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![WORKED EXAMPLE: CO FACTOR
18
• Ø=H/Lu=10/100 =0.1; 0.05<Ø<0.3
then Le=Lu
• Orography is significant
• Site 10 m from the crest of a Cliff
• x/Lu= 10/100=0.1
• z/Le= 12/100=0.12
• S=0.6
• Co=1+2sØ=1+2x0.6x0.1=1.12
• Ce(z)=2.5 (See last example)
• Qp = 2.5x [{co+0.6}/1.6]^2x
0.613x23.9^2 =2.5x 1.16x 350
=1015 PA](https://image.slidesharecdn.com/b018749e-7a63-407a-aa7f-35c9b888d07e-160630002404/75/Presentation-Wind-and-Eurocode-UK-18-2048.jpg)
Presentation Wind and Eurocode UK
- 1. Abdurahman Ahmed Wind &Eurocode June 1st 2016
- 2. CONTENTS 2 Introduction Scope of BSEN 1991-1-1-4 2005 +A1 2010 & UK National Annex (NA) Flow charts for obtaining peak velocity pressure Basic wind velocity pressure • Correction factors Orography significant or Not? Peak wind velocity pressure Wind pressure & Wind Forces References Q&A
- 3. INTRODUCTION 3 What: Wind loadingaccording to BS EN1991-1-4- 2005 & UK National Annex Why: Gaining Knowledge and sharing it How: through presentation/ worked examples After: you can calculate wind peak pressure by hand, know about the different coefficients, used terminology, know the UK National determinate Parameters (N.D.P)
- 4. SCOPE OF BSEN 1991-1-1-4 2005 WIND & NA 4 Give guidance on determination of wind actions for building structures and civil works. Applicable for buildings and civil structures up to 200 meters. Applicable for bridges having no span greater than 200 meters (with some criteria bases on dynamic response). Some structures are excluded from this Eurocode part 1-4.
- 5. FLOW CHARTS FORPEAK VELOCITY PRESSURE 5 NA includes 2 useful flow charts. fig. A. NA.1 (Country terrain) fig. A. NA.2 (Town terrain) Presentation layout will be based on these charts with some worked examples.
- 6. BASIC WIND VELOCITYPRESSURE: QB 6 Basis wind velocity: Vb Fundamental basic wind velocity: Vb,map • Obtaining from fig. NA.1 • Value of the wind at 10 m above ground in open country terrain, in a period of 10 minutes Correction factors: C
- 7. CORRECTION FACTORS: CALT 7 adjustwind speed of site above sea level: A factor adjust wind speed of site above ground level: Z factor NA gives 2 equations for the altitude factor: Calt Equation NA.2a may be used for any building (Conservative for tall buildings). Fig. 2 from BRE publication: Digest DG-436-1
- 8. CORRECTION FACTORS: CDIR 8 Factorfor wind directions. NA consider 12 directions of 30 degree (time consuming by hand calculation.) Considering 4 directions (like fig. 3) Value of Cdir=1 for all directions.
- 9. CORRECTION FACTORS: CSEASON 9 Factorfor seasons, table NA.2.7 from NA For temporary structures and for structures in the execution phase, season factor may be used For transportable structures C season = 1 For building, it should be taken eq. to 1
- 10. CORRECTION FACTORS: CPROB 10 Factorfor probability Cprob = 1 for return period of 50 years. Cprob = 0.9 for return period of 10 years. Cprob = 1.1 for return period of about 250 years.
- 11. BASIC WIND VELOCITYPRESSURE: QB 11 Fundamental basic wind velocity: Vb,map (see above) Factors (see above) Basis wind velocity: Vb Air density by NA = 1.226 kg/m3 Basic wind velocity pressure
- 12. OROGRAPHY SIGNIFICANT? YESOR NO 12 Orography = Topography is the topography features such as hills, cliffs , escarpmentsG Co = orography factor Used to account the speed up of the mean wind speed over hills, escarpments. Orography can increase the peak pressure by over 70% near the crest of a steep hill.
- 13. OROGRAPHY SIGNIFICANT? YESOR NO 13 When is Topography siginficant? The effets of orography should be considered by the shaded area in fig. NA. 2 Out site the shaded area Co may be taken as 1
- 14. OROGRAPHY SIGNIFICANT? NO 14 Outside shaded area Co = 1 Use equation NA.3a of NA.3b Determine Exposure factor Ce(z) • Distance to shore? • Effective height? Determine Exposure correction factor Ce,T for sites in Town terrain • Distance to edge of Town?
