1

PART5STRUCTURALLOADSANDDESIGN

TABLEOFCONTENTS

SECTION

5.1SCOPE2

5.2DEFINITIONS2

5.3DESIGNREQUIREMENTS3

5.4DESIGNLOADSANDEFFECTS6

5.5LIMITSTATEDESIGN7

5.6DEADLOADS.14

5.7LIVE(IMPOSED)LOADSDUETOUSEANDOCCUPANCY.14

5.8DYNAMICLOADING..19

5.9EFFECTSOFWIND..21

5.10EFFECTSOFEARTHQUAKE..58

APPENDIXA127

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PART5STRUCTURALLOADSANDPROCEDURES

5.1SCOPE

5.1.1 This section covers all dead loads and imposed loads which shall be

sustainedandtransmittedbyabuildingandcertainstructureswithoutexceeding

thestresslimitationsspecifiedelsewhereintheCode.Itappliesto:

(1) newbuildingsandnewstructures;

(2) alterationsandadditionstoexistingbuildingsandstructures;

(3) existingconstructionsonchangeofuse.

5.1.2Thispartofthecodedoesnotcover

(1) loadsonroadsandrailbridges;

(2) loadsonstructuressubjecttointernalpressurefromcontents,(e.g.bunkers

silosandwatertanks)whichshouldbecalculatedindividually;

(3) loadsduetomachineryvibration,exceptthoseduetosomegantrycranes;

(4) loadsduetolifts;

(5) loadsincidentaltoconstruction;

(6) testloads.

Theseloadsarecoveredbyspecialized(proprietory)documentsproducedbymanufacturers.

5.2DEFINITIONS

5.2.1 Unless otherwise specified the following definitions shall apply for the

purposesofthispartoftheCode.

DeadLoads:The forcedue tothestaticweightofallpermanentstructuraland

nonstructural components of a building, such aswalls, partitions, floors,

roofs,fixedserviceequipmentandallotherpermanentconstruction.

Live (Imposed) Loads: The load assumed to be produced by the intended

occupancyoruse includingdistributed,concentrated, impact, inertia forcesbut

excludingwindandearthquakeloads.

WindLoads:Allloadsduetotheeffectofwind,pressureorsuction.

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EarthquakeLoads:Allloadsduetotheeffectofearthquake.

5.3DESIGNREQUIREMENTS

5.3.1 (1) Buildings and their structural members including formwork and

falseworkshallbedesignedtohavesufficientstructuralcapacitytoresistsafely

andeffectivelyallloadsandeffectsofloadsandinfluencesthatmayreasonably

beexpected,havingregardtotheexpectedservicelifeofbuildings.

5.3.1(2)Allpermanentand temporary structuralmembers, including formwork

and falsework of a building, shall be protected against loads exceeding the

design loadsduringtheconstructionperiodexceptwhen,asverifiedbyanalysis

or test, temporary overloading of a structural member would result in no

impairmentofthatmemberoranyothermember.Inaddition,precautionsshall

be taken during all stages of construction to ensure that the building is not

damagedordistortedduetoloadsappliedduringconstruction.

5.3.2DesignBasis

Buildingsandtheirstructuralmembersshallbedesignedbyoneofthefollowing

methods:

(1) analysisbasedonwellestablishedprinciplesofmechanics;

(2) evaluationofagivenfullscalestructureoraprototype

byaloadingtest;

(3) Studiesofmodelanalogues(modeling).

5.3.3Deflections

(1) Structural members shall be designed so that their deflections under

expectedserviceloadswillbeacceptablewithregardto:

(a) theintendeduseofbuildingormember;

(b) possibledamagetononstructuralmembersandmaterials;

(c) possible damage to the structure itself and, where significant, the

additionaleffectsofloadsactingonthedeformedstructure.

(2) Deflectionslistedinclause5.3.3(1)shallbetakenintoaccountinallstructures

and structural members made of material susceptible to deflections,

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deformationsorchangesinloaddistributionduetocreep,shrinkageorother

effectsinthematerialsofwhichtheyarecomposed.

(3) Thelateraldeflectionofbuildingsduetodesignwindandgravityloadsshall

becheckedtoensurethatnonstructuralelements,whosenatureisknown

atthetimethestructuraldesigniscarriedout,willnotbedamaged.Except

asprovidedinClause5.3.3(4)andunlessotherwiseapproved,thetotaldrift

perstoreyunderdesignwindandgravityloadsshallnotexceed1/500ofthe

storeyheight.

(4) ThedeflectionlimitsrequiredinClause5.3.3(3)doesnotapplytoindustrial

buildings or sheds if it is known by experience that greatermovement is

acceptable.

5.3.4VibrationsofFloors

(1) Special considerations shall be given to floor systems susceptible to

vibration to ensure that such vibration is acceptable for the intended

occupancyofthebuilding.

(2) Lateral Deflections of Tall Buildings: Unusually flexible buildings and

buildingswhoseratioofheighttominimumeffectivewidthexceeds4to1

shall be investigated for lateral vibrations under dynamic wind loading.

Lateralaccelerationsof thebuilding shallbechecked toensure that such

accelerationsareacceptabletotheintendedoccupancyofthebuilding.

(3) Stability under Compressive stress: Provision shall be made to ensure

adequatestabilityofastructureasawhole,andadequatelateral,torsional

and local stability of all structural parts which may be subject to

compressivestress.

5.3.5DesigndrawingsandCalculations

(1) Structuraldrawings submittedwith theapplication tobuild shallbear the

signatureofthedesigner.

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(2)Drawingssubmittedwiththeapplicationtobuildshallindicateinadditionto

thoseitemsspecifiedelsewhereinothersectionsofPart5,applicabletoaspecific

material:

(a) the name and address of persons responsible for the structural

design;

(b)thecodeorstandardtowhichthedesignconforms;

(c)thedimensions,locationandsizeofallstructuralmembersinsufficient

detailtoenablethedesigntobechecked;

(d)sufficientdetailtoenabletheloadsduetomaterialsof

constructionincorporatedinthebuildingtobedetermined;

(e)allintendedusesandoccupancies;

(f) all effects and loads, other than dead loads used in the design of

structuralmembers.

(3)Thecalculationsandanalysismadeinthedesignofthestructuralmembers,includingpartsand

componentsofabuildingshallbeavailableuponrequestforinspectionbytheauthorityhaving

jurisdiction.

(4) Structural integrity: Buildings and structural systems shall provide such structural integrity,

strengthorotherdefenses that thehazardsassociatedwithprogressivecollapsedue to local

failurecausedbysevereoverloadsorabnormaleventsnotspecificallycovered inthissection

arereducedtoalevelcommensuratewithgoodengineeringpractice.

5.3.6InspectionofConstruction

(1) Inspectionof the constructionof anybuildingorpart thereof shallbe carriedoutby the

designer,orbyanothersuitablyqualifiedpersonresponsibletothedesigner,toensurethat

theconstructionconformswiththedesign.

(2) The designer or another suitably qualified person familiar with the design concept and

responsibletothedesigner,shallreviewallshopdrawingsandotherdrawingsrelevantto

thedesigntoensureconformancetothedesign.

(3) WorkmanshipandMaterials:Workmanshipandmaterialsshallbeinspectedandallreports

ofmaterial tests shall be reviewed by the designer or another suitably qualified person

responsibletothedesignerduringtheprocessofconstruction.

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(4) Offsite inspections:Where abuildingor a componentof abuilding is assembledoff the

buildingsite, inamannerthat itcannotbe inspectedonsite,approvedoffsite inspection

shallbeprovidedwhenrequiredbytheauthorityhaving jurisdictiontoensurecompliance

withthisCode.

(5) InspectionReports:Copiesofallinspectionreportsshallbemadeavailablebythedesigner

uponrequesttotheauthorityhavingjurisdiction.

5.4DESIGNLOADSANDEFFECTS

5.4.1(1)ExceptasprovidedforinClause5.4.2,thefollowingcharacteristicloads,forcesandeffects

shall be considered in the design of a building and its structural members and

connections:

GK Dead load: Is the selfweightof thestructureand theweightof finishes,ceilings,services

andpartitions (seeBS6399:Part1, Loadings forbuildings.Codeofpractice fordeadand

imposedloads)andAppendixA.

QK Live(orImposedorVariable)load:Dueto intendeduseandoccupancy(include loadsdue

tomovable partitions and vertical loads due to cranes) and rain (see BS 6399:Part1 and

Table5.6).

WK Wind load:Dependson the location, shapeanddimensionof thebuildings (seeBS6399:

Part2,Loadingsforbuildings:Codeofpracticeforwindloads)andSection5.9ofthisPart.

EnNominalearthloads:Earthandhydrostaticpressure,surcharge,horizontalcomponentsof

staticorinertiaforces(seeBS8004:CodeofpracticeforFoundations).

EEarthquakeload(SeeSection5.10ofthisPart)

T Contractionorexpansiondue to temperature changes, shrinkage,moisture

changes, creep in component materials, movement due to differential

settlementorcombinationthereof.

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5.4.2(1)Whereabuildingorstructuralmembercanbeexpectedtobe

subjectedtoloads,forcesorothereffectsnotlistedinClause5.4.1(1);

sucheffectsshallbetakenintoaccountinthedesignbasedonthemost

appropriateinformationavailable.

(2)Ifitcanbeshownbyengineeringprinciplesorifitisknownfrom

experience,thatneglectofsomeoralltheeffectsduetoTdonot

affectthestructuralsafetyandserviceability,theyneednotbe

consideredinthecalculations.

5.4.3 Structuraldesign shallbe carriedout in accordancewith Section5.5 Limit

StateDesign.

5.5LIMITSTATEDESIGN

5.5.1(1)InthissectionthetermLimitStatemeansthoseconditionsofabuildingstructure

inwhichthebuildingceasestofulfillthefunctionortosatisfytheconditionsforwhich

itwasdesigned.

LimitStateDesignadmitsthatastructurecanbecomeunsatisfactoryinvariousways,

allofwhichneedtobeconsideredagainstdefinedlimitsofacceptability.

Byprovidingsufficientmarginsofsafetyagainstinherentvariabilityinloading(actions),

materialproperties,environmentalconditions,designmethodsandconstruction

practices,limitstatedesignaimsatgivinganacceptableprobabilitythatthestructure

willperformsatisfactorilyduringitsintendedworkinglife.

Thelimitstatescanbeplacedintwocategories:

(a)Ultimatelimitstates,whicharethosecorrespondingtomaximumloadcarrying

capacityandsafetyofpeopleandthestructuree.g.

(i) Lossofequilibrium(overturning)ofpartorthewholeofthestructurewhenconsideredasarigidbody.

(ii) Ruptureofcriticalsectionsofthestructure.

(iii) Transformationofstructureintoamechanism.

(iv) Failurethroughexcessivedeformation.

(v) Deteriorationarisingoutoffatigueeffects.

(b) Serviceability limit states, which are related to the criteria governing normal use or

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durabilitye.g.

(i) Excessivedeformationswithrespecttonormaluseofstructure.

(ii) Prematureorexcessivecracking.

(iii) Undesirabledamage(corrosion).

(iv) Excessivedisplacementwithoutlossofequilibrium.

(v) Excessivevibrations.

(vi) Thecomfortofpeople.

(vii)Theappearanceofthestructure.

(2)Characteristicloads(GK,QK,WK,En,E,T)meansthoseloadsdefinedinClause5.4.1.

(3)Partialsafetyfactorstothevalueofloads(f),usedindesigninsection5.5.2thattakesaccount

ofthepossibilityofunfavourabledeviationsoftheactionvalues,uncertaintiesinmodelingthe

effectsofactions,andthesignificanceoftheparticularlimitstate.

