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Wind load - Multispan roofs
EuroCode - EN 1991 - Wind
Author: Design Forms s.r.o.
Created: 2/14/2017
Last updated: 2/22/2017
Price: 0.00 €
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Wind load - multispan roofs
Annotation:

Dialogue


National annex selector




Combobox "National Annex" is used for selecting proper annex for calculation of the wind load.

Wind load requires selection the national annex, because in Standard EN is many national decisions possible.

For explanation of the National annex parameters related to wind load select national annex from the list below.

BS National Annex


ČSN National Annex


DIN National Annex


ELOT National Annex


IS National Annex


LU National Annex


NBN National Annex


NEN National Annex


NF National Annex


ÖNORM National Annex


PN National Annex


SFS National Annex


SIST National Annex


SR National Annex


STN National Annex


General properties




General properties are similar to all wind load forms.

Checkbox "Print headline" represent official name for calculation. User can change it by uncheck "Print headline" and check "Print user defined headline" and write his own headline into appropriate string line.

Wind parameters


This group of parameters depend on selected national annex.

BS National Annex




Wind azimuth in degrees is used in calculation of directional factor cdir. Wind azimuth is from 0 ° to 360 ° from North in a clockwise direction.

Fundamental value of the basic wind velocity from the map vb,map in metres per second. Map can be found in National annex page, Figure NA.1

Turbulence intensity from the diagram Iv(z)map. Diagram can be found in National annex page, Figure NA.5

Turbulence intensity factor from the diagram kI,T. Diagram can be found in National annex page, Figure NA.6

CSN National Annex




Wind region is from I to V according map of the wind regions. Map can be found in National annex page.

DIN National Annex




Wind region is from WZ1 to WZ4 according map of the wind regions. Map can be found in National annex page.

ELOT National Annex


No special wind parameters are necessary for ELOT National annex.

IS National Annex




Wind azimuth in degrees is used in calculation of directional factor cdir. Wind azimuth is from 0 ° to 360 ° from North in a clockwise direction.

Fundamental value of the basic wind velocity from the map vb,map in metres per second. Map can be found in National annex page, Figure NA.1

Turbulence intensity from the diagram Iv(z)map. Diagram can be found in National annex page, Figure NA.5

Turbulence intensity factor from the diagram kI,T. Diagram can be found in National annex page, Figure NA.6

LU National Annex


No special wind parameters are necessary for LU National annex.

NBN National Annex




Wind region is from 1 to 4 according map of the wind regions. Map can be found in National annex page.

Wind azimuth in degrees is used in calculation of directional factor cdir. Wind azimuth is from 0 ° to 360 ° from North in a clockwise direction.

NEN National Annex




Wind region is from I to III according map of the wind regions. Map can be found in National annex page.

NF National Annex




Wind region is from 1 to 4 according map of the wind regions. Map can be found in National annex page.

Direction zone is from 1 to 3 according map of the wind directions. Map can be found in National annex page.

Wind azimuth in degrees is used in calculation of directional factor cdir. Wind azimuth is from 0 ° to 360 ° from North in a clockwise direction.

ONORM National Annex




According selected state in Austria can be selected the municipality which is the nearest to the construction site. Table of all possible municipalities can be found in National annex page.

PN National Annex




Wind region is from 1 to 3 according map of the wind regions. Map can be found in National annex page.

Wind azimuth in degrees is used in calculation of directional factor cdir. Wind azimuth is from 0 ° to 360 ° from North in a clockwise direction.

SFS National Annex




Wind regions in SFS are defined as:

a) Mainland in the entire country

b) Sea areas: open sea, scattered islands out in the open sea

c) In Lappland: at the top of mountains

d) In Lappland: at the bottom of mountains

SIST National Annex




Wind region is from 1 to 3 according map of the wind regions. Map can be found in National annex page.

SR National Annex




Fundamental value of the basic wind velocity from the map in metres per second. Map can be found in National annex page.

STN National Annex




Wind region is from I to II according map of the wind regions. Map can be found in National annex page. For higher altitude, two more regions are available.

Terrain parameters


Standard values exist. Different parameters can be defined in National annex.

Standard values




Terrain category is standardly from 0 to IV. Different terrain categories can be defined in National annex page.

Checkbox "Calculate orographic factor" allows calculation of orographic factor. In National annex can be specified procedure to calculate orographic factor. Standard procedure is in Annex A.3.

