Chap 4. Absorption by Roots Chap 5. Transpiration Chap 6. Photosynthesis
BNBC Part 6-Chap 2_26-08-2012
-
Upload
atikshahriar2012 -
Category
Documents
-
view
231 -
download
0
Transcript of BNBC Part 6-Chap 2_26-08-2012
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
1/131
Chapter 2
LOADS ON BUILDINGS AND STRUCTURES2.1 INTRODUCTION2.1.1 SCOPEThis chapter specifies the minimum design forces including dead load, live load, wind and earthquake loads,
miscellaneousloadsandtheirvariouscombinations.Theseloadsshallbeapplicableforthedesignofbuildings
andstructuresinconformancewiththegeneraldesignrequirementsprovidedinChapter1.
2.1.2 LIMITATIONS
Provisionsofthischaptershallgenerallybeappliedtomajorityofbuildingsandotherstructurescoveredinthis
code subject to normally expected loading conditions. For those buildings and structures having unusual
geometricalshapes,responsecharacteristicsorsite locations,orforthosesubjecttospecialloading including
tornadoes, special dynamic or hydrodynamic loads etc., sitespecific or casespecific data or analysis may be
required to determine the design loads on them. In such cases, and all other cases for which loads are not
specifiedinthischapter,loadinginformationmaybeobtainedfromreliablereferencesorspecialistadvicemay
besought.However,suchloadsshallbeappliedincompliancewiththeprovisionsofotherpartsorsectionsof
thisCode.
2.2 DEADLOADS
2.2.1 GENERAL
Theminimumdesigndeadloadforbuildingsandportionsthereofshallbedetermined inaccordancewiththe
provisionsofthissection.Inaddition,designoftheoverallstructureanditsprimaryloadresistingsystemsshall
conformtothegeneraldesignprovisionsgiveninChapter1.
2.2.2 DEFINITION
DeadLoad is thevertical loadduetotheweightof permanentstructuralandnonstructuralcomponents and
attachmentsofabuildingsuchaswalls,floors,ceilings,permanentpartitionsandfixedserviceequipmentetc.
2.2.3 ASSESSMENTOFDEADLOAD
Deadloadforastructuralmembershallbeassessedbasedontheforcesdueto:
weightofthememberitself,
weightofallmaterialsofconstructionincorporatedintothebuildingtobesupportedpermanentlyby
themember,
weightofpermanentpartitions,
weightoffixedserviceequipment,and
neteffectofprestressing.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
2/131
Part6
2
2.2.4 WEIGHTOFMATERIALSANDCONSTRUCTIONS
Inestimatingdead loads,theactualweightsofmaterialsandconstructionsshallbeused,providedthatinthe
absenceofdefiniteinformation,theweightsgiveninTables2.2.1and2.2.2shallbeassumedforthepurposes
ofdesign.
Table 2.2.1:UnitWeightofBasicMaterials
Material Unitweight(kN/m3) Material UnitWeight
(kN/m3)AluminiumAsphaltBrassBronzeBrickCementCoal, looseConcrete stone aggregate (unreinforced) brick aggregate (unreinforced)CopperCork, normal
Cork, compressedGlass, window (sodalime)
27.021.283.687.718.914.78.822.8*20.4*86.41.73.725.5
Granite, BasaltIron cast wroughtLeadLimestoneMarbleSand, drySandstoneSlateSteelStainless SteelTimberZinc
26.470.775.4111.024.526.415.722.628.377.078.755.911.070.0* for reinforced concrete, add 0.63 kN/m3for each 1% by volume of main reinforcement
2.2.5 WEIGHTOFPERMANENTPARTITIONS
When partition walls are indicated on the plans, their weight shall be considered as dead load acting as
concentrated lineloadsintheiractualpositionsonthefloor.Theloadsduetoanticipatedpartitionwalls,which
arenotindicatedontheplans,shallbetreatedasliveloadsanddeterminedinaccordancewithSec2.3.2.4.
2.2.6 WEIGHTOFFIXEDSERVICEEQUIPMENT
Weights of fixed service equipment and other permanent machinery, such as electrical feeders and other
machinery,heating,ventilatingandairconditioning systems,liftsandescalators,plumbingstacksandrisersetc.
shallbeincludedasdeadloadwheneversuchequipmentaresupported bystructuralmembers.
2.2.7 ADDITIONALLOADS
In evaluating the final dead loads on a structural member for design purposes, allowances shall be made for
additional loads resulting from the (i) difference between the prescribed and the actual weights of the
members and construction materials;(ii) inclusion offuture installations; (iii) changes in occupancy oruse of
buildings;and(iv)inclusionofstructuralandnonstructuralmembersnotcoveredinSec2.2.2and2.2.3.
2.3 LIVELOADS
2.3.1 GENERAL
Thelive loadsusedforthestructuraldesignoffloors,roof andthesupportingmembersshallbethegreatest
appliedloadsarisingfromtheintendeduseoroccupancyofthebuilding,orfromthestackingofmaterialsand
the use of equipment and propping during construction, but shall not be less than the minimum design live
loads set out by the provisions of this section. For the design of structural members for forces including live
loads,requirementsoftherelevantsectionsofChapter1shallalsobefulfilled.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
3/131
Chapter2
3
Table2.2.2DeadLoad
Material / Component / Member Weight perUnit Area(kN/m2) MaterialWeightperUnit Area(kN/m2)
Floor
Asphalt, 25 mm thickClay tiling, 13 mm thickConcrete slab (stone aggregate)* solid, 100 mm thicksolid, 150 mm thickGalvanized steel floor deck (excl. topping)Magnesium oxychloridenormal (sawdust filler), 25 mm thickheavy duty (mineral filler), 25 mm thickTerrazzo paving 16 mm thickRoofAcrylic resin sheet, corrugated 3 mm thick, standard corrugations3 mm thick, deep corrugationsAsbestos cement, corrugated sheeting (incl. lap and fastenings)
6 mm thick (standard corrugations)6 mm thick(deep corrugations)Aluminium, corrugated sheeting (incl. lap and fastenings)1.2 mm thick0.8 mm thick0.6 mm thickAluminium sheet(plain) 1.2 mm thick1.0 mm thick0.8 mm thickBituminous felt(5 ply) and gravelSlates 4.7 mm thick9.5 mm thickSteel sheet, flat galvanized 1.00 mm thick0.80 mm thick0.60 mm thickSteel, galvanized std. corrugated sheeting (incl. lap and fastenings)1.0 mm thick0.8 mm thick0.6 mm thickTiles terracotta (French pattern)concrete , 25 mm thickclay tiles
0.5260.2682.3603.5400.1470.3830.3450.5270.4310.0430.062
0.1340.1580.0480.0280.0240.0330.0240.0190.4310.3350.6710.0820.0670.0530.1200.0960.0770.5750.5270.60.9
WallsandPartitions
Acrylic resin sheet, flat, per mmthicknessAsbestos cement sheeting 4.5 mm thick6.0 mm thickBrick masonry work, excl. plaster burnt clay, per 100 mmthickness sandlime, per 100 mmthicknessConcrete (stone aggregate)* 100 mm thick150 mm thick250 mm thickFibre insulation board, per 10 mmthicknessFibrous plaster board, per 10 mmthicknessGlass, per 10 mm thicknessHardboard, per 10 mm thicknessParticle or flake board, per 10 mmthicknessPlaster board, per 10 mm thicknessPlywood, per 10 mm thicknessCeilingFibrous plaster, 10 mm thickCement plaster, 13 mm thickSuspended metal lath and plaster(two faced incl. studding)MiscellaneousFelt (insulating), per 10 mm thicknessPlaster cement, per 10 mm thickness
lime, per 10 mm thicknessPVC sheet, per 10 mm thicknessRubber paving, per 10 mm thicknessTerracotta Hollow Block Masonry 75 mm thick100 mm thick150 mm thick
0.0120.0720.1061.9101.9802.3603.5405.9000.0340.0920.2690.9610.0750.0920.0610.0810.2870.4800.0190.2300.1910.1530.1510.6710.9951.388
* for brick aggregate, 90% of the listed values may be used.2.3.2 DEFINITION
Live load is the load superimposed by the use or occupancy of the building not including the environmental
loadssuchaswindload,rainload,earthquakeloadordeadload.
2.3.3 MINIMUMFLOORLIVELOADS
The minimum floor live loads shall be the greatest actual imposed loads resulting from the intended use or
occupancyofthefloor,andshallnotbelessthantheuniformlydistributedloadpatternsspecifiedinSec2.3.4
ortheconcentratedloadsspecifiedinSec2.3.5whicheverproducesthemostcriticaleffect.Theliveloadsshall
beassumedtoactverticallyupontheareaprojectedonahorizontalplane.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
4/131
Part6
4
Table2.3.1 MinimumUniformlyDistributedLiveLoads,AndMinimumConcentratedLiveLoads
OccupancyorUse Uniform
kN/m2
Conc.
kN
Apartments(seeResidential)
Accessfloorsystems
Officeuse
Computeruse
2.4
4.79
8.9
8.9
Armoriesanddrillrooms 7.18
Assemblyareasandtheaters
Fixedseats(fastenedtofloor)
Lobbies
Movableseats
Platforms(assembly)
Stagefloors
2.87
4.79
4.79
4.79
7.18
Balconies(exterior)
Onone andtwofamilyresidencesonly,andnotexceeding19.3m2
4.79
2.87
Bowlingalleys,poolrooms,andsimilarrecreationalareas 3.59
Catwalksformaintenanceaccess 1.92 1.33
Corridors
Firstfloor
Otherfloors,sameasoccupancyservedexceptasindicated
4.79
Dancehallsandballrooms 4.79
Decks(patioandroof)Sameasareaserved,orforthetypeofoccupancyaccommodated
Diningroomsandrestaurants 4.79
Dwellings(seeResidential)
Elevatormachineroomgrating(onareaof2,580mm2) 1.33
Finishlightfloorplateconstruction(onareaof645mm2) 0.89
Fireescapes
Onsinglefamilydwellingsonly
4.79
1.92
Fixedladders SeeSection2.3.11
Garages(passengervehiclesonly)Trucksandbuses 1.92a,b
Grandstands(seeStadiumsandarenas,Bleachers)
Gymnasiumsmainfloorsandbalconies 4.79
Handrails,guardrails,andgrabbars SeeSection2.3.11Hospitals
Operatingrooms,laboratories
Patientrooms
Corridorsabovefirstfloor
2.87
1.92
3.83
4.45
4.45
4.45
Hotels(seeResidential)
Libraries
Readingrooms
Stackrooms
Corridorsabovefirstfloor
2.87
7.18c
3.83
4.45
4.45
4.45
Manufacturing
Light
Heavy
6.00
11.97
8.90
13.40
Marquees 3.59
OfficeBuildings
Fileandcomputerroomsshallbedesignedforheavierloadsbasedonanticipated
occupancy
Lobbiesandfirstfloorcorridors
Offices
Corridorsabovefirstfloor
4.79
2.40
3.83
8.90
8.90
8.90
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
5/131
Chapter2
5
Table2.3.1 MinimumUniformlyDistributedLiveLoads,AndMinimumConcentratedLiveLoads(Contd.)
