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Eurocode 1 - Actions on structures -

Eurocode 1 - Actions on structures - . Part 1-4: General actions Wind actions Dr.-Ing. Gerhard Scheuermann. CONTENTS. General Design situations Wind velocity and velocity pressure Wind actions Structural factor c s c d Pressure and force coefficients Terrain effects

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Eurocode 1 - Actions on structures -

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  1. Eurocode 1 - Actions on structures - Part 1-4: General actions Wind actions Dr.-Ing. Gerhard Scheuermann

  2. CONTENTS • General • Design situations • Wind velocity and velocity pressure • Wind actions • Structural factor cs cd • Pressure and force coefficients • Terrain effects • Procedures for determine the structural factor cs cd • Vortex shedding and aeroelastic instabilities • Dynamic characteristics of structures • Wind map

  3. National Annex (NA) - values/and or classes where alternatives are given in the Eurocodes - values to be used where a symbol only is given - country specific data, e.g. snow map or a wind map - the procedure to be used when alternative procedures are given - decisions on the application of Informative Annexes - reference to non-contradictory Annexes EUROCODE 1 – Part 1-4: Wind actionsGeneral remarks

  4. This part is applicable to buildings and civil engineering works (land-based structures) with heights up to 200 m Certain aspects necessary to determine wind actions on a structure need to be provided in the National Annex. Default values and methods are given in the main text, where the National Annex does not provide information. This part does not give guidance on local thermal effects on the characteristic wind, e.g. strong arctic thermal surface inversion or funnelling or tornadoes This part does not give guidance on the following aspects wind actions on lattice towers with non –parallel chords wind actions on guyed masts and guyed chimneys torsional vibrations, e.g. tall buildings with a central core vibrations where more than the fundamental mode needs to be considered. EUROCODE 1 – Part 1-4: Wind actionsGeneral remarks EN 1993-3-1

  5. The relevant wind actions shall be determined for each design situation identified in accordance with EN 1990: Ultimate limit state EUROCODE 1 – Part 1-4: Wind actionsDesign situations Q = 1,5 recommended values of  factors for buildings: 0 = 0,6 1 = 0,2 2 = 0,0

  6. Other actions – such as snow, traffic or ice – which will modify the effects due to wind should be taken into account (see also EN 1993-1-3, EN 1991-2 and ISO FDIS 12494 The changes of structure during stages of execution – such as different stages of the form of the structure, dynamic characteristics etc - should be taken into account (see EN 1991-1-6) Where in design windows and doors are assumed to be shut under storm conditions, the effect of these being open should be treated as an accidental design situation Fatigue due to effects of wind actions should be considered for susceptible structures EUROCODE 1 – Part 1-4: Wind actionsDesign situations

  7. Basic values : the fundamental values of the basic wind velocity vb,0 is the characteristic 10 minutes mean wind velocity, irrespective of wind direction and time of year, at 10m above ground level in open country terrain with low vegetation such as grass and isolated obstacles with separations of at least obstacle heights (category II). EUROCODE 1 – Part 1-4: Wind actionsWind velocity and velocity pressure The basic wind velocity shall be calculated with vb = cdir cseason vb,o where vb is the basic wind velocity, 10m above ground, cat. II vb,0 is the fundamental value of the basic wind velocity cdir is the directionsl factor (recommended 1,0) cseason is the season factor (recommended 1,0)

  8. Return period 50 years EUROCODE 1 – Part 1-4: Wind actionsWind velocity and velocity pressure  = 1,5

  9. Mean wind Variation with height vm(z) = cr(z)  c0(z)  vb where c0(z)is the orography factor , taken as 1, cr(z)is the roughness factorcr(z)= kr  ln (z / z0) for zmin  z  zmax cr(z)= cr(zmin)for z  zmin EUROCODE 1 – Part 1-4: Wind actionsWind velocity and velocity pressure

  10. Mean wind EUROCODE 1 – Part 1-4: Wind actionsWind velocity and velocity pressure

  11. Wind turbulence intensity Iv(z) EUROCODE 1 – Part 1-4: Wind actionsWind velocity and velocity pressure for z min z z max for z  z min

  12. Peak velocity pressure qp(z) EUROCODE 1 – Part 1-4: Wind actionsWind velocity and velocity pressure • is recommended with 1,25 kg/m³

  13. Peak velocity pressure qp(z) EUROCODE 1 – Part 1-4: Wind actionsWind velocity and velocity pressure

  14. calculation procedures peak velocity pressure qp wind pressures w, e.g. for cladding , fixings and structural parts wind forces Fw on structures, e.g. for overall wind effects EUROCODE 1 – Part 1-4: Wind actionsWind actions

  15. wind pressure on surfaces EUROCODE 1 – Part 1-4: Wind actionsWind actions we = qp(ze)  cpe wi = qp(zi)  cpi ze,iis the (decisive) reference height for the external/internal pressure cpe is the pressure coefficient for the external/internal pressure

  16. Wind forces EUROCODE 1 – Part 1-4: Wind actionsWind actions Fw,e = cscd we Aref Fw,i =  wi Aref Ff,e = cfr qp(ze)  Aref where. cs cd is the structural factor cfr is the friction coefficient Aref is the reference area of the structure or structural element

  17. Wind forces EUROCODE 1 – Part 1-4: Wind actionsWind actions Fw = cscdcf qp(ze)  Aref resp. Fw = cscd cf qp(ze)  Aref where. cs cd is the structural factor cf is the force coefficient for the structure or structural element Aref is the reference area of the structure or structural element

