Load Combination

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Doubt in Load Combinations in Steel Design (WSM)

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manoj.vaishyaSEFIMember

Joined:24Mar2008Posts:7

Posted:TueFeb03,20096:22amPostsubject:DoubtinLoadCombinationsinSteelDesign(WSM)

RespectedSirs,

IhavesomedoubtinLoadCombinationsinSteelDesign(WorkingStressMethod)asperIS800.

AsperrevisedcodeIS800:2007,Noincreaseinstressesareallowedwhenwindisthemajorloadintheloadcombination(i.e.,DL+WLcombinations).

AlsoasperoldcodeIS800:1984,Noincreaseinstressesareallowedwhenwindisthemajorloadintheloadcombination(i.e.,DL+WLcombinations).

IS800:1984Clause3.9.2IncreaseinPermissibleStressesinMembersProportionedforOccasionalLoadings3.9.2.1WindorearthquakeloadsStructuralsteelandsteelcastingsWhentheeffectofwindorEarthquakeloadistakenintoaccount,the.permissiblestressesSpecifiedmaybeexceededby33.3percent.Rivets,boltsandtensionrodsWhentheeffectofthewindorEarthquakeloadistakenintoaccount,thepermissiblestressesSpecifiedmaybeexceededby25percent.

3.3.4Wherethewindloadisthemainloadactingonthestructure,noincreaseinthepermissiblestressesisallowed.

ThefollowingSpecialPublications&HandbooksarebasedonthecodeIS800:1984inwhich33.3%increaseinstressesareallowedwhenwindisthemajorloadintheloadcombination(i.e.,DL+WLcombinations).

SP47(S&T):1988,SP:4O(S&T)1987&SP:38(S&T)19872.2.1LoadCombinationThefollowingloadcombinationhavebeenconsideredincalculatingthedesignforcesforbeamandcolumninaccordancewithIS875:1964.a)DL+LLb)0.75(DL+C,XWL,)c)0.75(DL+c,XWL2)d)0.75(DL+C,,XWL,)WhereC,=0.75forcolumnforcesifthebuildingheightislessthanorequalto30metres,C,=0.75forbeamforcesiftheheightofframeislessthanorequalto10metresandC,,=1.0forothercases.Inthecalculationofdesignforcesfordeadandwindloadcombination,theactualforceshavebeenreducedby25percenttoaccountfor33.3percentincreaseinallowablestressesunderthisloadcombination.

ItismyrequesttoyouPleasesuggestwhetherIcanincreasethestressesby33.3%forDL+WLcombinationsaspernewcodeornot.IfnotthenhowitistakenwhileusingoldISCodewhereisitmentionedthatnoincreaseinstressesisallowedwhenwindisthemajorloadinloadcombinations.

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18/05/2015 www.sefindia.org::ViewtopicDoubtinLoadCombinationsinSteelDesign(WSM)

http://www.sefindia.org/forum/viewtopic.php?t=4575 2/4

Thankingyou,

ManojD.Vaishya

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rahultelangSEFIMember

Joined:07Feb2009Posts:2Location:Pune

Posted:FriFeb27,20095:07amPostsubject:Re:ContributionofsnowloadatthetimeofEarthquake

*************************************************************DearSir,IhaveanquestionregardingsnowlaodatthetimeofEarthquakeload.HowmuchcontributionofsnowloadshouldbeconsideratthetimeofEarthquakeloading?(e.g.whensnowontopofroofthattimeifEarthquakeoccure,howmuchweightofsnowshouldbeconsidertoevaluateEQ.)OurIS1893doesentspecifyanyfactor.Theysimplytoldtotakeappropritesnowload.

RegardRahulTelang*****************************************************

manoj.vaishyawrote:

RespectedSirs,

IhavesomedoubtinLoadCombinationsinSteelDesign(WorkingStressMethod)asperIS800.

AsperrevisedcodeIS800:2007,Noincreaseinstressesareallowedwhenwindisthemajorloadintheloadcombination(i.e.,DL+WLcombinations).

AlsoasperoldcodeIS800:1984,Noincreaseinstressesareallowedwhenwindisthemajorloadintheloadcombination(i.e.,DL+WLcombinations).

IS800:1984Clause3.9.2IncreaseinPermissibleStressesinMembersProportionedforOccasionalLoadings3.9.2.1WindorearthquakeloadsStructuralsteelandsteelcastingsWhentheeffectofwindorEarthquakeloadistakenintoaccount,the.permissiblestressesSpecifiedmaybeexceededby33.3percent.Rivets,boltsandtensionrodsWhentheeffectofthewindorEarthquakeloadistakenintoaccount,thepermissiblestressesSpecifiedmaybeexceededby25percent.

3.3.4Wherethewindloadisthemainloadactingonthestructure,noincreaseinthepermissiblestressesisallowed.