BS and IS National Annexes








Three terrain categories are available in BS. Sea, Country and town. More information about BS terrain categories can be found in National annex page.

Roughness factor cr,diag is determined from the diagram Figure NA.3 Diagram can be found in National annex page.

Roughness correction factor cr,T is determined from the diagram Figure NA.4 Diagram can be found in National annex page.

Exposure factor ce,diag is determined from the diagram Figure NA.7 Diagram can be found in National annex page.

Exposure correction factor ce,T is determined from the diagram Figure NA.8 Diagram can be found in National annex page.

Distance upwind to shoreline in km is used in the diagrams mentioned above.

Distance inside town terrain in km is used in the diagrams mentioned above.

Checkbox "Calculate orographic factor" is used, if orographic factor should be calculated according Annex A.3

Orographic factor - Recommended Annex A.3 input




Orographic terrain can be Cliffs and escarpments or Hills and ridges.

Horizontal distance of the site from the top of the crest in metres. Use positive value for downwind slope and negative value for upwind slope.

Effective height of the hill in metres.

Actual length of the upwind slope in the wind direction in metres.

Actual length of the downwind slope in the wind direction in metres.

Construction parameters




Construction parameters depend on selected National annex.

Reference height above terrain in metres is the most important parameter. It define in which height is calculated wind pressure. If is necessary to calculate wind pressure in more heights, repeat calculation with propper height z.

Checkbox "Temporary structure or execution phase" is used, if season construction is designed and season factor is necessary.

Checkbox "Use accurate information about the obstructions height" is used, if average height of neighbouring structures is know in Terrain category IV.

Calculation


Basic values


Basic wind velocity is calculated as vb = cdir • cseason • vb,0 in metres per second.

Fundamental value of the basic wind velocity vb,0 is defined in selected National annex in metres per second. 

Directional factor cdir = 1.0 in standard. Different value can be defined in National annex page.

Season factor cseason = 1,0 in standard. A different value can be defined in National annex page.

Reference height above terrain in metres is the height in which is peak velocity pressure calculated. It is one of the most important values in the calculation.

Mean wind velocity


For DIN and ONORM are this and follows paragraphs unavailable. Instead of it, there is block "Wind parameters" where is calculation of wind parameters according National annex.

Mean wind velocity in metres per second is calculated as vm = cr • cO • vb

Terrain roughness factor cr depends on height above ground level and selected terrain category.

 for zmin ≤ z ≤ zmax

 for z ≤ zmin

where:

z0 is the roughness length

kr is terrain factor



where:

z0,II = 0,05 (terrain category II, Table 4.1)

zmin is the minimum height defined in Table 4.1

zmax is to be taken as 200 m



Table 4.1 - Terrain categories and terrain parameters




































Terrain category z0

[m]		 zmin

[m]
0   Sea or coastal area exposed to the open sea 0,003 1
I   Lakes or flat and horizontal area with negligible vegetation and without obstacles 0,01 1
II   Area with low vegetation such as grass and isolated obstacles (trees, buildings) with separations of at least 20 obstacle heights 0,05 2
III   Area with regular cover of vegetation or buildings or with isolated obstacles with separations of maximum 20 obstacle heights (such as villages, suburban terrain, permanent forest) 0,3 5
IV   Area in which at least 15 % of the surface is covered with buildings and their average height exceeds 15 m 1,0 10



Orography factor cO = 1 in normal cases.

Where orography increases wind velocities by more than 5 % the effects should be taken into account using the orography factor. Recommended procedure is given in Annex A.3. Different procedure can be specified in National annex.

Orographic factor - Recommended procedure according to Annex A.3


1) Calculation of the upstream slope



2) Decision if the calculation of orography factor is necessary

The effects of orography should be taken into account in the following situations:

a) For sites on upwind slopes of hills and ridges:

- where 0,05 < Φ ≤ 0,3 and |x| ≤ Lu / 2

b) For sites on downwind slopes of hills and ridges:

- where Φ < 0,3 and x < Ld / 2

- where Φ ≥ 0,3 and x < 1,6 • H

c) For sites on upwind slopes of cliffs and escarpments:

- where 0,05 < Φ ≤ 0,3 and |x| ≤ Lu / 2

d) For sites on downwind slopes of cliffs and escarpments:

- where Φ < 0,3 and x < 1,5 • Le

- where Φ ≥ 0,3 and x < 5 • H



3) Orography factor is than defined by:






