PenalInstitutions
Cellblocks
Corridors
1.92
4.79
Residential
Dwellings(one andtwofamily)
Uninhabitableatticswithoutstorage
Uninhabitableatticswithstorage
Habitableatticsandsleepingareas
Allotherareasexceptstairsandbalconies
Hotelsandmultifamilyhouses
Privateroomsandcorridorsservingthem
Publicroomsandcorridorsservingthem
0.48
0.96
1.44
1.92
1.92
4.79
Reviewingstands,grandstands,andbleachers 4.79d
Roofs
Ordinaryflat,pitched,andcurvedroofs
Roofsusedforpromenadepurposes
Roofsusedforroofgardensorassemblypurposes
Roofsusedforotherspecialpurposes
Awningsandcanopies
Fabricconstructionsupportedbyalightweightrigidskeletonstructure
Allotherconstruction
Primaryroofmembers,exposedtoaworkfloor
Singlepanelpointoflowerchordofrooftrussesoranypointalongprimary
structuralmemberssupportingroofsovermanufacturing,storage
warehouses,andrepairgarages
Allotheroccupancies
Allroofsurfacessubjecttomaintenance workers
0.96h
2.87
4.79
i
0.24(nonreduceable)
0.96
i
8.9
1.33
1.33
Schools
Classrooms
Corridorsabovefirstfloor
Firstfloorcorridors
1.92
3.83
4.79
4.45
4.45
4.45
Scuttles,skylightribs,andaccessibleceilings 0.89
Sidewalks,vehiculardriveways,andyardssubjecttotrucking 11.97e 35.60f
Stadiumsandarenas
Bleachers
Fixedseats(fastenedtofloor)4.79d
2.87d
Stairsandexitways
One andtwofamilyresidencesonly
4.79
1.92
g
Storageareasaboveceilings 0.96
Storagewarehouses(shallbedesignedforheavierloadsifrequiredfor
anticipatedstorage)
Light
Heavy
6.00
11.97
Stores
Retail
FirstfloorUpperloors
Wholesale,allfloors
4.793.59
6.00
4.454.45
4.45
Vehiclebarriers SeeSection2.3.11
Walkwaysandelevatedplatforms(otherthanexitways) 2.87
Yardsandterraces,pedestrian 4.79
aFloorsingaragesorportionsofabuildingusedforthestorageofmotorvehiclesshallbedesignedfortheuniformly
distributedliveloadsofTable2.3.1orthefollowingconcentratedload:(1)forgaragesrestrictedtopassengervehicles
accommodatingnotmorethanninepassengers,13.35kNactingonanareaof114mmby114mmfootprintofajack;
and(2)formechanicalparkingstructureswithoutslabordeckthatareusedforstoringpassengercaronly,10kNper
wheel.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
6/131
Part6
6
bGaragesaccommodatingtrucksandbusesshallbedesignedinaccordancewithanapprovedmethod,whichcontains
provisionsfortruckandbusloadings.
cTheloadingappliestostackroomfloorsthatsupportnonmobile,doublefacedlibrarybookstackssubjecttothe
followinglimitations:(1)Thenominalbookstackunitheightshallnotexceed2290mm;(2)thenominalshelfdepth
shallnotexceed305mmforeachface;and(3)parallelrowsofdoublefacedbookstacksshallbeseparatedbyaisles
notlessthan914mmwide.
dInadditiontotheverticalliveloads,thedesignshallincludehorizontalswayingforcesappliedtoeachrowofthe
seatsasfollows:0.350kNperlinearmeterofseatappliedinadirectionparalleltoeachrowofseatsand0.15kNper
linearmeterofseatappliedinadirectionperpendiculartoeachrowofseats.Theparallelandperpendicular
horizontalswayingforcesneednotbeappliedsimultaneously.
eOtheruniformloadsinaccordancewithanapprovedmethod,whichcontainsprovisionsfortruckloadings,shallalso
beconsideredwhereappropriate.
fTheconcentratedwheelloadshallbeappliedonanareaof114mmby114mmfootprintofajack.
gMinimumconcentratedloadonstairtreads(onareaof2,580mm2)is1.33kN.
hWhereuniformroofliveloadsarereducedtolessthan1.0kN/m2 inaccordancewithSection2.3.14.1andare
appliedtothedesignof structuralmembersarrangedsoastocreatecontinuity,thereducedroofliveloadshallbe
appliedtoadjacentspansortoalternatespans,whicheverproducesthegreatestunfavorableeffect.
iRoofsusedforotherspecialpurposesshallbedesignedforappropriateloadsasapprovedbytheauthorityhaving
jurisdiction.
2.3.4 UNIFORMLYDISTRIBUTEDLOADS
The uniformly distributed live load shall not be less than the values listed in Table 2.3.1, reduced as may be
specified in Sec 2.3.13, applied uniformlyover theentireareaof the floor, orany portion thereof to produce
themostadverseeffectsinthememberconcerned.
2.3.5 CONCENTRATEDLOADS
The concentrated load to be applied nonconcurrently with the uniformly distributed load given in Sec 2.3.4,
shall not be less than that listed in Table 2.3.1. Unless otherwise specified in Table 2.3.1 or in the following
paragraph,theconcentratedloadshallbeappliedoveranareaof300mmx300mmandshallbelocatedsoas
toproducethemaximumstressconditionsinthestructuralmembers.
Inareaswherevehiclesareusedorstored,suchascarparkinggarages,ramps,repairshopsetc.,provisionshallbemadeforconcentratedloadsconsistingoftwoormoreloadsspaced nominally 1.5moncentresinabsence
oftheuniformliveloads.Eachloadshallbe40percentofthegrossweightofthemaximumsizevehicletobe
accommodated and applied over an area of 750 mm x 750 mm. For the storage of private or pleasuretype
vehicles without repair or fuelling, floors shall be investigated in the absence of the uniform live load, for a
minimumconcentrated wheel load of 9 kN spaced 1.5mon centres,applied overanareaof750mmx750
mm. The uniform live loads for these cases are provided in Table 2.3.1 The condition of concentrated or
uniformliveloadproducingthegreaterstressesshallgovern.
2.3.6 PROVISIONFORPARTITIONWALLS
When partitions, not indicated on the plans, are anticipated to be placed on the floors, their weight shall be
included as an additional live load acting as concentrated line loads in an arrangement producing the most
severeeffectonthefloor,unlessitcanbeshownthatamore favourablearrangementofthepartitionsshall
prevailduringthefutureuseofthefloor.
Inthecaseoflight partitions,whereinthetotalweight permetrerunisnotgreaterthan5.5kN,auniformly
distributedlive loadmaybeappliedonthefloor in lieuoftheconcentrated line loadsspecifiedabove. Such
uniformliveloadpersquaremetre shallbeatleast33% oftheweightpermetrerunofthepartitions,subject
toaminimumof1.2kN/m2.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
7/131
Chapter2
7
2.3.7 MORETHANONEOCCUPANCY
Whereanareaofafloorisintendedfortwoormoreoccupanciesatdifferenttimes,thevaluetobeusedfrom
Table2.3.1shallbethegreatestvalueforanyoftheoccupanciesconcerned.
2.3.8 MINIMUMROOFLIVELOADS
Roofliveloadsshallbeassumedtoactverticallyovertheareaprojectedbytherooforanyportionofitupona
horizontal plane, andshallbe determinedasspecifiedinthe following sections:
2.3.8.1 REGULARPURPOSE - FLAT,PITCHEDANDCURVEDROOFS
Liveloadsonregularpurposeroofsshallbethegreatestappliedloadsproducedduringusebymovableobjects
suchasplantersandpeople,andthoseinducedduringmaintenancebyworkers,equipmentandmaterialsbut
shallnotbelessthanthosegiveninTable2.3.2.
2.3.8.2 SPECIAL PURPOSEROOFS
For special purposeroofs, live loads shall be estimated based on the actual weight depending on the type of
use,butshallnotbelessthanthefollowingvalues:
a)roofsusedforpromenadepurposes 3.0kN/m2
b)roofsused forassemblypurposes 5.0kN/m2
c)roofsusedforgardens 5.0kN/m2
d)roofsusedforotherspecialpurposes tobedeterminedas per Sec2.3.9
2.3.8.3 ACCESSIBLEROOFSUPPORTINGMEMBERS
Rooftrussesoranyotherprimaryroofsupportingmemberbeneathwhichafullceilingisnotprovided,shallbe
capableofsupporting safely, inadditionto other roof loads,aconcentrated loadat the locations asspecified
below:
a)
Industrial, Storage and Garage Buildings Any single panel point of thelower chord of a roof truss, or any point of other primary roof supportingmember 9.0 kNb) Building with Other Occupancies Any single panel point of the lower chordof a roof truss, or any point of other primary roof supporting member 1.3 kN2.3.9 LOADS NOTSPECIFIED
Live loads, not specified for uses or occupancies in Sec2.3.3,2.3.4 and 2.3.5, shallbedetermined from loads
resultingfrom:
a) weightoftheprobableassemblyofpersons;
b) weightoftheprobableaccumulationofequipmentandfurniture,and
c) weightoftheprobablestorageofmaterials.
2.3.10 PARTIALLOADINGANDOTHERLOADINGARRANGEMENTS
The full intensity of the appropriately reduced live load applied only to a portion of the length or area of a
structure or member shall be considered, if it produces a more unfavourable effect than the same intensity
appliedoverthefulllengthorareaofthestructureormember.
Where uniformly distributed live loads are used in the design of continuous members and their supports,
considerationshallbegiventofulldeadloadonallspansincombinationwithfullliveloadsonadjacentspans
andonalternatespanswhicheverproducesamoreunfavourable effect.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
8/131
Part6
8
Table 2.3.2 : Minimum Roof Live Loads(1)Type and Slope of Roof DistributedLoad, kN/m2 ConcentratedLoad, kNI Flat roof (slope = 0) 1.5 1.8II 1. Pitched or sloped roof (0 < slope < 1/3)2 Arched roof or dome (rise < 1/8 span) 1.0 0.9
III 1. Pitched or sloped roof (1/3 slope < 1.0)2. Arched roof or dome (1/8 rise < 3/8 span) 0.8 0.9IV 1. Pitched or sloped roof (slope 1.0)2. Arched roof or dome (rise 3/8 span) 0.6 0.9V Greenhouse, and agriculture buildings 0.5 0.9VI Canopies and awnings, except those withcloth covers same as given in I through IVabove based on the type andslope.Note : (1) Greater of this load and rain load as specified in Sec 2.6.3 shall be taken as the design live loadfor roof. The distributed load shall be applied over the area of the roof projected upon a horizontal planeand shall not be applied simultaneously with the concentrated load. The concentrated load shall beassumed to act upon a 300 mm x 300 mm area and need not be considered for roofs capable of laterallydistributing the load, e.g. reinforced concrete slabs.2.3.11 OTHERLIVELOADS
Live loadson miscellaneousstructuresandcomponents, suchashandrailsandsupportingmembers,parapets
and balustrades, ceilings, skylights and supports, and the like, shall be determined from the analysis of the
actualloadsonthem,butshallnotbelessthanthosegiveninTable2.3.3.
2.3.12 IMPACTANDDYNAMICLOADS
The live loads specified in Sec 2.3.3 shall be assumed to include allowances for impacts arising from normal
usesonly.However,forcesimposedbyunusualvibrationsandimpactsresultingfromtheoperationofinstalled
machineryandequipmentshallbedeterminedseparatelyandtreatedasadditionalliveloads.Liveloadsdueto
vibrationor impactshallbedeterminedby dynamicanalysisofthe supportingmemberor structure including
foundations, or from the recommended values supplied by the manufacture of the particular equipment or
machinery.Inabsenceofadefiniteinformation,valueslistedinTable2.3.4forsomecommonequipment,shall
beusedfordesignpurposes.
2.3.13 REDUCTION OFLIVELOADS
Exceptforroofuniformliveloads,allotherminimumuniformlydistributedliveloads,LoinTable2.3.1,maybe
reducedaccordingtothefollowingprovisions.
