ASCE 7-02

8/13/2019 ASCE 7-02

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I

II

III

IV

Wind Directionality Factor , Kd

Table 1-1

Non-Hurricane Prone Regions

and Hurricane Prone Regions

with V=85-100 mph and Alaska

CategoryHurricane Prone Regions

with V>100 mph

Table 6-1

Importance Factor, I (Wind Loads)

National defense facility

I

II

III

IV

Example:

Hospitals and emergency health care facility

Fire, rescue, ambulance, and police stations

Communication towers, fuel storage tanks,

Aviation and traffic control center

Day care with more than 150 capacity

Elementary and secondary school has more than 250 capacity

Low Hazard facility:

Agricultural facility, temporary facility, minor storage facility

All buildings and other structure not in I, III, and IV

Water storage and pump station

College has more than 500 capacity

Hearth care has more than 50 capacityJail and detention facility

Power station, water and sewage treatment facility

Building and other structures designed as essential facilities:

Buildings and other structures are substantial hazard to human life

Example:

Building with more than 300 people in one area

0.87

1.00

1.15

1.15

0.77

1.00

1.15

1.15

Table 6-4

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Kd*

0.85

0.85

0.85

0.90

0.95

0.95

0.85

Open Signs and Lattice Framework 0.85

0.85

0.95

Topographic Factor, Kzt - Method 2Figure 6-4

z/Lh

Topographic Multipliers for Exposure C

2-D

Escarp.

3-D

Asisym.

Hill

K2 Multiplier

2-D

Escarp.

All

Other

Cases

*Directionality Factor Kd has been calibrated wight

combination of loads specified in Section 2. This factor shall

only be applied when used in conjunction with load

combination specified in 2.3 and 2.4.

K1 Multiplier

2-D

Ridge

Solid Signs

Main Wind Force Resising System

Components and Cladding

Buildings

Structure Type

Arched Roofs

H/Lh x/Lh

Chimneys, Tanks, and Similar Structures

Trussed TowersTriangular, Square, Rectanglar

All other cross sections

Square

Hexagonal

Round

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0.20 0.29 0.17 0.21 0.00 1.00 1.00 0.00

0.25 0.36 0.21 0.26 0.50 0.88 0.67 0.10

0.30 0.43 0.26 0.32 1.00 0.75 0.33 0.20

0.35 0.51 0.30 0.37 1.50 0.63 0.00 0.30

0.40 0.58 0.34 0.42 2.00 0.50 0.00 0.40

0.45 0.65 0.38 0.47 2.50 0.38 0.00 0.50

0.50 0.72 0.43 0.53 3.00 0.25 0.00 0.603.50 0.13 0.00 0.70

4.00 0.00 0.00 0.80

0.90

1.00

1.50

2.00

Notes:

1 For values of H/Lh, x/Lh and x/Lh other than those shown, linear interpolation is permi

2 For H/Lh >0.5, assume H/Lh = 0.5 for evaluating K1 and substitute 2H for Lh for evaluat

3 Multipliers are based on the assumption that wind approaches the hill or escarpmentdirection of maximum slope.

4 Notation:

H : Height of hill or escarpment relative to the upwind terrain, in f

Lh : Distance upwind of crest to where the difference in ground el

height of hill or escarpment, in feet (meters).

K1 : Factor to account for shape of topographic feature and maxim

K2 : Factor to account for reduction in speed-up with distance upw

crest.

K3 : Factor to account for reduction in speed-up with height above

x : Distance (upwind or downwind) from the crest to the building

(meters).

z : Height above local ground level, in feet (meters).

μ : Horizontal attenuation factor.

γ : Height attenuation factor.

B C D

2-dimensional escarpments 0.75 0.85 0.95 2.5 1.5

3-dimensional axisym. Hill 0.95 1.05 1.15 4 1.5

Equations:

Kzt = (1 + K1 K2 K3)2

K1 determined from above table

1.3

γ

1.531.551.45

Hill Shape

2-dimensional ridges

(or valleys with negative

H in K1/(H/Lh)

K1/(H/Lh)

Exposure Upwind

of crest

Parameters for Speed-up Over Hills and Escarpments

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K2 = (1- |x|/(μLh))

K3 = e^(-γz/Lh)

