of 6 story structuralmodelswithvariousbracingpatterns(inverted V,multi X,zipper,andHexa)wereperformedinthiswork (IDA).TheseismicbehaviorofconventionalCBFswiththe comparable bracing arrangement was compared to the collapse performance of structural models. Using collapse fragility curves, the hybrid bracing system outperformed standardCBFsinstrongearthquakes.

Panumas Saingam (2020 Published by Elsevier): It is possible to seismically retrofit reinforced concrete (RC) buildings using buckling restrained braces (BRBs) and elastic steel frames. While analogous linearization may be usedtodistributeBRBsizesvertically,itignoresthe extra stiffnessowingtothecompositebehavior betweenRCand elastic steel frames, leading to an unduly cautious assessmentofBRBstiffnessneeds.Anapproachtoretrofit designusingcompositebehaviorisproposed.Thedetailed compositebehaviorismodelednumericallyandcalibrated against quasi static cyclic loading experiments. The suggested retrofit design technique is verified using a nonlinear response history analysis on a four story RC schoolbuilding.

Hanqin Wang,1 Yulong Feng (Hindawi Advances in Civil Engineering Volume 2019): Because buckling restrainedbraceshavelowpost yieldstiffness,multi story buckling restrained braced frames (BRBFs) exposed to earthquakesarepronetolateraldeformationsanddamage concentrations at particular stories (DCE). The DCE of BRBFs is investigated using nonlinear pushover and response history analysis. The DCE is compared for two different constructions and beam to column connections inthemainframe(MF).Accordingtotheseanalyses,BRBFs fitted with BRBs have a higher DCE than traditional moment resisting or conventional braced frames, and MF stiffness affects residual structural displacement and DCE. On the DCE of a 6 story BRBF dual system constructed to the Chinese seismic code, parametric studies are used to explore the influence of two stiffness distribution parameters (horizontal and vertical). They found that boosting MF stiffness and minimizing BRB stiffness variations across tales reduced the DCE of BRBFs. Finally, several damage performance measures are correlated. BRBFsshowlittlestatisticalcorrelationbetweenpeakand

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

residual drift responses. Thus, the DCE should be addressedintheBRBFdesign.

2. Module And Building Configuration

A reinforced concrete frame building with a located in zone II is studied in the first model. The building's plan areais13x19m,witheachtypicalstoreybeing3mtall.It has8baysintheXdirectionand10baysintheYdirection

ThePlanconfigurationconsistsof

Model1:G+26withsoftstory

Model2:G+26withasoftstorywithBRBBraces

Model3:G+26withasoftstorywithCrescentbraces

Model 4: G+26 with a soft story with crescent and BRB brace

Columns 300mmx600mm

Beams 230mmx500mm

Crescentbrace 500mmx500mm

BRB Starbrb20

Slabthickness 150mm

Concretegrade M30

Gradeofsteel HYSD415

Buildingdesigncode IS456 2000

Theseismicdatausedformodellingareasbelow:

a.Seismiczone IV b.Soiltype I c.Responsereductionfactor 5 d.Importancefactor 1

Theloadcombinationsconsideredareasgivenbelow.

a.1.5(DL+LL)

b.1.5(DL EQX) c.1.2(DL+LL+EQX) d.1.2(DL+LL EQX)

Theplanand3Dviewofthebuildingusedforthe modellingisasbelow:

3. Methodology

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Variousparameters,suchasstorydeformation,storydrift, baseshear, modal periods, andsoon,have beenanalysed. LinearstaticanalysisforG+26,StoreyBuildings,generated the results. Results Obtained based on story drifts (time period,displacement,andstiffness)andtheStoreyeffectof Symmetric buildings by comparing the structure's reactionstoa26 storybuildingwerediscussedindetailin subsequenttalks.

