chapter 7 - wind loads (egyptian load code)

8/18/2019 Chapter 7 - Wind Loads (Egyptian Load Code)

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Chapter 7

The effect of the wind on buildings

and facilities

1.7. The field

This chapter of the Code is specified in indicating the effect of the wind that should be considered when

designing buildings and facilities either as one unit or its components and parts individually.

1.1.7. Buildings and facilities should be designed to stand still against the effect of wind.

2.1.7. Designing a building should consider the effect of wind depending on the following:

1. The building as one unit.

2. Parts of the building as ceiling, walls, etc.

3. Windows, building’s front, etc.

3.1.7.When calculating the effect of wind loads on the walls, partitions and all the building’s parts

affected by pressure or withdrawal on both sides, the designed wind pressure on these parts is

considered the total of pressure or withdrawal on the first side and pressure or withdrawal on the

second side.

4.1.7. When calculating the effect of wind on the normal building and facilities, we use the method

mentioned in (3.7), for building and facilities with certain specialties like:

1. Buildings and facilities with unusual shape or design.

2. Buildings and facilities that might vibrate due to its hanging ceiling etc.

So the following is recommended:

1. Knowing the values of the maximum average of wind speed per hour from the nearest

metrological center to the building for all the available years of data with specifying the height of

calculation of wind speed and the nature of calculation area.2. The main wind pressure is calculated using the available information in the previous period and

analyzing it using the statistical method of maximum values to get the wind speed and the main

wind pressure.

3. Using the previous lab experiments applied on similar buildings, or the experiments done on the

model of the building itself in the wend speed experimental lap under similar natural

circumstances as much as possible to identify the effect of wind pressure on the external and

internal ceiling of the building.


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4. Using the dynamic method in the structural analysis to determine the effect of the wind on the

power and internal torque and change in shape.

5. The effect of the wind shouldn’t be less than the one resulted from using the designed wind load

stated in the Code.

2.7. Definitions

1. Wind Loads

Is the power affected by the wind in a direction perpendicular on the building’s and facilities roofs,

considered positive if it’s in the same direction of the roof (pressure), considered negative if it’s away

from the roof (withdrawal).

2. Pressure or withdrawal of wind

Is the wind loads effect divided by the area unit and its calculated by (kN/m2)

3. Full wind force

Is the total force of wind on a building and calculated by kN.

4. External wind load factor

Is the factor that indicates the wind load distribution on the external roof of the building.

5. Internal wind load factor

Is the factor that indicates the distribution of the wind load on the internal roof of the building.

6. Exposure Factor

Is the factor that indicates the distribution of wind load affected by the height of the building.

3.7. External pressure or withdrawal resulted from the wind effect on the buildings’ roofs as one unit

or its parts is calculated as follow:

(7.1) Pe = C e K q

Where:

Pe : External wind pressure that statistically affect the unit area of the external roof of the building

(kN/m2)

q : Original wind pressure (kN/m2

)

depending on the geographical location for the building and its valueis taken according to how its stated in ( 4.7)

k : Exposure factor and it varies with the height of the building from the surface of earth, and its value is

taken according to how its stated in (3.5.7)

C e : External wind pressure affecting the roofs of the buildings and depending on the geometrical shape

of the building using the following equation:


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(7.2) Pi = C e k q

Pi = Internal wind pressure statistically affecting the unit of area of the internal roof of the building and

in the direction of the roof if Pi as in the following shape using the unit (kN/m2) : ( Diagram 7.1 )

Vertical Sector

Horizontal Sector

Diagram 7.1 shapes that clarifies the distribution of the internal wind pressure C i in the case of

withdrawal and pressure.

k : Exposure factor and its value is constant with the full height of the building and its calculated

according to how its mentioned in (5.5.7)

C i : The factor of wind pressure on the internal building’s roof and it depends on the presence of

openings in the fronts of the building.


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q: Main wind pressure (kN/m2) and it depends on the geographical area of the building and its value is

considered according to how its mentioned in (4.7) of this chapter and its from the same q used in the

equation (1.7).

