eurocode 1-snow information
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7/23/2019 Eurocode 1-Snow Information
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Professor Haig Gulvanessian CBECivil Engineering and Eurocodes Consultant,
Visiting Professor, Imperial College London
EN 1991-1-3: Eurocode 1:Actions on Structures: Part 1-3:
Snow Loads
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Scope of Presentation
u Description of EN 1991-1-3 Eurocode 1: Part
1-3: Snow Loads
u Background research for snow maps for
Europe, Accidental (exceptional) loads etc.u Differences between EN 1991-1-3 and BS
6399: Part 3
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Professor Haig GulvanessianProfessor Haig Gulvanessian
EN 1991-1-3 provides guidance for the
determination of the snow load to be used for
the structural design of buildings and civil worksfor sites at altitudes under 1500m.
EN 1991-1-3 – Field of application
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Professor Haig GulvanessianProfessor Haig Gulvanessian
EN 1991-1-3 – Field of application
EN 1991-1-3 does not give guidance onspecialist aspects of snow loading, forexample:
u “impact snow loads” resulting from snow sliding off
or falling from a higher roof;u the additional wind loads which could result from
changes in shape or size of the building structuredue to the presence of snow or the accretion of ice;
u loads in areas where snow is present all the year;
u ice loading;u lateral loading due to snow (e.g. lateral loads exerted
by drifts).
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Professor Haig GulvanessianProfessor Haig Gulvanessian
EN 1991-1-3 - Contentsu Foreword
u Section 1: General
u Section 2: Classification of actions
u Section 3: Design situations
u Section 4: Snow load on the ground
u Section 5: Snow load on roofs
u Section 6: Local effects
u ANNEX A: Design situations and load arrangementsto be used for different locations
u ANNEX B: Snow load shape coefficients forexceptional snow drifts
u ANNEX C: European Ground Snow Load Mapsu ANNEX D: Adjustment of the ground snow load
according to return period
u ANNEX E: Bulk weight density of snow
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Professor Haig GulvanessianProfessor Haig Gulvanessian
EN 1991-1-3 – Determination of
Imposed roof snow loads
u Characteristic ground snow loads
• Ground snow load map
• Altitude function
u Coefficients• Shape coefficient – Roof shape
• Exposure coefficient – Topography
• Thermal coefficient – Thermal
transmittance of roofing material
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Professor Haig GulvanessianProfessor Haig Gulvanessian
EC funded European snow research
programme for development of EN 1991-1-3
Characteristic Snow Loads on the GroundDevelopment of a Ground Snow Load Map for Europe
u There were inconsistencies at borders between
existing national maps
u
The research developed a consistent approachu Produced regional maps. These are given in Annex
C of EN 1991-1-3
• Snow load with Altitude relationship
• Zone numbers & altitude function
• Geographical boundaries
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Ground Snow load map European Climatic
Regions: Member States presently covered
Proposal being prepared to extend map to cover the
whole of Europe
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Ground Snow load map –
United Kingdom and Ireland
0,50,54,54,5
0,30,333
0,20,222
0,040,0411
kN/mkN/m22
(A=0)(A=0)
ZoneZone
NN°°
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Ground Snow Load Map – Revised Maps for
National Annexes
u Revised UK and Republic of Ireland map
• Investigated small zones
• Increased the total number of zones
• Applied a normalising datum• Software to produce map
u Adopted in the UK National Annex
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Professor Haig GulvanessianProfessor Haig Gulvanessian
UK and Republic of Ireland
Ground Snow Load Map
Determination of Sk
Sk = (0,15 + [0,1Z + 0,05]) + ((A
– 100)/525))
Sk = Characteristic ground
snow load (kN/m2)
Z = Zone number (obtained
from map) A = Site altitude (m)
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Professor Haig GulvanessianProfessor Haig Gulvanessian
EC funded European snow research
programme for development of EN 1991-1-3
Characteristic Snow Loads on the
Ground
Development of a Ground Snow Load Map
for Europe
u Identified areas with exceptional snow falls
u Coefficients for the combination of actions
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Professor Haig GulvanessianProfessor Haig Gulvanessian
ClassificationClassification ofof actionsactions
u For particular conditions snow loads may betreated as accidental actions: “act ion, usual ly of
sho rt durat ion bu t of sign i f icant magn i tude, that
is un l ikely to occur on a g iven st ruc tu re dur ing
the design working l i fe”
Exceptional
snow load on
the ground
Exceptional
snow drifts
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Exceptional Ground Snow Loads
u In some regions, particularly southern Europe,
isolated and extremely infrequent very heavy
snow falls have occurred
u This has resulted in ground snow loads whichare significantly larger than those that
normally occur.
