Eurocode 1 - Actions on structures -

1
Eurocode 1 - Actions on structures -

• Part 1-4 General actions
• Wind actions
• Dr.-Ing. Gerhard Scheuermann

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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

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EUROCODE 1 Part 1-4 Wind actionsGeneral
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

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EUROCODE 1 Part 1-4 Wind actionsGeneral
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
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EUROCODE 1 Part 1-4 Wind actionsDesign
situations

• The relevant wind actions shall be determined for
  each design situation identified in accordance
  with EN 1990 Ultimate limit state

?Q 1,5
recommended values of ? factors for buildings ?0
0,6 ?1 0,2 ?2 0,0
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EUROCODE 1 Part 1-4 Wind actionsDesign
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

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EUROCODE 1 Part 1-4 Wind actionsWind 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)
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EUROCODE 1 Part 1-4 Wind actionsWind velocity
and velocity pressure

• Return period 50 years

? 1,5
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EUROCODE 1 Part 1-4 Wind actionsWind 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 ? z ? zmax cr(z)
  cr(zmin) for
  z ? zmin

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EUROCODE 1 Part 1-4 Wind actionsWind velocity
and velocity pressure

• Mean wind

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EUROCODE 1 Part 1-4 Wind actionsWind velocity
and velocity pressure

• Wind turbulence intensity Iv(z)

for z min ? z ? z max
for z ? z min
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EUROCODE 1 Part 1-4 Wind actionsWind velocity
and velocity pressure

• Peak velocity pressure qp(z)

• is recommended with 1,25 kg/m³

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EUROCODE 1 Part 1-4 Wind actionsWind velocity
and velocity pressure

• Peak velocity pressure qp(z)

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EUROCODE 1 Part 1-4 Wind actionsWind 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

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EUROCODE 1 Part 1-4 Wind actionsWind 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
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EUROCODE 1 Part 1-4 Wind actionsWind 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
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EUROCODE 1 Part 1-4 Wind actionsWind 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
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EUROCODE 1 Part 1-4 Wind actionsStructural
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

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EUROCODE 1 Part 1-4 Wind actionsStructural
factor cs cd

• Determination of cs cd

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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.

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EUROCODE 1 Part 1-4 Wind actionsPressure and
force coefficientsGeneral

• Asymmetric and counteracting pressures and forces

• Effects of ice and snow

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EUROCODE 1 Part 1-4 Wind actionsPressure
coefficients for buildings

• Vertical walls of rectangular plan buildings

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EUROCODE 1 Part 1-4 Wind actionsPressure
coefficients for buildings

• Vertical walls of rectangular plan buildings

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EUROCODE 1 Part 1-4 Wind actionsPressure
coefficients for buildings

• Flat roofs

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EUROCODE 1 Part 1-4 Wind actionsPressure
coefficients for buildings
Duopitch roofs

• Monopitch roofs

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EUROCODE 1 Part 1-4 Wind actionsPressure
coefficients for buildings
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EUROCODE 1 Part 1-4 Wind actionsPressure
coefficients for buildings

• Multispan roofs

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EUROCODE 1 Part 1-4 Wind actionsPressure
coefficients for buildings

• Vaulted roofs and domes

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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

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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

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EUROCODE 1 Part 1-4 Wind actionsForce
coefficients for canopy roofs
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EUROCODE 1 Part 1-4 Wind actionsForce
coefficients for canopy roofs
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EUROCODE 1 Part 1-4 Wind actionsFree standing
walls, parapets, fences and signboards
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EUROCODE 1 Part 1-4 Wind actionsFriction
coefficients
l 2b or 4h
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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
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EUROCODE 1 Part 1-4 Wind actionsCircular
cylinders

• External pressure coefficients

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EUROCODE 1 Part 1-4 Wind actionsCircular
cylinders