3.3.7. In some buildings and facilities that require calculation of wind pressure distribution over itsroofs specially those where the ratio of its height according to the rest of its dimension is high, its

preferred to calculate the total force of the wind over the building as a whole instead of calculating its

distribution over its area only, and the whole wind force is calculated using the following equation:

(7.3) F = C f k q A

Where:

F: The total force of wind over the building (kN/m2)

K: The exposure factor and its calculated according to (3.5.7)

q: Main wind pressure (kN/m2)

C f : Total force of wind factor

A : The area of the building front face of building facing the wind (m2)

4.7. Main wind force q

1.4.7. The wind force is calculated in this code using q (kN/m2) using the following equation:

(7.4) q = 0.5 x 10-3 ρ V² C t C s

Where:

V: The speed of the main wind (m/s) facing a storm of wind for a duration of 3 seconds at the heightof 10 meters away from the ground according table (1.7) with a probability of exceeding the

designed force not more that 2% in 50 years.

Ρ : Air density taken as 1.25 (Kgm/ m2)

C t : The factor of the topography of the land and it depends on the surface of the land’s topography

surrounding the building, table (2.7)


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C s : The factor of the origin and its calculated according to (a.7), and it’s the factor that consider the

effect of wind loads during the non-consequent occasion of the peak of wind’s pressure over the

building, where building is affected during the turbulence.

2.4.7. The value of V is taken from table (1.7) and this is according to the location of the building. Andfor the locations not mentioned in the table the speed of the main wind is taken to its nearest

location in the table.

(Table 1.7) The speed of the main wind V

LocationSpeed of the

main wind (m/s)

Marsa Matrouh / El Dabaa / El Zaafrana 42

El Saloum / Ras Sedr / EL Ain El Sokhna 39

Aswan / Asyout / Hurghada / Abo Souair / Alexandira / and coast locations 36

Cairo / El Dakhla / Siwa / Luxor 33

EL Minia / Fayoum / Tanta / Tahrir / Directorate of Tahrir / Damnhour / El

Mansoura

30

(Table 7.2) Topographic earth factor’s value (C t )

Land surface surrounding the buildingC tFactor

The land surrounding the building is flat, its inclination doesn’t exceed 5%, and to an area

half its diameter is 1 Km as a minimum1.0

The land surrounding the building is not generally flat:

Land inclination:

5% - 10%

10% - 15%

15% - 20%

More than 20%

1.20

1.40

1.60

1.80

Mountain, hills and similar surfaces 1.00

Mountains surfaces, top of shelves and the meeting points of inclining surfaces 1.80

5.7. Exposure factor k

1.5.7. Exposure factor is the factor that indicates the change in the wind pressure with the height and

it’s a factor that increases gradually with the increase of the height away for the land surface


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2.5.7. The location that are used in calculation the exposure factor k are divided into 3 locations

according to the length and the roughness of the land (Z0) (Ground roughness length)

* Exposure location (a): it includes the open exposure locations and locations with few barriers.

* Exposure location (b): it includes the locations with suburban barriers such as villages, suburbs and

small cities.

* Exposure location (c): includes city center exposure locations with huge and similar barriers.

3.5.7. The exposure factor k is calculated from Table (3.7)

(Table 3.7) Exposure factor (k ) Value

Exposure Area (a) (b) (c)

Ground’s length and

roughness (Z0) 0.05 0.3 1.00

Height z in meter Exposure Factor k

0 – 10 m 1.0 1.00 1.00

10 – 20 m 1.15 1.00 1.00

20 – 30 m 1.40 1.00 1.00

30 – 50 m 1.60 1.05 1.00

50 – 80 m 1.85 1.30 1.00

80 – 120 m 2.1 1.50 1.15

120 – 160 m 2.30 1.70 1.35

160 – 240 m 2.50 1.85 1.55

4.5.7. When calculating the external wind pressure, the height z is used in calculating the factor k , and

its height from the ground required for calculating the external wind pressure.

5.5.7. When calculating the internal wind pressure at any place inside the building, the height z that’s

used in calculating the factor k is as follow:

a. For the buildings with separated floors, the height requested for calculating the internal wind

pressure at, should be calculated from the surface of earth to the average ratio of each floor.

b. For other buildings the height requested for calculating internal wind pressure it should be calculated

from the land service till the average ratio for the openings of the external openings of the building.

(7-5) z =∑ .

∑

Where:


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the height of the opening (J) the area of the opening (J)

6.5.7. When calculating the full power of wind F , the height z that’s used in calculating the factor k is

the place at the height required for calculating the full wind power at this place away from the land

surface.