Orographic factor Limits
cO = 1 Φ < 0,05
cO = 1 + 2 • s • Φ 0,05 < Φ < 0,3
cO = 1 + 0,6 • s Φ > 0,3

where:

s is the orographic location factor

Φ is the upwind slope H/Lu in the wind direction

Le is the effective length of the upwind slope

Lu is the actual length of the upwind slope in the wind direction

Ld is the actual length of the downwind slope in the wind direction

H is the effective height of the feature

x is the horizontal distance of the site from the top of the crest

z is the vertical distance from the ground level of the site



Values of the effective length Le

















Type of slope (Φ = H/Lu)
Shallow (0,05 < Φ < 0,3) Steep (Φ > 0,3)
Le = Lu Le = H/0,3



Orographic location factor s for cliffs and escarpments



Orographic location factor s for hills and ridges



a) upwind section for all orography

For the ranges



take



where



when



take

s = 0

b) downwind section for cliffs and escarpments

For the ranges



take



where



For the range



interpolate between values for



when



use the values for



when



take

s = 0

c) downwind section for hills and ridges

For the ranges



take



where



when



take

s = 0

Displacement height - Recommended procedure according Annex A.5


For building in Terrain category IV, can be reference height of building on the upwind side lowered by displacement height hdis due to closely spaced buildings and other obstructions.



hdis = min(0,8 • have; 0,6 • h) for x ≤ 2 • have

hdis = min(1,2 • have - 0,2 • x; 0,6 • h) for 2 • have ≤ x ≤ 6 • have

hdis = 0 for x ≥ 6 • have

Peak velocity pressure


Function for calculation peak velocity pressure at height z can be defined in National annex. Recommended formula is:



where:

ρ is the air density, which depends on the altitude, temperature and barometric pressure. ρ can be defined in National annex, recommended value is 1,25 kg/m3.

vm is mean wind velocity

Iv is turbulence intensity. It can be defined in National annex. Recommended formula is:

 for zmin ≤ z ≤ zmax

Iv = Iv(zmin) for z ≤ zmin

kI is turbulence factor. It may be defined in National annex. Recommended value is 1,0

Explanation of symbols


A - Construction site altitude above sea level [m]

AE1 - Altitude above sea level in east direction in 500 m from the site [m]

AE2 - Altitude above sea level in east direction in 1000 m from the site [m]

AN1 - Altitude above sea level in north direction in 500 m from the site [m]

AN2 - Altitude above sea level in north direction in 1000 m from the site [m]

AO1 - Altitude above sea level in west direction in 500 m from the site [m]

AO2 - Altitude above sea level in west direction in 1000 m from the site [m]

AS1 - Altitude above sea level in south direction in 500 m from the site [m]

AS2 - Altitude above sea level in south direction in 1000 m from the site [m]

cdir - Directional factor

ce,diag - Exposure factor from the diagram

ce,T - Exposure correction factor from the diagram

cO - Orography factor

cr,diag - Roughness factor from the diagram

cr,T - Roughness correction factor from the diagram

cr - Roughness factor

cseason - Season factor

Dir - Wind azimuth [°]

DisShore - Distance upwind to shoreline [km]

DisTown - Distance inside town terrain [km]

h - Height of the construction [m]

H - Effective height of the hill [m]

have - Average height of buildings in the city [m]

hdis - Height in the distance in terrain category IV [m]

Iv(z)flat - Turbulence intensity from the diagram

Iv - Turbulence intensity

kI,T - Turbulence intensity factor from the diagram

Ld - Actual length of the downwind slope in the wind direction [m]

Lu - Actual length of the upwind slope in the wind direction [m]

qb,0 - Fundamental value of basic wind pressure [kN/m2]

qb - Basic wind pressure [kN/m2]

qp - Peak velocity pressure [kN/m2]

T - The absolute air temperature at the load condition [K]

vb,0,CHMI - Fundamental value of the basic wind velocity according CHMI [m/s]

vb,0 - Fundamental value of the basic wind velocity [m/s]

vb,map - Fundamental value of the basic wind velocity from the map [m/s]

vb - Basic wind velocity [m/s]

vm - Mean wind velocity [m/s]

vp - Gust wind velocity [m/s]

x - Horizontal distance of the site from the top of the crest [m]

xDis - Site distance from the other building [m]

z - Reference height above terrain [m]

z0 - Roughness length [m]

zmin - Minimum height [m]

ρ - Air density [kg/m3]