A n i n f o r m a t i o n s e r i e s f r o m t h e n a t i o n a l a u t h o r i t y o n c o n c r e t e m a s o n r y t e c h n o l o g y

NCMA TEK 14-23 1

DESIGN OF CONCRETE MASONRY INFILL

TEK 14-23Structural (2012)

INTRODUCTION

Masonryinfillreferstomasonryusedtofilltheopeninginastructuralframe,knownastheboundingframe.Thebound-ingframeofsteelorreinforcedconcreteiscomprisedofthecolumnsandupperandlowerbeamsorslabsthatsurroundthemasonryinfillandprovidestructuralsupport.Whenproperlydesigned,masonryinfillsprovideanadditionalstrong,ductilesystemforresistinglateralloads,in-planeandout-of-plane. Concretemasonry infills can be designed and detailedtobepartofthelateralforce-resistingsystem(participatinginfills)ortheycanbedesignedanddetailedtobestructurallyisolatedfromthelateralforce-resistingsystemandresistonlyout-of-planeloads(non-participatinginfills). Participatinginfillsformacompositestructuralsystemwiththeboundingframe,increasingthestrengthandstiffnessofthewallsystemanditsresistancetoearthquakeandwindloads. Non-participatinginfillsaredetailedwithstructuralgapsbetweentheinfillandtheboundingframetopreventtheunin-tendedtransferofin-planeloadsfromtheframeintotheinfill.Suchgapsarelatersealedforothercoderequirementssuchasweatherprotection,airinfiltration,energyconservations,etc. Constructionofconcretemasonryinfilledframesisrela-tivelysimple.First,theboundingframeisconstructedofeitherreinforcedconcreteorstructuralsteel,thenthemasonryinfillisconstructedintheportalspace.Thisconstructionsequenceallowstherooforfloortobeconstructedpriortothemasonrybeinglaid,allowingforrapidconstructionofsubsequentstoriesorapplicationofroofingmaterial. The2011editionofBuilding Code Requirements for Ma-sonry Structures(MSJCCode,ref.1)includesanewmandatorylanguageAppendixBforthedesignofmasonryinfillsthatcanbeeitherunreinforcedorreinforced.AppendixBprovidesastraightforwardmethod for thedesignandanalysisofbothparticipatingandnon-participatinginfills.Requirementsweredeveloped based on experimental research aswell as fieldperformance.

Related TEK: Keywords: buildingcodes,connectors,masonryinfill,structuraldesign

MASONRY INFILL LOAD RESPONSE

Severalstagesofin-planeloadingresponseoccurwithaparticipatingmasonryinfillsystem.Initially,thesystemactsasamonolithiccantileverwallwherebyslightstressconcentra-tionsoccuratthefourcorners,whilethemiddleofthepaneldevelopsanapproximatelypureshearstressstate.Asloadingcontinues,separationoccursattheinterfaceofthemasonryandtheframemembersat theoff-diagonalcorners.Onceagapisformed,thestressesatthetensilecornersarerelievedwhilethosenearthecompressivecornersareincreased. Asloadingcontinues,furtherseparationbetweenthema-sonrypanelandtheframeoccurs,resultingincontactonlyneartheloadedcornersoftheframe.Thisresultsinthecompositesystembehavingasabracedframe,whichleadstotheconceptof replacing themasonry infillwithanequivalentdiagonalstrut,asshowninFigure1.Theseconditionsareaddressedinthemasonrystandard.

Figure 1—Concrete Masonry Infill as a Diagonal Strut

2 NCMA TEK 14-23

Participatingmasonryinfillsresistout-of-planeloadsbyanarchingmechanism.Asout-of-planeloadsincreasebeyondtheelasticlimit,flexuralcrackingoccursinthemasonrypanel.Thiscracking(similartothatwhichoccursinreinforcedmasonry)allowsforarchingactiontoresisttheappliedloads,providedtheinfillisconstructedtighttotheboundingframeandtheinfillisnottooslender.