2.3.13.1 GENERAL
SubjecttothelimitationsofSections2.3.13.2through2.3.13.5,membersforwhichavalueofKLLATis37.16m2ormorearepermittedtobedesignedforareducedliveloadinaccordancewiththefollowingformula:
0.25 . (2.3.1)where,L=reduceddesignliveloadperm
2ofareasupportedbythemember;L0=unreduceddesignliveload
perm2ofareasupportedbythemember(seeTable2.3.1); KLL=liveloadelementfactor(seeTable2.3.5);AT=
tributaryareainm2
.Lshallnotbelessthan0.50L0formemberssupportingonefloorandLshallnotbelessthan
0.40L0formemberssupportingtwoormorefloors.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
9/131
Chapter2
9
Table 2.3.3:MiscellaneousLiveLoads
StructuralMemberorComponent LiveLoad(1)
(kN/m)1. Handrails, parapets and supports :a) Light access stairs, gangways etc.i) width 0.6 mii) width > 0.6 mb) Staircases other than in (a) above, ramps, balconies :i) Single dwelling and privateii) Staircases in residential buildingsiii) Balconies or portion thereof, stands etc. havingfixed seats within 0.55 m of the barriervi) Public assembly buildings including theatres,cinemas, assembly halls, stadiums, mosques,churches, schools etc.vi) Buildings and occupancies other than (i) through (iv) above
0.250.350.350.351.53.00.75
2. Vehicle barriers for car parks and ramps :a) For vehicles having gross mass 2500 kgb) For vehicles having gross mass > 2500 kgc) For ramps of car parks etc. 100(2)165(2)see note (3)Note : (1) These loads shall be applied nonconcurrently along horizontal and vertical directions,
except as specified in note (2) below.(2) These loads shall be applied only in the horizontal direction, uniformly distributed overany length of 1.5 m of a barrier and shall be considered to act at bumper height. For case2(a) bumper height may be taken as 375 mm above floor level.(3) Barriers to access ramps of car parks shall be designed for horizontal forces equal to50% of those given in 2(a) and 2(b) applied at a level of 610 mm above the ramp.Barriers to straight exit ramps exceeding 20 m in length shall be designed forhorizontal forces equal to twice the values given in 2(a) and 2(b).
Table2.3.4:MinimumLiveLoadsonSupportsandConnectionsofEquipmentduetoImpact(1)
EquipmentorMachinery Additionalloadduetoimpactaspercentage
ofstaticloadincludingselfweight
Vertical Horizontal
1. Lifts, hoists and related operatingmachinery 100% 2. Light machinery (shaft or motor driven) 20% 3. Reciprocating machinery, or power drivenunits. 50% 4. Hangers supporting floors and balconies 33% 5. Cranes :a) Electric overhead cranes 25% ofmaximumwheel loadi) Transverse to the rail :20% of the weight of trolleyand lifted load only, appliedonehalf at the top of each railii) Along the rail :10% of maximum wheel loadapplied at the top of each rail
b) Manually operated cranes 50% of thevalues in (a)above 50% of thevalues in (a) abovec) Caboperated travelling cranes 25% Not applicableNote : (1) All these loads shall be increased if so recommended by the manufacturer. Formachinery and equipment not listed, impact loads shall be those recommended bythe manufacturers, or determined by dynamic analysis.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
10/131
Part6
10
2.3.13.2 HEAVYLIVELOADS.
Liveloadsthatexceed4.79kN/m2shallnotbereduced.
EXCEPTION:Liveloadsformemberssupportingtwoormorefloorsmaybereducedby20percent.
2.3.13.3 PASSENGERCARGARAGES.
Theliveloadsshallnotbereducedinpassengercargarages.
EXCEPTION:Liveloadsformemberssupportingtwoormorefloorsmaybereducedby20percent.
2.3.13.4 SPECIALOCCUPANCIES.
Liveloadsof4.79kN/m2orlessshallnotbereducedinpublicassemblyoccupancies. Thereshallbenoreductionofliveloadsforcycloneshelters.
2.3.13.5 LIMITATIONSONONE-WAYSLABS.
Thetributaryarea,AT,foronewayslabsshallnotexceedanareadefinedbytheslabspantimesawidthnormal
tothespanof1.5timestheslabspan.
2.3.14 REDUCTIONINROOFLIVELOADS
Theminimumuniformlydistributedroofliveloads,LoinTable2.3.1,arepermittedtobereducedaccordingto
thefollowingprovisions.
2.3.14.1 FLAT,PITCHED,ANDCURVEDROOFS.
Ordinaryflat,pitched,andcurvedroofsarepermittedtobe designedforareducedroof liveload,asspecified
in Eq.2.3.2 or other controlling combinations of loads, as discussed later in this chapter, whichever produces
the greater load. In structures such as greenhouses, where special scaffolding is used as a work surface forworkmenandmaterialsduringmaintenanceandrepairoperations,alowerroofloadthanspecifiedinEq.2.3.2
shallnotbe usedunlessapprovedbytheauthorityhavingjurisdiction. Onsuchstructures,theminimumroof
liveloadshallbe0.58kN/m2.
Lr=LoR1R2where0.58 Lr 0.96 (2.3.2)
where
Lr=reducedroofliveloadperm2ofhorizontalprojectioninkN/m
2
ThereductionfactorsR1andR2shallbedeterminedasfollows:
R1=1forAt 18.58m2
=1.2 0.011Atfor18.58m2
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
11/131
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
12/131
Part6
12
building or structure projected onto a vertical plane normal to the assumed wind direction. The design wind
forceforopenbuildingsandotherstructuresshallbenotlessthan0.5kN/m2)multipliedbytheareaAf.
ComponentsandCladding:Thedesignwindpressureforcomponentsandcladdingofbuildingsshallnotbeless
thananetpressureof0.5kN/m2actingineitherdirectionnormaltothesurface.
2.4.2 DEFINITIONS
ThefollowingdefinitionsapplyonlytotheprovisionsofSection2.4:
APPROVED:Acceptabletotheauthorityhavingjurisdiction.
BASICWINDSPEED,V:Threesecondgustspeedat10mabovethegroundinExposureB(seeSection2.4.8.3)
havingareturnperiodof50years.
BUILDING, ENCLOSED: A building that does not comply with the requirements for open or partially enclosed
buildings.
BUILDING ENVELOPE: Cladding, roofing, exterior walls, glazing, door assemblies, window assemblies, skylight
assemblies,andothercomponentsenclosingthebuilding.
BUILDINGANDOTHERSTRUCTURE, FLEXIBLE:Slenderbuildingsandother structures thathave afundamental
naturalfrequencylessthan1Hz.
BUILDING,LOWRISE:Enclosedorpartiallyenclosedbuildingsthatcomplywiththefollowingconditions:
1.Meanroofheighthlessthanorequalto18.3m.
2.Meanroofheighthdoesnotexceedleasthorizontaldimension.
BUILDING,OPEN:Abuildinghavingeachwallatleast80percentopen.Thisconditionisexpressedforeachwall
bytheequationAo 0.8Agwhere
Ao=totalareaofopeningsinawallthatreceivespositiveexternalpressure(m2).
Ag=thegrossareaofthatwallinwhichAoisidentified(m2).
BUILDING,PARTIALLYENCLOSED:Abuildingthatcomplieswithbothofthefollowingconditions:
1.Thetotalareaofopeningsinawallthatreceivespositiveexternalpressureexceedsthesumoftheareasof
openingsinthebalanceofthebuildingenvelope(wallsandroof)bymorethan10percent.
2.Thetotalareaofopeningsinawallthatreceivespositiveexternalpressureexceeds0.37m2or1percentof
the area of that wall, whichever is smaller, and the percentage of openings in the balance of the building
envelopedoesnotexceed20percent.
Theseconditionsareexpressedbythefollowingequations:
1.Ao>1.10Aoi
2.Ao>0.37m2or>0.01Ag,whicheverissmaller,
andAoi/Agi 0.20
where
Ao,AgareasdefinedforOpenBuilding
Aoi= thesumoftheareasofopeningsinthebuildingenvelope(wallsandroof)notincludingAo,inm2.
Agi=thesumofthegrosssurfaceareasofthebuildingenvelope(wallsandroof)notincludingAg,inm2.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
13/131
Chapter2
13
BUILDING OR OTHER STRUCTURE, REGULAR SHAPED: A building or other structure having no unusual
geometricalirregularityinspatialform.
BUILDING OR OTHER STRUCTURES, RIGID: A building or other structure whose fundamental frequency is
greaterthanorequalto1Hz.
BUILDING, SIMPLE DIAPHRAGM: A building in which both windward and leeward wind loads are transmitted
throughfloorandroofdiaphragmstothesameverticalMWFRS(e.g.,nostructuralseparations).
COMPONENTSANDCLADDING:ElementsofthebuildingenvelopethatdonotqualifyaspartoftheMWFRS.
DESIGNFORCE,F:Equivalentstaticforcetobeusedinthedeterminationofwindloadsforopenbuildingsand
otherstructures.
DESIGNPRESSURE,p:Equivalentstaticpressuretobeusedinthedeterminationofwindloadsforbuildings.
EAVE HEIGHT, h: The distance from the ground surface adjacent to the building to the roof eave line at a
particularwall.Iftheheightoftheeavevariesalongthewall,theaverageheightshallbeused.
EFFECTIVE WIND AREA, A: The area used to determine GCp. For component and cladding elements, the
effectivewindareainFigs.2.4.11through2.4.17and2.4.19isthespanlengthmultipliedbyaneffectivewidth
thatneednotbelessthanonethirdthespanlength.Forcladdingfasteners,theeffectivewindareashallnotbe
greaterthantheareathatistributarytoanindividualfastener.
ESCARPMENT: Also knownasscarp,withrespect totopographiceffects inSection2.4.9,a cliffor steepslope
generallyseparatingtwolevelsorgentlyslopingareas(seeFig.2.4.4).
FREEROOF:Roof(monoslope,pitched,ortroughed)inanopenbuildingwithnoenclosingwallsunderneaththe
roofsurface.
GLAZING:Glassortransparentortranslucentplasticsheetusedinwindows,doors,skylights,orcurtainwalls.
GLAZING, IMPACT RESISTANT: Glazing that has been shown by testing in accordance with ASTM E1886 and
ASTM E1996 or other approved test methods to withstand the impact of windborne missiles likely to be
generatedinwindbornedebrisregionsduringdesignwinds.
HILL: Withrespect to topographic effects inSection2.4.9, a land surface characterized by strongrelief in any
horizontal direction(seeFig.2.4.4).
HURRICANE PRONE REGIONS: Areas vulnerable to hurricanes; in Bangladesh these areas include the
Sundarbans,southernpartsofBarisalandPatuakhali,Hatia,Bhola,easternpartsofChittagongandCoxsBazar
IMPACT RESISTANT COVERING: A covering designed to protect glazing, which has been shown by testing in
accordance with ASTM E1886 and ASTM E1996 or other approved test methods to withstand the impact of
windbornedebrismissileslikelytobegeneratedinwindbornedebrisregionsduringdesignwinds.
IMPORTANCEFACTOR,I:Afactorthataccountsforthedegreeofhazardtohumanlifeanddamagetoproperty.
MAIN WINDFORCE RESISTING SYSTEM (MWFRS): An assemblage of structural elements assigned to provide
supportandstabilityfortheoverallstructure.Thesystemgenerallyreceiveswindloadingfrommorethanone
surface.
MEAN ROOF HEIGHT,h: The average of the roof eave height and the height to the highest point on theroof
surface,exceptthat,forroofanglesoflessthanorequalto10o
,themeanroofheightshallbetheroofheave
height.
OPENINGS:Aperturesorholesinthebuildingenvelopethatallowairtoflowthroughthebuildingenvelopeand
thataredesignedasopenduringdesignwindsasdefinedbytheseprovisions.