6.7. Wind Pressure Distribution

1.6.7. General

1.1.6.7. The external wind pressure is the factor that indicates the distribution of pressure orwithdrawal of wind on the external surfaces of the building and it’s the factor that’s used in

calculating the wind pressure on unit area according to (1-7)

2.1.6.7. The external wind pressure should be indicated during calculating the effect of wind on thestructure of the building as one unit or its parts, also during calculating the effect of wind on windows

and fronts, etc…

3.1.6.7. The values of wind pressure factor depends on the geometrical structure of the building and

its dimensions.

4.1.6.7. The internal wind pressure factor is the factor that is used in indicating the wind pressuredistribution on the internal ceiling of the building and it’s the factor that should be indicated to

calculate its effect on the buildings’ internal and external walls, resurfacing and windows, but we

can’t calculate the effect of wind on the building as a whole unit (Diagram 1.7).

2.6.7. Rectangular Buildings

The values from the (Diagram 2.7a) for the rectangular buildings and is taken from the Table 4.7.and Diagram 2.7a.


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Vertical Sector

Horizontal Sector

Diagram (2.7a) The factor of external wind pressure distribution of buildings with rectangular front


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Diagram (2.7b) the factor of internal wind pressure distribution of buildings with rectangular front Table (4.7)

the factor of internal wind pressure of the buildings with rectangular fronts.

The places of openings* 1. Most of the openings front meeting the wind2. Most of the openings are in the back

3. Most of the openings are in the fronts parallel to the wind direction

4. Openings distributed on the 4 views

5. Most of the openings are in the front meeting the wind direction and the back view

+ 0.7

- 0.5

- 0.7

± 0.3

- 0.2

*The openings include doors and windows

3.6.7. Buildings with rectangular fronts and inclining ceilings

The value of of the buildings’ ceilings with rectangular fronts and inclining ceilings from the(Diagrams: 3.7, 4.7, 5.7) but for the value of inside the building it’s taken from the Table (4.7).

4.6.7. Ceiling of one floor buildings with several inclinations


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The value of is taken from the (Diagram 6.7) but for value of from inside the building is taken fromthe (Table 5.7).

Table (5.7) internal wind pressure for buildings with several inclinations

Places of Openings* 1. Most of the openings are facing the wind direction

2. Most of the openings are on the back side

3. Most of the openings are in the fronts parallel to the wind direction

4. Openings distributed on the 4 views

+ 0.8

– 0.3

– 0.3

± 0.3

*Openings include windows and doors.

Vertical Sector

(a) External wind pressure factor distribution on walls and ceilings.


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(b) The value of External wind pressure factor on ceilings facing windDiagram (3.7) the distribution of external wind pressure factor on buildings both sides inclination

Vertical Sector

Diagram (4.7) the distribution of external wind pressure factor on buildings with upside inclinationceilings


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Vertical Sector

Diagram (5.7) the distribution of external wind pressure factor

on buildings with downside inclination

ceilings

(a) Two sided inclined ceilings


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(b) Upside inclination ceilings

(b) Downside inclination ceilings

** Diagram (6.7) the distribution of external wind pressure factor on buildings with several inclination5.6.7. Walls and plates for commercials

In cases of walls and plates for commercials, etc.. the total wind force is calculated from the equation

(3.7) and the value of total wind force is taken from (Diagram 7.7) and this force is taken inconsideration during the designing the building.


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(a) Total wind force factor on walls and plates for commercials based on the ground

(b) Total wind force factor on walls and plates for commercials based away from the groundDiagram (7.7) Total wind force factor on walls and plates for commercials6.6.7. Chimneys, minarets, Lighthouses, and circular buildings

The factor of total wind force is calculated for chimneys, minarets, lighthouses and circular buildingsfrom Table (6.7), and the value of external wind pressure factor is taken from the Table (7.7) and theDiagram (8.7).

Table (6.7) total wind force effect on chimneys, minarets, lighthouses, circular buildings and similarbuildings


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Horizontal View

h/d

1 7 25

Square Shape (wind is perpendicular on the side)

Square Shape ( wind in the same direction of tendon)

Hexagon or Octagon Shape

Circular shape:

. Smooth surface without protrusions (d’/d = 0.0)

. Surface with percentage of protrusions (d’/d = 0.02)

. Surface with protrusions (d’/d = 0.08)

