Web Crippling Capacity of Cold Formed Steel Channel Sections With and Without Openings

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Web Crippling Capacity of Cold Formed Steel Channel Sections With and Without Openings

2

1Student, Dept. of Civil Engineering, St.Joseph’s College of Engineering& Technology, Kerala, India

2Asisstant Professor, Dept. of Civil Engineering, St.Joseph’s College of Engineering& Technology, Kerala, India ***

Abstract Steel is an important constructionmaterialsince ancient days. Among steel, ColdFormedSteel(CFS)aregetting more popular due to its advantages including light weight, high strength to weight ratio, resistance to fire etc. These are the sections which are shaped near room temperature. CFS channel sections are commonly used nowadays as bearing and non load bearing walls, partition walls, in multi rise buildings, framings. In this channel sections the holes are provided in the web portion for plumbing services and installation of ducts. However such opening made the section more vulnerable to failures including web crippling and web buckling. In this paper various parameters which affect the web crippling capacity of the channel sections are analyzed and the analysis is also done to find the optimum location of web holes in the channel sections.

Key Words: ColdFormedSteelSections,WebCrippling,Web Buckling

1. INTRODUCTION

Advancedstructuresarequitecommoninnowadaysdueto growthinconstructionindustry,Duetothisadvancement many industries are looking forward to develop and use sustainable building materials. Steel is an important construction material using nowadays due to its innumerableadvantageswhichmakeitasaperfectoption formodernbuildingconstruction.Therearemainly2types of steel used for the construction purposes. 1) Hot Rolled Steel Sections2)ColdFormed Steel Sections.Asthename indicates, CFS sections are the sections which are rolled, bended,pressedorshapedatnearroomtemperature.Wedo not need to provide extra heat for shaping them as it is requiredinhotrolledsteelsections.Inhotrollingprocess steelisrolledbyprovidinghightemperaturewhichismore than 1700 Fahrenheit. But such hot rolled steel have a tendencytoshrinkwhencooloff, thusgivinglesscontrolon sizeandshape.AdvantagesofCFSsectionsoverHotRolled Steel Sections includes CFS does not shrink, no heat is required to form shape, light weight, non combustible, won’t absorb moisture, resist fire and termites and high strengthtoweightratio.Nowadaysopeningsareprovidedin thewebportionofchannelsectionforeaseofinstallationof electrical or plumbing devices. Such holes result in the sections becoming more vulnerable to failures especially underconcentratedloadsappliednearthewebholes.Two commontypeoffailuresinCFSsectionsinclude1)Crippling

Failure2)BucklingFailure.Webcripplingfailureoccurredin CFS members at the web flange junction. This failure is mainly seen in the web elements due to the concentrated loads which are delivered through flange of the channel sections. The main reason for this failure is due to the applicationofstaticanddynamicloadstransversallywhich causes direct crushing of web. Buckling is another failure mode in CFS sections due to its thin walled cross section causinglossofstability.Thisfailureoccurswhenthecritical buckling stress in web is less than the compressive stress acting vertically.Itoccursbeforeyielding.

1.1 Aim

To perform the analysis on web crippling capacity of cold formedchannelsectionswithandwithoutopening

1.2 Objective

Tounderstandeffectofbearinglength,insidebentradius, web depth and flange width on web crippling capacity of channelsections.

Tostudyeffectofwebopeningandwebopeninglocationsin the web crippling and buckling capacity of the channel sections

1.3 Methodology

1) Modeling and analysis of channel sections with and withoutholeinANSYSWorkbenchbyvaryingparameters

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BearingLength

InsideBentRadius

WebDepth

FlangeWidth 2)ModelingandanalysisofchannelsectionsinANSYSby varyingwebholesdiametersandwebholelocations 3) Comparisonofresultsandgraphsofallmodelsforweb cripplingandwebbucklingstrength.

2. MODELING AND ANALYSIS

Channelsectionswithandwithoutwebholesaremodeledin ANSYS Workbench 2022. Material properties and section dimensionsarediscussedbelow.

2.1 Material Properties

Steelwiththefollowingpropertiesareusedformodelingthe channelsections

Poisson’sratio=0.3

YieldStrength=450Mpa

TangentStrength=0Mpa

2.2 Section Properties

Sectionusedischannelsectionwithandwithouthole.One loading plate and one supporting plate are provided. The meshsizeis5mmx5mmmeshforbearingplatesand3mmx 3mmmeshsizeisadoptedforbeam.Generallyprovidethe length of bearing plate as 50mm. Boundary Conditions includeforloadingplatetranslationinyaxisis 8,rotation aboutxaxisisfreeandallothertranslations&rotationsare fixedandforthesupportingplateallmovementsarefixed whereasrotationaboutxaxisisfree

Fig 3:Meshing

Fig 4:BoundaryConditionsforLoadingPlate

Fig 2:ChannelSectionWithHole

Fig 5:BoundaryConditionsforSupportingPlate

Fig -6:Schematicdiagramofmodeledchannelsection

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2.3 Varying Bearing Length

Bearingplateisusedtotransferconcentratedcompressive forces between two structural elements. Bearing length is thelengthalongthebeamunderwhichahighconcentration ofstressesistransferredtothesupportingstructurebelow.