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Exceptional Ground Snow LoadsExceptional Ground Snow Loads
S Ad = Cesl Sk
S Ad = Site exceptional ground snow load design value
(kN/m2
)Cesl = Coefficient (recommended value 2)
Sk = Site Characteristic ground snow load (kN/m2)
u Value for coefficient given in National Annex
u Treated as Accidental actions
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Action ψ 0 ψ 1 ψ 2
Imposed loads in buildings, category (see
EN 1991-1-1)
Category A : domestic, residential areas
Category B : office areas
Category C : congregation areas
Category D : shopping areas
Category E : storage areas
0,7
0,7
0,7
0,7
1,0
0,5
0,5
0,7
0,7
0,9
0,3
0,3
0,6
0,6
0,8
Category F : traffic area,
vehicle weight≤ 30kN
Category G : traffic area,
30kN < vehicle weight≤ 160kN
Category H : roofs
0,7
0,7
0
0,7
0,5
0
0,6
0,3
0Snow loads on buildings (see EN 1991-1-3)*
– Finland, Iceland, Norway, Sweden 0,70 0,50 0,20
– Remainder of CEN Member States, for sites
located at altitude H > 1000 m a.s.l.
0,70 0,50 0,20
– Remainder of CEN Member States, for sites
located at altitude H ≤ 1000 m a.s.l.
0,50 0,20 0
Wind loads on buildings (see EN 1991-1-4) 0,6 0,2 0
Temperature (non-fire) in buildings (see EN
1991-1-5)
0,6 0,5 0
NOTE The ψ values may be set by the National annex.* For countries not mentioned below, see relevant local conditions.
EN 1990: Table A1.1 - Recommended values of
ψ factors for buildings
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Professor Haig GulvanessianProfessor Haig Gulvanessian
EN 1991-1-3: Combination Coefficients for
other representative values for actions
u Representative values osk, 1sk and 2sk are defined
in EN 1990 Basis of Structural Design
u Values determined from analysis of daily data
u Recommended values for EN 1990 (< 1000 masl & >
1000 masl):Combination value coefficient 0 – 0,5 & 0,7
Frequent value coefficient 1 – 0,2 & 0,5
Quasi-permanent value coefficient 2 – 0,0 & 0,2
u
Value for coefficients given in National Annex to EN1990: Basis of Structural Design
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof Determination of Snow Load on the Roof
Nature of the loadThe design shall recognise that snow can be deposited on a roof in
many different patterns.
Properties of a roof or other factors causing different
patterns can include:u the shape of the roof;
u its thermal properties;
u the roughness of its surface;
u the amount of heat generated under the roof;
u the proximity of nearby buildings;
u the surrounding terrain;
u the local meteorological climate, in particular its windiness,temperature variations, and likelihood of precipitation (either as rainor as snow).
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof
Load arrangements
The following two primary load arrangements
are taken into account in EN 1991-1-3:
• undrifted snow load on roofs
• drifted snow load on roofs
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the RoofDetermination of Snow Load on the Roof – –
Definitions of undrifted and drifted snow on roof Definitions of undrifted and drifted snow on roof
undrifted snow load on the roof
load arrangement which describes the uniformlydistributed snow load on the roof, affected only bythe shape of the roof, before any redistribution of
snow due to other climatic actions.
drifted snow load on the roof
load arrangement which describes the snow load
distribution resulting from snow having been movedfrom one location to another location on a roof, e.g.by the action of the wind.
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Professor Haig GulvanessianProfessor Haig Gulvanessian
UndriftedSnowUndriftedSnow load on roofsload on roofs
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the RoofDetermination of Snow Load on the Roof – –
Definitions of undrifted and drifted snow on roof Definitions of undrifted and drifted snow on roof
undrifted snow load on the roof
load arrangement which describes the uniformlydistributed snow load on the roof, affected only bythe shape of the roof, before any redistribution of
snow due to other climatic actions.
drifted snow load on the roof
load arrangement which describes the snow load
distribution resulting from snow having been movedfrom one location to another location on a roof, e.g.by the action of the wind.
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Drifted Snow on Roof With wind speeds in the range of 4 to 5 m/s, much of
the snow is deposited in areas of ’aerod ynam ic shade ’
DRIFTED SNOW LOAD ARRANGEMENT
Model in wind tunnel
wind velocity of 4m/s
Aerodynamic
shade wind wind
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Drifted Snow on Roof
For situations where the wind velocity increases above 4
to 5 m/s snow particles can be picked up from the snow
cover and re-deposited on the lee sides, or on lower roofsin the lee side, or behind obstructions on the roof.
