wind loading to
TRANSCRIPT
-
8/7/2019 WIND LOADING TO
1/31
WIND LOADING TO
ASCE 7-05
-
8/7/2019 WIND LOADING TO
2/31
What is Wind?
Wind is the result of horizontal differencesin air pressure
These pressure differences are due touneven heating of the earths surface
-
8/7/2019 WIND LOADING TO
3/31
Hurricanes
Features of hurricanes:
High speed sustained winds up to 74 mi/h Typical diameter of 311 miles
Cyclonic effect with direction of spin controlled
by Coriolis effect
-
8/7/2019 WIND LOADING TO
4/31
The ingredientsThe ingredients
a hurricanea hurricane
needsneeds
Warm water above 27C
Converging winds
Unstable air
Humid air being pulled intothe storm(up to about18,000 ft)
Pre-existing winds comingfrom nearly the samedirection
An upper atmospherehigh-pressure area helpspump away air rising in the
storm
-
8/7/2019 WIND LOADING TO
5/31
SaffirSaffir--Simpson scaleSimpson scale
forhurricane categoriesforhurricane categories
Category Velocity
1 minute(km/hr)
Pressure(mb)
Damages
1 120 - 150 > 980 Minimum
2 150 175 965 980 Moderate
3 175 210 945 - 965 Extensive
4 210 250 920 - 945 Extreme
5 > 250 < 920 Catastrophic
-
8/7/2019 WIND LOADING TO
6/31
Wind loading
In general the pressures derived from wind come
from the dynamic part of Bernoullis equation:
2
21
Vq V!
-
8/7/2019 WIND LOADING TO
7/31
Standard Identification
ISO International Standard Organization
CUBiC Caribbean Uniform Building Code
ENV Eurocode
DRBC Dominican Republic Building Code
AIJ Japan Standard
AS Australian Standard
BNSCP Barbados Standard
Different internationalDifferent international
design standardsdesign standards
-
8/7/2019 WIND LOADING TO
8/31
Different calculations for designDifferent calculations for design
wind speeds and dynamicwind speeds and dynamic
pressurespressures
AS1170.2-89
BNSCP28
AIJ
DRBC-03
ENV 1991-2-4
CUBiC
ISO 4354
BuildingPressure/Force
PressureSpeedStandard
2ref21
refq V!
V
V
gusts3V
V
fi
rf
q!
zplae,pe qKKKCP !
peqCP !
221
ref Vq V!
221
ref Vq V!
2dztz2
1z IVKKKq V!
2H2
1h Uq V!
2z2
1h Vq V!
232121 SSVSq V!
0,refalttemdirref CCCCV !
REEUU gfgH !
itscat,zz MMMVV !
pihpz GCqGCqp !
peeexprefe CZCqW !
dynCfigexpref CCqW !
AGCqW ffhf !
-
8/7/2019 WIND LOADING TO
9/31
General Wind Load Definition
From the Wind Loads for Structural
Design the definition reads:
"The basic wind speed V is the 3-second
gust speed estimated to be exceeded on
the average only once in 50 years ..... at a
height of 10 m above the ground in an
open situation ....."
-
8/7/2019 WIND LOADING TO
10/31
Basic Wind Speed (V) to ASCE 7-
05
The basic wind speed corresponds to a 3-s gust speed at 33 ft (10 m) above ground
in exposure Category C
-
8/7/2019 WIND LOADING TO
11/31
Wind load considerations
Features of all wind codes, wind loading
affected by:
Averaging period,
Return period,
Height above ground,
Topography and ground roughness.
