![Introduc(on
• Flexible structures(e.g.
tall buildings and long-
span bridges) are
par(cularly sensi(ve
to dynamic interac(on
phenomena
– Theory of
aeroelas,city must be
embedded in the
structural design
Burj Khalifa, Dubai [828 m tall]
Akashi-Kaikyo Bridge, Kobe
[central span of 1,991 m]](https://image.slidesharecdn.com/windactionsaccordingtoec1-100211100136-phpapp01/75/Wind-Actions-According-To-EC1-5-2048.jpg)
![Map values of the basic wind velocity [m/s]
NA to BS EN 1991-1-4:2005, Figure NA.1
11
vb,map
= 22m/s](https://image.slidesharecdn.com/windactionsaccordingtoec1-100211100136-phpapp01/75/Wind-Actions-According-To-EC1-11-2048.jpg)
![calt= Al(tude factor
• It depends on:
– Al(tude of the site above the mean sea level, A [m]
– Reference height of the structure, zs [m]
– It is acceptable to use the value of calt for zs= 10 m for all
cases, as this is a conserva(ve assump(on
12
calt
=
1+ 0.001⋅A , zs
≤10m
1+ 0.001⋅A⋅
10
zs
⎛
⎝
⎜
⎞
⎠
⎟
0.2
, zs
>10m
⎧
⎨
⎪⎪
⎩
⎪
⎪](https://image.slidesharecdn.com/windactionsaccordingtoec1-100211100136-phpapp01/75/Wind-Actions-According-To-EC1-12-2048.jpg)
![cprob= Probability factor
• When required, this mul(plier
allows adjus(ng the annual risk of
being exceeded:
where R= 1/p is the return period,
while K and n are two parameters
defining the probabilis(c
distribu(on of extreme winds
– Suggested values: K= 0.2 and
n= 0.5
15
!!
cprob
=
1−K ⋅ln −ln 1− p( )( )
1−K ⋅ln −ln 1−0.02( )( )
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟
n
10 20 50 100 200 500 1000
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
R !years"cprob R"[years]"](https://image.slidesharecdn.com/windactionsaccordingtoec1-100211100136-phpapp01/75/Wind-Actions-According-To-EC1-15-2048.jpg)
Uploaded byAlessandro Palmeri
Wind Actions According To EC1
The document discusses the importance of considering wind forces on civil engineering structures, particularly the application of Eurocode 1 for evaluating wind loads. It emphasizes the need for structural engineers to understand the factors influencing wind loads and how to apply relevant calculations for different structures. Additionally, it covers concepts such as turbulence intensity, wind pressure coefficients, and the methodologies required to ensure the structural stability against wind forces.
More Related Content
Wind Actions According To EC1
- 1.
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- 4. Introduc(on • Wind is flowing air • Structures in the wind are subjected to forces which vary with (me and space – The level of turbulence of the wind can be measured by the turbulence intensity Iv, defined as the dimensionless coefficient of varia(on of the wind velocity, i.e. standard devia(on divided by mean value, i.e. !! Iv = σv vm vm 2Iv 4
- 5.
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- 8. Introduc(on • You will need to become familiar with two documents: – BS EN 1991-1-4:2005 • Eurocode 1: Ac(ons on structures, Part 1-4: General ac(ons, Wind ac(ons – NA to BS EN 1991-1-4:2005 • Corresponding UK Na(onal Annex – Both documents can be downloaded by using your account in the MyAthens website 8
- 9.
- 10.
- 11.
- 12. calt= Al(tude factor • It depends on: – Al(tude of the site above the mean sea level, A[m] – Reference height of the structure, zs [m] – It is acceptable to use the value of calt for zs= 10 m for all cases, as this is a conserva(ve assump(on 12 calt = 1+ 0.001⋅A , zs ≤10m 1+ 0.001⋅A⋅ 10 zs ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ 0.2 , zs >10m ⎧ ⎨ ⎪⎪ ⎩ ⎪ ⎪
- 13.
- 14.