DRIFTED SNOW LOAD ARRANGEMENT
Model in wind tunnel for multi - pitched roof wind velocity > 5 m/s
wind
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof
Drifted snow load on roofs
The National Annex may specify the use alternative driftpatterns dependent on climatic variation (maritime or
continental) for particular roof shapes. The alternatives apply for
specific locations
u where all the snow usually melts and clears between the
individual weather systems and where moderate to high windspeeds occur during the individual weather system. ( Annex B of
EN 1991-1-3: maritime)
u Where the snow that fall is more persistent and where snow
falling in calm conditions may be followed by further snow,
carried by another weather system driven by wind and there
may several repetitions of these events before there is any
significant thawing (Main text of EN 1991-1-3: continental)
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof
Snow loads on roofs for the persistent / transient design
situations are determined as follows:
s = µ i C e C t s k
where:µ i is the snow load shape coefficient
s k is the characteristic value of snow load on the
ground
C e is the exposure coefficient
C t is the thermal coefficient
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof
Snow loads on roofs for the accidental design situationswhere exceptional snow load is treated the accidentalaction is determines as follows
s = µ i C e C t s Ad
where:
µ i is the snow load shape coefficient
s Ad is the characteristic value of exceptional snow loadon the ground for the given location
C e is the exposure coefficient
C t
is the thermal coefficient
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof
Snow loads on for theSnow loads on for the accidental design situations whereaccidental design situations where
exceptional snow drift treated as the accidental actionexceptional snow drift treated as the accidental action andand
wherewhere Annex B Annex B (used in the UK) applies(used in the UK) applies
s =s = µ µ ii s s kk
Where:Where:
µ µ ii is the snow load shape coefficientis the snow load shape coefficient
s s kk is the characteristic value of snow load on theis the characteristic value of snow load on the
groundground
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof –
Exposure Coefficients
exposure coefficient
A coefficient (C e) defining the reduction or increase of snow
load on a roof of an unheated building, as a fraction of the
characteristic snow load on the ground.
The choice for C e should consider the future development
around the site. C e should be taken as 1,0 unless otherwise
specified for different topographies.
The National Annex may give the values of C e for differenttopographies.
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof –
Recommended Exposure Coefficients
Windswept topography, where (C e = 0,8 ) areflat unobstructed areas exposed on allsides without, or little shelter afforded byterrain, higher construction works ortrees.
Normal topography, where (C e = 1,0 ) areas
where there is no significant removal ofsnow by wind on construction work,because of terrain, other constructionworks or trees.
Sheltered topography, where (C e = 1,2 ) areasin which the construction work beingconsidered is considerably lower thanthe surrounding terrain or surroundedby high trees and/or surrounded byhigher construction works.
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof –
Recommended Exposure Coefficients
thermal coefficient A coefficient defining the reduction of snow load on roofsas a function of the heat flux through the roof, causingsnow melting.
The thermal coefficient C t is used to account for thereduction of snow loads on roofs with high thermaltransmittance (> 1 W/m2K), in particular for some glasscovered roofs, because of melting caused by heat loss.
For all other cases: C t = 1,0
Further guidance may be obtained from ISO 4355.
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Exposure (C e) and Thermal (C t) coefficients
u Recommended values obtained from European research
– Monitored snow accumulation
– UK data only small part of data set
u BS National Annex for EN 1991-1-3 specifies values of 1for both C e and C t
Design Situations and load arrangements to be used
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Design Situations and load arrangements to be used
for different locations (Table A1 of EN 1991-1-)
NOTE 1: Exceptional conditions are defined according to the National Annex.
NOTE 2: For cases B1 and B3 the National Annex may define design situations which apply for the particular local
effects described in Section 6 of EN 1991-1-3.