RECOGNIZEDLITERATURE:Publishedresearchfindingsandtechnicalpapersthatareapproved.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
14/131
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
15/131
Chapter2
15
GCpi=productofinternalpressurecoefficientandgusteffectfactortobeusedindeterminationofwindloads
forbuildings
gQ=peakfactorforbackgroundresponseinEqs.2.4.4and2.4.8
gR=peakfactorforresonantresponseinEq.2.4.8
gv=peakfactorforwindresponseinEqs.2.4.4and2.4.8
H=heightofhillorescarpmentinFig.2.4.4,inm.
h=meanroofheightofabuildingorheightofotherstructure,exceptthateaveheightshallbeusedforroof
angleoflessthanorequalto10o
,inm.
he=roofeaveheightataparticularwall,ortheaverageheightiftheeavevariesalongthewall
I=importancefactor
Iz=intensityofturbulencefromEq.2.4.5
K1,K2,K3=multipliersinFig.2.4.4toobtainKzt
Kd=winddirectionalityfactorinTable2.4.5
Kh=velocitypressureexposurecoefficientevaluatedatheightz=h
Kz=velocitypressureexposurecoefficientevaluatedatheightz
Kzt=topographicfactorasdefinedinSection2.4.9
L=horizontaldimensionofabuildingmeasuredparalleltothewinddirection,inm.
Lh = distance upwind ofcrest of hill or escarpment in Fig.2.4.4 to where the difference in ground elevation is
halftheheightofhillorescarpment,inm.
L=integrallengthscaleofturbulence,inm.
Lr=horizontaldimensionofreturncornerforasolidfreestandingwallorsolidsignfromFig.2.4.20,inm.
l=integrallengthscalefactorfromTable2.4.3inm.
N1=reducedfrequencyfromEq.2.4.12
n1=buildingnaturalfrequency,Hz
p=designpressuretobeusedindeterminationofwindloadsforbuildings,inN/m2
pL=windpressureactingonleewardfaceinFig.2.4.9,inN/m2
Pnet=netdesignwindpressurefromEq.2.4.2,inN/m2
Pnet30=netdesignwindpressureforExposureAath=9.1mandI=1.0fromFig.2.4.3,inN/m2.
Pp=combinednetpressureonaparapetfromEq.2.4.20,inN/m2.
Ps=netdesignwindpressurefromEq.2.4.1,inN/m2.
Ps30=simplifieddesignwindpressureforExposureAath=9.1mandI=1.0fromFig.2.4.2,inN/m2.
PW=windpressureactingonwindwardfaceinFig.2.4.9,inN/m2.
Q=backgroundresponsefactorfromEq.2.4.6
q=velocitypressure,inN/m2.
qh=velocitypressureevaluatedatheightz=h,inN/m2
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
16/131
Part6
16
qi=velocitypressureforinternalpressuredetermination,inN/m2.
qp=velocitypressureattopofparapet,inN/m2.
qz=velocitypressureevaluatedatheightzaboveground,inN/m2.
R=resonantresponsefactorfromEq.2.4.10
RB,Rh,RL=valuesfromEq.2.4.13
Ri=reductionfactorfromEq.2.4.16
Rn=valuefromEq.2.4.11
s=verticaldimensionofthesolidfreestandingwallorsolidsignfromFig.2.4.20,inm.
r=risetospanratioforarchedroofs.
V= basicwindspeedobtainedfromFig.2.4.1orTable2.4.1,inm/s.Thebasicwindspeedcorrespondstoa3s
gustspeed at10mabove ground inExposure Category Bhavingan annual probability ofoccurrence of
0.02.
Vi=unpartitionedinternalvolumem3
ZV =meanhourlywindspeedatheight ,m/s.W=widthofbuildinginFigs.2.4.12and2.4.14AandBandwidthofspaninFigs.2.4.13and2.4.15,inm.X=distancetocenterofpressurefromwindwardedgeinFig.2.4.18,inm.
x=distanceupwindordownwindofcrestinFig.2.4.4,inm.
z=heightabovegroundlevel,inm.
z=equivalentheightofstructure,inm.
zg=nominalheightoftheatmosphericboundarylayerusedinthisstandard.ValuesappearinTable2.4.3
zmin=exposureconstantfromTable2.4.3
=3sgustspeedpowerlawexponentfromTable2.4.3=reciprocaloffromTable2.4.3=meanhourlywindspeedpowerlawexponentinEq.2.4.14fromTable2.4.3=dampingratio,percentcriticalforbuildingsorotherstructures=ratioofsolidareatogrossareaforsolidfreestandingwall,solidsign,opensign,faceofatrussedtower,orlatticestructure
=adjustmentfactorforbuildingheightandexposurefromFigs.2.4.2and2.4.3
=integrallengthscalepowerlawexponentinEq.2.4.7fromTable2.4.3
=valueusedinEq.2.4.13(seeSection2.4.10.2)
=angleofplaneofrooffromhorizontal,indegrees
v=heighttowidthratioforsolidsign
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
17/131
Chapter2
17
2.4.4 METHOD1SIMPLIFIEDPROCEDURE
2.4.4.1 SCOPE
Abuildingwhosedesignwindloadsaredeterminedinaccordancewiththissectionshallmeetalltheconditions
of Sections 2.4.4.2 or 2.4.4.3. If a building qualifies only under 2.4.4.2 for design of its components and
cladding,thenitsMWFRSshallbedesignedbyMethod2orMethod3.
Limitations on Wind Speeds: Variation of basic wind speeds with direction shall not be permitted unlesssubstantiatedbyanyestablishedanalyticalmethodorwindtunneltesting.
2.4.4.2 MAINWIND-FORCERESISTINGSYSTEMS
ForthedesignofMWFRSsthebuildingmustmeetallofthefollowingconditions:
1.ThebuildingisasimplediaphragmbuildingasdefinedinSection2.4.2.
2.ThebuildingisalowrisebuildingasdefinedinSection2.4.2.
3. The building is enclosed as defined in Section 2.4.2 and conforms to the windborne debris provisions of
Section2.4.11.3.
4.ThebuildingisaregularshapedbuildingorstructureasdefinedinSection2.4.2.
5.ThebuildingisnotclassifiedasaflexiblebuildingasdefinedinSection2.4.2.
6. The building does not have response characteristics making it subject to across wind loading, vortex
shedding,instabilityduetogallopingorflutter;anddoesnothaveasitelocationforwhichchannelingeffectsor
buffetinginthewakeofupwindobstructionswarrantspecialconsideration.
7. The building has an approximately symmetrical crosssection in each direction with either a flat roof or a
gableorhiproofwith 45
.
8.ThebuildingisexemptedfromtorsionalloadcasesasindicatedinNote5ofFig.2.4.10,orthetorsionalload
casesdefinedinNote5donotcontrolthedesignofanyoftheMWFRSsofthebuilding.
2.4.4.3 COMPONENTSANDCLADDING
Forthedesignofcomponentsandcladdingthebuildingmustmeetallthefollowingconditions:
1.Themeanroofheighthmustbelessthanorequalto18.3m(h 18.3m).
2. The building is enclosed as defined in Section 2.4.2 and conforms to the windborne debris provisions of
Section2.4.11.3.
3.ThebuildingisaregularshapedbuildingorstructureasdefinedinSection2.4.2.
4. The building does not have response characteristics making it subject to across wind loading, vortex
shedding,instabilityduetogallopingorflutter;anddoesnothaveasitelocationforwhichchannelingeffectsor
buffetinginthewakeofupwindobstructionswarrantspecialconsideration.
5.Thebuildinghaseitheraflatroof,agableroofwith 45o,orahiproofwith 27
o.
2.4.4.4 DESIGNPROCEDURE
1.ThebasicwindspeedVshallbedeterminedinaccordancewithSection2.4.6.Thewindshallbeassumedto
comefromanyhorizontaldirection.
2.AnimportancefactorIshallbedeterminedinaccordancewithSection2.4.7.
3.AnexposurecategoryshallbedeterminedinaccordancewithSection2.4.8.3.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
18/131
Part6
18
4.Aheightandexposureadjustmentcoefficient,,shallbedeterminedfromFig.2.4.2.
2.4.4.4.1 MainWind-ForceResistingSystem.
Simplifieddesignwindpressures,ps,fortheMWFRSsoflowrisesimplediaphragmbuildingsrepresentthenet
pressures (sum of internal and external) to be applied to the horizontal and vertical projections of building
surfaces as shown in Fig. 2.4.2. For the horizontal pressures (zones A, B, C, D),ps is the combination of the
windwardandleewardnetpressures.psshallbedeterminedbythefollowingequation:
ps=KztIpS30 (2.4.1)
where
=adjustmentfactorforbuildingheightandexposurefromFig.2.4.2
Kzt=topographicfactorasdefinedinSection2.4.9evaluatedatmeanroofheight,h
I=importancefactorasdefinedinSection2.4.7
pS30=simplifieddesignwindpressureforExposureA,ath=9.1m,andforI=1.0,fromFig.2.4.2
MinimumPressures: Theloadeffectsofthedesignwindpressuresfromthissectionshallnotbelessthanthe
minimum loadcasefromSection2.4.4.1assumingthepressures,ps,forzonesA,B,C,andDallequalto+0.5
kN/m2,whileassumingzonesE,F,G,andHallequaltozerokN/m2.
2.4.4.4.2 ComponentsandCladding
Net design wind pressures, Pnet, for the components and cladding of buildings designed using Method 1
represent the net pressures (sum of internal and external) to be applied normal to each building surface as
showninFig.2.4.3.
pnetshallbedeterminedbythefollowingequation:
pnet=KztIPnet30 (2.4.2)
where
=adjustmentfactorforbuildingheightandexposurefromFig.2.4.3
Kzt=topographicfactorasdefinedinSection2.4.9evaluatedatmeanroofheight,h
I=importancefactorasdefinedinSection2.4.7
pnet30=netdesignwindpressureforExposureA,ath=9.1m,andforI=1.0,fromFig.2.4.3
Minimum Pressures : The positive design wind pressures,pnet, from this section shall not be less than +0.5
kN/m2,andthenegativedesignwindpressures,pnet,fromthissectionshallnotbelessthan0.5kN/m
2.
2.4.4.4.3 AirPermeableCladding
DesignwindloadsdeterminedfromFig.2.4.3shallbeusedforallairpermeablecladdingunlessapprovedtest
data or the recognized literature demonstrate lower loads for the type of air permeable cladding being
considered.
2.4.5 METHOD2ANALYTICALPROCEDURE
2.4.5.1 SCOPESANDLIMITATIONS
A building or other structure whose design wind loads are determined in accordance with this section shall
meetallofthefollowingconditions:
1.ThebuildingorotherstructureisaregularshapedbuildingorstructureasdefinedinSection2.4.2.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
19/131
Chapter2
19
2. The building or other structure does not have response characteristics making it subject to across wind
loading, vortex shedding, instability due to galloping or flutter; or does not have a site location for which
channelingeffectsorbuffetinginthewakeofupwindobstructionswarrantspecialconsideration.
Theprovisionsofthissectiontakeintoconsiderationtheloadmagnificationeffectcausedbygustsinresonance
with alongwind vibrations of flexible buildings or other structures. Buildings or other structures not meeting
therequirementsofSection2.4.4,orhavingunusualshapesorresponsecharacteristicsshallbedesignedusing
recognized literature documenting such wind load effects orshall use the wind tunnel procedure specified inSection0.
2.4.5.2 SHIELDING.
There shall be no reductions in velocity pressure due to apparent shielding afforded by buildings and other
structuresorterrainfeatures.
2.4.5.3 AIRPERMEABLECLADDING
DesignwindloadsdeterminedfromSection2.4.5shallbeusedforairpermeablecladdingunlessapprovedtest
dataorrecognizedliteraturedemonstratelowerloadsforthetypeofairpermeablecladdingbeingconsidered.
2.4.5.4 DESIGNPROCEDURE
1. The basic wind speedV and wind directionality factorKd shall be determined in accordance with Section
2.4.6.
2.AnimportancefactorIshallbedeterminedinaccordancewithSection2.4.7.
