Chapter 7 The effect of the wind on o n buildings and facilities
1.7. The field This chapter of the Code is spec ified 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 sti ll 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 et c.
So the following is recommended: 1. Knowing the values of the maximum average of wind speed per hour from the neare st 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 e xperimental lap under similar natural circumstances as much as possible to identify the e ffect of wind pressure on the ext ernal and internal ceiling of the building.
4. Using the dynamic method in the structural analysis to determine the effect of the wind on the t he power and internal torque and change in shape. 5. The effect of the wind shouldn’t shouldn’t be less than t he one resulted from using the designed wind load stated in the Code.
2.7. Definitions 1. Wind Loads Is the power affecte d by the wind in a direction perpendicular on the building’s and facilities roofs, considered positive if it’s in the same direct ion of the roof (pressure), considered negative if it’s aw ay 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/m 2) 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 t he 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 ar ea of the external roof of the building (kN/m2) q : Original wind pressure (kN/m 2) depending on the geographical location for the building and its value is 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:
(7.2) Pi = C e k q
Pi = Internal wind pressure statistically affecting the unit of area of the internal roo f of the building and in the direction of the roof if Pi as in the following shape using the unit (kN/m 2) : ( Diagram 7.1 )
Vertical Sector
Horizontal Sector
Diagram 7.1 shapes that clarifies the distribution of the internal wind pre ssure 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.
q: Main wind pressure (kN/m2) and it depends on the geographical area o f 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 its roofs 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 t he 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 o f 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 height of 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)
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 t o the location of the building. And for 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
Location Marsa Matrouh / El Dabaa / El Zaafrana El Saloum / Ras Sedr / EL Ain El Sokhna Aswan / Asyout / Hurghada / Abo Souair / Alexandira / and coast locations Cairo / El Dakhla / Siwa / Luxor EL Minia / Fayoum / Tanta / Tahrir / Directorate of Tahrir / Damnhour / El Mansoura
Speed of the main wind (m/s) 42 39 36 33 30
(Table 7.2) Topographic earth factor’s value (C t) Land surface surrounding the building 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 minimum The land surrounding the building is not generally flat: Land inclination: 5% - 10% 10% - 15% 15% - 20% More than 20% Mountain, hills and similar surfaces Mountains surfaces, top of shelves and the meeting points of inclining surfaces
C t Factor 1.0
1.20 1.40 1.60 1.80 1.00 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
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 Ground’s length and
(a)
(b)
(c)
0.05
0.3
1.00
Height z in meter 0 – 10 m 10 – 20 m
1.0 1.15
Exposure Factor k 1.00 1.00
1.00 1.00
20 – 30 m 30 – 50 m 50 – 80 m 80 – 120 m 120 – 160 m 160 – 240 m
1.40 1.60 1.85 2.1 2.30 2.50
1.00 1.05 1.30 1.50 1.70 1.85
1.00 1.00 1.00 1.15 1.35 1.55
roughness (Z0)
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 he ight 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 re quested for calculating internal wind pressure it should be c alculated from the land service till the average ratio for the openings of the external openings of the building. (7-5) z =
Where:
∑. ∑
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 or withdrawal 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 t he effect of wind on the structure of the building as one unit or its parts, also during calculating the effect of wi nd 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 pressure distribution on the internal ceiling of the building and it’s the factor that should be indicated t o 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 and Diagram 2.7a.
is taken from the Table 4.7.
Vertical Sector
Horizontal Sector Diagram (2.7a) The factor of exter nal wind pressure distribution of buildings with rectangular front
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 t he wind 2. Most of the openings are in t he 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 t he front meeting the wind direction and t he 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
The value of is taken from the (Diagram 6.7) but for value of the (Table 5.7).
Table (5.7) internal wind pressure
1. 2. 3. 4.
from inside the building is taken from
for buildings with several inclinations
Places of Openings* Most of the openings are facing the wind direction Most of the openings are on the back side Most of the openings are in the fronts parallel to the wind direction Openings distributed on the 4 views
*Openings include windows and doors.
Vertical Sector (a) External wind pressure factor
distribution on walls and ceilings.
+ 0.8 – 0.3 – 0.3 ± 0.3
(b) The value of External wind pressure factor
on ceilings facing wind
Diagram (3.7) the distribution of external wind pressure factor
on buildings both sides inclination
on buildings with upside inclination
Vertical Sector Diagram (4.7) the distribution of external wind pressure factor ceilings
Vertical Sector Diagram (5.7) the distribution of external wind pressure factor ceilings
on buildings with downside inclination
(a) Two sided inclined ceilings
(b) Upside inclination ceilings
(b) Downside inclination ceilings ** Diagram (6.7) the distribution of external wind pressure factor
on buildings with several inclination
5.6.7. 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 t his force is taken in
consideration during the designing the building.
(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 ground
Diagram (7.7) Total wind force factor
on walls and plates for commercials
6.6.7. Chimneys, minarets, Lighthouses, and circular buildings The factor of total wind force
is calculated for chimneys, minarets, lighthouses and circular buildings
from Table (6.7), and the value of exter nal wind pressure factor Diagram (8.7).