Persistent/transient
design
situation
[1] undrifted i C eC t sk
[2] drifted i C eC t sk(except for roof shapes
in Annex B)
Accidental design
situation (where snow
is the accidental
action)
[3] undrifted i C eC t
C esl sk
[4] drifted i sk (for roof
shapes in Annex B)
Persistent/transient
design
situation
[1] undrifted i C eC t sk
[2] drifted i C eC t sk(except for roof shapes
in Annex B)
Accidental design
situation (where snow
is the accidental
action)
[3] drifted i sk (for roof
shapes in Annex B)
Persistent/transient
design
situation
[1] undrifted i C eC t sk
[2] drifted i C eC t sk Accidental design
situation (where snow
is the accidental
action)
[3] undrifted i C eC tCesl sk
[4] drifted i C eC t C esl
sk
Persistent/transient
design
situation
[1] undrifted i C eC t sk
[2] drifted i C eC t sk
Clause 3.3(3)Clause 3.3(2)Clause 3.3(1)Clause 3.2(1)
Exceptional fallsExceptional driftNo exceptional fallsExceptional driftExceptional fallsNo exceptional driftNo exceptional fallsNo exceptional drift
Case B3Case B2 (e.g. UK)Case B1Case A
Exceptional conditionsNormal
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof –
Shape coefficients – Continental climates
u Section 5 of EN 1991-1-3 gives shape coefficients for
• Undrifted and Drifted snow load cases
• For the following roof shapes
u Mono-pitched
u
Pitchedu Multi-span
u Cylindrical
• Local effects
• Persistant/transient situations
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof –
Shape coefficients – Maritime climates
Annex B of EN 1991-1-3 gives
u Drifted load cases for:
• Multi-span roofs
• Roofs abutting and close to taller structures
• Drifting at projections, obstructions and parapetsu Annex B is based on guidance in BS6399: Part 3
u Considered as exceptional drifts due to classification of
load cases in section 5 of EN 1991-1-3
u Treated as Accidental actions
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof –
Shape coefficients – Mono-pitch roofs
u Snow shape
coefficients for mono-
pitch roofs
u Snow shape
coefficients shown
diagrammatically
2.0
1.0
0° 15° 30° 45° 60°
0.8
1.6
1
2
α
1
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof –
Shape coefficients – Duo-pitch roofs
1
1( 1) 1( 2)
0,5µ 1( 1) 1( 2)
1( 1)
0,5µ 1( 2)
2
Case (i)
Case (ii)
Case (iii)
2.0
1.0
0° 15° 30° 45° 60°
0.8
1.6
1
2
α
Snow shape coefficients for pitch roofs – Continental
climates
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof –Drifted Snow Load Arrangement for maritime climates
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof –
Drifted Snow Load Shape coefficients
maritime climates
0,01,2 (60 –
! )/30
0,8 +
0,4 (! -
15)/15
0,8i
! i "
60º
30º < ! i <
60º
15º < ! i #
30º
0º # ! i #
15º
Angle of
pitch of
roof
(! i , i=1,2)
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof –
Drifted Snow Load Shape coefficients
maritime climates
0,01,2 (60 –
! )/30
0,8 +
0,4 (! -15)/15
0,8i
! i " 60º30º < ! i < 60º15º < ! i # 30º0º # ! i # 15º Angle of pitch
of roof
(! i, for i =1,2)
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the Roof –
Shape coefficients – Multi-span roofs
2.0
1.0
0° 15° 30° 45° 60°
0.8
1.6
1
2
α
1
1( 1)
2 1 2
1( 1) 1( 1)
1( 2)
1( 2) 1( 2)
2( ) = ( 1+ 2)/2
Case (i)
Case (ii)
Snow shape coefficients for multi-span roofs
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Determination of Snow Load on the RoofDetermination of Snow Load on the Roof – – ShapeShape
coefficientscoefficients – –MultiMulti--span roofsspan roofs -- driftingdrifting
µ1(α1) µ1(α2) µ2(α)
α = (α1+ α2)/2
α α2 α
α2
Drifted load case
(Section 5 – Continental climate)
Exceptional Drif ted load case
(Annex B – Maritime climate)
h
b2 b1 b3
ls2 ls1
µ1
Local EffectsLocal Effects
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Local EffectsLocal EffectsDrifting at projections and obstructions
µ1 = 0,8 µ2 = γ h/sk
where
0,8 ≤ µ2 ≤ 2,0
γ = 2 kN/m3 (weight density of
snow)
l s = 2h 5 ≤ l s ≤ 15 m
Snow overhanging the edge of a roof (recommended for sites above 800 m a.s.l.)
se=k s2 / γ
where
γ = 3 kN/m3
γ k = 3 /d < d γ (National Annex)
d is in meters
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Professor Haig GulvanessianProfessor Haig Gulvanessian
EN 1991-1-3 Informative Annexes
u Annex C – European Ground snow load maps
– Majority produced during European Research project
u Annex D – Adjustment of ground snow load for return
period – Expression for data which follow a Gumbel probability
distribution
u Annex E – Densities of snow
– Indicative density values for snow on the ground
Differences between EN 1991 1
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Differences between EN 1991-1-
3 and BS6399: Part 3
u Small Buildings clause not included in EN 1991-1-3
u Imposed loads due to maintenance given in EN 1991-1-1
u Maximum altitude greater in EN 1991-1-3 (1,500m) than in BS 6399
Part 3 (500m)
u Zoned map in EN 1991-1-3 compared with isopleths in BS 6399:
Part 3
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Professor Haig GulvanessianProfessor Haig Gulvanessian
Thank you for yourattention
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