3. An exposure category or exposure categories and velocity pressure exposure coefficient Kz or Kh, as
applicable,shallbedeterminedforeachwinddirectioninaccordancewithSection2.4.8.
4.AtopographicfactorKztshallbedeterminedinaccordancewithSection2.4.9.
5.AgusteffectfactorGorGf,asapplicable,shallbedeterminedinaccordancewithSection2.4.10.
6.AnenclosureclassificationshallbedeterminedinaccordancewithSection2.4.11.
7.InternalpressurecoefficientGCpishallbedeterminedinaccordancewithSection2.4.12.1.
8. External pressure coefficients Cp or GCpf, or force coefficients Cf, as applicable, shall be determined in
accordancewithSection2.4.12.2or2.4.12.3,respectively.
9.Velocitypressureqzorqh,asapplicable,shallbedeterminedinaccordancewithSection2.4.11.5.
10.DesignwindloadporFshallbedeterminedinaccordancewithSections2.4.13.
2.4.6 BASICWINDSPEED
Thebasicwindspeed,V,usedinthedeterminationofdesignwindloadsonbuildingsandotherstructuresshall
be as given in Fig.2.4.1 except as provided in Section 2.4.6.1. The wind shall be assumed to come from anyhorizontal direction.
2.4.6.1 SPECIALWINDREGIONS
Thebasicwindspeedshallbeincreasedwhererecordsorexperienceindicatethatthewindspeedsarehigher
than those reflected in Fig. 2.4.1. Mountainous terrain, gorges, and special regions shall be examined for
unusualwindconditions.Theauthorityhavingjurisdictionshall,ifnecessary,adjustthevaluesgiveninFig.2.4.1
to account for higher local wind speeds. Such adjustment shall be based on adequate meteorological
informationandothernecessarydata.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
20/131
Part6
20
2.4.6.2 LIMITATION
Tornadoeshavenotbeenconsideredindevelopingthebasicwindspeeddistributions.
2.4.6.3 WINDDIRECTIONALITYFACTOR
Thewinddirectionalityfactor,Kd,shallbedeterminedfromTable2.4.5.Thisfactorshallonlybeappliedwhen
usedinconjunctionwithloadcombinationsspecifiedinChapter2ofPart6ofthiscode.
2.4.7 IMPORTANCEFACTOR
An importance factor, I, for the building or other structure shall be determined from Table 2.4.2 based on
buildingandstructurecategorieslistedinSection1.2.4.
2.4.8 EXPOSURE
Foreachwinddirectionconsidered,theupwindexposurecategoryshallbebasedongroundsurfaceroughness
thatisdeterminedfromnaturaltopography,vegetation,andconstructedfacilities.
2.4.8.1 WINDDIRECTIONSANDSECTORS
Foreachselectedwinddirectionatwhichthewind loadsaretobeevaluated,theexposureofthebuildingor
structure shall be determined for the two upwind sectors extending 45o either side of the selected wind
direction.
TheexposuresinthesetwosectorsshallbedeterminedinaccordancewithSections2.4.8.2and2.4.8.3andthe
exposureresultinginthehighestwindloadsshallbeusedtorepresentthewindsfromthatdirection.
2.4.8.2 SURFACEROUGHNESSCATEGORIES
A ground surface roughness within each 45o
sector shall be determined for a distance upwind of the site as
defined in Section 2.4.8.3 from the categories defined in the following text, for the purpose of assigning an
exposurecategoryasdefinedinSection2.4.8.3.
SurfaceRoughnessA:Urbanandsuburbanareas,woodedareas,orotherterrainwithnumerouscloselyspaced
obstructionshavingthesizeofsinglefamilydwellingsorlarger.
Surface RoughnessB:Open terrain with scattered obstructions havingheights generally lessthan 9.1 m.This
categoryincludesflatopencountry,grasslands,andallwatersurfacesinhurricaneproneregions.
Surface Roughness C: Flat, unobstructed areas and water surfaces outside hurricane prone regions. This
categoryincludessmoothmudflatsandsaltflats.
2.4.8.3 EXPOSURECATEGORIES
Exposure A: Exposure A shall apply where the ground surface roughness condition, as defined by Surface
Roughness A, prevails in the upwind direction for a distance of at least 792 m or 20 times the height of the
building,whicheverisgreater.
EXCEPTION:Forbuildingswhosemeanroofheightislessthanorequalto9.1m,theupwinddistancemaybe
reducedto457m.
ExposureB:ExposureBshallapplyforallcaseswhereExposuresAorCdonotapply.
Exposure C: Exposure C shallapply where theground surface roughness, as defined by Surface Roughness C,
prevailsintheupwinddirectionforadistancegreaterthan1,524mor20timesthebuildingheight,whichever
isgreater.ExposureCshallextendintodownwindareasofSurfaceRoughnessAorBforadistanceof200mor
20timestheheightofthebuilding,whicheverisgreater.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
21/131
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
22/131
Part6
22
IfsiteconditionsandlocationsofstructuresdonotmeetalltheconditionsspecifiedinSection2.4.9.1thenKzt=
1.0.
2.4.10 GUSTEFFECTFACTOR
2.4.10.1 RIGIDSTRUCTURES
ForrigidstructuresasdefinedinSection2.4.2,thegusteffectfactorshallbetakenas0.85orcalculatedbythe
formula:
0.925 1 1.711.7 (2.4.4) 10 (2.4.5)where the intensity of turbulence at height where the equivalent height of the structure definedas 0.6h, but not less than zminfor all building heights h. zminand c are listed for each exposure in Table
2.4.3;gQ
andgv
shall be taken as 3.4. The background responseQ
is given by 110.63 . 2.4.6whereB,haredefinedinSection2.4.3;and=theintegrallengthscaleofturbulenceattheequivalentheightgivenby
10 (2.4.7)in which land are constants listed in Table 2.4.3.2.4.10.2 FLEXIBLEORDYNAMICALLYSENSITIVESTRUCTURES
For flexible or dynamically sensitive structures as defined in Section 2.4.2 natural period greater than 1.0second, the gusteffect factor shall be calculated by 0.925
1 1.7 1 1.72.4.8
gQand gv shall be taken as 3.4 andgRis given by 2ln3600 0.577
2ln3600
2.4.9
R,theresonantresponsefactor,isgivenby
1 0.53 0.47 (2.4.10) 7.47 1 10.3 (2.4.11)
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
23/131
Chapter2
23
(2.4.12) 1 12 1 for 0 (2.4.13a) 1 for 0 2.4.13b
wherethesubscript
inEq.2.4.13shallbetakenash,B,andL,respectively,whereh,B,andLaredefinedin
Section2.4.3.
n1=buildingnaturalfrequency
R=Rhsetting =4.6/R=RBsetting =4.6/R=RLsetting =15.4 /=dampingratio,percentofcritical=meanhourlywindspeedatheightdeterminedfromEq.2.4.14.
10 (2.4.14)
whereandareconstantslistedinTable2.4.3andV isthebasicwindspeedinkm/h.2.4.10.3 RATIONALANALYSIS
InlieuoftheproceduredefinedinSections2.4.10.1and2.4.10.2,determination ofthegusteffectfactorbyany
rationalanalysisdefinedintherecognizedliteratureispermitted.
2.4.10.4 LIMITATIONS
Where combined gusteffect factors and pressure coefficients (GCp, GCpi, and GCpf ) are given in figures andtables,thegusteffectfactorshallnotbedeterminedseparately.
2.4.11 ENCLOSURECLASSIFICATIONS.
2.4.11.1 GENERAL
For the purpose of determining internal pressure coefficients, all buildings shall be classified as enclosed,
partiallyenclosed,oropenasdefinedinSection2.4.2.
2.4.11.2 OPENINGS
Adeterminationshallbemadeoftheamountofopeningsinthebuildingenvelopetodeterminetheenclosure
classificationasdefinedinSection2.4.11.3.
2.4.11.3 WIND-BORNEDEBRIS
Glazinginbuildingslocatedinwindbornedebrisregionsshallbeprotectedwithanimpactresistantcoveringor
be impactresistantglazingaccordingtotherequirementsspecified in ASTM E1886and ASTME1996orother
approvedtestmethodsandperformancecriteria.ThelevelsofimpactresistanceshallbeafunctionofMissile
LevelsandWindZonesspecifiedinASTME1886andASTME1996.
EXCEPTIONS:
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
24/131
Part6
24
i. GlazinginCategoryII,III,orIVbuildingslocatedover18.3mabovethegroundandover9.2m
aboveaggregatesurfaceroofslocatedwithin458mofthebuildingshallbepermittedtobe
unprotected.
ii. GlazinginCategoryIbuildingsshallbepermittedtobeunprotected.
2.4.11.4 MULTIPLECLASSIFICATIONS
If a building by definition complies with both the open and partially enclosed definitions, it shall be
classifiedasanopenbuilding.Abuildingthatdoesnotcomplywitheithertheopenorpartiallyenclosed
definitionsshallbeclassifiedasanenclosedbuilding.
2.4.11.5 VELOCITYPRESSURE
Velocitypressure,qz,evaluatedatheightzshallbecalculatedbythefollowingequation: 0.000613 ; (kN/m2), Vinm/s (2.4.15)whereKd is the wind directionality factor,Kz is the velocity pressure exposure coefficient defined in Section
2.4.8.6,KztisthetopographicfactordefinedinSection2.4.9.2,andqh isthevelocitypressurecalculatedusing
Eq. 2.4.15 at mean roof heighth. The numerical coefficient 0.000613 shall be used except where sufficient
climaticdataareavailabletojustifytheselectionofadifferentvalueofthisfactorforadesignapplication.
2.4.12 PRESSUREANDFORCECOEFFICIENTS.
2.4.12.1 INTERNALPRESSURECOEFFICIENTS
InternalPressureCoefficient.Internalpressurecoefficients,GCpi,shallbedeterminedfromFig.2.4.5basedon
buildingenclosureclassificationsdeterminedfromSection2.4.11.
Reduction Factor for Large Volume Buildings, Ri: For a partially enclosed building containing a single,
unpartitioned large volume, the internal pressure coefficient, GCpi, shall be multiplied by the following
reductionfactor,Ri: 1.0 or 0.5
1 11 6951
1.0 (2.4.16)where
Aog=totalareaofopeningsinthebuildingenvelope(wallsandroof,inm
2
)
Vi=unpartitionedinternalvolume,inm3
2.4.12.2 EXTERNALPRESSURECOEFFICIENTS.
Main WindForce Resisting Systems: External pressure coefficients for MWFRSs Cp are given in Figs. 2.4.6,
2.4.7,and2.4.8.Combinedgusteffectfactorandexternalpressurecoefficients,GCpf,aregiveninFig.2.4.10for
lowrisebuildings.ThepressurecoefficientvaluesandgusteffectfactorinFig.2.4.10shallnotbeseparated.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
25/131
Chapter2
25
ComponentsandCladding:Combinedgusteffectfactorandexternalpressurecoefficientsforcomponentsand
claddingGCparegiveninFigs.2.4.11through2.4.17.Thepressurecoefficientvaluesandgusteffectfactorshall
notbeseparated.
2.4.12.3 FORCECOEFFICIENTS
ForcecoefficientsCfaregiveninFigs.2.4.20through2.4.23.
2.4.12.4 ROOFOVERHANGS
Main WindForce Resisting System: Roof overhangs shall be designed for a positive pressure on the bottom
surfaceofwindwardroofoverhangscorrespondingtoCp=0.8 incombinationwith thepressures determined
fromusingFigs.2.4.6and2.4.10.
ComponentsandCladding:For allbuildings, roofoverhangsshall be designedforpressures determinedfrom
pressurecoefficientsgiveninFigs.2.4.11B,C,D.