Sectionused 150x45x13mm i) withouthole ii) withhole(diameterofhole=60mm)

Fig 7:Sectionwithbearingplates

The above mentioned channel sections are modeled by varying bearing length from 20 mm to 60 mm in order to find the effect of bearing length on the strength of the channelsections.Thetabulardatashowingtheresultsare givenbelow

Table 1: WebCripplingLoad(KN)inChannelSection withoutholecorrespondingtodifferentbearinglength

Table 3: WebCripplingLoad(KN)inChannelSection withholecorrespondingtodifferentbearinglength

Table -2: WebBucklingLoad(KN)inChannelSection withoutholecorrespondingtodifferentbearinglength

Table -4: WebBucklingLoad(KN)inChannelSectionwith holecorrespondingtodifferentbearinglength

2.4 Varying Flange Width

Inordertodeterminetheeffectofflangewidthonthe web crippling capacity of the channel sections four modelsofchannelsectionswithandwithoutholesare modelledandanalysed.Inthissectiontheflangewidth isvariedbetween28mmto64mm.

Sectionsmodelledinclude 150x28x13mm 150x34x13mm 150x45x13mm 150x64x13mm

Fig 8:Channelsectionwithbf=flangeWidth

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Table 5: WebCripplingLoad(KN)inChannelSection withoutholecorrespondingtodifferentflangewidth

2.5 Varying Bent Radius

Sectionused 150x45x13mm i) Withouthole ii) withhole(diameter=60mm)

Innerbentradiusisvaried between1.5mmto3.5mmin thisanalyse.

Table -6: WebBucklingLoad(KN)inChannelSection withoutholecorrespondingtodifferentflangewidth

Fig -9:ChannelsectionwithRi=BentRadius

Table 9: WebCripplingLoad(KN)inChannelSection withoutholecorrespondingtodifferentbentradius

Table 7: WebCripplingLoad(KN)inChannelSection withholecorrespondingtodifferentflangewidth

Table -8: WebBucklingLoad(KN)inChannelSectionwith holecorrespondingtodifferentflangewidth

Table -10: WebBucklingLoad(KN)inChannel Sectionwithoutholecorrespondingtodifferentbent radius

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Table 11: WebCripplingLoad(KN)inChannelSection withholecorrespondingtodifferentbentradius

Table 13: WebCripplingLoad(KN)inChannelSection withoutholecorrespondingtodifferentwebheight

Table 12: WebBucklingLoad(KN)inChannelSection withholecorrespondingtodifferentbentradius

Table 14: WebBucklingLoad(KN)inChannelSection withoutholecorrespondingtodifferentwebheight

2.7 Varying Diameter of the Web Hole

2.6 Varying Height of the Web Portion

Slendernessofthewebportionplaysimportantroleinthe strengthofthechannelsection.Inordertoknowtheeffectof height of the web portion in web crippling capacity, six channelsectionsaremodeledbyvaryingwebheightfrom 100mmto150mm. Sectionsmodeledare

100x45x13mm

110x45x13mm

120x45x13mm

130x45x13mm

140x45x13mm

150x45x13mm

Opening areprovidedinthewebportionforinstallationof ducts,electricalandplumbingservices.Howeversuchholes can reduce the strength of the channel sections to some extent. In order to know the effect of holes in the web crippling capacity of the channel section, sections are modeledbyprovidingholeswithvaryingdiameterunderthe bearing plate and the analyses are conducted on. The diameterusedintheseanalysesisvariedbetween0mmto 60mmandthechannelsectionusedis150x50mmx13mm

Fig 10:ModeledFigureinANSYS

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Table 15: WebCripplingLoad(KN)inChannelSection withoutholecorrespondingtodifferentwebheight

Fig 12:x/h=0.6

Table 17: WebCripplingLoad(KN)inChannelSection correspondingtodifferentx/hratio

Table 16: WebBucklingLoad(KN)inChannelSection withoutholecorrespondingtodifferentwebheight

2.8 Varying Locations of Web Hole

Locationsofwebholes have agreateffectindetermining thestrength ofthechannel sections.In order toknow the effectofthelocationsofwebholesinthechannelsections differentmodelsareanalyzedbyvaryingthedistanceofweb holesfromthebearingplates.Thedistancefromthebearing plates(x)toheightofthechannelsection(h)isvariedfrom0 to0.6

