162162

Section 1608 Section 1608 -- Wind LoadsWind Loads

nn Wind SpeedWind Speednn ExposureExposurenn TopographyTopographynn Return PeriodReturn Periodnn Methods & ProceduresMethods & Proceduresnn ExamplesExamples

163163

Basic Wind SpeedsBasic Wind Speeds50 Year Return Period50 Year Return Period

164164

33--Second Gust VelocitiesSecond Gust Velocities50 Year Return Period50 Year Return Period

165165

Wind VelocityWind Velocitynn Basic Wind Speed (70 mph)Basic Wind Speed (70 mph)

•• Fixed distance/Variable timeFixed distance/Variable time•• Average Wind SpeedAverage Wind Speed

nn 33--Second Gust Wind Speed (90 mph)Second Gust Wind Speed (90 mph)•• Variable distance/Fixed timeVariable distance/Fixed time•• Gust Portion of Wind ProfileGust Portion of Wind Profile•• National Weather Service MeasurementsNational Weather Service Measurements•• News Media ReportNews Media Report•• Includes Hurricane I FactorIncludes Hurricane I Factor

166166

Exposure DefinitionsExposure Definitions

nn Exposure AExposure A--Deleted due to variabilityDeleted due to variabilitynn Exposure BExposure B--Urban & Dense SuburbanUrban & Dense Suburban

•• 2630 Ft or 10H Continuous Roughness2630 Ft or 10H Continuous Roughness•• 60% to 80% of all buildings60% to 80% of all buildings

nn Exposure CExposure C--Open TerrainOpen Terrainnn Exposure DExposure D--Shorelines, flats, lakesShorelines, flats, lakes

•• Open Water >1 MileOpen Water >1 Mile

167167

Wind Load ExposureWind Load Exposure

Exposure A Exposure B Exposure C & D

168168

ExposureExposure--RoughnessRoughness

Exposure B

169169

Topographic EffectsTopographic EffectsKzt=(1+K1*K2*K3)2

K1=Feature ShapeK2=Location from CrestK3=Building Height

170170

Wind LoadWind Load--Return PeriodReturn Period

171171

IBC 2003 MethodsIBC 2003 Methods

nn Section 6 ASCE 7Section 6 ASCE 7•• Exceptions:Exceptions:

nn Simplified MethodSimplified Methodnn SBCCI (R2 & R3 Buildings)SBCCI (R2 & R3 Buildings)nn AF & PA (1 & 2 Family Residences)AF & PA (1 & 2 Family Residences)nn NAAMM (Flagpoles)NAAMM (Flagpoles)nn TIA/EIA (Antenna)TIA/EIA (Antenna)

172172

MethodsMethods

nn Method 1Method 1--Simplified ProcedureSimplified Procedurenn Method 2Method 2--AnalyticalAnalytical

•• RigidRigidnn Less than 60 FeetLess than 60 Feetnn All buildingsAll buildings

•• FlexibleFlexiblenn Gust FactorGust Factor

nn Method 3Method 3--Wind TunnelWind Tunnel

173173

IBC 2003/ASCE 7IBC 2003/ASCE 7

nn Method 1Method 1--Simplified ProcedureSimplified Procedure•• ConditionsConditions•• ProcedureProcedure•• DeterminationDetermination

nn MWRS TableMWRS Tablenn Components & Cladding TableComponents & Cladding Table

174174

Method 1Method 1--ConditionsConditionsnn Simple DiaphragmSimple Diaphragmnn Flat RoofFlat Roofnn <60 ft Height<60 ft Heightnn EnclosedEnclosed BuldingBuldingnn Regular ShapeRegular Shapenn Rigid (<1 Sec Period)Rigid (<1 Sec Period)nn No Topographic EffectsNo Topographic Effectsnn Approximately SymmetricalApproximately Symmetrical

175175

Method 1Method 1--ProcedureProcedure

nn λλ--Adjustment FactorAdjustment Factornn IwIw--Importance FactorImportance Factornn PsPs--Wind PressureWind Pressure