2.4.12.5 PARAPETS
Main WindForce Resisting System: The pressure coefficients for the effect of parapets on the MWFRS loads
aregiveninSection2.4.14.2
Components and Cladding: The pressure coefficients for the design of parapet component and cladding
elementsaretakenfromthewallandroofpressurecoefficientsasspecifiedinSection2.4.14.3.
2.4.13 DESIGNWINDLOADSONENCLOSEDANDPARTIALLYENCLOSED
BUILDINGS.
2.4.13.1 GENERAL
SignConvention:Positivepressureactstowardthesurfaceandnegativepressureactsawayfromthesurface.
CriticalLoadCondition:Valuesofexternalandinternalpressuresshallbecombinedalgebraicallytodetermine
themostcriticalload.
TributaryAreasGreaterthan65m2:Componentandcladdingelementswithtributaryareasgreaterthan65m
2
shallbepermittedtobedesignedusingtheprovisionsforMWFRSs.
2.4.13.2 MAINWIND-FORCERESISTINGSYSTEMS
Rigid Buildings of All Heights: Design wind pressures for the MWFRS of buildings of all heights shall be
determinedbythefollowingequation: kN m (2.4.17)where
q=qzforwindwardwallsevaluatedatheightzabovetheground
q= qhforleewardwalls,sidewalls,androofs,evaluatedatheighth
qi= qhforwindwardwalls,sidewalls, leewardwalls,androofsofenclosedbuildingsandfornegative internal
pressureevaluationinpartiallyenclosedbuildings
qi= qzforpositiveinternalpressureevaluation in partiallyenclosedbuildingswhereheightzisdefinedasthe
levelofthehighestopeninginthebuildingthatcouldaffectthepositiveinternalpressure.Forbuildingssitedin
windbornedebrisregions,glazingthat isnot impactresistantor protectedwithan impactresistantcovering,
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
26/131
Part6
26
shallbetreatedasanopeninginaccordancewithSection2.4.11.3.Forpositiveinternalpressureevaluation, qi
mayconservativelybeevaluatedatheighth(qi=qh)
G= gusteffectfactorfromSection2.4.10
Cp=externalpressurecoefficientfromFig.2.4.6or2.4.8
(GCpi)=internalpressurecoefficientfromFig.2.4.5
qandqishallbeevaluatedusingexposuredefinedinSection2.4.8.3.Pressureshallbeappliedsimultaneously
onwindwardandleewardwallsandonroofsurfacesasdefinedinFigs.2.4.6and2.4.8.
LowRise Building: Alternatively, design wind pressures for the MWFRS of lowrise buildings shall be
determinedbythefollowingequation: kN m (2.4.18)where
qh=velocitypressureevaluatedatmeanroofheighthusingexposuredefinedinSection2.4.8.3
(GCpf)=externalpressurecoefficientfromFig.2.4.10
(GCpi)=internalpressurecoefficientfromFig.2.4.5
Flexible Buildings: Design wind pressures for the MWFRS of flexible buildings shall be determined from the
followingequation: kN m (2.4.19)whereq,qi,Cp,and(GCpi)areasdefinedinSection2.4.13.2andGf=gusteffectfactorisdefinedasinSection
2.4.10.
Parapets:ThedesignwindpressurefortheeffectofparapetsonMWFRSsofrigid,lowrise,orflexiblebuildings
withflat,gable,orhiproofsshallbedeterminedbythefollowingequation:
kN m (2.4.20)
where
pp= combined net pressure on the parapet due to the combination of the net pressures from the front and
back parapet surfaces. Plus (and minus) signs signify net pressure acting toward (and away from) the front
(exterior)sideoftheparapet
qp= velocitypressureevaluatedatthetopoftheparapet
GCpn= combinednetpressurecoefficient
= +1.5forwindwardparapet
= 1.0forleewardparapet
2.4.13.3 DESIGNWINDLOADCASES
The MWFRS of buildings of all heights, whose wind loads have been determined under the provisions of
Sections2.4.13.2,shallbedesignedforthewindloadcasesasdefinedinFig.2.4.9.Theeccentricitye forrigid
structures shall be measuredfromthe geometriccenterofthebuilding faceand shall be considered for each
principalaxis(eX,eY).Theeccentricitye forflexiblestructuresshallbedeterminedfromthefollowingequation
andshallbeconsideredforeachprincipalaxis(eX,eY):
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
27/131
Chapter2
27
1.7 1 1.7 (2.4.21)where
eQ= eccentricity easdeterminedforrigidstructuresinFig.2.4.9
eR= distancebetweentheelasticshearcenterandcenterofmassofeachfloor
,gQ,Q,gR,R shallbeasdefinedinSection2.4.3Thesignoftheeccentricitye shallbeplusorminus,whichevercausesthemoresevereloadeffect.
EXCEPTION: Onestory buildings withh less than or equal to 9.1 m, buildings twostories or less framed with
lightframe construction, and buildings two stories or less designed with flexible diaphragms need only be
designedforLoadCase1andLoadCase3inFig.2.4.9.
2.4.13.4 COMPONENTSANDCLADDING.
LowRise Buildings and Buildings with h 18.3 m: Design wind pressures on component and cladding
elementsoflowrisebuildingsandbuildingswithh 18.3mshallbedeterminedfromthefollowingequation:
kN m (2.4.22)where
qh= velocitypressureevaluatedatmeanroofheighthusingexposuredefinedinSection2.4.8.5
(GCp)= externalpressurecoefficientsgiveninFigs.2.4.11through2.4.16
(GCpi )= internalpressurecoefficientgiveninFig.2.4.5
Buildingswithh>18.3m:Designwindpressuresoncomponentsandcladdingforallbuildingswithh > 18.3m
shallbedeterminedfromthefollowingequation: kN/m (2.4.23)where
q=qzforwindwardwallscalculatedatheightzabovetheground
q=qhforleewardwalls,sidewalls,androofs,evaluatedatheighth
qi=qhforwindwardwalls, sidewalls, leewardwalls,and roofsofenclosedbuildingsandfornegative internal
pressureevaluationinpartiallyenclosedbuildings
qi=qzforpositive internal pressureevaluation inpartiallyenclosedbuildingswhereheightz is definedas the
levelofthehighestopeninginthebuildingthatcouldaffectthepositiveinternalpressure.Forbuildingssitedin
windbornedebrisregions,glazingthat isnot impactresistantorprotectedwithan impactresistantcovering,
shallbetreatedasanopeninginaccordancewithSection2.4.11.3.Forpositiveinternalpressureevaluation,qi
mayconservativelybeevaluatedatheighth(qi=qh)
(GCp)=externalpressurecoefficientfromFig.2.4.17.
(GCpi)= internalpressure coefficient given inFig. 2.4.5.qandqishall beevaluated usingexposure defined in
Section2.4.8.3.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
28/131
Part6
28
2.4.13.5 ALTERNATIVEDESIGNWINDPRESSURESFORCOMPONENTSAND
CLADDINGINBUILDINGSWITH18.3M< h < 27.4M
AlternativetotherequirementsofSection2.4.13.2,thedesignofcomponentsandcladdingforbuildingswitha
meanroofheightgreaterthan18.3mandlessthan27.4mvaluesfromFigs.2.4.11through2.4.17shallbeused
only if the height to width ratio isoneor less(except as permitted by Note 6of Fig. 2.4.17) andEq.2.4.22 is
used.
Parapets:Thedesignwindpressureonthecomponentsandcladdingelementsofparapetsshallbedesignedbythefollowingequation: (2.4.24)where
qp=velocitypressureevaluatedatthetopoftheparapet
GCp=externalpressurecoefficientfromFigs.2.4.11through2.4.17
GCpi=internalpressurecoefficientfromFig.2.4.5,basedontheporosityoftheparapetenvelope.
Twoloadcasesshallbeconsidered.LoadCaseAshallconsistofapplyingtheapplicablepositivewallpressure
fromFig.2.4.11Aor2.4.17tothefrontsurfaceof theparapetwhile applyingthe applicablenegativeedgeorcorner zone roof pressure from Figs.2.4.11 through 2.4.17 to the back surface. Load Case B shall consist of
applying the applicable positive wall pressure from Fig. 2.4.11A or 2.4.17 to the back of the parapet surface,
and applying the applicable negative wall pressure from Fig. 2.4.11A or 2.4.17 to the front surface. Edge and
cornerzonesshallbearrangedasshowninFigs.2.4.11through2.4.17.GCpshallbedeterminedforappropriate
roof angle and effective wind area from Figs.2.4.11 through 2.4.17. If internal pressure is present, both load
casesshouldbeevaluatedunderpositiveandnegativeinternalpressure.
2.4.14 DESIGNWINDLOADSONOPENBUILDINGSWITHMONOSLOPE,
PITCHED,ORTROUGHEDROOFS.
2.4.14.1 GENERAL
Sign Convention: Plus and minus signs signify pressure acting toward and away from the top surface of the
roof,respectively.
Critical Load Condition: Net pressure coefficientsCN include contributions from top and bottom surfaces. All
loadcasesshownforeachroofangleshallbeinvestigated.
2.4.14.2 MAINWIND-FORCERESISTINGSYSTEMS
ThenetdesignpressurefortheMWFRSsofmonoslope,pitched,ortroughedroofsshallbedeterminedbythe
followingequation:
(2.4.25)
where
qh= velocity pressure evaluated at mean roof heighthusing the exposure as defined in Section 2.4.8.3 that
resultsinthehighestwindloadsforanywinddirectionatthesite
G= gusteffectfactorfromSection2.4.10
CN= netpressurecoefficientdeterminedfromFigs.2.4.18Athrough2.4.18D.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
29/131
Chapter2
29
For free roofs with an angle of plane of roof from horizontal less than or equal to 5o and containing fascia
panels,thefasciapanelshallbeconsideredaninvertedparapet.Thecontribution ofloadsonthefasciatothe
MWFRSloadsshallbedeterminedusingSection2.4.13.5withqp equaltoqh .
2.4.14.3 COMPONENTANDCLADDINGELEMENTS
Thenetdesignwindpressureforcomponentandcladdingelementsofmonoslope,pitched,andtroughedroofs
shallbedeterminedbythefollowingequation: (2.4.26)where
qh= velocity pressure evaluated at mean roof heighthusing the exposure as defined in Section 2.4.8.3 that
resultsinthehighestwindloadsforanywinddirectionatthesite
G= gusteffectfactorfromSection2.4.10
CN= netpressurecoefficientdeterminedfromFigs.2.4.19Athrough2.4.19C.
2.4.15 DESIGNWIND
LOADS
ON
SOLID
FREE
STANDING
WALLS
AND
SOLID
SIGNS
Thedesignwindforceforsolidfreestandingwallsandsolidsignsshallbedeterminedbythefollowingformula: kN (2.4.27)where
qh= thevelocitypressureevaluatedatheighth(definedinFig.2.4.20)usingexposuredefinedinSection2.4.8.3
G= gusteffectfactorfromSection2.4.10
Cf= netforcecoefficientfromFig.2.4.20
AS= thegrossareaofthesolidfreestandingwallorsolidsign,inm2
2.4.16 DESIGNWINDLOADSONOTHERSTRUCTURES
Thedesignwindforceforotherstructuresshallbedeterminedbythefollowing
equation: kN (2.4.28)where
qz= velocitypressureevaluatedatheightzofthecentroidofareaAfusingexposuredefinedinSection2.4.8.3
G= gusteffectfactorfromSection2.4.10
Cf= forcecoefficientsfromFigs.2.4.21through2.4.23.
