Item File 20485 Eurocode 1-4-A-wind

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Eurocode for Windload

Text of Item File 20485 Eurocode 1-4-A-wind

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 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 EUROCODE 1 Part 1-4: Wind actions General remarks 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 actions General remarks 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. EN 1993-3-1 EUROCODE 1 Part 1-4: Wind actions Design situations The relevant wind actions shall be determined for each design situation identified in accordance with EN 1990: Ultimate limit state > + + +11, , 0 ," "1 , 1 ," " " ", ,j i i kQi i Q kQQPP j kGj G > + + +11, , 2" "1 ,) ( " " " ",1 , 2 1 , 1j i i kQi kQ or Aj kG d recommended values of factors for buildings: 0 = 0,6 1 = 0,2 2 = 0,0 Q = 1,5 EUROCODE 1 Part 1-4: Wind actions Design situations 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 actions Wind velocity and velocity pressure 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). 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) EUROCODE 1 Part 1-4: Wind actions Wind velocity and velocity pressure Return period 50 years 0 10 20 30 40mittlere Windgeschwindigkeit in m/s RangfolgenstatistikLSQ-FitUnterschreitenswahrscheinlichkeit0.9990.9950.9900.9500.9000.5000.1000.0010.0100.99950.9999"Jahresextremwerte"0.98vm,50=21.4m/s = 1,5 EUROCODE 1 Part 1-4: Wind actions Wind velocity and velocity pressure 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 factor cr(z) = kr ln (z / z0) for zmin s z s zmax cr(z) = cr(zmin) for z s zmin 07 , 0, 0019 , 0 ||.|

\| =IIrzzkEUROCODE 1 Part 1-4: Wind actions Wind velocity and velocity pressure Mean wind EUROCODE 1 Part 1-4: Wind actions Wind velocity and velocity pressure Wind turbulence intensity Iv(z) ( ) ( )minz I z I v v = for z min s z s z max ( ) ( ) ( ) z v k v kz vz ImI b rmvv = = o for z < z min EUROCODE 1 Part 1-4: Wind actions Wind velocity and velocity pressure Peak velocity pressure qp(z) ( ) ( ) | | ( ) ( ) b e m v p q z c z v z I z q = + =2217 1 is recommended with 1,25 kg/m ( ) ( )221b e b e p v z c q z c q = = EUROCODE 1 Part 1-4: Wind actions Wind velocity and velocity pressure Peak velocity pressure qp(z) ( ) ( )221b e b e p v z c q z c q = = EUROCODE 1 Part 1-4: Wind actions Wind actions 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 actions Wind actions wind pressure on surfaces we = qp(ze) cpe wi = qp(zi) cpi ze,i is the (decisive) reference height for the external/internal pressure cpe is the pressure coefficient for the external/internal pressure EUROCODE 1 Part 1-4: Wind actions Wind actions Wind forces Fw,e = cs cd 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 EUROCODE 1 Part 1-4: Wind actions Wind actions Wind forces Fw = cs cd cf qp(ze) Aref resp. Fw = cs cd 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 EUROCODE 1 Part 1-4: Wind actions Structural factor cs cd 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 actions Structural factor cs cd Determination of cs cd ( )( )s vs v pd sz I R B z I kc c + + +=7 12 12 2EUROCODE 1 Part 1-4: Wind actions Pressure and force coefficients General 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. EUROCODE 1 Part 1-4: Wind actions Pressure and force coefficients General Asymmetric and counteracting pressures and forces Effects of ice and snow EUROCODE 1 Part 1-4: Wind actions Pressure coefficients for buildings Vertical walls of rectangular plan buildings EUROCODE 1 Part 1-4: Wind actions Pressure coefficients for buildings Vertical walls of rectangular plan buildings EUROCODE 1 Part 1-4: Wind actions Pressure coefficients for buildings Flat roofs EUROCODE 1 Part 1-4: Wind actions Pressure coefficients for buildings Monopitch roofs Duopitch roofs EUROCODE 1 Part 1-4: Wind actions Pressure coefficients for buildings EUROCODE 1 Part 1-4: Wind actions Pressure coefficients for buildings Multispan roofs EUROCODE 1 Part 1-4: Wind actions Pressure coefficients for buildings Vaulted roofs and domes EUROCODE 1 Part 1-4: Wind actions Pressure 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 EUROCODE 1 Part 1-4: Wind actions Pressure 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 EUROCODE 1 Part 1-4: Wind actions Force coefficients for canopy roofs EUROCODE 1 Part 1-4: Wind actions Force coefficients for canopy roofs EUROCODE 1 Part 1-4: Wind actions Free standing walls, parapets, fences and signboards EUROCODE 1 Part 1-4: Wind actions Friction coefficients l = 2b or 4h EUROCODE 1 Part 1-4: Wind actions Structural elements Structural elements with rectangular sections Structural elements with sharp edged sections Structural elements with regular polygonal section cf = cf,0 r A EUROCODE 1 Part 1-4: Wind actions Circular cylinders External pressure coefficients EUROC