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EUROPEAN STANDARDDRAFTNORME EUROPENNE prEN 13474-3EUROPISCHE NORM June 2008
ICS
Descriptors :
English version
Glass in building - Determination of the strength of glass panes - Part 3: General method of
calculation and determination of strength of glass by testing
Verre dans la construction - Glas im Bauwesen -
This draft European Standard is submitted to the CEN members for CEN enquiry. It has been drawn up
by Technical Committee CEN/TC129.
If this draft becomes a European Standard. CEN members are bound to comply with the
CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.
This draft European Standard was established by CEN in three official versions (English, French,
German). A version in any other language made by translation under the responsibility of a CEN member
into its own language and notified to the Central Secretariat has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France,
Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden,
Switzerland and United Kingdom.
CEN
European Committee for StandardisationComit Europen de Normalisation
Europisches Komitee fr Normung
Central Secretariat: rue de Stassart 36, B-1050 Brussels
___________________________________________________________________________________
c CEN 1991 Copyright reserved to CEN members
Ref. No. prEN 13474-3:2008
CEN TC33 WG6 n. 0109
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Contents list
Foreword
Introduction
1 Scope
2 Normative references
3 Definitions
4 Symbols and abbreviations
5 Requirements
5.1 Basis of determination of glass strength
5.2 General requirements
5.3 Material partial factor
5.4 Process of determining the load resistance of glass
6 Mechanical and physical properties of glass
6.1 Values
6.2 Approximate values
7 Actions
7.1 Assumptions related to the actions and combinations of actions
7.2 Combinations of actions7.3 Wind action
8 Strength and stress
8.1 Allowable stress for annealed glass
8.2 Allowable stress for prestressed glass
9 Calculation principles and conditions
9.1 General method of calculation
9.2 Calculation method for laminated glass and laminated safety glass
9.3 Calculation method for insulating glass units
Annex A (normative): Principles of determining the load resistance of glass by testing
Annex B (informative): Calculation formulae for stress and deflection for large deflections of
rectangular panes supported on all edges
Annex C (informative): Procedure for obtaining the simplified method used in prEN 13474-1
from the four edge supported non-linear method given in prEN 13474-3
Annex D (informative): Calculation process for insulating glass units
Annex YN (informative): Proposal for a model of a National Annex (informative)
Annex ZN (informative): Proposal for a model of a National Annex (informative)
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Foreword
This draft European Standard has been prepared by the Technical Committee CEN TC 129
Glass in Building, the secretariat of which is held by IBN.
CEN/TC 129/WG 8 Mechanical Strength prepared the draft Glass in building -Determination of the strength of glass panes - Part 3: General method of calculation and
determination of strength of glass by testing.
CEN/TC 129 has decided to submit Part 3 of this draft European Standard to the CEN
enquiry.
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Introduction
European Standard prEN 13474 gives the principles of determining the strength of glass for
resistance to loads.
Part 1 of this European Standard gives simple methods for determining by calculation theresistance to load of glass used in fenestration.
Part 2 of this European Standard gives simple methods for determining by calculation the
resistance to load of glass used in common non-structural applications other than
fenestration.
Part 3 of this European Standard gives the general method of calculation of the strength and
load resistance of glass and determination of the load resistance of glass by testing.
The principles of determining the strength of glass to resist loads are based on the structural
Eurocode EN 1990: Basis of structural design. The actions are determined in accordance
with the structural Eurocode series EN 1991: Basis of structural design - Actions on
structures, including the National annexes.
In the design processes, the safety aspect is part of national competency. For that reason this
European Standard foresees that, to conform the rules applied by the Eurocodes, the material
partial factor Mis subject to nationally to determine parameters:
a first value for the ultimate limit state (ULS);
a second value for the serviceability limit state.
Those values can be found in an informative (National) annex to this European Standard.
When a Member State does not use its prerogative and no values for the material partial
factor has been determined, the recommended values given in this European Standard should
be used.
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1 Scope
This European Standard gives the principles of determining the strength of glass to resist
loads. It gives:
the general method of calculation, and determination of load resistance by testing for any application.
For simple calculation of the load resistance of glass products for fenestration or for common
applications other than fenestration, refer to prEN 13474-1 and prEN 13474-2.