- 15. cprob= Probability factor • When required, this mul(plier allows adjus(ng the annual risk of being exceeded: where R= 1/p is the return period, while K and n are two parameters defining the probabilis(c distribu(on of extreme winds – Suggested values: K= 0.2 and n= 0.5 15 !! cprob = 1−K⋅ln −ln 1− p( )( ) 1−K ⋅ln −ln 1−0.02( )( ) ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟ n 10 20 50 100 200 500 1000 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 R !years"cprob R"[years]"
- 16. qb= Basic wind pressure • The dynamic pressure due to the wind is the kine(c energy per unit volume of the flowing air – The density of the air is assumed to be ρair= 1.226 kg/m3. • This is only a “nominal” or “reference” value of the wind pressure, as the above equa(on assumes a uniform, laminar flow of the air, and does not account for the effects of the turbulence and varia(on with the height 16 qb = 1 2 ρair ⋅vb 2
- 17. qp= Peak wind pressure • The “basic” value of wind pressure qb can be transformed into the “peak” value qp(z), varying with the height z, taking into account: – The roughness of the surrounding terrain; – The site’s proximity to the coast; – How far the site is located within a town (if applicable) • This is done with two coefficients: – “Proximity to shoreline” exposure coefficient ce(z-hdis); – “Site within town” exposure modifier ce,T(z-hdis), • both depending on the height of nearby structures through the “displacement height” hdis 17 !! qp (z)= ce (z−hdis )⋅ce,T (z−hdis )⋅qb
- 18.
- 19. hdis= Displacement height • In the UK NA, this quan(ty effec(vely accounts for the reduc(on in the wind velocity due to the presence of closely spaced buildings and other obstruc(ons 19 hdis = min 0.6h,0.8have{}, 0 ≤ x ≤ 2have min 0.6h,1.2have −0.2x{ }, 2have < x < 6have 0 , x ≥ 6have ⎧ ⎨ ⎪⎪ ⎩ ⎪ ⎪
- 20.
- 21.
- 22.
- 23.
- 24.
- 25. External and internal wind pressure • External (cpe) and internal (cpi) pressure coefficients are required to get the actual pressures on different external (we(ze)) and internal (wi(zi)) areas from the peak velocity pressure – ze and zi being the per(nent reference height • In general, both cpe and cpi contribute to the total wind load on the envelope of the building 25 we (ze ) = cpe ⋅qp (ze ) wi (zi ) = cpi ⋅qp (zi ) ⎧ ⎨ ⎪ ⎩⎪
- 26.
- 27. Internal wind pressure / Dominant face 27 • A face of a building should be regarded as “dominant” when the area of openings at that face, Aopen,dom, is at least twice the area of openings and leakages in the remaining faces of the building considered, Aopen,non-dom • In this case the internal pressure should be taken as a frac(on of the external pressure at the openings of the dominant face, that is: – cpi = 0,75 cpe , for Aopen,dom= 2 Aopen,nondom ; – cpi = 0,90 cpe , for Aopen,dom≥ 3 Aopen,nondom ; – Interpola(on for 2 < Aopen,dom/Aopen,nondom < 3
- 28.
- 29. External wind pressure 29 • External pressure coefficients depends on the size of the loaded area A= Aref, along with the posi(on (zone) in the building • Two limi(ng values are provided by the Eurocode, which can be used for: small elements, with an area of 1 m2 or less, cpe,1; and large elements, with an area of 10 m2 or more, cpe,10 • For intermediate situa(ons, i.e. 1 < A < 10 m2, a logarithmic interpola(on is suggested: !! cpe = cpe,1 −(cpe,1 −cpe,10 )⋅log10 (A) Why must cpe,10 be always < cpe,1 ?
- 30.
- 31.
- 32. Wind forces 32 • External and internal pressures allow compu(ng the wind forces on external (Fw,e) and internal (Fw,i) surfaces where cs and cd are “size factor” and “dynamic factor”, respec(vely, while Aref is the reference area for each surface considered in the summa(on – The product cscd accounts for the effects of: i) the non- simultaneous occurrence of peak wind pressures on the surface (cs) and ii) the vibra(ons of the structure due to turbulence (cd) !! Fw,e =cs ⋅cd ⋅ we (ze )⋅Aref surfaces ∑ Fw,i = wi (zi )⋅Aref surfaces ∑ ⎧ ⎨ ⎪ ⎩ ⎪
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