IN-PLANE SHEAR FOR PARTICIPATING INFILLS

Forparticipatinginfills,themasonryiseithermortaredtighttotheboundingframesothattheinfillreceiveslateralloadsimmediatelyastheframedisplaces,orthemasonryisbuiltwithagapsuchthattheboundingframedeflectsslightlybeforeitbearsupontheinfill.Ifagapexistsbetweentheinfillandtheframe,theinfillisconsideredparticipatingifthegapislessthan3/8in.(9.5mm)andthecalculateddisplacements,accordingtoMSJCCodeSectionB3.1.2.1.However,thein-fillcanstillbedesignedasaparticipatinginfill,providedthecalculatedstrengthandstiffnessarereducedbyhalf. Themaximumheight-to-thicknessratio(h/t)ofthepar-ticipatinginfillislimitedto30inordertomaintainstability.Themaximum thicknessallowed isone-eighthof the infillheight. TheMSJCCoderequiresparticipatinginfillstofullyin-filltheboundingframeandhavenoopenings—partialinfillsorinfillswithopeningsmaynotbeconsideredaspartofthelateralforceresistingsystembecausestructureswithpartialinfillshavetypicallynotperformedwellduringseismicevents.Thepartialinfillattractsadditionalloadtothecolumnduetoitsincreasedstiffness;typically,thisresultsinshearfailureofthecolumn. Thein-planedesignisbasedonabracedframemodel,withthemasonryinfillservingasanequivalentstrut.ThewidthofthestrutisdeterminedfromEquation1(seeFigure1).

inf

0.3cosstrut strut

w = Eqn.1

where:

inf

inf

4sin 2

4m net strut

strutbc bc

E tE I h

= Eqn.2

Thetermλstrut,developedbyStaffordSmithandCarter(ref.2)inthelate60s,isthecharacteristicstiffnessparameterfortheinfillandprovidesameasureoftherelativestiffnessof the frameand the infill.Design forces in theequivalentstrut are then calculated based on elastic shortening of thecompression-onlystrutwithinthebracedframe.TheareaofthestrutusedforthatanalysisisdeterminedbymultiplyingthestrutwidthfromEquation1bythespecifiedthicknessoftheinfill. The infill capacity can be limited by shear cracking,compressionfailure,andflexuralcracking.Shearcrackingcanbecharacterizedbycrackingalongthemortarjoints(whichincludes stepped and horizontal cracks) and by diagonaltensile cracking.Thecompression failuremodeconsistsof

eithercrushingofthemasonryintheloadeddiagonalcornersorfailureoftheequivalentdiagonalstrut.Thediagonalstrutisdevelopedwithinthepanelasaresultofdiagonaltensilecracking.Flexuralcrackingfailureisrarebecauseseparationatthemasonry-frameinterfaceusuallyoccursfirst;then,thelateralforceisresistedbythediagonalstrut. Asdiscussedabove,thenominalshearcapacityisdeterminedastheleastof:thecapacityinfillcornercrushing;thehorizon-talcomponentoftheforceintheequivalentstrutatarackingdisplacementof1in.(25mm);or,thesmallestnominalshearstrengthfromMSJCCodeSection3.2.4,calculatedalongabedjoint.Thedisplacementlimitwasfoundtobeabetterpredictorofinfillperformancethanadriftlimit. Generally, the infill strength is reached at lower dis-placementsforstiffboundingcolumns,whilemoreflexiblecolumns result in the strengthbeing controlled at the 1-in.(25-mm)displacementlimit.WhileMSJCCodeSection3.2isforunreinforcedmasonry,useofequationsfromthatsec-tiondoesnotnecessarilyimplythattheinfillmaterialmustbeunreinforced.TheequationsusedinMSJCCodeSection3.2aremoreclearlyrelatedtofailurealongabedjointandarethereforemoreappropriatethanequationsfromMSJCCodeSection3.3forreinforcedmasonry. Theequationsusedinthecodearetheresultofcomparingnumerousanalyticalmethodstoexperimentalresults.Theyarestrengthbased.Theexperimentalresultsusedforcomparisonwere a mixture of steel and reinforced concrete boundingframeswithclayandconcretemasonry.Whilesomemethodspresentedbyvariousresearchersarequitecomplex,thecodeequationsarerelativelysimple.

OUT-OF-PLANE FLEXURE FOR PARTICIPATING INFILLS

Theout-of-planedesignofparticipatinginfillsisbasedonarchingoftheinfillwithintheframe.Asout-of-planeforcesareappliedtothesurfaceoftheinfill,atwo-wayarchdevelops,provided that the infill is constructed tight to theboundingframe.Thecodeequationmodelsthistwo-wayarchingaction. Aspreviouslymentioned,themaximumthicknessallowedforcalculationfortheout-of-planecapacityisone-eighthoftheinfillheight.Gapsbetweentheboundingframeoneitherthesidesor topof the infill reduce thearchingmechanismtoaone-wayarchandareconsideredbythecodeequations.Boundingframemembersthathavedifferentcrosssectionalpropertiesareaccountedforbyaveragingtheirpropertiesforuseinthecodeequations.