Table (6.7) total wind force buildings
is taken from the Table (7.7) and the
effect on chimneys, minarets, lighthouses, circular buildings and similar
1 1.30
h/d 7 1.4
25 2.0
Square Shape ( wind in the same direction of tendon)
1
1.1
1.5
Hexagon or Octagon Shape
1
1.2
1.4
0.5 0.7 0.8
0.6 0.8 1.0
0.7 0.9 1.2
Horizontal View Square Shape (wind is perpendicular on the side)
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)
Where: d' : depth of protrusion d : dimension or diameter of the horizontal sector h : height
Table (7.7) External wind pressure similar buildings
h/d = 1 + 1.0 + 0.8 + 0.1 - 0.7 - 1.2 - 1.6 - 1.7 - 1.2 - 0.7 - 0.5 - 0.4 - 0.4 - 0.4
effect on chimneys, minarets, lighthouses, circular buildings and
External wind Pressure Factor h/d = 7 + 1.0 + 0.8 + 0.1 - 0.8 - 1.7 - 2.2 - 2.2 - 1.7 - 0.8 - 0.6 - 0.5 - 0.5 - 0.5
h/d = 25 + 1.0 + 0.8 + 0.1 - 0.9 - 1.9 - 2.5 - 2.6 - 1.9 - 0.9 - 0.7 - 0.6 - 0.6 - 0.6
The values in Table (7.7) is used as follow: 1. Semi-smooth external surface such as normal co ncrete surface or regular buildings
Φ 0
1530°° 4560°° 75°° 90 105°° 120° 135 150°° 165° 180
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
= 0.8 = ± 0.3
= 0.1
b. Closed Chimney c. Minarets
Diagram (8.7) external wind pressure factor distribution circular buildings
on Chimneys, minarets, Lighthouses, and
7.6.7. Surfaces with nodes External wind pressure factor Diagram (a.9.7)
on surfaces with nodes are calculated based on Table (8.7) or the
Table (8.7) External wind pressure factor
on surfaces with nodes
State
Height away from sea-level
Surface above the building
0.1 0.2 0.3 0.4 0.5 0.6
(a) Front quarter ( facing wind) - 0.9 ( - 0.9 , Zero ) ( - 0.3 , 0.15 ) 0.40 0.675 0.95
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
(b) Middle
(c) Back quarter
- 0.8 - 0.9 - 1.0 - 1.1 - 1.2 - 1.3
- 0.5 - 0.5 - 0.5 - 0.5 - 0.5 - 0.5
- 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 as follow:
is calculated at the domes’ surfaces using Table (8.7) and the diagram (b.9.7)
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 t he dome symmetry the front quarter (a) and t he back quarter (c) consequently
(a) Surfaces with nodes
(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 take n 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 surfaces
Horizontal surface inclination ( Degrees ) zero – 10 20 30
± 0.90 ± 1.10 ± 1.30
a/d 0.35 0.45 0.50
(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) by
considering the used area for calculating the whole wind power is the area of the constructed buildings facing wind.
Table (10.7) wind power Shape of the tower from a Horizontal view
∗
The shape/
and its effect on towers
Square Corners or organs with flat sides
Triangle Circular
Corners or organs with flat sides
Circular
Zero 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00
4.00 3.50 3.00 2.60 2.30 2.05 1.90 1.85 1.85 1.90 2.00
2.40 2.20 1.85 1.65 1.5 1.45 1.45 1.50 1.60 1.80 2.00
3.60 3.20 2.70 2.35 2.05 1.90 1.80 1.80 1.80 1.90 2.00
2.00 1.80 1.60 1.45 1.35 1.35 1.40 1.45 1.60 1.80 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 exceed 1.20
in (0.75e + 1) where its value shouldn’t
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
Zero 0.10 0.20 0.30 0.40 0.50 0.70 1.00
2.00 1.90 1.80 1.70 1.70 1.60 1.60 2.00
1 < 6 1.20 1.20 1.20 1.20 1.50 1.50 1.50 2.00
Circular
1 ≥ 6 0.80 0.80 0.90 1.10 1.10 1.10 1.40 2.00
Where: e : the ratio of area of structural organs falling in the fame perpendicular to the wind direction to the whole area
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 e ffect 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 w ith less after its horizontal fall.
A3. For cases not mentioned in (4.1.7) and in (A2) and in structural factor for general facilities shapes illustrated 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 building surfaces 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) () = n +
(A.2a)
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 can be estimated in the primary calculation of normal buildings using:
(A.2b)
= h
h: Building’s height (meter) 5.a Turbulence intensity
(A.3)
is calculated at the height
using:
= ()
Where:
: height and roughness of land (meter) t aken from Table (3.7)
zr: height away from land surface ( meter ), diagram (a.7) 6.a Background factor
(A.4)
is calculated using:
B = +. ()
() = ( ) = 0.670.05In() (A-4a)
Where:
()
Turbulence length scale (meter)
Length scale reference its value is 300 meter
Height scale its value is 300 meter
b building width (meter) h building height (meter) 7.a Resonance response factor
(A.5)
is calculated using:
= SL(,n)ℎ . (zr,) . SL(,n) = [+. (zr,)] f L(,n) = .() () = 0.67 .√
(A.5a)
(A.5b) (A.5c)
Where:
SL(,n) f L(,n) ()
Non dimensional power spectral density function
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 origin 0.015, 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()(,) = ℎ = .()(,) =
(A.5f)
) for for
Diagram (a.7) general shapes of buildings that includes certain cases in calculating the origin factor