(4)Partialsafetyfactorstothevaluesofmaterialproperties(m)usedindesign.Thismakes

allowances forsubstandardmaterialsor for thedeteriorationofmaterialsduring the lifeof

thestructure.

(5) Actioncombinationfactor,,whichforimposed(variable)loads,areusedinmultiplying

characteristicvalues toobtain representativevalues.Theuseof factors reduce thedesign

valuesofmorethanonevariableloadwhentheyacttogether(seeTable5.3).

(6) Forimposed(variable)loads,underEurocode(see5.3):

representativevalues=characteristicvaluex

(7) Inmostcases,thedesignvalueofanaction(loadcombination)canbeexpressedas:

designvalue=representativevaluexf

5.5.2MethodsofLimitStateDesign

5.5.2.1Ghana,BritishSystemGS(BS8110:Part1)

5.5.2.1.1RequiredStrengthforUltimateLimitState

(1)TherequiredstrengthRprovidedtoresistdead loadGKand imposed loadQKshallbeat least

equalto:

R=1.4GK+1.6QK(51)

(2)Inthedesignofastructureormember,ifresistancetothestructuraleffectsofaspecifiedwind

loadWK,mustbe includedinthedesignthefollowingcombinationsofGK,QKandWKshallbe

investigatedindeterminingthegreatestrequiredstrengthR.

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R=1.2GK+1.2QK+1.2WK(52)

wherethecasesofQKhavingitsfullvalueorbeingcompletelyabsentshallbothbecheckedto

determinethemostsevereconditionusing

R=0.9GK+1.4WK(53)

Inanycase,thestrengthofthememberorstructureshallnotbelessthanrequiredbyEq.(51).

(3) If resistance tospecifiedearthquake loadsor forcesEmustbe included in thedesign, refer to

Section5.10ofthisPartonEffectsofEarthquake.

(4) If lateralearthpressureHmustbe included indesign thestrengthRshallbeat leastequal to

1.4GK + 1.6QK + 1.6H but where GK or QK reduce the effect of H (i.e. favourable), the

corresponding coefficients shall be taken as 0.90 for GK and zero for QK i.e. the governing

equationsare:

R=1.4GK+1.6QK+1.6H

R=0.9GK+1.6H

R=1.4GK+1.6QK

(6) ForlateralloadsFduetoliquids,theprovisionsforClause5.5.2.1.1(4)shallapply,except

that1.4Fshallbesubstituted for1.6H.Theverticalpressureof liquidsshallbeconsideredas

deadload,withdueregardtovariationinliquiddepth.

(6)Wherethestructuraleffectsofdifferentialsettlement,creep,shrinkageortemperatureTmaybe

significantthegoverningequationshallbe

R=1.2GK+1.2QK+1.2T

TheaboveactionsaresummarizedinTable5.1

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Table5.1LoadcombinationsforUltimateLimitState

Load

Combination

LoadType

DeadLoad ImposedLoad Earthand

Water

pressure

Wind

Adverse Beneficial Adverse Beneficial

1.DeadandImposed

(andearthandwater

pressure)

1.4 1.0 1.6 0 1.4

2.DeadandWind

(andearthandwater

pressure)

1.4 1.0 1.4 1.4

3. Dead, Wind and

Imposed (and earth

andwaterpressure)

1.2 1.2 1.2 1.2 1.2 1.2

5.5.2.1.2ValuesforaServiceabilityLimitState

Abuilding and its structural components shallbe checked for serviceability limit

statesasdefinedinClause5.5.1(b).Wheremorethanone loadcontributestothe

stressinthememberthecombinationofloadsshallbeassumedtobe:

GK+((QK+(EorWK)+T))

Whereshallbeequalto:

(a)1.0whenonlyoneoftheloadsQK,(EorWK)andTact;

(b)0.70whentwooftheloadsQK,(EorWK)andTact;

(c)0.60whenalloftheloadsQK,(EorWK)andTact.

5.5.2.2EurocodeSystemGS(BSEN1990,1991,1992)

OneofthemaindifferencesbetweentheEurocodesandtheBritish/Ghanaiansystem istheuseof

differentpartialsafetyfactorsandtheoptiontorefine/reduceloadfactorswhendifferentloadcases

arecombined.

5.5.2.2.1RequiredstrengthforUltimateLimitState

The design loads are obtained bymultiplying the characteristic loads by the appropriate partial

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safetyfactor,f,fromTable5.2.

Whenmorethanoneimposedload(variableaction)ispresent,thesecondaryimposedloadmaybe

reducedbytheapplicationofacombinationfactor,0(seeTable5.4).

Thebasicloadcombinationfortherequiredstrengthatultimatelimitstateforatypicalbuildingis:

R=GGK+QQK1+Q0QKi

where:

QK1,QK2,QK3etc.aretheactionsduetovertical imposed loads,wind load,snowetc.,QK1beingthe

leadingactionforthesituationconsidered.

The unfavourable and favourable factors should be used so as to produce themost onerous

condition.Generally,permanentactions fromasingle loadsourcemaybemultipliedbyeitherthe

unfavourableorthefavourablefactor.

Table5.2ActionCombinationsforUltimateLimitStates(BSEN1990:TableNA.A1.2(B))

Option PermanentActions

(DeadLoads)

VariableActions

(Imposed,WindLoads)

Earthand

Water*

Unfavourable Favourable Leading Others(i>1)

1 1.35GK 1.0GK 1.5QK,1 1.50,iQK,i 1.35QK

2a 1.35GK 1.0GK 1.50,1QK,1 1.50,iQK,i 1.35QK

2b 1.25GK 1.0GK 1.5QK,1 1.50,iQK,i 1.35QK,i

*Note: Ifthewaterpressurecalculated isthemostunfavourablevaluethatcouldoccurduringthe lifeofthestructure,a

partialfactorof1.0maybeused.

BasedonTable5.2,asummaryofEurocodePartialLoadFactorsisgiveninTable5.3for

theultimatelimitstate.

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Table5.3Partialsafetyfactorsforloadsattheultimatelimitstate

LimitState

PermanentActions

(GK)

VariableActions

Leadingvariableaction

(QK,1)

Accompanyingvariable

actions

(QK,I)

Unfavourable

Favourable

Unfavourable

Favourable Unfavourable

Favourable

(a)Static

equilibrium1.10 0.90 1.50 0.00 1.50 0.00

(b)Structural

strength1.35 1.00 1.50 0.00 1.50 0.00

(c)Asan

alternative

to(a)and(b)

aboveto

designfor

both

situations

withoneset

of

calculations

1.35 1.15 1.50 0.00 1.50 0.00

(d)Geotechni

calstrength1.35 0.00 1.35 0.00 1.35 0.00

5.5.2.2.2ValuesforServiceabilityLimitState

Theaction (load) combination for checking the requirementat the serviceability limit

stateisgenerallyoftheform:

GK+QK,1+0,iQK,i

Where, GK, QK,1 and QK,i are permanent action (dead load), leading variable action

(imposed load)andother secondaryvariableactions (wheremore thanone imposed

load contributes to the stresses) respectively. In the case of the secondary variable

load(s),theireffect(s)maybereducedbytheapplicationofthecombinationfactorsas

given inTable5.4.The corresponding load cases for the serviceability limit statesare

giveninTable5.5.

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Table5.4Combinationreductionfactors,,forbuildings

Action 0 1 2

Domestic,residentialarea 0.7 0.5 0.3

Officearea 0.7 0.5 0.3

Congregationareas 0.7 0.7 0.6

Shoppingareas 0.7 0.7 0.6

Storageareas 1.0 0.9 0.8

Trafficarea

Vehicle30kN0.7 0.7 0.6

Trafficarea

30kNVehicle160kN0.7 0.5 0.3

Roofs 0.7 0.0 0.0

Windloads 0.5 0.2 0.0

Temperature(nonfire) 0.6 0.5 0.0

Table5.5ServiceabilityLoadcases

Designrequirement Action

Combinations

Permanent(Dead

load)Actions

GK

Variable(Imposedload)

Actions

LeadingQK,1 OthersQK,i

Functionand

damagetoelements,

includingpartitions

andfinishes

Characteristic 1.0 1.0 0

Usercomfort,useof

machinery,avoiding

pondingofwater

Frequent 1.0 1 2

Appearanceofthe

structureorelement

Quasi

permanent

1.0 2 2

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5.6DEADLOADS

5.6.1(1)DeadloadsshallbecalculatedfromunitweightgiveninAppendixAtothispartorfrom

materialsnotprovidedforinthatAppendixasspecifiedoragreeduponwiththe

Authorityhavingjurisdiction.

(2) Whenpartitionsareshown inplans,theiractualweightsshallbe included inthedead

load.Forallfloorsinwhichpartitionwallsareormaybeintendedbutarenotlocated

on the plans, the beams and the floor slabswhere these are capable of effective

lateraldistributionoftheload,shallbedesignedtocarryinadditiontootherloads,a

uniformlydistributed loadpersquaremetreofnot lessthanonethirdoftheweight

permetrerunofthefinishedpartitions,butnot lessthan1kN/m2 ifthefloor isused

forofficepurposes.

5.7LIVE(IMPOSED)LOADSDUETOUSEANDOCCUPANCY

5.7.1TheminimumliveloadtobeprovidedforshallbeassetoutintheClausesofthisPart,or,

wherenotcoveredby theseClauses,as specifiedoragreeduponwith the

AdministeringAuthority.Inallcasestheliveloadorloadsshallbesoplaced

that incombinationwithdead loadthemaximumstressesareproduced in

thememberormembersbeingdesigned.

5.7.2FloorLiveLoads

(1) Theminimum floor live loads to be provided for shall be taken as being

equaltoanequivalentuniformstaticLoadorconcentratedloadwhichever

produces greater stresses and shall be based on the intended use and

occupancy as set out in Table 5.6 of this Clause. The concentrated loads

applied over a specified area of a square with a 300mm side shall be

locatedsoastocausemaximumeffects.

Table5.6provides fornormaleffectsofordinary impactandacceleration

butdoesnotincludeanyallowanceforspecialconcentratedloads.Special

provisionshallbemade formoving loadsother than those ingarages for

machineryandotherconcentratedloadsassetoutinSection5.8.

(2) Theconcentrated imposed loadneednotbeconsideredwhere the floor

slabiscapableofeffectivelateraldistributionofthisload.

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(3) Allbeamsshallbedesignedtocarrythedistributionloadappropriatetothe

usestowhichtheyaretobeputasgiveninTable5.6.

(4) Beams, ribsand joists spacedatnotmore than1metre centresmaybe

designedasfloorslabs.

(5) Where inTable5.6novaluesaregiven for concentrated load, itmaybe

assumed that the tabulated distributed load is adequate for design

purposes.

(6) Whereanareaoffloor isintendedfor2ormoreoccupanciesatdifferent

times,thevaluetobeusedfromTable5.6shallbethegreatestvaluefor

anyoftheoccupanciesconcerned.

(7)Whentheoccupancyofabuildingischangedthebuildingshallconformto

therequirementsofthispartoftheCodeforthenewoccupancy.

5.7.3 ReductioninTotalImposedFloorLoads

(1)Exceptasprovidedforin5.7.3(2)and5.7.3(3),thereductioninassumedtotal

imposed floor loadsdefinedbelowmaybe taken indesigning columns,piers,

walls,theirsupportandfoundations.Forpurposesof5.7.2(1)to5.7.3(3),aroof

mayberegardedasafloor.

Let, Le be the imposed load upon the roof and let L1, L2, L3 Ln be the

respective imposed loadsuponthe floorsnumbered1,2,3 nstarting from

thetopofthebuilding.