NON-PARTICIPATING INFILLS

Becausenon-participatinginfillssupportonlyout-of-planeloads,theymustbedetailedtopreventin-planeloadtransferinto the infill. For this reason, MSJC Code Section B.2.1requirestheseinfillstohaveisolationjointsatthesidesandthetopoftheinfill.Theseisolationjointsmustbeatleast3/8 in.(9.5mm)andsizedtoaccommodatetheexpecteddesigndisplacements of the bounding frame, including inelasticdeformationduetoaseismicevent,topreventtheinfillfromreceivingin-planeloadings.Theisolationjointsmaycontain

NCMA TEK 14-23 3

fillermaterialaslongasthecompressibilityofthematerialistakenintoconsiderationwhensizingthejoint. Mechanicalconnectorsandthedesignoftheinfillitselfensurethatnon-participatinginfillssupportout-of-planeloads.Connectorsarenotallowed to transmit in-plane loads.Themasonryinfillmaybedesignedtospanvertically,horizontally,orboth.Themasonrydesignofthenon-participatinginfilliscarriedoutbasedontheapplicableMSJCCodesectionsforreinforcedorunreinforcedmasonry(Section3.2forunrein-forcedinfillandSection3.3forreinforcedinfillusingstrengthdesignmethods).Notethatthereareseismicconditionswhichmayrequiretheuseofreinforcedmasonry. Becausetheysupportonlyout-of-planeloads,non-partici-patinginfillscanbeconstructedwithfullpanels,partialheightpanels,orpanelswithopenings.Thecorrespondingeffectsontheboundingframemustbeincludedinthedesign.

BOUNDING FRAME FOR PARTICIPATING INFILLS

TheMSJCCodeprovidesguidanceonthedesignloadsappliedtotheboundingframemembers;however,theactualmemberdesignisgovernedbytheappropriatematerialcodeandisbeyondthescopeoftheMSJCCode. Thepresenceofinfillwithintheboundingframeplaceslocalized forces at the intersection of the framemembers.MSJCCodeSectionB.3.5helpsthedesignerdeterminetheappropriateaugmentedloadsfordesigningtheboundingframemembers.Framemembers inbaysadjacent toaninfill,butnotincontactwiththeinfill,shouldbedesignedfornolessthantheforces(shear,moment,andaxial)fromtheequivalentstrutframeanalysis.Intheeventofinfillfailure,theloadingrequirementonadjacentframemembersensuresadequacyintheframedesign,thuspreventingprogressivecollapse. Theshearandmomentappliedtotheboundingcolumnmustbeat least the results from theequivalent strut frameanalysismultipliedbyafactorof1.1.Theaxialloadsarenottobelessthantheresultsofthatanalysis.Additionally,thehorizontalcomponentof theforcein theequivalentstrut isaddedtothedesignshearfortheboundingcolumn. Similarly,theshearandmomentappliedtotheboundingbeamorslabmustbeatleasttheresultsfromtheequivalentstrutframeanalysismultipliedbyafactorof1.1,andtheaxialloadsarenottobelessthantheresultsofthatanalysis.Theverticalcomponentoftheforceintheequivalentstrutisaddedtothedesignshearfortheboundingbeamorslab. Theboundingframedesignshouldalsotakeintoconsider-ationthevolumetricchangesinthemasonryinfillmaterialthatmayoccurovertimeduetonormaltemperatureandmoisturevariations.Shrinkageofconcretemasonryinfillmaterialmayopengapsbetweentheinfillandtheboundingframethatneedto be addressed.Guidance for these volumetric changes isprovidedinMSJCCodeSection1.7.5.

CONNECTORS

Mechanicalconnectorsbetweentheboundingframeandthe infill provide out-of-plane support of the masonry, forboth participating and non-participating infills. Connectorsarerequiredonlyforthedirectionofspan(i.e.,atthetopand

bottomoftheinfillforinfillspanningvertically,forexample).The connectors must be designed to support the expectedout-of-planeloadsandmaynotbespacedmorethan4ft(1.2m)apartalongtheperimeteroftheinfill.Figure2showsanexampleofamechanicalconnectorcomposedofclipanglesweldedtothebottomflangeofthesteelbeam. Connectors for both participating and non-participatinginfills are not permitted to transfer in-plane loads from theboundingframetotheinfill.Forparticipatinginfills,in-planeloadsareassumedtoberesistedbyadiagonalcompressionstrut(seeFigure1),whichdoesnotrelyuponmechanicalconnectorstotransferin-planeload.Research(ref.3)hasshownthatwhenconnectorstransmitin-planeloadstheycreateregionsoflocal-izedstressandcancauseprematuredamagetotheinfill.Thisdamagethenreducestheinfill'sout-of-planecapacitybecausearchingactionisinhibited.