  18. Determination of cs cd For buildings with a height less than 15 m, the value of cs cd may be taken as 1 For facade and roof elements having a natural frequency greater than 5 Hz , the value of cs cd may be taken as 1 For framed buildings which have structural walls and which are less than 100m high and whose height is less than 4 times the in-wind-depth, the value of cs cd may be taken as 1 For chimneys with circular cross-sections whose height is less than 60 m and 6,5 times the diameter, the value of cs cd may be taken as 1 EUROCODE 1 – Part 1-4: Wind actionsStructural factor cs cd

  19. EUROCODE 1 – Part 1-4: Wind actionsStructural factor cs cd • Determination of cs cd

  20. EUROCODE 1 – Part 1-4: Wind actionsPressure and force coefficientsGeneral • Choice of aerodynamic coefficient • Pressure coefficients for buildings and circular cylinders for internal and external pressures • Net pressure coefficients for canopy roofs, free-standing walls, parapets and fences • Friction coefficients • Force coefficients for signboards, structural elements with rectangular cross section, structural elements with sharp edged section, structural elements with regular polygonal section, flags etc.

  21. EUROCODE 1 – Part 1-4: Wind actionsPressure and force coefficientsGeneral • Asymmetric and counteracting pressures and forces • Effects of ice and snow

  22. EUROCODE 1 – Part 1-4: Wind actionsPressure coefficients for buildings • Vertical walls of rectangular plan buildings

  23. EUROCODE 1 – Part 1-4: Wind actionsPressure coefficients for buildings • Vertical walls of rectangular plan buildings

  24. EUROCODE 1 – Part 1-4: Wind actionsPressure coefficients for buildings • Flat roofs

  25. EUROCODE 1 – Part 1-4: Wind actionsPressure coefficients for buildings Duopitch roofs • Monopitch roofs

  26. EUROCODE 1 – Part 1-4: Wind actionsPressure coefficients for buildings

  27. EUROCODE 1 – Part 1-4: Wind actionsPressure coefficients for buildings • Multispan roofs

  28. EUROCODE 1 – Part 1-4: Wind actionsPressure coefficients for buildings • Vaulted roofs and domes

  29. EUROCODE 1 – Part 1-4: Wind actionsPressure coefficients for buildings • Internal pressure • The internal pressure depends on the size and distribution of the openings • It should be taken into account if the openings are larger than 0,1% and not • larger than 30% of the face area • In certain cases the internal pressure may be handled as an accidental load

  30. EUROCODE 1 – Part 1-4: Wind actionsPressure coefficients for buildings • Pressure on walls or roofs with more than one skin • The wind force is to be calculated separately on each skin • The permeability  of a skin is defined as the ratio of the total area of the opening to the total area of the skin. A skin is defined as impermeable if  is less than 0,1 % • If only one skin is permeable, then the wind force on the impermeable skin should be determined from the difference between the internal and the external wind pressure

  31. EUROCODE 1 – Part 1-4: Wind actionsForce coefficients for canopy roofs

  32. EUROCODE 1 – Part 1-4: Wind actionsForce coefficients for canopy roofs

  33. EUROCODE 1 – Part 1-4: Wind actionsFree standing walls, parapets, fences and signboards

  34. EUROCODE 1 – Part 1-4: Wind actionsFriction coefficients l = 2b or 4h

  35. EUROCODE 1 – Part 1-4: Wind actionsStructural elements • Structural elements with rectangular sections • Structural elements with sharp edged sections • Structural elements with regular polygonal section cf = cf,0· r· A

  36. EUROCODE 1 – Part 1-4: Wind actionsCircular cylinders • External pressure coefficients

  37. EUROCODE 1 – Part 1-4: Wind actionsCircular cylinders • Force coefficients • Force coefficients for vertical cylinders in a row arrangement cf = cf,0· 

  38. EUROCODE 1 – Part 1-4: Wind actionsSpheres

  39. EUROCODE 1 – Part 1-4: Wind actionsLattice structures and scaffoldings cf = cf,0· 

  40. EUROCODE 1 – Part 1-4: Wind actionsFlags

  41. EUROCODE 1 – Part 1-4: Wind actionsEffective slenderness  and end-effect   = A/Ac

  42. EUROCODE 1 – Part 1-4: Wind actionsAnnex A (informative) – Terrain effects • Illustrations of the upper roughness of each terrain category

  43. EUROCODE 1 – Part 1-4: Wind actionsAnnex A (informative) – Terrain effects • Illustrations of the upper roughness of each terrain category

  44. EUROCODE 1 – Part 1-4: Wind actionsAnnex A (informative) – Terrain effects • Numerical calculation of orography coefficients vm: mean wind velocity at height z above terrain vmf: mean wind velocity above flat terrain co = vm/vmf

  45. EUROCODE 1 – Part 1-4: Wind actionsAnnex A (informative) – Terrain effects • Numerical calculation of orography coefficients

  46. EUROCODE 1 – Part 1-4: Wind actionsAnnex A (informative) – Terrain effects • Neighbouring structures – Displacement height

  47. EUROCODE 1 – Part 1-4: Wind actionsProcedures for determining the structural factor cscd • Spectrum of the response

  48. EUROCODE 1 – Part 1-4: Wind actionsProcedures for determining the structural factor cscd • Detailed procedure

  49. EUROCODE 1 – Part 1-4: Wind actionsProcedures for determining the structural factor cscd • Background factor B² • conservative: B² = 1

  50. EUROCODE 1 – Part 1-4: Wind actionsProcedures for determining the structural factor cscd • Resonance response factor R² • Peak factor kp

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