Forthedesignofthepointsofsupportthefollowingimposedloadsmaybe

adopted:

Supportsunderroof LO

Supportsundertopfloor(floor1) LO+L1

Supportsunderfloor2LO+0.95(L1+L2)

Supportsunderfloor3LO+0.9(L1+L2+L3)

Supportsunderfloor4LO+0.85(L1+L2+L3+L4)

Supportsunderfloorn LO+ (L1+L2+L3Ln)

Thecoefficient(3+n)/2nisvalidforn>5

Forfactoriesandworkshopsdesignedfor5kN/m2ormore,thereductions

shownabovemaybetakenprovidedtheloadingassumedisnotlessthanit

wouldhavebeenifallfloorshadbeendesignedfor5kN/m2withnoreductions.

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(2)Whereasinglespanofabeamorgirdersupportsnotlessthan46m2offloorat

onegenerallevel,theimposedloadmay,inthedesignofbeamorgirder,be

reducedby5%foreach46m2supported,subjecttoamaximumreductionof

25%.Thisreductionorthatgivenin5.7.3(1),whicheverisgreater,maybe

takenintoaccountinthedesignofcolumnsorothertypemembersupporting

suchabeam.

(3)Noreductionshallbemadeforanyplantormachinerywhichisspecifically

allowedfororforbuildingsforstoragepurposes,warehouses,garagesand

thoseofficeareaswhichareusedforstorageandfilingpurposes.

5.7.4RoofLiveLoadsotherthanWindLoadsorRainLoads.

(1) FlatRoofs

Flat roofs towhich there is no direct access (except only such cases as is

necessaryforcleaningandrepairs)shallwithstandanimposedloadof

0.25kN/m2measuredonplanoraloadof0.9kNconcentratedonasquare

with300mmsidewhicheverproducesthegreaterstress.

(2) On flat floorswhereaccess (in addition to thatnecessary for cleaningand

repair)isprovidedtotheroof,allowanceshallbemadeforanimposedload

of1.5kN/m2measuredonplanora loadof1.8kNconcentratedonasquare

witha300mmside.

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Table5.6UsesandLoads

OccupancyorUse

IntensityofDistributedLoads(kN/m2)

ConcentratedLoadtobeappliedunlessotherwisestatedoverany

squarewitha300mmside(kN/m2)

1. Residential

MultifamilyhousePrivateapartmentsPublicroomsCorridors

4.02.05.04.0

4.51.84.5

2. DwellingsNotexceeding2storeysExceeding2storeys

1.52.0

1.41.8

3. Hotels Guestrooms Publicrooms CorridorsservingpublicroomsCorridorsabovefirstfloor

2.05.05.04.0

1.84.54.54.5

4. OfficebuildingsAreas(notincludingcomputerrooms)locatedinbasementandfirstfloorFile,roomsinofficesFloorsabovefirstfloorAreawithcomputingdataprocessingandsimilarequipmentToiletrooms

5.05.02.53.52.0

4.54.52.74.5

5. Assemblyareaswithfixedseatsincluding:AuditoriaChurchesCourtroomsLecturehallsTheatresandotherareaswithsimilaruses

4.0

6. Assemblyareaswithoutfixedseatsincluding:ArenasBalconiesDancefloorsDiningareasFoyersandentrancehallGrandstandsReviewingstandsGymnasiaMuseumsStadiaStagesandotherareaswithsimilaruses

5.0

3.6

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7. DrillroomsandDrillhalls 5.0 9.0

8. Garageforpassengercarsunloadedbusesandlighttrucksnotexceeding2500kgincludingdrivewaysandrampsAll repairworkshops forall typesof vehicleandparking forvehicles exceeding 2500kg grossweight including drivewaysandramps

2.5

Tobedeterminedbutnot lessthan5.0

9.0

To be determined but not less than9.0

9. LibrariesReadingandstudyroomswithoutbookstorageRoomswithbookstorage(eg.Publiclendinglibraries)StackRooms

2.54.0

2.4Foreachmetrestackheightwithaminimumof6.5

4.54.57.0

10. SchoolsandCollegesClassroomsDormitoriesGymnasiaKitchensLaboratiesincludingequipment

3.01.55.0

Tobedeterminedbutnot lessthan3.0Tobedeterminedbutnot lessthan3.0

2.71.83.6

4.5

4.5

11. HospitalsBedroomsandWardsLaundriesToiletrooms UtilityroomsXrayroomandOperatingtheatres

2.03.02.02.0

2.0

1.84.54.5

4.512. Factories

LightMediumHeavy

5.07.510.0

4.56.79.0

13. WarehousesGeneralstoragespaceinindustrialandcommercialbuildings

10.0

9.0

(3) SlopingRoofsuptoangleof65otothehorizontalshallwithstandanimposed

loadof0.25kN/m2measuredonplanoraverticalloadof0.9kNconcentrated

onasquarewith300mmsidewhicheverproducesthegreaterstress.

(Note:ForconcentratedloadsPigeaudsorWestergaardstheorymaybeused)

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(4) CurvedRoofs

The imposed loadonacurved roofshallbecalculatedbydividing the roof

intonot lessthan fiveequalsegmentsand thenbycalculatingthe loadon

each,appropriatetoitsmeanslopeinaccordancewith5.7.4(1)to5.7.4(3).

(5) Roof coverings and purlins at a slope of less than 450 shall be capable of

carryingaloadof0.9kNconcentratedonanysquarewith125mmside.

5.8DYNAMICLOADING

5.8.1 Where loads arising from machinery, runways, cranes and other plant

producing dynamic effects are supported by or communicated to the

framework,allowanceshallbemade forthesedynamiceffects, including

impact,by increasingthedeadweightvaluesbyanadequateamount. In

ordertoensureeconomy indesign,theappropriatedynamic increase for

allmembersaffectedshallbeascertainedasaccuratelyaspossible.

5.8.2Theminimumdesign loaddue toequipment,machineryonotherobjectsor

persons that may produce impact, is the total weight of equipment or

machinery plus its maximum lifting capacity, or appropriate live load,

multiplied by an appropriate factor listed in Table 5.7; except in cases

wheretheactualmultiplyingfactorhasbeensuppliedbythemanufacturer

orsupplieroftheequipment inwhichcasethisfactorshallbeusedin lieu

ofthose listed inTable5.7.Wheredynamiceffectssuchasresonanceand

fatigueare likely tobe importantasaresultofvibrationofequipmentor

machinery,adynamicanalysisshallbecarriedout.

Table5.7ImpactLoads

Impactdueto Factor

Operationofmotordrivencranes

Operationofhanddrivencranes

Liveloadsonhangersupportedfloorsandstairs

Supportsforlightmachinery,shaftormotordriven

Supportsforreciprocatingmachineryorpowerdrivenunits

1.25

1.10

1.33

1.20

1.50

20

5.8.3Theminimumhorizontaldesignloadsoncranesrunwayrailsare:

(a) Lateralforcewhichshallbe:

(i) forpoweroperatedcranetrolleys,20%and forhandoperatedtrolleys,10%ofthe

sumoftheweightsoftheliftedloadsandofthecranetrolleyexcludingotherparts

ofthecrane;

(ii) appliedatthetopoftherail,onehalfineachsideoftherunway,and

(iii) consideredactingineitherdirectionnormaltotherunwayrail.

(b) Longitudinalforcewhichshallbe:

(i) 10percentofthemaximumwheelloadsofthecrane,and

(ii) appliedatthetopoftherail.

5.8.4(1)LoadsonRailings

Theminimumdesignloadappliedhorizontallyatthetopofarailingwhichguardsadropofmore

than460mmshallbe:

(a)5.8kN/mforexteriorbalconiesofindividualresidentialunitsandaconcentratedloadof

0.9kNappliedconcurrently;

(b)1.5kN/mforexitsandstairs;

(c)2.2kN/mforassemblyoccupancies,exceptforgrandstandsandstadia;

(d)3.6kN/mforgrandstandsandstadiaincludingramps;

(e)4.4kN/mforvehicleguardrailsforparkinggaragesapplied530mmabove

the roadway and minimum total load of (11kN) uniformly

distributedover each vehicle space applied 530mm above the

roadway,and

(f) O.6kNconcentratedloadappliedatanypointforindustrialcatwalksand

otherareaswherecrowdingbymanypeopleisveryimprobable.

(2)Theminimumdesignloadappliedhorizontallytopanelsunderrailingswhich

guardadropofmorethan460mmshallbe1.0kN/m2.

(3)Theminimumdesign loadappliedverticallyatthetopofarailingwhichguardsa

drop of more than 460mm shall be 1.5kN/m acting separately from the

horizontalloadprovidedinClause5.8.4(1).

(4)Grandstandsandanybuildingusedforassemblypurposestoaccommodatelarge

numbersofpeopleatonetimeshallbedesignedtoresistallinertiaswayforces

21

producedbyuseandoccupancyof thebuildingorstructure.The inertia force

shall be not less than 0.30kN/m of seat parallel to each row of seats or

0.2kN/mofseatperpendiculartoeachrowofseats.

5.9EFFECTSOFWIND

5.9.1Scope

ThisSubsectiondealswithmethodsforcalculatingwindloadsthatshouldbetaken

into accountwhen designing buildings, structures and components of buildings

andstructures.

Itdoesnotapplytobuildingorstructureswhose lightweight, low frequencyand

1owdampingpropertiesmakethemsusceptibletovibration.

5.9.2Definitions

Unlessotherwisespecified, the followingdefinitionsshallapply for thepurposes

ofthisSubsection.

1. Breadth:Thedimensionofthebuildingnormaltothedirectionofthewind.

2. Depth:Thedimensionofthebuildingmeasuredinthedirectionofwind.

3. Height:Theheightofabuildingabovethegroundadjoiningthatbuilding.

4. Length:Thegreaterhorizontaldimensionofabuildingabove, theground

adjoining that building; or the length, between supports, of an individual

structuralmember.

5. Width: The lesser horizontal dimension, of a building above the ground

adjacent to thatbuilding,or thewidthofa structuralmemberacross the

directionofthewind.

6. Heightaboveground:Thedimensionabovegenerallevelofthegroundto

windward.

7. Element of Surface Area: The area of surface over which the pressure

coefficientistakentobeconstant.

8. Effective Frontal Area: The area normal to the direction of thewind or

shadowarea.

9. DynamicPressureofWind:Thefreedynamicpressureresultantfrom

thedesignwindspeed.

10. Pressure Coefficient: The ratio of the pressure acting at a point on a

22

surfacetothedynamicpressureoftheincidentwind.

11. ForceCoefficient:Anondimensionalcoefficientsuchthat

thetotalwindforceonabodyistheproductoftheforce

coefficientmultipliedbythedynamicpressureofthe

Incidentwindandtheappropriateareaasdefinedin

text.

12. Topography:Thenatureoftheearthssurfaceas

influencedbythehillandvalleyconfigurations.

13. GroundRoughness:Thenatureof theearths surfaceas influencedby

smallscale obstruction such as trees and buildings (as distinct from

topography)

Note:BreadthandDepthofabuildingaretothedirectionof

wind.LengthandWidtharedimensionsrelatedtotheplanform.

5.9.3Nomenclature

A = elementofsurface

Ae = effectivefrontalarea

b = breadth

Cf = forcecoefficient

Cfn = normalforcecoefficient

Cft = transverseforcecoefficient

Cf1 = frictionaldragcoefficient

Cp = pressurecoefficient

Cpe = externalpressurecoefficient

Cpi = internalpressurecoefficient

d = depth

D = diameter

F = force

Fn = normalforce

Ft = transverseforce

F1 = frictionalforce

h = height

H = heightaboveground

23

j = widthofmemberasindicatedindiagram

ja = widthofmemberacrossdirectionofwind

k = aconstant

K = reductionfactor

l = length

p = pressureonsurface

Pe = externalpressure

Pi = internalpressure

B = totalloadintensity

q = dynamicpressureofwind(stagnationpressure)

Re = Reynoldsnumber

S1 = topographyfactor

S2 = groundroughness,buildingsizeandheightabovegroundfactor

S3 = astatisticalfactor

V = basicwindspeed

Vs = designwindspeed

w = widthofbuilding

w1 = baywidthinmultibaybuildings

= windangle(fromagivenaxis)

= aerodynamicsolidityratio

= shieldingfactor

v = kinematicviscosity

= geometricsolidityratio

5.9.4ProcedureforcalculatingWindLoadsonStructures

(1)Thewindloadonastructureshouldbecalculatedfor:

a) thestructureasawhole;

b)individualstructuralelementssuchasroofsandwalls;

c) individualcladdingunitsandtheirfixings.