C D

ft (m) Case 1 Case 2 Case 1 & 2 Case 1 & 2

0-15 0-4.6 0.70 0.57 0.85 1.03

20 6.1 0.70 0.62 0.90 1.08

25 7.6 0.70 0.66 0.94 1.12

30 9.1 0.70 0.70 0.98 1.16

40 12.2 0.76 0.76 1.04 1.22

50 15.2 0.81 0.81 1.09 1.27

60 18 0.85 0.85 1.13 1.31

70 21.3 0.89 0.89 1.17 1.34

80 24.4 0.93 0.93 1.21 1.38

90 27.4 0.96 0.96 1.24 1.40

100 30.5 0.99 0.99 1.26 1.43

120 36.6 1.04 1.04 1.31 1.48

140 42.7 1.09 1.09 1.36 1.52

160 48.8 1.13 1.13 1.39 1.55

180 54.9 1.17 1.17 1.43 1.58

200 61 1.20 1.20 1.46 1.61

250 76.2 1.28 1.28 1.53 1.68

300 91.4 1.35 1.35 1.59 1.73

350 106.7 1.41 1.41 1.64 1.78400 121.9 1.47 1.47 1.69 1.82

450 137.2 1.52 1.52 1.73 1.86

500 152.4 1.56 1.56 1.77 1.89

Notes:

1 Case 1: a. All components and caldding

b. Main wind force resisting system in low-rise buldings designed

Case2: a. All wind wind force resting systems in builings except those in

designed using Figure 6-10.

b. All main wind force resisting systems in other strustures.

2 The velocity pressure exposure coefficient Kz may be determined from the following f

For 15 ft. ≤ z ≤ zg For z < 15 ft

Kz = 2.01 (z/zg)^(2/α) Kz = 2.01 (15/zg)^(2/α)

Note: z shall not be taken less than 30 feet for Case 1 in exposure B.

3 α and zg are tabulated in Table 6-2.

4 Linear interpolation for intermediate values of height z is acceptable.

5 Expousre categories are defined in 6.5.6.

Height aboveground level, z

Exposure (Note 1)

B

Table 6-3

Velocity Pressure Exposure Coeffients, Kh and Kz

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Exposure α Zg (ft) a^ b^ ᾱ ƃ c

B 7 1200 0.14286 0.84 0.25 0.45 0.3

C 9.5 900 0.10526316 1 0.1538462 0.65 0.2

D 11.5 700 0.08695652 1.07 0.1111111 0.8 0.15

*zmin = minimum height used to ensure that the equivalent height z ‾ is greater of 0.6h or zmin.

For buildings with h ≤ zmin, z ‾ shall be taken as zmin

Exposure

C

1

1.3

1

1

Round (D √qz > 2.5) 0.5

(D √qz > 5.3, D in m, qz in N/m^2) 0.7

0.8

Round (D √qz ≤ 2.5)

(D √qz ≤ 5.3, D in m, qz in N/m^2)

6.5.3 Exposure Categories

Apply where the ground surface roughness condition, as defined by Surgace Roughne

upwind direction for a distance of at least 2600 ft (792 m) or 20 times the height of t

Apply for all cased where Exposures B or D do not apply

Apply where the ground surface roughness condition, as defined by Surgace Roughneupwind direction for a distance greater than 5000 ft (1524 m) or 20 times the height

greater

Description

B

D

DFlat, unobstructed areas and water surfaces outside hurricane prone regi

smooth mud flats, salt flats , and unbroken ice.

DescriptionSurface Roughness

6.5.6.2 Surface Roughness Categories

COpen terrain with scattered obstructions having heights generally less the

includes flat open country, grasslands, and all water surfaces in hurricane

Table 6-2

Terrain Exposure Constants

Urban and suburban areas, wooded areas, or other terrain with numerou

having the size of single-family dwellings or largerB

Chimneys, Tanks, Rooftop Equipment, & Similar Structures

Force Coefficients, Cf

Figure 6-21

Moderately smooth

Rough (D'/D =0.02)

Very rough (D'/D = 0.08)

ALL

Cross-Section Type of Surface

0.7

Square (wind normal to face)

Square (wind along diagonal)

Hexagonal or octagonal

ALL

ALL

ALL

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Notes:

1 The design wind force shall be calcualted based on the area of the structure projecte

to the wind direction. The force shall be assumed to act paralled to the wind directio

2 Linear interpolation is permitted for h/D values other than shown.

3 Notation:

D diameter of circular cross-section and least horzontal dimension of squar

octagonal cross-sections at elevation under consideration, in feet (metersD' depth of protruding element such as ribs and spoilers, in feet (meters); an

h Height of structure, in feet (meters); and

qz velocity pressure evaluated at height z above ground, in pounds per squa

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k3 Multiplier

2-D

Ridge

2-D

Escarp.