-
8/7/2019 WIND LOADING TO
12/31
Features of ASCE basic wind
speed (V)
Averaging time based on 3 second gust
Return period based on 50 yr return period
H
eight 10m
Exposure Category C
-
8/7/2019 WIND LOADING TO
13/31
Vg Z
FOREST, SUBURB
5010
100
300
OPEN SOIL
gZ
Zg = Height wind gradient
400
V
500
1/7
ZZ
1/9.6
EXPOSURE B - EXPOSURE C -
Effects of terrainEffects of terrainroughness androughness andheight on windheight on wind
speedsspeeds
-
8/7/2019 WIND LOADING TO
14/31
Sketch showing effects ofSketch showing effects oftopography on wind velocity ontopography on wind velocity ona hilly islanda hilly island
10 m
80Vs
100Vg
60
gV100
g
120sV
Vs
V
100gV
40
100
Open sea Wind ward Speed up over Sheltered leeward
coast
Speed up
Coast hill crest
-
8/7/2019 WIND LOADING TO
15/31
Procedures used in ASCE 7-05
Basic Procedure Analytical Procedure
Wind Tunnel Procedure
-
8/7/2019 WIND LOADING TO
16/31
Limitations of Basic & Analytical
P
rocedures Factors not taken into consideration:
Across wind loading as a result of vortex
shedding or instability due to galloping and
fluttering
Does not have a site location for which
channeling effects or buffeting in the wake of
upwind obstructions warrant specialconsideration
-
8/7/2019 WIND LOADING TO
17/31
Across Wind Loading
Vortex shedding
-
8/7/2019 WIND LOADING TO
18/31
Turbulent flow on highTurbulent flow on high--riserisebuildings due to upwindbuildings due to upwindobstructionsobstructions
-
8/7/2019 WIND LOADING TO
19/31
Other limitations of Basic
P
rocedure
Simple diaphragm building Low Rise
-
8/7/2019 WIND LOADING TO
20/31
-
8/7/2019 WIND LOADING TO
21/31
Enclosure Classification of
Buildings to ASCE 7-05
Open
Partially enclosed
Enclosed- That which does not fall into the
first 2 classifications
-
8/7/2019 WIND LOADING TO
22/31
Features of both Methods
The wind loads are calculated for:
1) MWFRS- Mean Wind Force ResistingSystem a main feature of which receives
wind loading from more than one surface
2) Components and cladding (C&C):elements that do not meet MWFRS
definition
-
8/7/2019 WIND LOADING TO
23/31
Basic ProcedureBasic Procedure
-
8/7/2019 WIND LOADING TO
24/31
-
8/7/2019 WIND LOADING TO
25/31
NotationNotation FactorFactor What does it mean?What does it mean?
Directionality
Takes into account the probability that themaximum wind has the same direction asthat of the maximum pressure
Importance IFactor based on type of structure andbuilding use
ExposureRepresents the wind velocity at a z heightabove the ground
Topography
Takes into account the fact that thestructure may be located on top of a hill oron an escarpment, increasing the windvelocity
dK
zK
ztK
Meaning of factors inMeaning of factors in
ASCEASCE--77
-
8/7/2019 WIND LOADING TO
26/31
NotationNotation FactorFactor What does it mean?What does it mean?
Gust effect factor GRepresents the turbulence-structureinteraction and the dynamicamplification of the wind
External pressurecoefficient
Estimates the wind pressure on thebuilding, external walls
Internal pressurecoefficient
Reflects the internal pressure due towall opening uantity and sizes
Design pressure p Represents the design pressure
Design force FRepresents the net force on openstructures
pC
piC
Meaning of factors inMeaning of factors in
ASCEASCE--77
-
8/7/2019 WIND LOADING TO
27/31
2dztz2
1 IVKKKq V!
Modified basic pressureModified basic pressure--
ASCEASCE--77
Modified basic pressure inModified basic pressure in
ASCEASCE--7 to accommodate local7 to accommodate local
parametersparameters
-
8/7/2019 WIND LOADING TO
28/31
Analytical ProcedureAnalytical Procedure
Rigid primary systemsRigid primary systems
Flexible primary systemsFlexible primary systems
p = q GCp - qi (GCpi)
p = qGfCp - qi (GCpi)
-
8/7/2019 WIND LOADING TO
29/31
Analytical Procedure contdAnalytical Procedure contd
Components and claddingComponents and cladding
p = qh [(GCp) - (GCpi) ]
-
8/7/2019 WIND LOADING TO
30/31
Design pressure diagramDesign pressure diagram
on gabled roof buildingon gabled roof building
U
h
L
z
GCpqz
qGCph
q GCphq GCph
Wind
direction
-
8/7/2019 WIND LOADING TO
31/31
THE END