EXAMPLE 1: DESIGN OF PARTICIPATING MASONRY INFILL WALL FOR IN-PLANE LOADS

ConsiderthesimplestructureofFigure3.Theeastandwestsidewallsareconcretemasonryinfillslaidinrunningbond,whilethenorthandsouthwallsarestore-frontstypicalofconveniencestores.Steelframessupportallgravityloadsandthelateralloadintheeast-westdirection.Theboundingcolumns areW10x45s orientedwith the strong axis in theeast-westdirection.TheboundingbeamsabovethemasonryinfillareW10x39s.Themasonryinfillresiststhelateralloadinthenorth-southdirection. Usenominal8-in.(203-mm)concretemasonryunits,f'm = 1,500psi(10.34MPa),andTypeSPCLmortar.Assumehol-lowunitswithface-shellbeddingonly.Thetotalwallheightmeasures16ft-10in.(5.1m)totheroofwiththeinfillbeing16

Figure 2—Example of Mechanical Infill Connector

Clipanglesat4ft(1.2m)o.c.,weldedtothetopofthebottomflangeofbeam,butnotattachedtomasonry

4 NCMA TEK 14-23

ft(4.9m).Thebuildingisloadedwithawindloadof24lb/ft2 calculatedperASCE7-10(ref.6)inthenorth-southdirection.Theroofactsasaone-waysystem,transmittinggravityloadstothenorthandsouthroofbeams.InfillandboundingbeampropertiesaresummarizedinTables1and2. MSJCCodeSectionB.3.4.3requiresVn inftobethesmall-estofthefollowing:• (6.0in.)tnet inf f'm• the calculated horizontal component of the force in theequivalentstrutatahorizontalrackingdisplacementof1.0in.(25mm)

• Vn /1.5,whereVnisthesmallestnominalshearstrengthfromMSJCCodeSection3.2.4,calculatedalongabedjoint.

MSJC Code Section 3.2.4 requires the nominal shearstrengthnotexceedtheleastofthefollowing:• 3.8An mf ′

• 300An

• 56An+0.45Nvforrunningbondmasonrynotfullygroutedandformasonrynotlaidinrunningbond,constructedofopenendunits,andfullygrouted

• 90An+0.45Nvforrunningbondmasonryfullygrouted• 23Anformasonrynotlaidinrunningbond,constructedof

otherthanopenendunits,andfullygrouted

Asaresultofthewindloading,thereactiontransmittedtotheroofdiaphragmis:Reaction= 1/2(24lb/ft2)(16.83ft) = 202lb/ft(2.95kN/m)

TotalroofreactionactingononesideoftheroofisReaction= (202lb/ft)(30ft) = 6,060lb(27.0kN)

Figure 3—Convenience Store Layout for Design Examples 1 & 2

Infilled Wall Elevation

Plan View of Store

16ft(4.9m)

10in.(254mm)

W10x39

W10x45

8in.(203mm)Concretemasonryunits

30ft(9.14m)

30ft(9.14m)

Masonryinfill

W10x45column(typ.)

Storefront

PlanView

Storefront

NCMA TEK 14-23 5

Thisreactionisdividedevenlybetweenthetwomasonryinfills,sotheshearperinfillis3,030lb(13.5kN).

Usingtheconservativeloadingcaseof0.9D+1.0W, Vu=1.0Vunfactored=1.0(3,030lb)=3,030lb(13.5kN) To be conservative, the axial load to themasonry infill istakenaszero.

To ensurepractical conditions for stability, the ratioof thenominalverticaldimensiontothenominalthicknessislimitedto30forparticipatinginfills.Theratioforthisinfillis:h/t =192in./8in.=24<30Theratioislessthan30andtheinfillisthereforeacceptableasaparticipatinginfill.

ThewidthoftheequivalentstrutiscalculatedbyEquation1(MSJCCodeEquationB-1):

inf0.3cosstrut strut

w =

where λstrutisgivenbyEquation2(CodeEquationB-2).