Af= projectedareanormaltothewindexceptwhereCf isspecifiedfortheactualsurfacearea,m2
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
30/131
Part6
30
2.4.17 ROOFTOPSTRUCTURESANDEQUIPMENTFORBUILDINGSWITHH
18.3M
TheforceonrooftopstructuresandequipmentwithAflessthan(0.1Bh)locatedonbuildingswithh 18.3m
shallbedeterminedfromEq.2.4.28, increasedbyafactorof1.9.Thefactorshallbepermittedtobereduced
linearlyfrom1.9to1.0asthevalueofAfisincreasedfrom(0.1Bh)to(Bh).
2.4.18 METHOD3WINDTUNNELPROCEDURE
2.4.18.1 SCOPE
Wind tunnel tests shall be used where required by Section 2.4.5.1. Wind tunnel testing shall be permitted in
lieuofMethods1and2foranybuildingorstructure.
2.4.18.2 TESTCONDITIONS
Windtunnel tests, or similar tests employing fluidsotherthan air, usedforthe determinationof design wind
loads for any building or other structure, shall be conducted in accordance with this section. Tests for the
determinationofmeanandfluctuatingforcesandpressuresshallmeetallofthefollowingconditions:
i. Thenaturalatmosphericboundarylayerhasbeenmodeledtoaccountforthevariationof
windspeedwithheight.
ii. Therelevantmacro (integral)lengthandmicrolengthscalesofthelongitudinal component
ofatmosphericturbulencearemodeledtoapproximatelythesamescaleasthatusedtomodel
thebuildingorstructure.
iii. Themodeledbuildingorotherstructureandsurroundingstructuresandtopographyare
geometricallysimilartotheirfullscalecounterparts,exceptthat,forlowrisebuildings
meetingtherequirementsofSection2.4.5.1,testsshallbepermittedforthemodeledbuilding
inasingleexposuresiteasdefinedinSection2.4.8
iv. Theprojectedareaofthemodeledbuildingorotherstructureandsurroundingsislessthan8
percentofthetestsectioncrosssectionalareaunlesscorrectionismadeforblockage.
v. Thelongitudinal pressuregradientinthewindtunneltestsectionisaccountedfor.vi. Reynoldsnumbereffectsonpressuresandforcesareminimized.
vii. Responsecharacteristicsofthewindtunnelinstrumentationareconsistentwiththerequired
measurements.
2.4.19 DYNAMICRESPONSE
Tests for the purpose of determining the dynamic response of a building or other structure shall be in
accordance with Section 2.4.18.2. The structural model and associated analysis shall account for mass
distribution,stiffness,anddamping.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
31/131
Fig. .4.1 Basic ind speed Vb) map of
31
angladesh
Chapter2
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
32/131
Part6
32
MainWindForceResistingSystem Method1 h 18.3 m
Figure2.4.2 DesignWindPressures Walls&Roofs
EnclosedBuildings
Notes:1. Pressures shown are applied to the horizontal and vertical projections, for exposure A, at h=9.1m,I=1.0, and Kzt=1.0. Adjust to other conditions using Equation 2.4.1.2. The load patterns shown shall be applied to each corner of the building in turn as the reference corner. (See Figure2.4.10)3. For the design of the longitudinal MWFRS use = 0, and locate the zone E/F, G/H boundary at the midlength of thebuilding.4. Load cases 1 and 2 must be checked for 25 < 45. Load case 2 at 25 is provided only for interpolation between25 to 30.5. Plus and minus signs signify pressures acting toward and away from the projected surfaces, respectively.6. For roof slopes other than those shown, linear interpolation is permitted.7. The total horizontal load shall not be less than that determined by assuming ps= 0 in zones B & D.8. The zone pressures represent the following:Horizontal pressure zones Sum of the windward and leeward net (sum of internal and external) pressures onvertical projection of:A End zone of wall C Interior zone of wall
B End zone of roof D Interior zone of roofVertical pressure zones Net (sum of internal and external) pressures on horizontal projection of:E End zone of windward roof G Interior zone of windward roofF End zone of leeward roof H Interior zone of leeward roof9. Where zone E or G falls on a roof overhang on the windward side of the building, use EOH and GOH for the pressureon the horizontal projection of the overhang. Overhangs on the leeward and side edges shall have the basic zonepressure applied.10. Notation:a: 10 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than either 4% of leasthorizontal dimension or 0.9 m.h: Mean roof height, in feet (meters), except that eave height shall be used for roof angles
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
33/131
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
34/131
Part6
34
ComponentsandCladdingMethod1 h 18.3m
Figure2.4.3 DesignWindPressures Walls&Roofs
EnclosedBuildings
Notes:1. Pressures shown are applied normal to the surface, for exposure A, at h= 9.1m, I= 1.0, and Kzt= 1.0. Adjust toother conditions using Equation 2.4.2.2. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.3. For hip roofs with 25, Zone 3 shall be treated as Zone 2.4. For effective wind areas between those given, value may be interpolated, otherwise use the value associatedwith the lower effective wind area.5. Notation:a: 10 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than either 4% of leasthorizontal dimension or 0.9 m.h: Mean roof height, in feet (meters), except that eave height shall be used for roof angles
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
35/131
Chapter2
35
ComponentsandCladdingMethod1 h 18.3m
Figure2.4.3(cont'd) NetDesignWindPressures Walls&Roofs
EnclosedBuildings
RoofOverhangNetDesignWindPressure,Pnet30 (kN/m2)
(ExposureAath=9.1mwithl=1.0)Zone EffectiveWindArea(m2)Basic Wind Speed V (m/s)40.23 44.7 49.17 53.64 58.11 62.58 67.05 75.99
Roof0to7degrees
2 0.930 1.005 1.239 1.502 1.785 2.096 2.431 2.790 3.5842 1.860 0.986 1.220 1.473 1.756 2.058 2.388 2.742 3.5222 4.648 0.962 1.191 1.440 1.713 2.010 2.330 2.675 3.4362 9.296 0.947 1.168 1.412 1.680 1.971 2.287 2.627 3.3733 0.930 1.656 2.043 2.470 2.943 3.450 4.005 4.594 5.9053
1.860 1.297 1.603 1.938 2.3112.708 3.144 3.609 4.632
3
4.648 0.828 1.024 1.240 1.4741.727 2.005 2.302 2.957
3 9.296 0.479 0.584 0.708 0.842 0.986 1.144 1.311 1.684
Roof>
7to27
degrees
2 0.930 1.302 1.603 1.943 2.311 2.713 3.144 3.613 4.6372 1.860 1.302 1.603 1.943 2.311 2.713 3.144 3.613 4.6372 4.648 1.302 1.603 1.943 2.311 2.713 3.144 3.613 4.6372 9.296 1.302 1.603 1.943 2.311 2.713 3.144 3.613 4.6373 0.930 2.187 2.699 3.268 3.885 4.560 5.292 6.072 7.8003 1.860 1.971 2.436 2.948 3.507 4.115 4.775 5.479 7.0393 4.648 1.689 2.086 2.526 3.005 3.526 4.091 4.694 6.0343 9.296 1.479 1.823 2.206 2.627 3.082 3.574 4.106 5.268
Roof>2
7to45
degrees
2 0.930 1.182 1.460 1.766 2.101 2.464 2.861 3.282 4.2162 1.860 1.148 1.416 1.713 2.038 2.393 2.775 3.182 4.0912 4.648 1.101 1.359 1.641 1.952 2.292 2.660 3.052 3.9242
9.296
1.062 1.311 1.587 1.8902.220 2.574 2.952 3.795
3
0.930 1.182 1.460 1.766 2.1012.464 2.861 3.283 4.216
3 1.860 1.148 1.416 1.713 2.038 2.393 2.775 3.182 4.0913 4.648 1.101 1.359 1.641 1.952 2.292 2.660 3.053 3.9233 9.296 1.062 1.311 1.589 1.890 2.220 2.574 2.952 3.795
AdjustmentFactor
forBuildingHeightandExposure,
Mean roof
height(m)
Exposure
A B C4.6 1.00 1.21 1.476.1 1.00 1.29 1.557.6 1.00 1.35 1.619.15 1.00 1.40 1.6610.7 1.05 1.45 1.7012.2 1.09 1.49 1.7413.7 1.12 1.53 1.7815.2 1.16 1.56 1.8116.8 1.19 1.59 1.8418.3 1.22 1.62 1.87
UnitConversion1.0ft=0.3048m;1.0psf=0.0929m2;1.0psf=0.0479KN/m
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
36/131
Part6
36
TopographicFactor,Kzt Method2
Figure2.4.4
Topographic Multipliers for Exposure BH/Lh K1Multiplier x/Lh
K2Multiplier z/Lh K3 Multiplier2-D
Ridge
2-D
Escarp.
3-D
Axisym.Hill
2-D
Escarp.
All
OtherCases
2-D
Ridge
2-D
Escarp.
3-D
Axisym.Hill0.20 0.29 0.17 0.21 0.00 1.00 1.00 0.00 1.00 1.00 1.000.25 0.36 0.21 0.26 0.50 0.88 0.67 0.10 0.74 0.78 0.670.30 0.43 0.26 0.32 1.00 0.75 0.33 0.20 0.55 0.61 0.450.35 0.51 0.30 0.37 1.50 0.63 0.00 0.30 0.41 0.47 0.300.40 0.58 0.34 0.42 2.00 0.50 0.00 0.40 0.30 0.37 0.200.45 0.65 0.38 0.47 2.50 0.38 0.00 0.50 0.22 0.29 0.140.50 0.72 0.43 0.53 3.00 0.25 0.00 0.60 0.17 0.22 0.093.50 0.13 0.00 0.70 0.12 0.17 0.064.00 0.00 0.00 0.80 0.09 0.14 0.040.90 0.07 0.11 0.031.00 0.05 0.08 0.021.50 0.01 0.02 0.00
2.00 0.00 0.00 0.00Notes:1. For values of H/Lh,x/Lhandz/Lhother than those shown, linear interpolation is permitted.2. For H/Lh> 0.5, assume H/Lh= 0.5 for evaluating K1and substitute 2Hfor Lhfor evaluating K2andK3.3. Multipliers are based on the assumption that wind approaches the hill or escarpment along thedirection of maximum slope.4. Notation:
H: Height of hill or escarpment relative to the upwind terrain, in meters.Lh: Distance upwind of crest to where the difference in ground elevation is half the height ofhill or escarpment, in meters.K1: Factor to account for shape of topographic feature and maximum speedup effect.K2: Factor to account for reduction in speedup with distance upwind or downwind of crest.K3: Factor to account for reduction in speedup with height above local terrain.x: Distance (upwind or downwind) from the crest to the building site, in meters.z
: Height above local ground level, in meters.W
: Horizontal attenuation factor.: Height attenuation factor.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
37/131
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
38/131
Part6
38
MainWindForceResistingSystem Method2 AllHeights
Figure2.4.6 ExternalPressureCoefficients,Cp Walls&Roofs
Enclosed,PartiallyEnclosedBuildings
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
39/131
Chapter2
39
MainWindForceResistingSystem Method2 AllHeights
Figure2.4.6(cont) ExternalPressureCoefficients,Cp Walls&Roofs
Enclosed,PartiallyEnclosedBuildings
Wall PressureCoefficients,Cp
Surface L/B Cp UseWithWindwardWall Allvalues 0.8 qzLeewardWall 01 0.5 qh
2 0.3
>4 0.2
SideWall Allvalues 0.7 qhRoofPressureCoefficients,Cp,forusewithqh
Wind
Direction
Windward Leeward
Angle, (degrees) Angle, (degrees)
h/L 10 15 20 25 30 35 45 >60# 10 15 >20
Normal
To ridge
for >100
1.0 1.3**0.18 1.00.180.70.18
0.50.0* 0.30.2 0.20.2 0.0*0.3 0.01 0.7 0.6 0.6Normal
Toridge
for
2h 0.3, 0.18
> 1.00 to h/2 1.3**, 0.18 Area (m 2) Reduction Factor
< 9.3 sq m 1.0> h/2 0.7, 0.18 23,2 sq m 0.9> 92.9 sq m 0.8Notes:1. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.2. Linear interpolation is permitted for values of L/B,h/Land other than shown. Interpolation shall only becarried out between values of the same sign. Where no value of the same sign is given, assume 0.0 forinterpolation purposes.3. Where two values of Cpare listed, this indicates that the windward roof slope is subjected to eitherpositive or negative pressures and the roof structure shall be designed for both conditions. Interpolation forintermediate ratios of h/Lin this case shall only be carried out between C p values of like sign.4. For monoslope roofs, entire roof surface is either a windward or leeward surface.5. For flexible buildings use appropriate Gfas determined by Section 2.4.10.6. Refer to Figure 2.4.7 for domes and Figure 2.4.8 for arched roofs.7. Notation:B
: Horizontal dimension of building, in meter, measured normal to wind direction.L
: Horizontal dimension of building, in meter, measured parallel to wind direction.h: Mean roof height in meters, except that eave height shall be used for e 10 degrees.z: Height above ground, in meters.G: Gust effect factor.qz,qh: Velocity pressure, in N/m2, evaluated at respective height.: Angle of plane of roof from horizontal, in degrees.8. For mansard roofs, the top horizontal surface and leeward inclined surface shall be treated as leewardsurfaces from the table.9. Except for MWFRS's at the roof consisting of moment resisting frames, the total horizontal shear shall notbe less than that determined by neglecting wind forces on roof surfaces.#For roof slopes greater than 80, use Cp= 0.8
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
40/131
Part6
40
MainWindForceResistingSystem Method2 AllHeights
Figure2.4.7 ExternalPressureCoefficients,Cp Domed Roofs
Enclosed,PartiallyEnclosedBuildings andStructures
Note:1. Two load cases shall be considered:Case A. Cpvalues between A and B and between B and C shall be determined by linearinterpolation along arcs on the dome parallel to the wind direction;Case B. Cpshall be the constant value of A for 25 degrees, and shall be determined by linearinterpolation from 25 degrees to B and from B to C.2.