• Force coefficients

cf cf,0 ??
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EUROCODE 1 Part 1-4 Wind actionsSpheres
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EUROCODE 1 Part 1-4 Wind actionsLattice
structures and scaffoldings
cf cf,0 ??
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EUROCODE 1 Part 1-4 Wind actionsFlags
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EUROCODE 1 Part 1-4 Wind actionsEffective
slenderness ? and end-effect ??
? A/Ac
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EUROCODE 1 Part 1-4 Wind actionsAnnex A
(informative) Terrain effects

• Illustrations of the upper roughness of each
  terrain category

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EUROCODE 1 Part 1-4 Wind actionsAnnex A
(informative) Terrain effects

• Illustrations of the upper roughness of each
  terrain category

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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
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EUROCODE 1 Part 1-4 Wind actionsAnnex A
(informative) Terrain effects

• Numerical calculation of orography coefficients

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EUROCODE 1 Part 1-4 Wind actionsAnnex A
(informative) Terrain effects

• Neighbouring structures Displacement height

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EUROCODE 1 Part 1-4 Wind actionsProcedures
for determining the structural factor cscd

• Spectrum of the response

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EUROCODE 1 Part 1-4 Wind actionsProcedures
for determining the structural factor cscd

• Detailed procedure

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EUROCODE 1 Part 1-4 Wind actionsProcedures
for determining the structural factor cscd

• Background factor B²
• conservative B² 1

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EUROCODE 1 Part 1-4 Wind actionsProcedures
for determining the structural factor cscd

• Resonance response factor R²
• Peak factor kp

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EUROCODE 1 Part 1-4 Wind actionsProcedures
for determining the structural factor cscd

• Number of loads for dynamic response

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EUROCODE 1 Part 1-4 Wind actionsProcedures
for determining the structural factor cscd

• cscd values for different types of structures

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EUROCODE 1 Part 1-4 Wind actionsVortex
shedding and aeroelastic instabilities
Kraftwerk Ferrybridge, GB, am 5. Nov. 1965
Einsturz von 3 Schalenkühltürmen aus Stahlbeton
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EUROCODE 1 Part 1-4 Wind actionsVortex
shedding and aeroelastic instabilities

• Criteria for vortex shedding

vcrit,i ? 1,25 vm where vcrit,i is the
critical wind velocity for mode i vm is the
characteristic 10 minutes mean wind velocity at
the cross section where vortex shedding
occurs
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EUROCODE 1 Part 1-4 Wind actionsVortex
shedding and aeroelastic instabilities

• Vortex shedding action

Fw(s) m(s)(2?ni,y)² ?i,y(s) yF,max
where m(s) is the vibrating mass of the
structure per unit length ni,y is the
natural frequency ?I,y(s) is the mode shape
of the structure normalised to 1
at the point with the max. displacement yF,max
is the maximum displacement over time of the
point with ?I,y(s) equal to 1
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EUROCODE 1 Part 1-4 Wind actionsVortex
shedding and aeroelastic instabilities

• Galloping
• Interaction effects

vCG ? 1,25 vm with vCG 2 Sc n1,y b /
aG
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EUROCODE 1 Part 1-4 Wind actionsDynamic
characteristics of structures

• General
• natural frequencies
• modal shapes
• equivalent masses
• logarithmic decrements of damping

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EUROCODE 1 Part 1-4 Wind actionsDynamic
characteristics of structures

• Fundamental frequency

for multi-storey buildings with a height larger
than 50m
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EUROCODE 1 Part 1-4 Wind actionsDynamic
characteristics of structures

• Logarithmic decrement of dumping

? ?s ?a ?d
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EUROCODE 1 Part 1-4 Wind actionsWind map
Historische Orkane 1976 Capella 1984
Münchener Hagelsturm 1990 Winterstürme Daria
(Jan), Vivian (Febr), Wiebke
(Febr), Gesamtschaden in Preisen
von 1990 25 Mrd. DM
1999 Lothar
Modell für einen Europa Orkan zur Prognose des
Sturmrisikos in Deutschland und den
Benelux-Staaten (Münchner Rück)
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EUROCODE 1 Part 1-4 Wind actionsWind map
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EUROCODE 1 Part 1-4 Wind actionsWind map