(2)Inthecaseofpartiallycompletedstructures,thewindloadwilldependonthe

methodandsequenceofconstructionandmaybecritical.Incalculatingthe

temporary higher wind loads, themaximum design wind speed Vsmay be

assumednot tooccurduring the short constructionperiod and a reduced

24

factor S3 used. It is recommended that the graphs of Fig.5.6 should not be

extrapolatedforperiodslessthantwoyears.

(3)Theassessmentofwindloadshouldbemadeasfollows:

a) ThebasicwindspeedVappropriatetotheareawherethestructure

istobeerectedisdeterminedasspecifiedin5.9.5(2)

b) ThebasicwindspeedismultipliedbyfactorsS1,S2andS3togivethe

designwindspeedVs(see5.9.5(3)).

Vs=VS1S2S3

c) Thedesignwindspeedisconvertedtodynamicpressureq=kVS.2

Table5.11givescorrespondingvaluesofqandVs

d) Thedesignexternalpressureorsuctionatanypointonthesurface

ofthebuildingisgivenby:

p=Cpq

A negative value of Cp indicates suction. The resultant load on an

element or cladding depends on the algebraic difference of the

external pressure or suction and the internal pressure or suction

maybecalculatedfrom:

F=(CpeCpi)qA

AnegativevalueofFindicatesthattheresultantforceisoutwards.

The totalwind loadona structuremaybeobtainedbyavectorial

summationoftheloadsonallthesurfaces.

e) Where a value of force coefficient, Cf, is available, the totalwind

loadonthebuildingasawholeismoreconvenientlyobtainedfrom:

F=CfqAe

PressurecoefficientsaregiveninTables5.14and5.20forarangeof

building shapes.Force coefficientsaregiven inTables5.21 to5.25

foruncladstructures.

25

5.9.5 DesignWindSpeed,VS

(1)General:ThedesignwindspeedVsshouldbecalculatedfrom

Vs=VS1S2S3

Thebasicwindspeedtableisspecifiedin5.9.5(2)andthefactorsS1,S2,S3

in5.9.5(3).

(2)BasicWindSpeed:

a) The basicwind velocity is themaximum 3second gust speed at a

height of 10m above ground likely to be exceeded on the average

notmore thanonce in50years, inopencountry.Thevaluesare

shownby isophleths(lineofequalwindspeed)onthemapinFig.

5.1.Table5.8 gives basic wind speeds to be used in some major

townsinGhana.

b) Itshouldbeassumedthewindmayblowfromanydirection.

Table5.8BasicWindSpeed(inmetrespersecond)forsomemajortowns

m/s

1. Accra 29

2. Takoradi 29

3. Kumasi 36

4. Tamale 34

5. Ada 34

6. Saltpond 29

7. Axim 29

8. Ho 29

9. Akuse 34

10. KeteKrachi 38

11. Wenchi 38

12. Yendi 45

13. Wa 44

14. Navrongo 35

15. Bole 36

26

Fig.5.1:WindSpeeds(m/sec)

27

(3)WindSpeedFactors

(a)Topography Factor, S1: The basicwind speed, V, takes account of the

general level of site above sea level. This does not allow for local

topographic(orographic)featuressuchashills,valleys,cliffescarpmentsor

ridges,whichcansignificantlyaffectthewindspeedintheirvicinity.

ThefactorS1isameasureoftheenhancementthatoccursinwindspeeds

overhills,cliffsandescarpments.

Theeffectoftopography istoacceleratewindnearthesummitofhillsor

crestsofcliffs,escarpmentsorridgesanddeceleratethewindinvalleysor

nearthefootofcliffs,steepescarpmentsorridges.

Table5.9givesrecommendedvaluesofS1

Table5.9TopographyFactorS1

Topography

category

Description ValueofS1

1 Allcasesexceptin2and3below 1.0

2 Very exposed hillslopes andcrests where acceleration of

windisknowntooccur.

Valleysshapedsothatfunnelingofwindmayoccur.

Sites that are known to beabnormallywindy due to some

localinfluence.

1.1

3 Steepsidedenclosedvalleys,sheltered

fromallwinds.

0.9

28

(i) EffectofaClifforEscarpmentontheEquivalentHeightaboveground.

ThevalueofS1inTable5.9canbeexplicitlycalculatedfortheeffectofacliffor

escarpmentatasite.

Theeffectoftopographywillbesignificantatasitewhentheupwardslope()

isgreaterthan3(or0.05slope),andbelowthat,thevalueofS1maybetaken

to be equal to 1.0. The value of S1 varies between 1.0 and 1.36 for slopes

greaterthan3.

The influenceof the topographic feature isconsidered toextend1.5Leupwind

and2.5Ledownwindofthesummitorcrestofthefeature,whereLeisthe

effectivehorizontallengthofthehilldependingontheslopeasindicatedin

Fig.5.2.ThevaluesofLeforthevariousslopesaregiveninTable5.10.

Ifthezonedownwindfromthecrestofthefeatureisrelativelyflat(

29

Fig. 5.2a: Topographical dimensions General notations

30

Fig.5.2:Topographicaldimensions(a)HillandRidge,(b)Cliffand

Escarpment

31

32

Category1Category2Category3

Fig. 5.5: Categories of Ground Roughness

33

(b)GroundRoughness,BuildingSizeandHeightaboveground,FactorS2

The effect of wind on a building, structure or part thereof depends on

ground roughness variation ofwindwith height above ground and size of

buildingorcomponentunderconsideration.ThefactorS2takesaccountofthe

influencesonwindeffectlistedabove.

(i)GroundRoughness

Thegroundroughnesshasbeendividedintothreecategoriesandbuildings

andtheirelementsintothreeclassesasfollows:

GroundRoughness1:Open,levelornearlylevelcountrywithnoobstructions.

Examplesaremostofthecoastalregionoutsidemajorurbanandsuburban

areas,airfieldsandareassurroundingtheVoltaLake.

GroundRoughness2:Opencountrywithfewtreesandhouses.Examplesarefarmlandand

mostoftheareasoftheNorthandUpperRegionsoutsidemajorurbancentres.

GroundRoughness3:Areascoveredbylargeobstructions.Examplesareforestareas,

townsandtheirsuburbs.Fig.5.5showsareasofthecountryoutsidemajortownsandsuburbs

wherethedifferentcategoriesshouldbegenerallyapplicable.

(ii)CladdingandBuildingsize

Naturalwindsareturbulentandcontinuallyfluctuating.Thereisevidenceavailablethatfor

buildingsandcomponentsofbuildingsmoresusceptibletotheactionofwind,the3second

gustspeedshouldbeusedindesignwhileforotherbuildingsalongeraveragingtimecouldbe

used.Asaconsequenceofthis,3classeshavebeenselected.

ClassA:Allunitsofcladding,glazingandroofingandtheirimmediatefixingsandindividual

membersofuncladstructures.

ClassB:Allbuildingsandstructureswhereneitherthegreatesthorizontaldimensionnorthe

greatestverticaldimensionexceeds50m.

ClassC:Allbuildingsandstructureswhosegreatesthorizontaldimensionorgreatestvertical

dimensionexceeds50m.

ThevalueofS2forvariationforwindspeedwithheightabovegroundforvariousgroundroughness

categories and building size classes are given in Table 5.12. The height to be used for the

34

determinationofS2shouldbetakenastheheightfromthemeangroundleveladjoiningthebuilding

tothetopofthebuilding.Alternatively,thestructuremaybedividedintoconvenientpartsandwind

loadoneachpartcalculated,usingS2factorthatcorrespondstotheheightabovegroundofthetop

of thepart.Thedynamicpressure shouldbeassumed toactuniformlyover the structureorpart

respectively.

(c) Factorforbuildinglife,S3

The factor S3 takes into account the intended lifespan of the building or structure and the

acceptablecalculatedrisk.Thereisalwaysanelementofriskthatagivendesignwindspeedmaybe

exceeded inastormofexceptionalviolence.Thegreaterthe lifespanofthestructure,thegreater

therisk. Fig.5.6showsvaluesofS3equivalenttoaperiodofexposureof50yearsplottedagainst

intendedlifespanordesignlifeinyears.

Normally,wind loadsoncompletedstructuresandbuildingsshouldbecalculatedatS3=1except

for:

(i) temporarystructures;

(ii) structureswherealongerperiodofexposuretowindmayberequired;

(iii) structureswheregreaterthannormalsafetyisrequired.

Theperiodofexposureshouldneverbetakenaslessthan2years.

Example: Calculate the design speed for a tower 20m high, situated in a well wooded area (

roughnesscategory3)andfor100yearprobablelifenearanabruptescarpmentofheight35m.The

tower is locatedaroundHo.Thecrestoftheescarpment is10meffectivedistance fromtheplains.

Thetowerislocatedonthedownwindside,5mfromthecrest.

Tan=10/35=0.2857,=15.74

X=+5Le=10mH=20mX/Le=+5/10=+0.5H/Le=20/10=2

BasicwindspeedforHo,V=29m/s(Fig.5.1,Table5.8)

S3factorfor100yrprobablelifewithprobabilitylevelof0.63=1.05(Fig.5.6)

S2 factor for 20m for a well wooded area (ground roughness category 3)(Class B) = 0.90 (Fig.5.5,Table5.12)

S1factorfortopography:

ForX/Le=+0.5andH/Le=2(Fig.5.2);sfactorfromFig.5.3is=0.05

35

FromTable5.11,factorC=1.2Z/Le=1.2x20/10=2.4

S1=1+Cxs=1+0.05x2.4=1.12

Designwindspeed=Vs=VxS1xS2xS3

=29(1.12)(0.9)(1.05)=30.7m/s

NoteonFig.5.6

Forexample,usingthegraphforprobabilitylevel0.63foraperiodofexposureequalto100yearssay,S3=1.05i.e.there

istheprobabilitylevelof0.63thataspeedwhichis1.05timestheoncein50yearswindspeedobtainedfromFig.5.1

willbeexceededatleastoncein100years.

5.9.6DynamicPressureoftheWind

Using thevalueof thedesign speedVsobtained from section5.9.5, thedynamicpressureof the

windqaboveatmosphericpressuremaybecalculatedfrom

where:k=0.613inSIunits(N/mandm/s)

Table5.13givescorrespondingvaluesofVsandq.