Theangleoftheequivalentdiagonalstrut,θstrut,istheangleoftheinfilldiagonalwithrespecttothehorizontal.θstrut=tan-1(hinf / linf)=tan-1(192in./360in.)=28.1o

UsingEquation2,thecharacteristicstiffnessparameter,λstrut,forthisinfillisthen:  

   

     

=0.0392in.-1

Theresultingstrutwidthisthen:

inf 1

0.3 8.7 in.0.0392in. cos (28.1 )

w −= =×

Thestiffnessoftheequivalentbracedframeisdeterminedbyasimplebracedframeanalysiswherethestiffnessisbasedontheelasticshorteningofthediagonalstrut.Thestrutareaistakenasthewidthofthestrutmultipliedbythenetthicknessoftheinfill.

Thestiffnessis:2 2

inf inf inf3

cosstiffness = m net mAE w t E ld d

=

wheredisthediagonallengthoftheinfill,34ft(10.3m)inthiscase.

2

3

in.8.7 in. 2.5in. 1,350,000psi 30ft 12ftstiffness =

in.34ft 12ft

× × × ×

×

=56,030lb/in.(818kN/m)

Thenominalshearcapacity,Vn,isthentheleastof:• (6.0in.)tnet inf f'm=(6.0in.)(2.5in.)(1,500psi)=22,500lb• (56,030lb/in.)(1in.)=56,030lb• (3.8 mf ′ An)/1.5=[3.8 1,500 psi (30ftx30in.2/ft)]/1.5 =88,304lb• (300An)/1.5=[300(30ftx30in.2/ft)]/1.5=180,000lb• (56An+0.45Nv)/1.5=[56(30ftx30in.2/ft)+0.45x0]/1.5 =33,600lb

Vn=22,500lb(100kN)

Table 2—Bounding Frame Properties for In-Plane LoadsProperty: Value: NotesModulusofelasticityofboundingbeams,Ebb 29,000,000psi

(200,000MPa)Modulusofelasticityofboundingcolumns,Ebc 29,000,000psi

(200,000MPa)Momentofinertiaofboundingbeamsforbendingintheplaneoftheinfill,Ibb

209in.4 (8.7x10-5m4)

Boundingbeamstrongaxis

Momentofinertiaofboundingcolumnsforbendingintheplaneoftheinfill,Ibc

53.4in.4 (2.2x10-5m4)

Boundingcolumnweakaxis

Table 1—Infill PropertiesProperty: Value: NotesVerticaldimensionofinfill,hinf 192in.(4,877mm)Planlengthofinfill,linf 360in.(9,144mm)Specifiedthicknessofinfill,tinf 7.625in.(194mm)Netthicknessofinfill,tnet inf 2.5in.(64mm) Faceshellthicknessx2Specifiedcompressivestrengthofmasonry,f'm 1,500psi(10.34MPa)Modulusofelasticityofmasonryincompression,Em 1,350,000psi(9,300MPa)

6 NCMA TEK 14-23

Thedesignshearcapacityis:ϕVn =0.6x22,500lb=13,500lb(60kN) Thedesignshearcapacityfarexceedsthefactoreddesignshearof3,030lb(13.5kN),sotheinfillissatisfactoryforshear.

Additionally,theprovisionsofMSJCCodeSectionB.3.5re-quirethatthedesignerconsidertheeffectsoftheinfillontheboundingframe.Toensureadequacyoftheframemembersandconnections,theshearandmomentresultsoftheequiva-lentstrutframeanalysisaremultipliedbyafactorof1.1.Thecolumndesignsmustincludethehorizontalcomponentoftheequivalentstrutforce,whilethebeamdesignsmustincludetheverticalcomponentoftheequivalentstrutforce.Theaxialforcesfromtheequivalentstrutframeanalysismustalsobeconsideredinboththecolumnandbeamdesigns.

EXAMPLE 2: DESIGN OF PARTICIPATING MASONRY INFILL WALL FOR OUT-OF-PLANE LOADS

Designtheinfillfromthepreviousexampleforanout-of-planewindloadWof24lb/ft2(1.2kPa)perASCE7-10actingontheeastwall,usingTypeSPCLmortar,andunitswithanominal thicknessof8 in.(203mm).Assumehollowunitswithface-shellbeddingonlyandthattheinfillisconstructedtighttotheboundingframesuchthattherearenogapsatthetoporsidesoftheinfill.SeeTable3forframeproperties. MSJCCodeSectionB.3.6providestheequationsforthenominalout-of-planeflexuralcapacity.MSJCCodeEquationB-5requiresthattheflexuralcapacityoftheinfillbe:

0.75 2

inf inf 2.5 2.5inf inf

105 arch archn mq f t

l h

′= +

where:

0.252inf

inf

1 35arch bc bcE I hh

= <

0.252inf

inf

1 35arch bb bbE I ll

= <

αarch=0ifasidegapispresent, βarch=0ifatopgapispresent,and tinf < 1/8 hinf.