P=P=λλ**IIww*P*Pss

176176

Method 1Method 1--DeterminationDetermination

177177

ASCE 7ASCE 7--0202

nn Method 2Method 2--Analytical ProcedureAnalytical Procedure•• ConditionsConditions•• ProcedureProcedure•• DeterminationDetermination

nn Rigid FormulaRigid Formula•• Less than 60 FtLess than 60 Ft•• All BuildingsAll Buildings

nn Flexible FormulaFlexible Formula

178178

Method 2Method 2--ConditionsConditions

nn Regular ShapeRegular Shapenn No Dynamic Wind EffectsNo Dynamic Wind Effects

179179

Method 2Method 2--ProceduresProceduresStep 1Step 1

nn KzKz--Exposure/HeightExposure/Heightnn KztKzt--TopographyTopographynn KdKd--Building Configuration & Wind DirBuilding Configuration & Wind Dirnn VelocityVelocity--MapsMapsnn II--UseUse

q=0.00256Kq=0.00256Kzz**KKztzt**KKdd*V*V22*I*I

180180

Method 2Method 2--MWRS ProcedureMWRS ProcedureRigidRigid--Buildings Less than 60 FtBuildings Less than 60 Ft

nn GCpfGCpf--External Pressure CoefficientExternal Pressure Coefficientnn GCpiGCpi--Internal Pressure CoefficientInternal Pressure Coefficient

p=p=qqhh*(*(GCGCpfpf--GCpGCpii))

181181

Method 2Method 2--MWRS DeterminationMWRS DeterminationRigidRigid--Buildings Less than 60 FtBuildings Less than 60 Ft

182182

Method 2Method 2--MWRS ProcedureMWRS ProcedureRigidRigid--All Building HeightsAll Building Heights

nn GG--Gust Effect (0.85 Rigid Buildings)Gust Effect (0.85 Rigid Buildings)nn CpCp--External Pressure CoefficientExternal Pressure Coefficientnn GCpiGCpi--Internal Pressure CoefficientInternal Pressure Coefficient

p=q*G*Cp=q*G*Cpp--qqii**GCGCpipi

183183

Method 2Method 2--MWRS DeterminationMWRS DeterminationRigidRigid--All Building HeightsAll Building Heights

184184

Method 2Method 2--MWRS Procedure MWRS Procedure Flexible BuildingsFlexible Buildings

nn GfGf--Gust Effect (Flexible)Gust Effect (Flexible)nn CpCp--External Pressure CoefficientExternal Pressure Coefficientnn GCpiGCpi--Internal Pressure CoefficientInternal Pressure Coefficient

p=q*p=q*GGff*C*Cpp--qqii**GCGCpipi

185185

Method 2Method 2--Flexible FormulaFlexible FormulaGust FactorGust Factor

GfGf=0.925=0.925((1+1.7I1+1.7Izz√√(g(g22QQQQ22+g+g22RRRR22))))1+1.7g1+1.7gvvIIzz

wherewhere ggRR==√√(2ln(3600n(2ln(3600n11))+))+ 0.5770.577√√(2ln(3600n(2ln(3600n11))))

where R=where R=√√((1/((1/ββ)R)RnnRRhhRRBB(0.53+0.47R(0.53+0.47RLL))))wherewhere RRnn==7.47N7.47N11

(1+10.3N(1+10.3N11)^5/3)^5/3etcetc…………..

186186

Method 2Method 2--Load CasesLoad CasesMWRSMWRS

•Case 1-100% Ea Dir•Case 2-75% Ea Dir•Case 3-Case 1 w/15%e•Case 4-Case 2 w/15%e

187187

Method 2Method 2--C & C ProcedureC & C Procedure

nn GCGCpp--External Pressure CoefficientExternal Pressure Coefficientnn GCGCpipi--Internal Pressure CoefficientInternal Pressure Coefficient

p=p=qqhh*(*(GCGCpp--GCGCpipi) (h<60) (h<60’’))

p=q*p=q*GCGCpp--qqii**GCGCpipi (h>60(h>60’’))

188188

Method 2Method 2--C & C DeterminationC & C Determinationnn LocationLocationnn Tributary AreaTributary Areann Walls/RoofsWalls/Roofs

189189

ASCE 7ASCE 7--0202

nn Method 3Method 3--Wind Tunnel ProcedureWind Tunnel Procedure•• Irregular ShapeIrregular Shape•• Flexible (>1 sec)Flexible (>1 sec)•• WakeWake•• ChannelingChanneling•• Dynamic EffectsDynamic Effects

190190

Dynamic Wind EffectsDynamic Wind Effectsnn Vortex SheddingVortex Shedding

191191

Dynamic Wind EffectsDynamic Wind Effectsnn GallopingGalloping

192192

Dynamic Wind EffectsDynamic Wind Effects

nn FlutterFlutter--Flutter occurs when aFlutter occurs when atorsionaltorsional disturbance in the structuredisturbance in the structureincreases theincreases the angle of attackangle of attack of theof thebridge (that is, the angle betweenbridge (that is, the angle betweenthe wind and the bridge)the wind and the bridge)