Values denoteCp
to be used with
wherehD+f
is the height at the top of the dome.3.
Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.4. Cpis constant on the dome surface for arcs of circles perpendicular to the wind direction; forexample, the arc passing through BBB and all arcs parallel to BBB.5. For values of hD/Dbetween those listed on the graph curves, linear interpolation shall bepermitted.6. =0 degreeson dome springline, = 90 degrees at dome center top point. f is measured fromspringline to top.7. The total horizontal shear shall not be less than that determined by neglecting wind forces roofsurfaces.8. Forf/Dvalues less than 0.05. use Figure 2.4.6.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
41/131
Chapter2
41
MainWindForceRes.Sys./CompandClad.Method2 AllHeightFigure2.4.8 ExternalPressureCoefficients,Cp ArchedRoofs
Enclosed,PartiallyEnclosedBuildingsandStructures
Condition Risetospan
ratio,r
CpWindward
quarter
Center
half
Leeward
quarter
Roof on elevated structure 0 < r< 0.2 0.9 0.7 r 0.50.2 r< 0.3* l.5 r 0.3 0.7 r 0.50.3 r 0.6
2.75r
0.7 0.7 r
0.5Roof springing from groundlevel 0
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
42/131
Part6
42
MainWindForceResistingSystem Method2 AllHeightsFigure2.4.9 DesignWindLoadCases
Case 1. Full design wind pressure acting on the projected area perpendicular to each principal axisof the structure, considered separately along each principal axis.Case 2. Three quarters of the design wind pressure acting on the projected area perpendicular toeach principal axis of the structure in conjunction with a torsional moment as shown,considered separately for each principal axis.Case 3. Wind loading as defined in Case 1, but considered to act simultaneously at 75% of thespecified value.Case 4. Wind loading as defined in Case 2, but considered to act simultaneously at 75% of thespecified value.Notes:1. Design wind pressures for windward and leeward faces shall be determined in accordance
with the provisions of 2.4.13 as applicable for building of all heights.2. Diagrams show plan views of building.3. Notation:Pwx,PwY:Windward face design pressure acting in the x,yprincipal axis, respectively.PLX,PLY:Leeward face design pressure acting in the x,yprincipal axis, respectively.e(eX+ey): Eccentricity for the x,yprincipal axis of the structure, respectively.MT: Torsional moment per unit height acting about a vertical axis of the building.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
43/131
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
44/131
Part6
44
MainWindForceResistingSystem Method2 h 18.3m
Figure2.4.10(contd) ExternalPressureCoefficients,GCpf LowriseWalls&
RoofsEnclosed,PartiallyEnclosedBuildings
RoofAngle (degrees)BuildingSurface
1 2 3 4 5 6 1E 2E 3E 4E05 0.40 0.69 0.37 0.29 0.45 0.45 0.61 1.07 0.53 0.4320 0.53 0.69 0.48 0.43 0.45 0.45 0.80 1.07 0.69 0.643045 0.56 0.21 0.43 0.37 0.45 0.45 0.69 0.27 0.53 0.4890 0.56 0.56 0.37 0.37 0.45 0.45 0.69 0.69 0.48 0.48Notes:1. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.2. For values of other than those shown, linear interpolation is permitted.3. The building must be designed for all wind directions using the 8 loading patterns shown. The loadpatterns are applied to each building corner in turn as the Reference Corner.4. Combinations of external and internal pressures (see Figure 2.4.5) shall be evaluated as required toobtain the most severe loadings.5. For the torsional load cases shown below, the pressures in zones designated with a T (1T, 2T, 3T,4T) shall be 25% of the full design wind pressures (zones 1, 2, 3, 4).Exception: One story buildings with hless than or equal to 9.1m, buildings two stories or lessframed with light frame construction, and buildings two stories or less designed with flexiblediaphragms need not be designed for the torsional load cases.Torsional loading shall apply to all eight basic load patterns using the figures below applied at eachreference corner.6. Except for momentresisting frames, the total horizontal shear shall not be less than thatdetermined by neglecting wind forces on roof surfaces.7. For the design of the MWFRS providing lateral resistance in a direction parallel to a ridge line or forflat roofs, use = 0 and locate the zone 2/3 boundary at the midlength of the building.8. The roof pressure coefficient GCpf, when negative in Zone 2 or 2E, shall be applied in Zone 2/2Efora distance from the edge of roof equal to 0.5 times the horizontal dimension of the building parallelto the direction of the MWFRS being designed or 2.5 times the eave height, he, at the windwardwall, whichever is less; the remainder of Zone 2/2E extending to the ridge line shall use thepressure coefficient GCpffor Zone 3/3E.
9.
Notation:a
: 10 percent of least horizontal dimension or0.4h
, whichever is smaller, but not less than either4% of least horizontal dimension or 0.9 m.h: Mean roof height, in meters, except that eave height shall be used for 10.: Angle of plane of roof from horizontal, in degrees.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
45/131
Chapter2
45
ComponentsandCladdingMethod2 h 18.3m
Figure2.4.11.A ExternalPressureCoefficients,GCp Walls
Enclosed,PartiallyEnclosedBuildings
Notes:1. Vertical scale denotes GCPto be used with qh-2. Horizontal scale denotes effective wind area, in square meters.3. Plus and minus signs signify pressures acting toward and away from the surfaces,respectively.4. Each component shall be designed for maximum positive and negative pressures.5. Values of GCPfor walls shall be reduced by 10% when 10 0.6. Notation:a:10 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less thaneither 4% of least horizontal dimension or 0.9m.h:Mean roof height, in meters, except that eave height shall be used for 10 0.: Angle of plane of roof from horizontal, in degrees.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
46/131
Part6
46
ComponentsandCladdingMethod2 h 18.3m
Figure2.4.11.B ExternalPressureCoefficients,GCp GableRoofs 70
Enclosed,PartiallyEnclosedBuildings
Notes:
1. Vertical scale denotes GCPto be used with qh-2. Horizontal scale denotes effective wind area, in square meters.3. Plus and minus signs signify pressures acting toward and away from the surfaces,respectively.4. Each component shall be designed for maximum positive and negative pressures.5. If a parapet equal to or higher than 0.9m is provided around the perimeter of the roof with 70, the negative values of GC0in Zone 3 shall be equal to those for Zone 2 and positivevalues of GCPin Zones 2 and 4 shall be set equal to those for wall Zones 4 and 5 respectivelyin figure 2.4.11A.6. Values of GCPfor roof overhangs include pressure contributions from both upper and lowersurfaces.7. Notation:a:10 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less thaneither 4% of least horizontal dimension or 0.9m.h:
Eave height shall be used for 100
.: Angle of plane of roof from horizontal, in degrees.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
47/131
Chapter2
47
ComponentsandCladdingMethod2 h 18.3m
Figure2.4.11.C ExternalPressureCoefficients,GCp Gable/HipRoofs70
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
48/131
Part6
48
ComponentsandCladdingMethod2 h 18.3mFigure2.4.11.D ExternalPressureCoefficients,GCp GableRoofs27
0
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
49/131
Chapter2
49
ComponentsandCladdingMethod2 h 18.3mFigure2.4.12 ExternalPressureCoefficients,GCp
SteppedRoofsEnclosed,PartiallyEnclosedBuildings
Notes:On the lower level of flat, stepped roofs shown in Fig. 2.4.12, the zone designations and pressurecoefficients shown in Fig. 2.4.11B shall apply, except that at the roofupper wall intersection(s), Zone 3shall be treated as Zone 2 and Zone 2 shall be treated as Zone 1. Positive values of GCpequal to those forwalls in Fig. 2.4.11A shall apply on the crosshatched areas shown in Fig. 2.4.12.Notation:b: 1.5h1in Fig. 2.4.12, but not greater than 30.5 m.h: Mean roof height, in meters.hi: h1or h2in Fig. 2.4.12; h= h1+h2;h1 3.1 m; hi/h= 0.3 to 0.7.W: Building width in Fig. 2.4.12.Wi:W1
orW2
orW3
in Fig. 2.4.12.W=W1+W2
orW1+W2+W3
;Wi/W
= 0.25 to 0.75.e
: Angle of plane of roof from horizontal, in degrees.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
50/131
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
51/131
Chapter2
51
ComponentsandCladdingMethod2 h 18.3m
Figure2.4.14.A ExternalPressureCoefficients,GCp MonoslopeRoofs
30
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
52/131
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
53/131
Chapter2
53
ComponentsandCladdingMethod2 h 18.3m
Figure2.4.15 ExternalPressureCoefficients,GCp SawtoothRoofs
Enclosed,PartiallyEnclosedBuildings
Notes:
1. VerticalscaledenotesGCPtobeusedwithqh
2. HorizontalscaledenoteseffectivewindareaA,insquarefeet(squaremeters).
3. Plusandminussignssignifypressuresactingtowardandawayfromthesurfaces,respectively.
4. Eachcomponentshallbedesignedformaximumpositiveandnegativepressures.
5. For 100
ValuesofGCPfromFig.2.4.11shallbeused.
6. Notation:
a: 10 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than
either4%ofleasthorizontaldimensionor0.9m.
h:Meanroofheightinmetersexceptthateaveheightshallbeusedfor00
100.
W:Buildingwidth,inmeters.
:Angleofplaneofrooffromhorizontal,indegrees.
-
8/10/2019 BNBC Part 6-Chap 2_26-08-2012
54/131
Part6
54
ComponentsandCladdingMethod2 AllHeights
Figure2.4.16 ExternalPressureCoefficients,GCp DomedRoofs
Enclosed,PartiallyEnclosedBuildings
ExternalPressureCoefficientsforDomeswithacircularBase, degrees NegativePressures PositivePressures PositivePressures0 90 0 60 61 90GCp 0.9 +0.9 +0.5Notes:1. Values denote Cpto be used with