Usingtheconservativeloadingcaseof0.9D+1.0W,thedesignwindloadpressureis: q = 1.0W=1.0x24psf=24psf(1.15kPa) tinf = 7.625in.<(1/8)(192in.),OK

0.252

infinf

1arch bc bcE I h

h=

4 2 0.251 (29,000,000psi 248in. (192in.) )192in.

= × ×

= 21lb0.25(31N0.25)<35

0.252inf

inf

1arch bb bbE I l

l=

4 2 0.251 (29,000,000psi 45in. (360in.) )360in.

= × ×

= 10lb0.25(15N0.25)<35  

 

      =41.4psf(2.0kPa)

ThedesignflexuralcapacityisϕVn=0.6x41.4psf=24.8psf(1.2kPa) Thedesignflexuralcapacityexceedsthefactoreddesignwindloadpressureof24lb/ft2(1.2kPa),sotheinfillissatisfactoryforout-of-planeloading

NOTATIONSAn = netcross-sectionalareaofamember,in.2(mm2)D = deadload,psf(Pa)d = diagonallengthoftheinfill,in.(mm)Ebb = modulusofelasticityofboundingbeams,psi(MPa)Ebc = modulusofelasticityofboundingcolumns,psi

(MPa)Em = modulusofelasticityofmasonryincompression,

psi(MPa)f'm = specified compressive strength ofmasonry, psi

(MPa)h = effectiveheightoftheinfill,in.(mm)hinf = verticaldimensionofinfill,in.(mm)Ibb = momentofinertiaofboundingbeamforbending

intheplaneoftheinfill,in.4(mm4)Ibc = momentofinertiaofboundingcolumnforbending

intheplaneoftheinfill,in.4(mm4)linf = planlengthofinfill,in.(mm)Nv = compressiveforceactingnormaltoshearsurface,

lb(N)qn inf = nominalout-of-planeflexuralcapacityofinfillper

Table 3—Bounding Frame Properties for Out-of Plane LoadsProperty: Value: NotesMomentof inertiaofboundingbeamsforbending in theplaneof theinfill,Ibb

45in.4(1.9x10-5m4) Beamweakaxis

Momentofinertiaofboundingcolumnsforbendingintheplaneoftheinfill,Ibc

248in.4(1.0x10-4m) Columnstrongaxis

AllotherdesignparametersarethesameasusedinExample1.

NCMA TEK 14-23 7

unitarea,psf(Pa)t = nominalthicknessofinfill,in.(mm)tinf = specifiedthicknessofinfill,in.(mm)tnet inf = netthicknessofinfill,in.(mm)Vn = nominalshearstrength,lb(N)Vn inf = nominalhorizontalin-planeshearstrengthofinfill,

lb(N)Vu = factoredshearforce,lb(N)Vunfactored = unfactoredshearforce,lb(N)

W = outofplanewindload,psf(Pa)winf = widthofequivalentstrut,in.(mm)αarch = horizontalarchingparameterforinfill,lb0.25(N0.25)βarch = verticalarchingparameterforinfill,lb0.25(N0.25)λstrut = characteristic stiffness parameter for infill, in.-1

(mm-1)θstrut = angleofinfilldiagonalwithrespecttothehori-

zontal,degreesϕ = strengthreductionfactor

8 NCMA TEK 14-23

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REFERENCES1. Building Code Requirements for Masonry Structures,TMS402-11/ACI530-11/ASCE5-11.ReportedbytheMasonryStandards

JointCommittee,2011.2. Stafford-Smith,B.andCarter,C.(1969)"AMethodfortheAnalysisofInfilledFrames."Proceedings of the Institution of Civil

Engineers,44,31-48.3. Dawe,J.L.,andSeah,C.K.(1989a)."BehaviorofMasonryInfilledSteelFrames."Canadian Journal of Civil Engineering,

Ottowa,16,865-876.4. Tucker,CharlesJ."InfillingtheFrameWithMasonry."Structure,May2012.5. Tucker,CharlesJ."ChangingMasonryStandards:MasonryInfills."Structure,Feb.2012.6. Minimum Design Loads for Buildings and Other Structures,ASCESEI7-10.AmericanSocietyofCivilEngineersStructural

EngineeringInstitute,2010.