193193

Example 1Example 1--Simplified ProcedureSimplified Procedurenn CriteriaCriteria

•• 130 mph130 mph•• Exposure CExposure C•• Flat TerrainFlat Terrain•• EnclosedEnclosed•• I=1.0I=1.0

194194

Example 1Example 1-- Simplified ProcedureSimplified ProcedureMWRSMWRS--Figure 6Figure 6--22

•Roof Pressure=-32 psf•Wall Pressure=27 psf•λ=1.21

Roof=-39 psfMWRS=33 psf

(Includes Internal Pressure)

195195

Example 1Example 1--Simplified ProcedureSimplified ProcedureC & C Wall PressuresC & C Wall Pressures--Figure 6Figure 6--33

nn TribTrib Area=15(15/3)=75Area=15(15/3)=75 sfsf

Zone 4 p=27.2*1.21=33Zone 4 p=27.2*1.21=33 psfpsfZone 4 p=Zone 4 p=--29.8*1.21=29.8*1.21=--3636

Zone 5 p=27.2*1.21=33Zone 5 p=27.2*1.21=33Zone 5 p=Zone 5 p=--34.3*1.21=34.3*1.21=--4242

196196

Example 1Example 1--Simplified ProcedureSimplified ProcedureC & C Roof JoistsC & C Roof Joists--Figure 6Figure 6--33

nn TribTrib Area=30*5=150Area=30*5=150 sfsfor 30*30/3=300or 30*30/3=300 sfsf

Zone 1 p=9.8*1.21=12Zone 1 p=9.8*1.21=12 psfpsfZone 1 p=Zone 1 p=--27.8*1.21=27.8*1.21=--3434

Zone 2&3 p=9.8*1.21=12Zone 2&3 p=9.8*1.21=12Zone 2&3 p=Zone 2&3 p=--33*1.21=33*1.21=--4040

197197

Example 1Example 1--Simplified ProcedureSimplified ProcedureC & C Roof PanelsC & C Roof Panels--Figure 6Figure 6--33

nn TribTrib Area=10Area=10 sfsfZone 1 p=12.4*1.21=15Zone 1 p=12.4*1.21=15 psfpsfZone 1 p=Zone 1 p=--30.4*1.21=30.4*1.21=--3737Zone 2 p=12.4*1.21=15Zone 2 p=12.4*1.21=15Zone 2 p=Zone 2 p=--51*1.21=51*1.21=--6262Zone 3 p=12.4*1.21=15Zone 3 p=12.4*1.21=15Zone 3 p=Zone 3 p=--77*1.21=77*1.21=--9393

198198

Example 1Example 1--Simplified ProcedureSimplified ProcedureTributary Area EffectTributary Area Effect

199199

Example 2Example 2--Analytical MethodAnalytical Methodnn CriteriaCriteria

•• 90 mph90 mph•• Exposure BExposure B•• Flat TerrainFlat Terrain•• EnclosedEnclosed•• I=1.0I=1.0•• 33--DD AxisymmetricalAxisymmetrical

HillHill

200200

Example 2Example 2--Analytical MethodAnalytical MethodMWRS, C & CMWRS, C & C

nn qqzz=0.00256*=0.00256*KKzz**KKztzt**KKdd*V*V22 II•• KKdd=0.85=0.85•• KKzz=0.57 Case II MWRS=0.57 Case II MWRS

=0.7 Case I C & C=0.7 Case I C & CMWRSMWRS qqzz=0.00256*0.57*=0.00256*0.57*KKztzt*0.85*90*0.85*9022 1.01.0

=10.04*=10.04*KKztztC & CC & C qqzz=0.00256*=0.00256*KKzz**KKztzt**KKdd*V*V22 II

=12.3*=12.3*KKztzt

201201

Example 2Example 2--Analytical MethodAnalytical MethodMWRS, C & CMWRS, C & C

H/L=0.4H/L=0.4KK11=0.95*0.4=0.38=0.95*0.4=0.38KK22=(1=(1--250/(1.5*600))=0.72250/(1.5*600))=0.72KK33=e=e--4(15)/6004(15)/600=0.9=0.9

KKztzt=(1+0.38*0.72*0.9)=(1+0.38*0.72*0.9)22=1.56=1.56nn q(MWRS)=15.7q(MWRS)=15.7 psfpsfnn q(C&C)=19.2q(C&C)=19.2 psfpsf

202202

Wind LoadsWind Loads--SummarySummary

nn Variable ConditionsVariable Conditionsnn Lots of Different ParametersLots of Different Parametersnn Number of ProceduresNumber of Procedures

nn More complex than you thinkMore complex than you think