36

Table5.12GroundRoughness,BuildingsizeandHeightaboveground,FactorS2

H(m)

1.OpenCountrywithnoobstructions

2.OpenCountrywithfewtreesandhouses

3.Towns,Suburbs,Forestareas

Class Class ClassA B C A B C A B C

3orless

5

10

15

20

30

40

50

60

80

100

120

140

160

180

200

0.83

0.88

1.00

1.03

1.06

1.09

1.12

1.14

1.15

1.18

1.20

1.22

1.24

1.25

1.26

1.27

0.78

0.83

0.95

0.99

1.01

1.05

1.08

1.10

1.12

1.15

1.17

1.19

1.20

1.22

1.23

1.24

0.73

0.78

0.90

0.94

0.96

1.00

1.03

1.06

1.08

1.11

1.13

1.15

1.17

1.19

1.20

1.21

0.72

0.79

0.93

1.00

1.03

1.07

1.10

1.12

1.14

1.17

1.19

1.21

1.22

1.24

1.25

1.26

0.67

0.74

0.88

0.95

0.98

1.03

1.06

1.08

1.10

1.13

1.16

1.18

1.19

1.21

1.22

1.24

0.63

0.70

0.83

0.91

0.94

0.98

1.01

1.04

1.06

1.09

1.12

1.14

1.16

1.18

1.19

1.21

0.64

0.70

0.78

0.88

0.95

1.01

1.05

1.08

1.10

1.13

1.16

1.18

1.20

1.21

1.23

1.24

0.60

0.65

0.74

0.83

0.90

0.97

1.01

1.04

1.06

1.10

1.12

1.15

1.17

1.18

1.20

1.21

0.55

0.60

0.69

0.78

0.85

0.92

0.96

1.00

1.02

1.06

1.09

1.11

1.13

1.15

1.17

1.18

Table5.13ValuesofqinSIUnits(N/m2)

Vs

(m/s)

0

1.0

2.0 3.0 4.0 5.0 6.0 7.0

8.0 9.0

10

20

30

40

50

60

70

61

245

552

981

1530

2210

3000

74

270

589

1030

1590

2280

88

297

628

1080

1660

2360

104

324

668

1130

1720

2430

120

353

709

1190

1790

2510

138

383

751

1240

1850

2590

157

414

794

1300

1920

2670

177

447

839

1350

1990

2750

199

481

885

1410

2060

2830

221

516

932

1470

2130

2920

(Note:Todetermineqforaspeedofsay33m/s lookunder3alongtherowcorrespondingto30whichgivesq=668N/m2).

37

5.9.7PressureCoefficientsandForceCoefficients

(1)General:Theforceonabuildingorstructureorpartthereofisobtainedbymultiplyingthe

dynamicpressurebyacoefficientthatisdependentontheshapeofthebuildingorstructure

andbytheareaofthebuildingorstructureorpartthereof.

Thetwotypesofcoefficientsare:

(a) pressurecoefficientCpwhichreferstoaparticularsurfaceorpartofbuilding;

(b) force coefficient Cf which refers to the building as a whole. The values of these

coefficients are given in Tables 5.14 to 5.23. These tables may be used for other

buildingsofgenerallysimilarshape.

(2)PressureCoefficients:Theaveragevaluesgiveninthetablesareforcriticalwinddirectionsin

oneormorequadrants.Inordertodeterminethemaximumwindloadonabuildingthetotal

loadshouldbecalculatedfromeachofthesurfacesorpartsofthesurfacesofthebuilding.

Coefficientsoflocaleffectsarealsogiven.Thesearetobeusedincalculatingloadsforlocalareas

butnotforcalculatingtheloadonentirestructuralelementssuchasroofandwalls.Insuch

locations,theconstructionmustbeadequatetoresistthelocalforces(additionalnailing,

anchoringetc.).

Furthermore,itshouldbenotedthattheselocalforcescanactinashakingmannerand

resultinfatiguefailures.

Thenetdesignloadduetowindonindividualcladdingandtheirfixings,roofsandwallsshouldbe

thealgebraicdifferenceoftheexternalpressureorsuctionandthedesigninternalpressureor

suctionfrom:

F=(CpeCpi)qA

ValuesofCpearegiveninTables5.14,5.15,5.16andvaluesofCpiinsection5.9.7(3).

(3)InternalPressureCoefficient:Itisnormallydifficulttoestimatetheinternalpressurecoefficient

forabuildingasthecoefficientdependsonpermeabilitythroughwindows,ventilationlouvres,

leakagegapsarounddoorsandwindowsandcladding.Itisrecommendedthatforwallandroof

loadingtheinternalpressurecoefficientshouldbedeterminedasfollows:

38

(a)Where there is only negligible probability of dominant opening occurring during a severe

storm, shouldbe takenas+0.2or 0.3whicheverproduces thegreatereffecton the

buildingormemberconcerned.

(b)Whereadominantopeningislikelytooccur, shouldbetakenas7.5%ofthevalueof

outsidetheopening.

(4)ForceCoefficients:Forcecoefficientsvaryforthewindactingondifferentfacesofabuildingor

structure.Indeterminingthecriticalload,thetotalwindloadshouldbecalculatedforeachwind

direction.Thetotalwindloadonaparticularbuildingorstructureisgivenby:

F=CfqAe

Thedirectionoftheforceisspecificinthetable.

Wherethewindloadiscalculatedbydividingtheareaintoparts,thevalueofCfappliedtoeachpart

shouldbethatforthebuildingasawhole.

(6) FrictionalDrag:Forcertaintypesofbuildingsitisnecessarytotakeintoaccountafrictional

drag inaddition to thewind loadcalculated from5.9.7(2)and5.9.7(4).The frictionaldrag

maybeneglectedforrectangularcladbuildingswheretheratiod/hord/bisgreaterthan4.

Thefrictionaldraginthedirectionofthewindisgivenbythefollowing:

ifhb,F=Cfqb(d4h)+Cfq2h(d4h)

or

ifhb,F=Cfqb(d4b)+Cfq2h(d4h)

Thefirstterm ineachformularepresentsthedragontheroofandthesecondthedragon

thewalls.

=0.01forsmoothsurfaceswithoutcorrugationsorribsacrossthewinddirection.

=0.02forsurfaceswithribsacrossthewinddirection.

0. =0.04surfaceswithribsacrossthewinddirection.

For other buildings the frictional drag will be indicated, where necessary, in tables of

pressurecoefficientsandforcecoefficients.

39

Table5.14:PressurecoefficientCpeforwallsofRectangularcladbuildings

BUILDING

HEIGHT

RATIO

BUILDING

PLAN

RATIO

ELEVATION PLAN WIND

ANGLE

Cpe forsurface LocalCpe

A B C D

h/w

1

40

Fig. 5.15: External pressure coefficients (Cpe) for Pitched roofs of rectangular clad

buildings

41

42

Table5.16:PressurecoefficientCfeformonopitchRoofsofrectangularcladbuildings

withh/w

43

Table5.17:Forcecoefficients(Cf)forRectangularclad(actinginthedirectionofthewind)

44

Table5.18:Pressurecoefficients(Cpe)forPitchedRoofsofMultispanbuildings

(allspansequal)withhw

45

Table5.19:Pressurecoefficients(Cpe)forSawtoothRoofsofmultispanbuildings

(allspansequal)withhw

46

Table5.20:Pressurecoefficients(Cp)forCanopyRoofswith1/2h/w

47

Table5.21:Forcecoefficient(Cf)forcladbuildingsofuniformsection

(actingindirectionofwind)

48

Table5.21(cont.)

49

Table5.21(cont.)

50

Table5.22:PressuredistributionaroundCylindricalstructures

Forthepurposeofcalculatingthewindforcesthatactinawayastodeformacylindricalstructure

thevaluesofCpe inTable5.22maybeused.Theyapplyonly insupercritical flow (i.e. theyshould

onlybeusedwhereD>0.3m).Theymaybeusedforwindblowingnormaltotheaxisofcylinders

havingtheiraxisnormaltothegroundplane(i.e.chimneys,silos)andtocylindershavingtheiraxis

51

parallelwiththegroundplane(i.e.horizontaltanks)providedtheclearancebetweenthetankand

thegroundisnotlessthanD.

histheheightofaverticalcylinderorlengthofahorizontalcylinder.Wherethereisafreeflowof

airaroundbothends,histobetakenashalfthelengthwhencalculatingh/D.Interpolationmaybe

usedforintermediatevaluesofh/D.

In the calculation of the load on the periphery of the cylinder, the value Cpi shall be taken into

account.

Foropenendedcylinderswhereh/D 0.3;Cpimaybetakenas0.8.

Foropenendedcylinderswhereh/D 0.3;Cpimaybetakenas0.5

5.9.8 ForceCoefficientsforUncladStructures

(1) General:Thissectionappliestopermanentlyuncladstructuresandstructuralframeworks

whiletemporarilyunclad.

Structuresthatbecauseoftheirsizeandthedesignwindvelocity,are inthesupercritical

flowregimemayneedfurthercalculationtoensurethatthegreatestloadsdonotoccurat

somewindspeedbelowthemaximumwhentheflowwillbesubcritical.

(2) Force coefficients of individualmembers: The coefficients refer tomembersof infinite

length.Formembersof finite length, thecoefficientsshouldbemultipliedbya factorK

thatdependson the ratio l/ja,where l is the lengthof thememberand ja is thewidth

acrossthedirectionofthewind.ValuesofKaregiveninTable5.23.

Whereanymemberabutsontoaplateorwall insuchawaythatfreeflowofairaround

thatendofthemember isprevented,theratiol/jashouldbedoubledforthepurposeof

determiningK.Whenbothendsofamemberaresoobstructed,theratioshouldbetaken

asinfinity.

52

Table5.23ValuesofReductionFactorKformembersoffinitelengthandslenderness

l/jaorl/D 2 5 10 20 40 50 100

Circularcylinder,subcriticalflow

Circularcylinder,supercriticalflow

Flatplateperpendiculartowind

0.58

0.80

0.62

0.62

0.80

0.68

0.68

0.82

0.69

0.74

0.90

0.81

0.82

0.98

0.87

0.87

0.99

0.90

0.98

1.0

0.95

1.0

1.0

1.0

5.9.8(3)(a) Flatsidedmembers: The force coefficient in Table5.24 are given for twomutually

perpendiculardirectionsrelativetoareferenceaxisonthestructuralmember.Theyaredesignated

CfnandCftandgivetheforcesnormalandtransverse,respectively,tothereferenceplaneaswillbe

apparentfromthediagrams.

Forcecoefficientsareforwindnormaltothelongitudinalaxisofthemember.

Normalforce:F=Cfnqklj

Transverseforce:F=Cftqklj

(b)Circularsections:Forcircularsections,theforcecoefficientsCf,whicharedependentuponvalues

ofDVs,aregiven inTable5.25.ThevaluesofCfgiven in this tableare suitable forall surfacesof

evenlydistributedroughnessofheight lessthan1/100diameter i.e. forallnormalsurface finishes

andformembersofinfinitelength.

Force,F=Cfqkld

53

Table5.24:ForcecoefficientsCfnandCftforindividualstructuralmembers(flatsides)of

infinitelength

54

Table5.25ForceCoefficientsCfforindividualstructuralmembersofCircularSectionandInfinteLengthFlowregime ForcecoefficientCf

Subcriticalflow DVs 6m2/s

Re 4.1x105 1.2

Supercriticalflow

6 DVs 12m2/s

4.1x105 Re 8.2x105

0.6

12 DVs 33m2/s

8.2x105 Re 22.6x105

0.7

DVs 33m2/s

Re 22.6x105

0.8

Reynoldsnumber,Re>=

where:Disthediameterofthemember

Vsisthedesignwindspeed,and

vistheKinematicviscosityoftheair,whichis1.6x105m2/sat15oCandstandard

atmosphericpressure.

(c)Wiresandcables:TheforcecoefficientsforwiresandcablesgiveninTable5.26aredependent

uponvaluesofDVs.

Table5.26ForceCoefficientsCfforWiresandCables(1/D>100)

FlowRegime Smooth

surfacewire

Moderately wire

(galvanized or

painted)

Fine stranded

cables

Thick stranded

cables

DVs 0.6m2/s

DVs 0.6m2/

DVs 6m2/s

DVs 6m2/s

1.2

0.5

1.2

0.7

1.2

0.9

1.3

1.1

55

(4)Singleframes: Ingeneral,themostunfavourablewind loadonasingle frameoccurswhen

the windisatrightanglestotheframe.

Thewindloadactingonasingleframeshouldbetakenas

F=CfqAe

where;Aeistheeffectiveareaofframenormaltothewinddirection.