ThefollowingSpecialPublications&HandbooksarebasedonthecodeIS800:1984inwhich33.3%increaseinstressesareallowedwhenwindisthemajorloadintheloadcombination(i.e.,DL+WLcombinations).

SP47(S&T):1988,SP:4O(S&T)1987&SP:38(S&T)19872.2.1LoadCombinationThefollowingloadcombinationhavebeenconsideredincalculatingthedesignforcesforbeamandcolumninaccordancewithIS875:1964.a)DL+LLb)0.75(DL+C,XWL,)c)0.75(DL+c,XWL2)d)0.75(DL+C,,XWL,)WhereC,=0.75forcolumnforcesifthebuildingheightislessthanorequalto30metres,C,=0.75forbeamforcesiftheheightofframeislessthanorequalto10metresandC,,=1.0forothercases.Inthecalculationofdesignforcesfordeadandwindloadcombination,theactualforceshavebeenreducedby25percenttoaccountfor33.3percentincreaseinallowablestressesunderthisloadcombination.

ItismyrequesttoyouPleasesuggestwhetherIcanincreasethestressesby33.3%forDL+WLcombinationsaspernewcodeornot.IfnotthenhowitistakenwhileusingoldISCodewhereisitmentionedthatnoincreaseinstressesisallowedwhenwindisthemajorloadinloadcombinations.

Thankingyou,

ManojD.Vaishya

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Dr.N.SubramanianGeneralSponsor

Posted:FriFeb27,20093:30pmPostsubject:Re:ContributionofsnowloadatthetimeofEarthquake

HiRahulTelang

IampastingtheAbstractfromapaperbyProf.O'RourkewhoisanauthorityonSnowloads.Hopeithelps.

Subramanian

18/05/2015 www.sefindia.org::ViewtopicDoubtinLoadCombinationsinSteelDesign(WSM)

http://www.sefindia.org/forum/viewtopic.php?t=4575 3/4

Joined:21Feb2008Posts:4881Location:Gaithersburg,MD,U.S.A.

RoofSnowLoadforSeismicDesignCalculations

byMichaelJ.ORourke,M.ASCE,(Prof.ofCiv.Engrg.,RensselaerPolytechnicInst.,Troy,NY12180)andRobertS.Speck,Jr.,A.M.ASCE,(Prin.Associate,RyanBiggsAssociatesP.C.,Troy,NY)

JournalofStructuralEngineering,Vol.118,No.9,September1992,pp.23382350,

Abstract:Thelateralloadsimposedonastructureduringanearthquakearefunctionsofthepeakgroundaccelerationandthetotalmassofthestructureamongotherparameters.Forstructureslocatedinsnowyregions,thequestionarisesastotheappropriateroofsnowloadtobeusedinearthquakecalculations.Variouscodesandloadstandardssuggestvaluesforthesnowload,whichistobecombinedwithdeadloadinearthquakeanalysis.Inthispaperstatisticalinformationondailygroundsnowloadsandstatisticalinformationontheconversionfactorbetweenroofandgroundloadsareusedtodetermineappropriateroofsnowloadsforearthquakeanalysis.Asdefinedherein,theappropriateroofsnowloadissuchthattheexceedanceprobabilityforthedesignseismicbaseshearisidenticaltotheexceedanceprobabilityforthedesignpeakgroundacceleration.Theanalysissuggeststhattheappropriateroofsnowloadforseismiccalculationsis20%ofthe50yearmeanrecurrenceintervalgroundsnowload.***

DearSir,IhaveanquestionregardingsnowlaodatthetimeofEarthquakeload.HowmuchcontributionofsnowloadshouldbeconsideratthetimeofEarthquakeloading?(e.g.whensnowontopofroofthattimeifEarthquakeoccure,howmuchweightofsnowshouldbeconsidertoevaluateEQ.)OurIS1893doesentspecifyanyfactor.Theysimplytoldtotakeappropritesnowload.

RegardRahulTelang*****************************************************

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FARAGeneralSponsor

Joined:31May2010Posts:14Location:NewDelhi

Posted:FriSep21,20123:40pmPostsubject:

DearSeniorsetc.

ihavetodesignsteeltrussasperoldcodeIS:8001984.CansomeonepleaseguidemeregardingtheloadcombinationsrequiredforFoundationcheck,permissibleincreaseinSBC,permissibleincreaseinstressesinsteelmembers.TheprimaryloadcaseareDeadload,LiveLoadnWindload.FewthingsIgotfromcodelikepermissibleincreaseinstressesinsteelmembersis33.3%forWind+DeadButwhataboutD+L+W,Waitingforthereply.

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18/05/2015 www.sefindia.org::ViewtopicDoubtinLoadCombinationsinSteelDesign(WSM)

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