3-D

Asisym.

Hill

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1.00 1.00 1.00

0.74 0.78 0.67

0.55 0.61 0.45

0.41 0.47 0.30

0.30 0.37 0.20

0.22 0.29 0.14

0.17 0.22 0.090.12 0.17 0.06

0.09 0.14 0.04

0.07 0.11 0.03

0.05 0.08 0.02

0.01 0.02 0.00

0.00 0.00 0.00

tted.

ing K2 and K3.

along the

eet (meters).

vation is half the

um speed-up effect.

ind or downwind of

local terrain.

site, in feet

4

1.5

μ

1.5

Downwind

of Crest

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using Figure 6-10.

low-rise buildings

ormula:

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l (ft) ε‾ zmin (ft)*

320 0.333333 30

500 0.2 15

650 0.125 7

7 25

1.4 2

1.1 1.5

1.2 1.4

0.6 0.7

0.8 0.9

1 0.2

ss B, prvails in the

e building, whichever is greater

ss D, prvails in theof the building, whichever is

ns. This category includes

an 30 ft (9.1 m). This category

prone regions.

s closely spaced obstructions

h/D

0.8 1.2

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on a plae normal

.

, hexagonal of

); d

e foot (N/m^2)

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Design Wind Speed V

Structure classification from Table 1-1 Class

Exposure category from Sect. 6.5.6 Exposure

Topographic Factor form Sect. 6.5.7) Kzt

Height of stack/tank h

Height of stack/tank base above ground HbDiameter or Width of surface normal to wind D

Wind directionality factor in Table 6-4 Kd

Damping ration, percent critical for buildings or other structures β

Determination of Gust Effect Factor, G:

Flexible?

Parameters form Table 6-2

Reciprocal of α from Table 6-2 a^

Mean hourly wind speed factor in Eq. 6-14 from Table 6-2 b^

Mean hourly wind speed power law exponent in Eq. 6-14 from Table 6-2 ᾱ

3-second gust speed factor from Table 6-2 ƃ

Turbulence intensity factor in Eq. 6-5 from Table 6-2 c

Integral length scale factor from Table 6-2 l

Integral length scale power law exponent in Eq. 6-7 from Table 6-2 ε‾

Exposure constant from Table 6-2 zmin

Calculated parameters

Equivalent height of the structure z‾

Intensity of turbulence from Eq. 6-5 Iz‾

Integral length scale of turbulence at the equivalent height Lz‾

Background response factor from Eq. 6-6 Q

Peak factor for background response in Eqs. 6-4 and 6-8 gQ

Peak factor for wind respinse in Eqs. 6-4 and 6-8 gv

Guset effect factor G

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90 mph Z (ft) Kz qz (psf)

II 5 0.57 11.32

B 10 0.57 11.32

1 15 0.57 11.32

100 ft 20 0.62 12.29

5 ft 25 0.67 13.103 ft 30 0.70 13.80

0.95 35 0.73 14.42

40 0.76 14.98

45 0.79 15.50

50 0.81 15.97

55 0.83 16.41

60 0.85 16.82

65 0.87 17.21

0.143 75 0.91 17.93

0.840 85 0.94 18.58

0.250 95 0.97 19.18

0.450 105 1.00 19.74

0.300

320.000 ft

0.333

30.000 ft

60 ft

0.27155

390.56718

0.88664

3.4

3.4

0.00098

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I Determine α, zg, I:

II α = 7

III Zg = 1200

IV I = 1

B

C

D

ID 4.974615

t 0.15231 in

OD 5 ft

I 0.618313 ft^4

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Basic wind speed V

Importance factor I

Velocity pressure exposure coefficient evaluated al height z Kz

Topographic factor as defined in Section 6.5.7 Kzt

Wind directionality factor in Table 6-4 Kd

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ASCE 7-02