The forcecoefficientsforasingle frameconsistingof(a)flatsidedmembersor(b)circular

sectionmembersinwhichallthemembersoftheframehaveDVsvaluelessorgreaterthan

6m2/saregiveninTable5.27.

Table5.27EffectiveForceCoefficientsCfforSingleFrames

Solidityratio

ForcecoefficientCffor:Flatsidedmembers CircularSections

SubcriticalflowDVs 6m2/s

SupercriticalflowDVs 6m2/s

0.10.20.30.40.50.751.0

1.91.81.71.71.61.62.0

1.21.21.21.11.11.52.0

0.70.80.80.81.41.42.0

Thesolidityratioisequaltotheeffectiveareaofaframenormaltothewinddirectiondividedby

theareaenclosedbytheboundaryoftheframenormaltothewinddirection.

(5) Multipleframestructures:Thissectionappliestostructureshavingtwoormoreparallelframes

wherethewindwardframemayhaveashieldingeffectupontheframesto leeward.Thewind

loadonthewindwardframeandanyunshelteredpartsofotherframesshouldbecalculatedas

in5.9.8(3),butwind loadon thepartsof frames thatareshelteredshouldbemultipliedbya

shieldingfactorn,whichisdependentuponthesolidityratioofthewindwardframe,thetypeof

membercomprisingthe frameandthespacingratioofthe frames.Thevaluesoftheshielding

factoraregiveninTable5.28.

Wheretherearemorethantwoframesofsimilargeometryandspacing,thewindloadonthe

thirdandsubsequentframesshouldbetakenasequaltothatonthesecondframe.

56

Table5.28ShieldingFactor,n

SpacingRatio

Valueofnforanaerodynamicsolidityratioof:

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8&

over

Upto1.0

2.0

3.0

4.0

5.0

6.0andover

1.0

1.0

1.0

1.0

1.0

1.0

0.96

0.97

0.97

0.98

0.98

0.99

0.90

0.91

0.92

0.93

0.94

0.95

0.80

0.82

0.84

0.86

0.88

0.90

0.68

0.71

0.74

0.77

0.80

0.83

0.54

0.58

0.63

0.67

0.71

0.75

0.44

0.49

0.54

0.59

0.64

0.69

0.37

0.43

0.48

0.54

0.60

0.66

Thespacingratioisequaltothedistance,centretocentre,oftheframes,beamsorgirdersdivided

bytheleastoveralldimensionoftheframe,beamorgirdermeasuredatrightanglestothedirection

ofthewind.

Aerodynamicsolidityratio, =solidityratio()xaconstant

wheretheconstantis:

1.6forflatsidedmembers;

1.2 for circular sections in the subcritical rangeand for flatsidedmembers in conjunctions

withsuchcircularsections;

0.5 forcircularsections inthesupercriticalrangeand for flatsidedmembers inconjunction

withcircularsections.

(6)LatticeTowers:

(a) Lattice towers of square and equilateral triangular sections constitute special cases for

whichitisconvenienttouseoverallforcecoefficientinthecalculationofwindload.Thewind

loadshouldbecalculatedfortheconditionwhenthewindblowsagainstanyface.

Thewindloadactinginthedirectionofthewindshouldbetakenas:

F=CfqAe

TheoverallforcecoefficientCfisgiveninTables5.29,5.30and5.31.

57

Table5.29OverallForceCoefficientCfforTowerscomposedof

Flatsidedmembers

Solidityratio Forcecoefficientoffor:

Squaretowers Equilateraltriangulartowers0.1

0.2

0.3

0.4

0.5

3.8

3.3

2.8

2.3

2.1

3.1

2.7

2.3

1.9

1.5

Forsquarelatticetowersthemaximumloadoccurswhenthewindblowsontoacorner.

Itmaybetakenas1.2timestheloadforthefaceonwind.

For triangular lattice towers the wind load may be assumed to be constant for any

inclinationofthewindtoface.

(b) Since it isonly in very few caseswith lattice towers composedofmembersof circular

sectionthat all the members of a lattice tower are entirely in either subcritical or

supercritical flow,wind forcecalculationsshouldbecarriedoutasdescribed in5.9.8(4) for

singleframes,dueaccountbeingtakenoftheshieldingfactorsin5.9.8(5).

When it can be shown that all themembers of the tower arewholly in the same flow

regimetheoverallforcecoefficientsCfgiveninTables5.29and5.30maybeused.

Solidityratioofaframe=.Forlatticesteeltowers,typicallyvariesbetweenabout0.1and

0.3

58

Table5.30OverallForceCoefficientCfforSquareTowerscomposedof

RoundedMembers

Solidityratiooffrontface,

ForcecoefficientCffor:Subcriticalflow

DVs

59

5.10EFFECTSOFEARTHQUAKES

5.10.1SCOPEANDFIELDOFAPPLICATION

5.10.1.1 This Code sets down minimum design requirements to be met when dealing with

seismic situations i.e. situations inwhich theearthquake action is consideredas a critical

actioninconjunctionwithotherdeadloadsorliveloads.Itappliesto:

(1) ReinforcedandPrestressed concretebuildings forordinaryuses,having structural

resistingsystemsbelongingtooneofthreetypesdefinedbelow:

(a) Frame System: A system in which both vertical loads and lateral forces are

resistedbyspaceframes.

(b)WallSystem:Asysteminwhichbothverticalloadsandlateralforcesareresisted

bystructuralwallseithersingleorcoupled.

(c)DualSystem:Asystem inwhichsupportforvertical load isessentiallyprovided

byaspaceframe.Resistancetolateralactioniscontributedto,inpart,bytheframe

systemandalsoinpartbystructuralwalls,isolatedorcoupled.

5.10.2DEFINITIONSANDNOTATIONS

Definitions

Crosstie: A continuousbarwithaminimumdiameterof6mm, havinga1350 hookwitha

tendiameterextensionatoneend,anda900hookwithasixdiameterextensionattheotherend.

Thehooksshallengagehoopbarsandbesecuredtolongitudinalbars.

Hoop: Aclosedtieorcontinuouslywouldtiewithaminimumdiameterof6mmtheendsofwhich

have1350hookswithtendiameterextensionsthatenclosesthelongitudinalreinforcement.

Boundaryelements: Portions along the edges of walls and diaphragms strengthened by

longitudinal and transverse reinforcement. Boundary elements do not necessarily require an

increaseof thicknessof thewallordiaphragms.Edgeopeningswithinwallsanddiaphragmsmay

alsohavetobeprovidedwithboundaryelements.

60

Notations

A= peakgroundacceleration

Ac= confinedareameasuredtooutsideperipheraltransversereinforcement.

Ag= grosssectionalareaofconcrete

Cd=designseismiccoefficient

Cg =centreofmass

Ck =centreofstiffness

E =designseismicaction(symbolic)

I =importancefactor

Mu,d= ultimatemomentofaconcretesection,evaluatedwithfactoredvaluesofconcreteand

steelstrengths

M+u,d= ultimatemomentofaconcretesection,evaluatedwithcharacteristicvaluesofconcrete

andsteelstrengths.

Nd= designaxialforceunderthemostunfavourable loadcombination includingtheseismic

action.

K =behaviourfactor

S =sitecoefficient

Si =soiltypeindex

Vcd =shearforcecarriedbyconcreteinbeamorcolumnsections

a=plandimensionofthebuildinginthedirectionorthogonaltothatofseismicaction

bw =webwidthofaconcretesection

h,b =heightandwidthofbeams,majorandminorsidesincolumns

h,b = distancebetweenreinforcementbars locatedattheendsofsides inandb,respectively,

measuredtooutsidetheperipheralbars

61

d=distancefromcentreofstiffnessandcentreofgravityofthegenericfloor

Sh=spacingoftransversereinforcementinbeams,columnsandwalls.

fcd=designconcretestrength

h=heightofafloor

lw=horizontalwalllength

hw = totalheightofawall

hn = verticaldistancebetweenfloorsinwalls

= spectralamplificationfactor

= parameteroftheelasticresponsespectrum

i = distributionfactor

n = overcapacityfactor

el = elasticinterstoreydriftundertheseismicactions

= ratiobetweenmaximumandminimumshearforceatabeamend

= deformabilityindex

= amplificationfactorfortorsionaleffects

w = dynamicmagnificationfactor

Rd = sheardesignstressofconcrete

62

5.10.3 DESIGNCRITERIA

5.10.3.1ReliabilityDifferentiation

Structuresshallbeclassifiedunderthefollowingreliabilitylevels:

(1) Class I: Buildings that are required to remain functional and to suffer reduced

damage after a strong seismic attack (e.g. essential rescue facilities such as

hospitals, fireandpolicestations,electricitystationsetc.buildingswith likely large

numberofoccupantssuchasschools,audienceorspectaclehalls,etc).

(2) ClassII:Buildingsnotincludedin5.10.3.1(1)

(3) Thedifferent reliability levelsproper toeachClassshallbeobtainedbyamplifying

thedesignactionwithafactorI,calledimportancefactor.

5.10.3.2DuctilityLevels

Structural systems covered by the Codemay be designed to possess different ductility

levelsaccordingtothefollowingclassification:

(1) DuctilityLevelI(DLI)isthatpropertostructuresproportionedinaccordancetoBS

8110(1985)withadditionalrequirementsondetailingcontainedin5.10.8.

Thisductilitylevel,Iissuitableforlowrisebuildings.

(2) DuctilityLevelII(DLII)forthislevelseismicprovisionsaretobeadopted,enabling

the structure to enter the inelastic range of response under repeated reversed

loading,whileavoidingprematurebrittletypefailures.

(3) DuctilityLevelIII(DLIII)specialproceduresfortheevaluationofdesignactionand

fortheproportioninganddetailingoftheelementsaretobeadoptedtoensurethe

developmentofselectedstablemechanismsassociatedwithlargeenergydissipation

capacities. DL IIIstructuresshouldbepreferredwhenever largeuncertaintiesexist

(e.g.Localamplificationeffectsofdifficultevaluationetc).

63

5.10.4 METHODSOFASSESSMENT

5.10.4.1Basicdata

5.10.4.1.1MaterialCharacteristics

5.10.4.1.1(1)Concrete

Normalconcretegradesshallsatisfythefollowingrequirements(Table5.10.4.1)

Table5.10.4.1

DuctilityLevel MinimumGrades

DLI C20

DLII C20

DLIII C25

5.10.4.1.1(2)Steel

(a) DLIandDLIIStructures

Thereinforcingsteelisdefinedbyitscharacteristicstrength.

(b) DLIIIStructures

Thefollowingadditionalrequirementsshallbesatisfied.

(i) It must be proven the steel used possesses adequate ductility under

repeatedreverseddeformations.

(ii) Steel grades with characteristic strengths higher than S400 (400N/mm2)

shallnotbeused,unlessitisdemonstratedthattheuseofhighergradesin

specialsectionarrangementsdoesnotaffectunfavourablytheductility.

(iii) Theactualyieldstressshallnotexceeditsnormalvaluesbymorethan15%.

64

m

(iv) The ratioofthemeanvalueoftheultimatestrengthtoactualyieldstress

shallnotbelessthan1.25forS220and1.15forS400

(v) Only high bond steel shall be used for flexural reinforcement, unless

adequateprovisionsaretakentoensurebondandanchorage.

5.10.4.1.2MaterialSafetyFactor,

Design values of strength for concrete and steel shall be obtained from their respective

characteristicvaluesbyusingthefactors:

Concrete c =1.5

Steel s =1.15

5.10.4.1.3StructureBehaviourFactors

(1) The values of the behaviour factor K, defining the intensity of the design action

(section5.10.5.3)asa functionof the structural typeandof the selectedductility

level,aregiveninTable5.10.4.2

Table5.10.4.2DESIGNBEHAVIOURFACTORS

StructuralSystemDuctility

LevelI

Ductility

LevelII

Ductility

LevelIII

Frame

WallandDual

2

2

3.5

3

5

4

(2) ThevaluesofKinTable5.10.4.2forwallanddualstructuresapplyif,atleast50%of

thelateralforceinbothdirectionsisresistedbycoupledwalls.