1.30

1

1

0.5

0.7

0.8

1.4

1.1

1.2

0.6

0.8

1.0

2.0

1.5

1.4

0.7

0.9

1.2

Where:

d' : depth of protrusion

d : dimension or diameter of the horizontal sector

h : height

Table (7.7) External wind pressure effect on chimneys, minarets, lighthouses, circular buildings andsimilar buildings

External wind Pressure Factor Φ h/d = 1 h/d = 7 h/d = 25

+ 1.0 + 1.0 + 1.0 0

+ 0.8 + 0.8 + 0.8 15° + 0.1 + 0.1 + 0.1 30° - 0.7 - 0.8 - 0.9 45° - 1.2 - 1.7 - 1.9 60° - 1.6 - 2.2 - 2.5 75° - 1.7 - 2.2 - 2.6 90° - 1.2 - 1.7 - 1.9 105° - 0.7 - 0.8 - 0.9 120° - 0.5 - 0.6 - 0.7 135° - 0.4 - 0.5 - 0.6 150° - 0.4 - 0.5 - 0.6 165° - 0.4 - 0.5 - 0.6 180°

The values in Table (7.7) is used as follow:

1. Semi-smooth external surface such as normal concrete surface or regular buildings


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2. The value <

Where

d : diameter in meter

q : main wind pressure kn/

Internal wind Pressure factor:

a. Chimneys: chimney works with its full power = 0.1 b. Closed Chimney = 0.8 c. Minarets = ± 0.3

Diagram (8.7) external wind pressure factor distribution on Chimneys, minarets, Lighthouses, andcircular buildings

7.6.7.

Surfaces with nodes

External wind pressure factor on surfaces with nodes are calculated based on Table (8.7) or theDiagram (a.9.7)

Table (8.7) External wind pressure factor on surfaces with nodes


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State Height away from

sea-level

(a) Front

quarter (

facing

wind)

(b) Middle (c) Back

quarter

Surface above the

building

0.1

0.2

0.3

0.4

0.5

0.6

- 0.9

( - 0.9 , Zero )

( - 0.3 , 0.15 )

0.40

0.675

0.95

- 0.8

- 0.9

- 1.0

- 1.1

- 1.2

- 1.3

- 0.5

- 0.5

- 0.5

- 0.5

- 0.5

- 0.5

Surface on the

floor

0.1

0.2

0.3

0.4

0.5

0.6

0.15

0.30

0.45

0.60

0.75

0.9

- 0.8

- 0.9

- 1.0

- 1.10

- 1.20

- 1.30

- 0.5

- 0.5

- 0.5

- 0.5

- 0.5

- 0.5

8.6.7. Domes Surfaces

External wind pressure is calculated at the domes’ surfaces using Table (8.7) and the diagram (b.9.7)as follow:

The upper half of the dome’s surface and the side quarters with the lower half of the dome symmetry

the wind pressure by half (b)

The front quarters facing the wind direction and also the back with the lower half of the dome

symmetry the front quarter (a) and the back quarter (c) consequently

(a) Surfaces with nodes


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(b) Ceilings with domes

Diagram (9.7) distribution of external wind pressure on ceilings with nodes and domes.

9.6.7. Umbrellas surfaces

The value of the wind power on the umbrellas surfaces is taken from Table (9.7)The full wind power in the direction of withdrawal or pressure perpendicular to the surface and the

center of its effect is clarified in the Diagram (10.7)

Table (9.7) total wind power on the umbrellas surfacesHorizontal surface inclination (

Degrees )

a/dzero – 10

20

30

± 0.90

± 1.10

± 1.30

0.35

0.45

0.50


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(a) Umbrella shaped ceilings with one side inclination

(b) Umbrella shaped ceilings with two sides’ inclination

Wind powers are taken either taken together or each individually in the direction most affecting the

building

Diagram (10.7) clarifies the effect center of total wind power on the umbrella shaped ceilings

10.6.7. Gamalon Towers

1.10.6.7. The whole wind power and its effect on towers are calculated from Table (10.7) byconsidering the used area for calculating the whole wind power is the area of the constructed

buildings facing wind.

Table (10.7) wind power and its effect on towersShape of the

tower from a

Horizontal view

Square Triangle

The shape/∗ Corners or organswith flat sides

CircularCorners or organs

with flat sidesCircular


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Zero

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

4.00

3.50

3.00

2.60

2.30

2.05

1.90

1.85

1.85

1.90

2.40

2.20

1.85

1.65

1.5

1.45

1.45

1.50

1.60

1.80

3.60

3.20

2.70

2.35

2.05

1.90

1.80

1.80

1.80

1.90

2.00

1.80

1.60

1.45

1.35

1.35

1.40

1.45

1.60

1.80

1.00 2.00 2.00 2.00 2.00

* Where e is the ratio between the areas of constructing organs facing the tower to the total area facing

the tower.