Table 18: WebBucklingLoad(KN)inChannelSection correspondingtox/hratio

Fig 11:x/h=0

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3. GRAPHS AND DISCUSSIONS

3.1 Effect of Bearing Length

Chart 1:EffectofBearingLengthinWebCripplingLoad ofChannelSectionWithoutHole

Chart 3:EffectofBearingLengthinWebBucklingLoad

Bearinglengthplaysanimportantroleindeterminingthe web crippling capacity of the channel section. With the increaseinthebearinglengththewebcripplingcapacityof the channel section increases. From the analysis it was clearedthatwebcripplingcapacityofchannelsectionswith bearinglength60mmisgreaterthan20mm.Thebuckling strengthofthechannelsectionsdecreaseswithincreasein thebearinglength.Byprovidingthewebholesthestrengthof thechannelsectionsdecreases,sothereisahugedecreasein web buckling strength of the channel section with hole comparedwiththesectionswithouthole

3.2Effect

of Flange Width

Chart -2:EffectofBearingLengthinWebCripplingLoad ofChannelSectionWithHole

Chart 4:EffectofFlangeWidthinWebCripplingLoadof ChannelSection

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Flange width affect the web crippling capacity of the channel sections. Web crippling capacity is high for 150x28x13mmandisvery lowfor150x64x13mm.From theanalysesitisclearthatwithincreaseintheflangewidth ofthechannelsectionwebcripplingcapacitydecreases.With the increase in the flange width web buckling strength increases.

3.3 Effect of Bent Radius

Chart 5:EffectofBentRadiusinWebCripplingLoadof ChannelSection

3.4 Effect of web Height

Chart 6:EffectofBentRadiusinWebBucklingLoadof ChannelSection

In the analysis with the bent radius of the channel sections is varied between 1.5 mm to 3.5 mm. From the analysisitisclearthatthechannelsectionswithbentradius 2.5mmshowhighwebcripplingcapacitycomparedtoother sections.Thewebcripplingcapacityofthechannelsections increasefrom1.5mmto2.5mm.Beyond2.5mmtheweb cripplingcapacityofthechannelsectionincrease

Chart 7:EffectofheightofWebinWebBucklingLoadof ChannelSection

WebHeightaffectsthestrengthofthechannelsections.In theanalysisthewebheightofthechannelsectionsisvaried between100mmto150mm.Fromtheanalysisitiscleared that the channel sections having more web height is more vulnerabletofailure.Thewebbucklingloadof100x45x13 mm channel section is very high compared to that of the sectionhavingdimensions150x45x13mm.

3.5 Effect of diameter of web hole

Chart 8:EffectofDiameterofHolesinWebBucklingLoad ofChannelSection

Intheanalysisthewebholeswithvariousdiametersis provided at the center of the channel section, under the bearingplateinordertoknowhowitaffectsthestrengthof thechannelsection.Diameterofholeusedinthesectionis variedbetween0mmto60mm.Fromtheanalysisitisclear thatprovidingholesdirectlyunderthebearingplatedonot makeahugeeffectinreducingthewebcripplingcapacityof the channel sections. However it has a drastic effect in

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reducing the buckling strength of the channel sections. By increasingthediameterofwebholesthebucklingstrengthof thechannelsectionsisreduced.

3.6 Effect of location of web holes

Chart 9:EffectofLocationofWebHolesinWebBuckling LoadofChannelSection

Fromtheanalysisitisclearthatthelocationofwebholes does not affect the web crippling capacity of the channel sections. But at the same time it affects the web buckling strengthofthechannelsections.Themodelwithx/hratio0.6 havinghighbucklingstrengthcomparedtothesectionwith x/hratio0.Byincreasingthedistanceofwebholesfromthe bearing plate the web buckling strength of the channel sectionsincrease.

4. CONCLUSION

This paper is mainly aimed to know more about the web crippling capacity of the channel sections. Different parameterslikelengthofthebearingplate,innerbentradius, webheight,flangewidth,diameterofwebholeandlocation ofwebholesvariedinchannelsectionsinordertoknowhow itaffectthewebcripplingandwebbucklingstrengthofthe sections and came to the conclusion that web crippling capacity ofthechannel sections increases withincreasein bearing length and bent radius up to 2.5 mm. With the increaseintheflangewidthofthechannelsectiontheweb cripplingcapacitydecreases.Howeverthediameterofweb hole,locationofthewebholesandheightofthewebportion donotaffectthewebcripplingcapacityinalargeextentbut affect the web buckling strength. Decrease in the holes diametersandincreaseinthex/hratiocanincreasetheweb bucklingstrengthofthechannelsections.Atthesametime increaseinthewebheightcandecreasethestrengthofthe channelsections.

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