(3) If condition5.10.4.1.3(2) isnot satisfied, theKvalues forwallanddual structures

shallbereducedbyafactorof0.7.

(4) Ductility Level I is permitted only for Class II structures in areas of moderate

seismicity.

65

(5) ClassIstructurestobebuiltinhighseismicityareasshallbepreferablydesignedfor

ductilitylevelIII.Ifappropriate,KvaluesrelativetoDLIIcouldbeusedinthiscase.

5.10.4.1.4DesignLoadCombination

Thefundamentalcombinationofloadeffectstobeusedforlimitstatesverification(Section

5.10.7.4)is

Sd=S(G+P+E+iQik)...5.10.4.1.1

whereG= allpermanentloadsattheirnormalvalue

P= thelongtermprestressingforce

E= thedesignseismicactionasdefinedinSect.5.10.5.3.4

Qik= fractile valuesof extremedistributionsof all live loadswhosedurationof

applicationislongenoughfortheprobabilityoftheirjointoccurrenceswith

earthquakeactiontobeconsidered.

I= factorsrequiredtochangethefractilevaluesQiktotheaveragevaluesofQikintheirinstantaneousdistribution(SeeTable5.10.4.3)

S=SiteCoefficient

Table5.10.4.3:COMBINATIONFACTORIFORLIVELOADS

Liveloadsfrompersonsandequipment 0.3

Liveloadsfrompersonsatplaceswithlikelihoodof

largenumberofoccupants(halls)0.5

Longtermstorage(warehouse,libraries) 0.9

Liveloadsonstaircasesandcorridors 1.0

66

5.10.4.2Structuralanalysis

5.10.4.2.1BuildingConfiguration

Abuildingshallbeclassifiedasregularwhenthefollowingconditionsaresatisfied,regarding

bothplanandverticalconfiguration.

(a)PlanConfiguration

(i) The building has an approximately symmetrical plan configuration with

respect to,at least twoorthogonaldirectionsalongwhich theearthquake

resistingelementsareoriented.Whenreentrantcornersarepresent,they

donotexceed25percentofthebuildingexternaldimension.

(ii) Atanystoreythedistance(measured inthedirectionorthogonaltothatof

the seismic action) between the centre ofmass and that of the stiffness

doesnotexceedl5%oftheresistanceradiusdefinedasthesquarerootof

theratioofstoreytorsionalandtranslationstiffnesses.

(b)VerticalConfiguration

(i) The stiffness and mass properties are approximately uniform along the

buildingheight.

(ii) In framestructures, theratiobetweenactualshearcapacity (sumofshear

forces contributed by all vertical elements at their design strengths) and

designsheardoesnotdiffermore than20percent, forany twostoreysof

thebuilding.

(iii) Inthecaseofagradualsetbackalong itsheight,thesetbackatanyfloor is

notgreaterthan l0%oftheplandimension inthedirectionofthesetback.

Thisclauseneednotbecompliedwithifthesetbackoccurswithinthelower

l5%ofthetotalheightofthebuilding.

5.10.4.2.2ApplicationofSeismicAction

(1) HorizontalAction

(i) The seismic actions shall be applied to the building in the directions

producingineachelementthemostunfavourableeffect.

67

i

(ii) Inbuildingshavingoneaxisofsymmetry,theseismicactioncanbeassumed

asactingseparatelyalongthisaxisanditsorthogonaldirection

(2) VerticalAction

(i) The vertical component of the seismic action shall be considered in the

designofnonverticalcantileversandofprestressedbeams.

5.10.4.2.3AnalyticalModel

(1) The determination of the seismic effects on the structure shall be based on an

idealized mathematical model which is adequate for representing the actual

behaviours; themodel shall also account for all nonstructural elements that can

influencetheresponseofthemainresistingsystem.

(2) Forthepurposeofthepresentcode,thedeterminationofthe loadeffectsdueto

designforcesmaybebasedonalinearelasticmodelofthestructuralsystem.

(3) Regular buildings can be designed according to the simplifiedmethod of analysis

(indicatedasequivalentstaticanalysis)describedin5.10.4.2.4providedtheirheight

doesnotexceed80m,andthefundamentalperiodisshorterthan2secs.

(4) Ifconditions in5.10.4.2.3.(3)arenotsatisfiedor ifthebuilding isof irregulartype,

thedynamicmethodin5.10.4.2.5shallbeapplied.

5.10.4.2.4EquivalentStaticAnalysis

(1) HorizontalDesignForces

(a) The design lateral force to be applied at each floor level in the direction

beinganalysed,shallbegivenby:

F=Cd. i .Wi....5.10.4.2.1whereCd=designseismiccoefficient,equalinvaluetothedesignresponse

spectrum,asgiveninSection5.10.5.3.4

= distribution factor, depending on the height of the floor,

measuredfromthebuildingbase

68

K1 . . S. A . I = C d

h W W h =

ii

ii i

i

Wi=totalgravityloadatfloori

(b) IncaseswheretheperiodTisnotcalculatedfrommethodsofmechanicsCd

shallbetakenas:

...5.10.4.2.2

(c) Thedistributionfactoriisgivenbythefollowingexpression

...5.10.4.2.3

wherehiistheheightoffloorifromthefoundationlevel.

(2) TorsionalEffects

(a) Ateachfloorofthebuilding,thelateraldesignforceshallbeassumedtobe

displaced from itsnominal locationat thedistancese1ande2 illustrated in

Figure5.10.4.1,whichever ismostunfavourable foreverymember tobe

checked.

Fig.5.10.4.1TorsionalEffects

(b) Theexpressionsfore1ande2are:

e1=0.5d+0.05a ...5.10.4.2.4

e2=0.05a ...5.10.4.2.5

69

ax 0.6 + 1 =

0.10 h.V

K . . W = l e

(c) The total shear force and torsionalmoment at the generic floor shall be

distributed to the various resisting elements below that floor with due

consideration of their relative stiffness as well as of the stiffness of the

diaphragm.

(d) SymmetricalCases:Whencompletesymmetryofstiffnessandmassabout

one axis parallel to the direction of the seismic excitation exists, torsion

effectscanbeaccountedforbymeansofthefollowingsimplifiedprocedure:

(i) thelateraldesignforceshallbeappliedatthefloorcentreofgravity,

tobedistributedtothevariouselementsasabove;

(ii) theactions ineachoftheelementsshallbefurthermultipliedbya

factordefinedas:

...5.10.4.2.6

where x is thedistanceof theelement from the floor centreofgravity,

measuredperpendicularlytothedirectionofseismicaction.

(3) SecondOrderEffects

(a) Secondordereffectsonstoreyshearsandmomentsneednotbeconsidered

whenthefollowingconditionissatisfiedateveryfloor:

where =deformabilityindex

V=seismicdesignshearforceactingacrossthestoreyconsidered

el=elasticinterstoreydriftduetodesignaction

K=behaviourfactor

h=floorheight

W=totalgravityloadabovetheconsideredstorey

70

(b) Thedeformabilityindex,shallnotinanycaseexceedthevalue0.20;

(c) For0.10

71

(4) TorsionalEffects

(a) Ateach floorof thebuilding themass contributing to inertia forces shallbe

assumed to be displaced from its nominal location by the amount "0.05a

whichever ismoreunfavourablefortheelementtobechecked, abeingthe

dimension of the building in the direction orthogonal to that of the

consideredseismicaction.

(b) When thebuilding isanalysedbymeansofplanarmodels (Clause5.10.4.2.5

(1)),torsionaleffectscanbeaccountedforbyincreasingtheactioneffectsdue

tothetranslationaloscillationsofthebuildingbythefactordefinedas:

=1+0.6x/a

wherexisthedistanceoftheplanarelementconsideredfromthefloorcentre

ofgravity,measuredperpendiculartothedirectionoftheseismicaction.

(5) Secondordereffects

Clause5.10.4.2.4(3)applies.

72

5.10.5 SEISMICACTION

5.10.5.1SeismicZones

FortheapplicationofthisCode,aseismicriskmap(Fig5.10.5.1)hasbeenusedtodiscretize

the area of Ghana into a number of zones. Within each zone the normalized ground

accelerationisassignedaconstantvalueasshowninTable5.10.5.1.

Fig.5.10.5.1SeismicRiskMapOfGhana

73

Table5.10.5.1:DEFINITIONOFSEISMICZONES

SeismicZone

AssignedHorizontalDesignGroundAcceleration:A

(gunitsofgravity)

0

1

2

3

0

0.15

0.25

0.35

5.10.5.2CharacteristicsofSeismicActions

(1) For thepurposeof thecode, thegroundmotion shallbeadequatelydescribedby

meansof:

(a) thepeakgroundaccelerationAmax,treatedasarandomvariableofknown

distribution;

(b) one or more response spectra for horizontal motion, having a form

appropriatefortheareaandfirmsoilconditions,normalizedtoAmax=1and

probabilisticallycharacterized;

(c) one ormore response spectra for verticalmotion, scaled to 2/3 of the

correspondencehorizontalmotionresponsespectra.

(2) Forparticularzones,forinstance,wheregeologicalevidenceindicatesthepossibility

of near field type of shocks (for which the response spectrum concept is

inadequate)orwherethere isextensiveanddeepsoil layering (forwhichselective

amplification can occur) the expected characteristics of ground motion shall be

determinedbyspecialstudies.

74

5.10.5.3 DesignSeismicAction

5.10.5.3.1 NormalizedElasticResponseSpectrum

For the purpose of this Code, the shape of the standard (rocky or firm soil condition)

elasticresponsespectrumnormalizedtoaunitpeakgroundaccelerationshallbe idealized

asshowninFig.1.4.2.

Fig.5.10.5.2NormalisedElasticResponseSpectrum

5.10.5.3.2SiteEffects

When more detailed knowledge of the effects of local soil conditions and on the

characteristicsofgroundmotionsarrivingatthesite frompossiblydifferentsources isnot

availabletheprocedureinClause5.10.5.3.2(1)and(2),and5.10.4.4.3shallbeapplied.

(1) SoilProfileTypes

Theeffectsofsiteconditionsonbuildingresponseshallbeestablishedbasedonthe

soilprofiletypesdefinedasfollows:

i SOILPROFILES1:

Rockofanycharacteristiceithershalelikeorcrystalline(suchmaterialmaybe

characterizedbyashearwavevelocitygreaterthan800mm/sec);orstiffsoil

conditionswhere the soildepth is less than60mand thesoil typeoverlying

rockarestabledepositsofsandsgravelorstifferclays.

75

ii SOILPROFILES2:

Deep cohesionlessor stiff clay soil conditions, including siteswhere the soil

depth exceeds 60m and the soil typesoverlying rock are stabledepositsof

sands,gravelsorstiffclay.

iii SOILPROFILES3:

Softtomedium stiff claysand sands, characterizedby l0mormoreof soft

medium stiff clay with or without intervening layers of sand and other

cohesionlesssoils.

Inlocationswheresoilpropertiesarenotknowninsufficientdetailtodeterminethesoilprofiletype

orwheretheprofiledoesnotfitanyofthethreetypes,soilprofileS2shallbeused.