Base 0 0 0 0 0 0 0 0 0

Story1 1.5 0.627 1.399 0.25 0.383 0.14 0.188 0.171 0.229

Story2 4.5 0.857 1.712 0.473 0.699 0.348 0.481 0.382 0.526

Story3 7.5 1.103 2.051 0.722 1.059 0.584 0.822 0.622 0.872

Story4 10.5 1.379 2.432 0.999 1.461 0.85 1.206 0.89 1.262

Story5 13.5 1.678 2.848 1.301 1.901 1.141 1.629 1.185 1.69

Story6 16.5 2.001 3.297 1.626 2.373 1.455 2.086 1.503 2.153

Story7 19.5 2.344 3.775 1.972 2.875 1.792 2.574 1.842 2.647

Story8 22.5 2.706 4.281 2.337 3.405 2.148 3.091 2.201 3.168

Story9 25.5 3.086 4.813 2.719 3.959 2.523 3.633 2.578 3.715

Story10 28.5 3.482 5.368 3.117 4.536 2.914 4.198 2.971 4.286

Story11 31.5 3.892 5.945 3.529 5.133 3.319 4.784 3.379 4.877

Story12 34.5 4.316 6.542 3.954 5.749 3.738 5.39 3.8 5.487

Story13 37.5 4.75 7.157 4.391 6.381 4.169 6.012 4.233 6.113

Story14 40.5 5.195 7.788 4.837 7.028 4.61 6.649 4.675 6.755

Story15 43.5 5.649 8.434 5.292 7.688 5.059 7.3 5.126 7.409

Story16 46.5 6.109 9.093 5.753 8.359 5.516 7.961 5.585 8.075

Story17 49.5 6.576 9.763 6.22 9.039 5.978 8.632 6.048 8.75

Story18 52.5 7.047 10.442 6.692 9.727 6.445 9.311 6.517 9.433

Story19 55.5 7.521 11.128 7.166 10.421 6.915 9.995 6.988 10.122

Story20 58.5 7.997 11.819 7.642 11.119 7.386 10.684 7.46 10.814

Story21 61.5 8.474 12.514 8.118 11.82 7.858 11.374 7.934 11.509

Story22 64.5 8.95 13.211 8.594 12.521 8.328 12.065 8.406 12.204

Story23 67.5 9.424 13.907 9.067 13.22 8.797 12.755 8.876 12.898

Story24 70.5 9.895 14.601 9.538 13.917 9.263 13.441 9.343 13.589

Story25 73.5 10.363 15.291 10.005 14.61 9.724 14.123 9.806 14.275

Story26 76.5 10.826 15.977 10.467 15.297 10.181 14.8 10.265 14.956

Story27 79.5 11.284 16.656 10.923 15.978 10.632 15.469 10.717 15.63

Story28 82.5 11.736 17.33 11.374 16.652 11.076 16.132 11.164 16.297

Table 1: story displacement for G+26 building

Story1 1.5 0.000418 0.000933 0.000167 0.000256 9.30E 05 0.000125 0.000114 0.000153

Story2 4.5 7.90E 05 0.000111 7.50E 05 0.000108 7.00E 05 0.0001 7.10E 05 0.000101

Story3 7.5 8.40E 05 0.000121 8.40E 05 0.000122 7.90E 05 0.000115 8.00E 05 0.000117

Story4 10.5 9.40E 05 0.000135 9.30E 05 0.000136 8.90E 05 0.000129 9.00E 05 0.000131

Story5 13.5 0.000102 0.000147 0.000101 0.000148 9.70E 05 0.000142 9.90E 05 0.000144

Story6 16.5 0.00011 0.000158 0.000109 0.000159 0.000105 0.000154 0.000107 0.000156

Story7 19.5 0.000117 0.000168 0.000116 0.00017 0.000113 0.000164 0.000114 0.000166

Story8 22.5 0.000123 0.000178 0.000123 0.000179 0.00012 0.000174 0.000121 0.000176

Story9 25.5 0.000129 0.000187 0.000129 0.000188 0.000126 0.000183 0.000127 0.000185

Story10 28.5 0.000135 0.000195 0.000134 0.000196 0.000131 0.000191 0.000132 0.000193

Story11 31.5 0.00014 0.000203 0.000139 0.000203 0.000137 0.000199 0.000137 0.000201

Story12 34.5 0.000144 0.00021 0.000143 0.00021 0.000141 0.000206 0.000142 0.000207

Story13 37.5 0.000148 0.000216 0.000147 0.000216 0.000145 0.000212 0.000146 0.000213

Story14 40.5 0.000151 0.000222 0.000151 0.000221 0.000149 0.000217 0.000149 0.000219

Story15 43.5 0.000154 0.000227 0.000154 0.000226 0.000152 0.000222 0.000152 0.000224

Story16 46.5 0.000157 0.000231 0.000156 0.00023 0.000154 0.000226 0.000155 0.000228

Story17 49.5 0.000159 0.000235 0.000158 0.000234 0.000156 0.00023 0.000157 0.000231

Story18 52.5 0.00016 0.000238 0.00016 0.000236 0.000158 0.000232 0.000158 0.000234

Story19 55.5 0.000161 0.00024 0.000161 0.000238 0.000159 0.000235 0.000159 0.000236

Story20 58.5 0.000162 0.000241 0.000161 0.00024 0.000159 0.000236 0.00016 0.000237

Story21 61.5 0.000162 0.000242 0.000161 0.00024 0.000159 0.000236 0.00016 0.000238

Story22 64.5 0.000162 0.000242 0.000161 0.00024 0.000159 0.000236 0.00016 0.000238