2.10.6.7. If in a horizontal view the shape of the tower is triangular the designed wind power is taken

perpendicular to the area exposed to wind from the front view of the tower.

3.10.6.7. If in a horizontal view the shape of the tower is square, designed wind power is taken in two

cases:

a. perpendicular to the front of the building

b. in the diametrical direction multiplied by wind power in (0.75e + 1) where its value shouldn’texceed 1.20

11.6.7. Gamalon Framing

Full wind power

on frames is calculated from Table (11.7)

Table (11.7) wind power on frames

Shape / e Organs with flat sides

Circular16 <

16 ≥

Zero 2.00 1.20 0.80

0.10 1.90 1.20 0.80

0.20 1.80 1.20 0.90

0.30 1.70 1.20 1.10

0.40 1.70 1.50 1.10

0.50 1.60 1.50 1.10

0.70 1.60 1.50 1.40

1.00 2.00 2.00 2.00

Where:

e : the ratio of area of structural organs falling in the fame perpendicular to the wind direction to the

whole area


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d : diameter in meter

q: wind pressure at the requested height kn/

Annex (7.A)

Structural Factor A1. Structural factor is the factor that takes in consideration the effect of wind during a non-consequent

wind pressure peak on the building with the effect of buildings vibration during turbulence.

A2. The value of structural factor is considered 1.00 in the following cases:

1. Building and facilities with height less than 60 meters

2. Net shape towers (Gamalon towers)

3. Buildings and facilities their heights are lowered four times with less after its horizontal fall.

A3. For cases not mentioned in (4.1.7) and in (A2) and in structural factor for general facilities shapesillustrated in the diagram (a.7) its calculated according to the following equation:

(A-1) = +√++ ≥ 1

Where:

g is the peak factor indicated the ratio between the maximum value for the variable part of the time

registry to the measurement of inclination and its value is indicated according to (a.4)

Turbulence intensity at height zr and its value is indicated according to (a.5) Background factor that takes in consideration the lack of total engagement between buildingsurfaces and its value is indicated according to (6.a)

Resonance response factor takes in consideration the turbulence effect on the vibration during

resonance and its value is indicated according to (7.a)

4.a the peak factor g is calculated according to the following equation:

(A-2) = 2In(TƲ) . ()

(A.2a) = n +


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Where:

T : time length with value 3600 Seconds

ν : Up-Crossing Frequency ( hertz)

In : Main natural logarithm ( e = 2.718 )

n : Natural frequency origin (hertz) and its calculated with dynamical origin analysis, and its value canbe estimated in the primary calculation of normal buildings using:

(A.2b) = h

h: Building’s height (meter)

5.a Turbulence intensity is calculated at the height using:

(A.3) = ()

Where:

: height and roughness of land (meter) taken from Table (3.7)

zr: height away from land surface ( meter ), diagram (a.7)

6.a Background factor is calculated using:

(A.4) B = +. ()

(A-4a)

() = ( )

= 0.67 0.05 In()

Where:

() Turbulence length scale (meter)


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Length scale reference its value is 300 meter Height scale its value is 300 meterb building width (meter)

h building height (meter)

7.a Resonance response factor is calculated using:

(A.5) = SL(,n)ℎ (A.5a) SL(,n) = . (zr,)[+. (zr,)]. (A.5b) f L(,n) = .()

(A.5c) () = 0.67 . √ Where:

SL(,n) Non dimensional power spectral density functionf L(,n) Spectrum variance() the average wind speed per hour at height () Evanescence factor, can be indicated according to the type of origin; iron origin 0.01, combined origin0.015, concrete origin 0.02

V main wind speed according to Table (1.7)

k exposure factor according to Table (3.7)

ℎ Aerodynamic admittance factor, indicated according to :(A.5d) = ( 1 −) And the value of L in the previous equation is taken like h or b consequently:

(A.5e

= .ℎ(,)

()) for

= ℎ

(A.5f) = .(,)() for =


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Diagram (a.7) general shapes of buildings that includes certain cases in calculating the origin factor

chapter 7 - wind loads (egyptian load code)

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