- 15. WORKED EXAMPLE 15 Building outside of Leeds. 60x35x12= LxBxH, altitude = 50 m, distance to sea = 100 kM, at edge of Town • Determine Vb,map fig NA.1 = 22.8 m/s • Calt = 1+0.01A= 1+0.001x50=1.05 • Vb,0 = Vb,map x Calt = 22.8 x 1.05 = 23.9 m/s • Vb = Cdir x Cseason x Vb,o = 23.9 m/s (Cdir, Cseason taken =1) • Orography check? • Ø=H/Lu=2/100=0.02 (halfway of Hill) < 0.05 : Orography not significant. • Hdisp=0, Zef=12-0=12 m • Qb=Ce(z)xCe,tx0.613xVb^2= 2.5x1x0.613x23.9^2= 2.5x 350 = 875 Pa
- 16. OROGRAPHY SIGNIFICANT? YES& Z<50 M 16 Orography is significant In side shaded area: Co > 1 Determine Co factor Building height <50 m. Use equation NA.4a (z<50m)
- 17. OROGRAPHY SIGNIFICANT? YES& Z<50 M 17 Co factor? Get from Annex A of EN Determine ø (slope angle) Determine factor s Determine Co factor Ø=0.05 >> 2.8 degree angle Ø=0.3 >> 17 degree angle
- 18. WORKED EXAMPLE: COFACTOR 18 • Ø=H/Lu=10/100 =0.1; 0.05<Ø<0.3 then Le=Lu • Orography is significant • Site 10 m from the crest of a Cliff • x/Lu= 10/100=0.1 • z/Le= 12/100=0.12 • S=0.6 • Co=1+2sØ=1+2x0.6x0.1=1.12 • Ce(z)=2.5 (See last example) • Qp = 2.5x [{co+0.6}/1.6]^2x 0.613x23.9^2 =2.5x 1.16x 350 =1015 PA
- 19. OROGRAPHY SIGNIFICANT? YES& Z>50 M 19 Orography is significant In side shaded area: Co > 1 Determine Co factor (see above) Building height>50 m. Use equation NA.4b (z>50m) Building z>200 m: out side of the scope of this NA (specific studies required)
- 20. OROGRAPHY SIGNIFICANT: YES& Z>50 M 20 Vm = mean wind velocity Orography factor: Co (see above) Roughness factor: Cr(z) Correction of Cr,T(z) in Town terrain) Mean wind velocity: Vm
- 21. WORKED EXAMPLE: ROUGHNESSFACTOR 21 Roughness factor Roughness Correction factor for sites in Town terrain. Limitation for Hdisp=3 m?
- 22. OROGRAPHY SIGNIFICANT: YES& Z>50 M 22 Turbulence Intencity: Iv(z) in flat terrain Correction of KI,T in Town terrain Orography factor: Co (see above) Turbulence Intencity: Iv(z)
- 23. WORKED EXAMPLE: TURBULENCE 23 TurbulenceIntensity in flat terrain Turbulence Correction factor for sites in Town terrain.
- 24. PEAK VELOCITY PRESSURE:QP 24 Calculation of peak velocity pressure with this equation
- 25. WIND PRESSURE (W) AND WIND FORCES (F) 25 External or Internal Wind pressure Cpe, Cpi: clause 7.2 for buildings Cpe1: for area less than 1 m2 Cpe 10: for area greater than 1 m2 Cpi: open, close building. CsCd= Size and dynamic factor: can be calculated separately according to NA May have a favorable effect
- 26. WORKED EXAMPLE: CSCDFACTOR 26 • Office building with plan of 60mx20m with a height of 10 m in town terrain: CsCd? • Option 1: Clause 6.2(1) of EN 1991-1-4: CsCd is equal to 1 for building < 15 meters. • Option 2: separately cal. h/b= 10/60=0.167 >> Cd=1 • table NA.3: z=10, B+H=60+10=70, zone C>> Cs=0.77 , CsCd = 0.77 (23% reduction)
- 27. CONCLUSION: 27 Scope of BSEN 1991-1-1-4 2005 Wind & NA Flow chart for obtaining peak velocity pressure Basic wind velocity pressure • Correction factor: Calt, Cdir, Cseason, Cprob When orography is significant Peak wind velocity pressure • Roughness factor • Orograpfy factor • Turbulence factor • Correction factor for sites in Town terrain Internal en external factors Size and dynamic factors Illustration with worked examples
- 28. REFERENCES: 28 BS EN 1991-1-42005 +A1 2010 NA to BS EN 1991-1-4 2005 +A1 2010 PD 6688-1-4:2015 (Published Document): Background information to the National Annex to BS EN 1991-1-4 and additional guidance. CCIP-Wind loading: chapter 2.6 WSP worked example introduction to 1991-1-4 from 2009 BRE publication in Digest DG-436-1, 2 Additional online search
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