Story23 67.5 0.000161 0.000241 0.00016 0.000239 0.000158 0.000235 0.000159 0.000237

Story24 70.5 0.00016 0.000239 0.000159 0.000238 0.000157 0.000234 0.000158 0.000235

Story25 73.5 0.000158 0.000237 0.000157 0.000236 0.000155 0.000232 0.000156 0.000233

Story26 76.5 0.000156 0.000235 0.000155 0.000233 0.000153 0.000229 0.000154 0.000231

Story27 79.5 0.000154 0.000232 0.000153 0.00023 0.000151 0.000226 0.000152 0.000228

Story28 82.5 0.000152 0.000229 0.000151 0.000227 0.000149 0.000223 0.00015 0.000225

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ISSN:2395 0056

TIMEPERIOD

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1 2 3 4 5 6 7 8 9 10 11 12

TIME PERIOD (SEC) MODES

STORY STIFFNESS IN X DIR

NORMAL WITH SOFT STORY SOFT STORY WITH BRB

SOFT STORY WITH BRB

SOFT STORY WITH CRESCENT BRACE

30000000

25000000

20000000

15000000

10000000

5000000

35000000 story stiffness bottom story

5. CONCLUSION

STORY STIFFNESS IN Y DIR

NORMAL WITH SOFT STORY

SOFT STORY WITH BRB & CRESCENT BRACE 0

NORMAL WITH SOFT STORY

SOFT STORY WITH BRB

SOFT STORY WITH CRESCENT BRACE

SOFT STORY WITH BRB & CRESCENT BRACE 0 2000000 4000000 6000000 8000000 10000000 12000000 14000000 16000000 18000000 stiffness

bottom story

Figure7: Time Period for G+26 Figure8: Story stiffness for G+26 in x dir Figure9: Story stiffness for G+26 in x dir

SOFT STORY WITH BRB

SOFT STORY WITH CRESCENT BRACE

SOFT STORY WITH BRB & CRESCENT BRACE

As the soft story occurs in the building, the story displacement grows. Because of the soft story, the structure's rigidity is lowered,whichincreasesthemaximumstorydisplacement.

• The increased BRBs can provide the MRF with initial stiffness and energy dissipation, minimizing structural displacement reactionduringearthquakes.TheBRBstiffnessratiobetweenstorieshasanimpactontheframe'sdamagemechanism.

• The total stiffness of the column is added to the lateral strength; bracing is applied at each story. As a result, the lowest floor'spoorstrengthcausesfailure,especiallyduringanearthquake.Abuilding'sstrengthisconsideredweakandeasytofail duringanearthquakeifitlacksanylateralloadresistancecomponents,suchasbracing.

• The soft story's findings significantly impact the structural behavior and capability of the structure when subjected to seismicforces.

• Displacement and story drift has grown due to structural flaws; displacement rose on specific floors when the soft story loweredtheinertiaforce.

•Storydriftvaluesarewithinthe1893allowedlimit,whichis0.004timesthestoryheight.

•Becausesoft storyhaslimitedflexibilitytosustainlateralloads,theperiodofthestructureisdeterminedbyitsstiffness.

6. SCOPE OF FURTHER STUDY

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In the present thesis, an analysis of a multi story building under the effect of discontinuity in stiffness, which is the soft story,isstudied.

Thepresentworkcanextendtoanexhaustivestudyofvarioustypesofirregulars.Ageneralizedconclusionforthedesign ofsuchirregularbuildingscanbemade,whichcanhelpunderstandthebehaviorofsuchirregularbuilding.

ISSN:2395 0056

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Hybridbracedframewithbuckling restrainedand strong braces to mitigate soft story Author links open overlay panel, Niloufar Mashhadiali, Research,Volume,June2021,106610. 

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Damage Concentration Effect of Multi storey Buckling RestrainedBracedFramesHanqinWang, AdvancesinCivilEngineering/2019 

Ashwini S Gudur1 Prof. H S Vidyadhar2: Dynamic WindAnalysisofTallBuildingProvidedwithSteel Bracing as Per Proposed Draft for Indian Wind CodeandEffectofSoftStorey(Part2) 

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Liang Li, Guoqiang Li, and Tianhua Zhou, "Experimental Study on the Seismic Behavior of a Steel Concrete Hybrid Structure with Buckling Restrained Braces," Hindawi Advances in Civil EngineeringVolume2020,ArticleID9232138,20 pages. 

Deepak VasantraoPatil and C. M. Deshmukh, "Comparative Study of Conventional Braces and Buckling Restrained Braces in Steel Frame Structure," International Journal of Engineering Researchand Technology(IJERT),Vol.8Issue11, November 2019.