(2)SiteCoefficient

ThesitecoefficientS isusedtomodifythestandardelasticresponsespectrumtoaccountforthe

sitecondition.ItsvaluesaregiveninTable5.10.5.2

Table5.10.5.2:SITECOEFFICIENT

SoilCoefficient SoilProfileType

S1 S2 S3

S 1.0 1.2 1.5

5.10.5.3.3SiteDependantNormalizedElasticResponseSpectrum

The sitedependantnormalizedelastic spectra for the three soilprofiles are shown in Fig

5.10.5.3,theirordinatesbeingdefinedasthesmallestfromthefollowingexpressions:

Ras=1+(1).T/T1

Ras=forsoiltypesS1,S2,S3

=0.8forsoilS3ifA,asdefinedinClause5.10.5.3.4,isgreaterthan0.3g

Ras=S..(T/T1)

76

Incaseoflackofspecificsiterelatedinformationthefollowingcanbeassumed

T1=0.12secsT2=0.4secs

=2.5=2/3

However,forsoiltypeS3thevalueT1=0.25secs.canbeadopted.

Spectraforverticalmotionsmaybedeterminedwithsufficientaccuracybymultiplyingthe

ordinatesofthespectraforhorizontalmotionsbyafactorof2/3.

Fig5.10.5.3SiteDependentNormalizedElasticSpectra

5.10.5.3.4DesignResponseSpectrum

The ordinates of design response spectrum are given by the smallest of the following

expressions:

forsoiltypeS1,S2andS3,or

)(K1 . . A . I . 8 0. = (T) a R forsoiltypeS3ifA>0.3g

)(.)(. 2K1

TT S. . A . I = (T) a R

)(K1..A.I (T)aR =

77

Where:

I istheimportancefactordefinedinSection5.10.3.1(3)(seeTable5.10.5.3)

A isthepeakgroundaccelerationtobeadoptedfortheseismiczoneof interest(%ofg

Table5.10.5.1)

S isthesitecoefficientasgiveninTable5.10.5.2

K isthebehaviourfactorgiveninTable5.10.4.1.3

Inthecaseoflackofspecificsiterelatedinformation,andT2areassignedthefollowingvalues:

=2.5,=2/3,T2=0.4secs.

Table5.10.5.3:IMPORTANCEFACTOR

Class Factor

I

II

1.4

1.0

5.10.6 DESIGNACTIONS

5.10.6.1General

Structuralelementsshallbedimensionedandverified(seesection5.10.7)fordesignactions

asdefinedinthissection.

5.10.6.2DuctilityLevelI:DLI

DLIstructuresshallbedimensioneddirectlyonthebasisoftheresultsofstructuralanalysis,

withapossibleredistributionofactioneffectsinaccordancewithBS.8110(1985)

5.10.6.3DuctilityLevelII:DLII

(1)Elementssubjecttobending( f . A . 1 . 0 N cdgd )

(a)Bendingmoments:

78

The design bendingmoments shall be those obtained from linear analysis of the

structure for the load combination given by equation 5.10.4.1.1. Redistribution

accordingtoBS.8110(1985)ispermitted.

(b)ShearForces:

(i) The design shear forces shall be determined from the condition of static

equilibriumoftheelementsubjectedtotherelevanttransverseload,ifany,

andarationalcombinationoftheendmoments.

(ii) Theendmoments shallcorrespond to thedesign flexural strengthsof the

endactionsbasedonactualreinforcementprovided.

(iii) Thealgebraicratiobetweenthemaximumandminimumvaluesofshearat

eachendsectionshallbedenotedby.Thevalueofshouldnotbetakenlessthanminusone(Fig.5.10.6.1).

A VA,d (I) B AVA,d (II)B

VA,d=VA,d+MA+M1B VA,d=VA,dM1A+MB

L L

Fig 5.10.6.1 - DESIGN SHEAR FORCES

79

(2)ElementsSubjecttobendingandaxialforce( f . A 1 . 0 > N cdgd )

(a) Axialforcesandbendingmoments

(i) Forregularstructures,threestoreysandhigher,towhichequivalentstaticanalysis

hasbeenapplied,thecolumnmomentduetolateralforcesaloneshallbemultiplied

bythedynamicamplificationfactorwasgivenbythefollowingexpressions:

PlanarFrames

w=0.6T1+0.85(1.3

80

(iii) Columnmoments in addition shall satisfy the conditionon the relative strengthbetween

columnsandbeamsframingintoajointasspecifiedinClause5.10.7.1(3).

(b) ShearForces

(i) In evaluating thedesign shear forces from the conditionof static equilibrium the

designendmomentsshallbethoseproducingmaximumshearforceobtainedfrom

analysis,modifiedifappropriatebythedynamicmagnificationfactor.

(3) StructuralWalls

(a) The design actions shall be those obtained from a linear analysis of the building

modifiedasappropriateinaccordancewithClauses5.10.6.3(1)(b)to5.10.6.3(3)(c).

(b) Redistribution

(i) Thedistributionofthetotalforcetothevariouswalls,asobtainedfromtheelastic

analysismay bemodified provided the global equilibrium ismaintained and the

maximumvalueoftheactioninanywallisnotreducedbymorethan30%

(ii) Inacoupledwall,theelasticshearforceinthecouplingbeamscanalsobemodified

with amaximum reduction of 20% provided that corresponding increases in the

shearcapacitiesofbeamsatotherfloorsaremade.

(c) BendingMomentDesignEnvelope

Thedesignmomentsalong theheightof thewall shallbe thosegivenbya linear

envelopeofthecalculatedmomentdiagram,verticallydisplacedbyadistanceequal

tothehorizontallengthofthewall.(Fig.5.10.6.3)

81

Fig5.10.6.3BENDINGMOMENTDESIGNENVELOPE

(d) EarthquakeInducedAxialLoadinCoupledWalls

(i) Thedesignaxial load inthewallsduetothe lateralactionshallbecomputedusing

theshearstrengthsofthecouplingbeamsabovethesectionconsidered,calculated

byusingcharacteristicvaluesofconcreteandsteelstrength.

(ii) The shear strength of the beams calculated in 5.10.6.3(3)(d)(i) shall be further

amplifiedbyafactorof1.25

(e) DynamicMagnificationFactors

(i) Wheretheequivalentstaticanalysisisadopted,theshearforcesinthewallsshallbe

magnifiedbythedynamicamplification factorwasgivenbytheexpressionbelow

forbuildingsupto5storeyshigh

w=0.1N+0.9.........1.5.3

whereNisthenumberofstoreys

(ii) Forwalls taller than five storeys,w, shallbe linearly increasedup to thevalueof

w=1.8forN=15

82

5.10.6.4DuctilityLevelIII:DLIII

(1) Elementssubjecttobending( f . A . 1 . 0 N cdgd )

(a) Bendingmoments:Thedesignbendingmomentsshallbethoseobtainedfromlinear

analysisofthestructure.RedistributionaccordingtoBS8110(1985)ispermitted.

(b) ShearForces:

(i)Thedesignshearforcesshallbedeterminedfromtheconditionsofequilibriumofthe

elementsubjectedtotherelevanttransverseloads,ifany,andtoarationaladverse

combinationofendmoments,asspecifiedin5.10.6.4(1)(b)(iii)

(ii) Theendmomentsshallcorrespondtothedesignflexuralstrengthsoftheendsections

basedonactualreinforcementprovided,multipliedbythefactor 1.25 = n (iii) Thealgebraicratiobetweenthemaximumandminimumvaluesofshearforceata

sectionshallbedenotedby.Forthepurposestofollow,thevalueofshould

notbetakensmallerthanminusone.(Fig5.10.6.4)

AVA,d(1) B AVA,d(11) B

VA,d=VA,d+MA+M1B VA,d=VA,dM1A+MB

L L

Fig 5.10.6.4 DESIGN SHEAR FORCES

83

) 1.8 w (1.3 0.85 + T 0.6 = w 1

) 1.9 w (1.5 1.10 + T 0.5 = w 1

(2) Elementssubjecttobendingandaxialforce( f . A . 1 . 0 > N cdgd )

(a) Axialforcesandbendingmoments

(i) The axial forces and bending moments to be used for column design shall be determined

fromalinearanalysisofstructures,eventuallyredistributedaccordingtoBS8110(1985).

(ii)For regular structures, three storeys and higher, towhich equivalent static analysis has been

applied, the columnmomentdue to the lateral forces alone, shall bemultipliedby thedynamic

magnificationfactor,w,asgivenbythefollowingexpressions:

Planarframes:

5.10.6.4

Spatialframes:

5.10.6.5

whereT1,isthefundamentalperiodofthestructures.

(iii) Thevaluesof thedynamic factor,wasgiven in5.10.6.4(2)(a)(ii)areapplicable to storeys

withintheuppertwothirdsofthebuildingheight.Belowthislevelalinearvariationof,w,

shouldbeassumed;thevalueat first floor levelshouldbe takenas1.3and1.5 forplanar

andspatialframesrespectively.(Fig5.10.6.5)

84

Fig.5.10.6.5ValuesofDynamicFactor

(iv) Columnmomentsshallsatisfytheconditionontherelativestrengthbetweencolumnsand

beamsframingintoajoint(see5.10.7.1(3))

(b) Shearforces

(i)Inevaluatingthedesignshearforcesfromtheconditionsofstaticequilibriumthedesignend

momentsshallbethemostadverseonesasobtainedfromtheanalysisofthestructure.

(ii)Theendmomentsascalculatedaboveshallbefurtheramplified,ifappropriatebythedynamic

magnificationfactors,andbythe n factor: 1.10 = n

(3) BeamColumnJoints

(a) Thedesignactionsshallbethoseinducedinthejointwhenthedesignultimate

momentsofthebeamorbeamsmultipliedbyafactorn,equalto1.25aredeveloped,

exceptincaseswhenhingesarepermittedtoforminthecolumns(seeClause5.10.7.1(3))

Theaxialforceinthecolumnshallbetheminimumcorrespondingtothedesign

seismicactions.

85

V - f ) A + A ( = V colyds2s1njh

(b) HorizontalShearForce(Vjh)

(i) InteriorJoint(seeFig.5.10.6.6)

The shear force Vjh across a typical interior jointwithout prestressingmay be calculated

from:

........ 5.10.6.6

where

Vcol=2l1.M1+l2M2/(lc+lc).........5.10.6.7

l1nl2n

with

l1,l2=centretocentrespanofadjacentbeams

l1n,l2n=clearspansofadjacentbeams

lc,l'c=centretocentreupperandlowercolumnheights

M1,M2=designendmomentsofbeamsmultipliedby 1.25 = n forspansl1andl2 respectively.

As1,As2=topandbottomsteelinbeam

86

( ) l + l / M . ll 2 = V cc11n

1col

hb . V = V

c

bjhjv

Fig.5.10.6.6DesignShearActionsatBeamColumnJoints

(ii) Externaljoints

Forexternaljointsequation1.5.6stillapplieswhileequation5.10.6.7becomes

5.10.6.8

(c)VerticalShearForce(Vjv)

Theverticalshearforcemaybeapproximatelyasfollows:

5.10.6.9

where

bb=depthofbeam

hc=widthofcolumn

87

(d) Whentwononcoplanarframeshavecommonjoints,verificationofthesejoints

maybeconsideredineachdirectionseparately.

(4) StructuralWalls

(a) Thedesignactionsshallbethoseobtainedfromalinearanalysisofthebuilding

modifiedasappropriateinaccordancewithclause5.10.6.4(b)(f)

(b) Redistribution

(i) Thedistributionofthetotalforcetothevariouswalls,asobtainedfromthe

elasticanalysis,maybesubsequentlymodified,providedtheglobalequilibriumis

maintainedandthemaximumvalueoftheactioninanywallisnotreducedby

morethan30%

(ii) Inacoupledwall,theelasticshearforcesinthecouplingbeamscanalso

bemodifiedwithamaximumreductionof20%providedcorresponding

increasesintheshearcapacitiesofbeamsatotherfloorsaremade

(c) BendingMoment