This European Standard does not determine suitability for purpose. Resistance to applied
loads is only one part of the design process, which may also need to take into account:
environmental factors (e.g. sound insulation, thermal properties), safety characteristics (e.g. fire performance, breakage characteristics in relation to human
safety, security)
2 Normative references
This European Standard incorporates, by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions
of any of these publications apply to this European Standard only when incorporated by
amendment or revision. For undated references, the latest edition of the publication referred
to applies.
EN 572 Glass in Building - Basic soda lime silicate glass products
EN 572-1 Glass in Building - Basic soda lime silicate glass products - Part 1:
Definitions and general physical and mechanical properties
EN 1036 Glass in building - Mirrors from silver coated float glass for internal use
EN 1096 Glass in building - Coated glass
EN 1296 Glass in building - Insulating glass units
EN 1748-1 Glass in Building - Basic borosilicate glass products
EN 1748-1-1 Glass in Building - Basic borosilicate glass products - Part 1: Definitions
and general physical and mechanical properties
EN 1748-2 Glass in Building - Basic glass ceramics productsEN 1748-2-1 Glass in Building - Basic glass ceramics products - Part 1: Definitions and
general physical and mechanical properties
EN 1863 Glass in building - Heat strengthened soda lime silicate glass
EN 1863-1 Glass in building - Heat strengthened soda lime silicate glass - Part 1:
Definition and description
EN 1990 Eurocode Basis of structural design
EN 1991 Actions on structures
EN 1991-1-4 Wind actions
EN 1997 Geotechnical design
EN 1998 Design of structures for earthquake
EN 12150 Glass in building - Thermally toughened soda lime silicate safety glass
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EN 12150-1 Glass in building - Thermally toughened soda lime silicate safety glass -
Part 1: Definition and description
EN 12337 Glass in building - Chemically strengthened soda lime silicate glass
EN 12337-1 Glass in building - Chemically strengthened soda lime silicate glass - Part
1: Definition and description
EN ISO 12543 Glass in building - Laminated and laminated safety glassEN ISO 12543-1 Glass in building - Laminated and laminated safety glass - Part 1:
Definitions and description of component parts
EN 13024 Glass in building - Thermally toughened borosilicate safety glass
EN 13024-1 Glass in building - Thermally toughened borosilicate safety glass - Part 1:
Definition and description
prEN 13474-1 Glass in building - Determination of the strength of glass panes - Part 1:
Glass and glass products for fenestration
prEN 13474-2 Glass in building - Determination of the strength of glass panes - Part 2:
Common glass applications other than fenestration
EN 14178 Glass in Building - Basic alkaline earth silicate glass products
EN 14178-1 Glass in Building - Basic alkaline earth silicate glass products - Part 1:
Definitions and general physical and mechanical properties
EN 14179 Glass in building - Heat soaked thermally toughened soda lime silicate
safety glass
EN 14179-1 Glass in building - Heat soaked thermally toughened soda lime silicate
safety glass - Part 1: Definition and description
EN 14321-1 Glass in building - Thermally toughened alkaline earth silicate safety glass
EN 14321-1 Glass in building - Thermally toughened alkaline earth silicate safety glass
- Part 1: Definition and description
EN 14449 Glass in building - Laminated glass and laminated safety glass -
Evaluation of conformity/Product Standard
3 Definitions
3.1 annealed glass
Glass which has been treated during manufacture to minimise the residual stress in the glass,
allowing it to be cut by scoring and snapping. Examples are float glass, drawn sheet glass,
patterned glass and wired glass.
3.2 effective thickness (of laminated glass)
A thickness calculated for laminated glass which, when used in place of the glass thickness in
an engineering formula, will result in a reasonably accurate determination of the deflection of
and / or stress in the laminated glass.
3.3 prestressed glass
Glass which has been subjected to a strengthening treatment, by heat or chemicals, which
induces a compressive surface stress into the whole surface of the glass, balanced by a tensile
stress within the body of the glass. Examples are thermally toughened safety glass, heatstrengthened glass and chemically strengthened glass.
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3.4 structures and infill panels
3.4.1 main Structure
The beams, the columns, the floor forming the main structure of
the building (see figure 1).
Note. These are structural for so far that they carry themselves
and secondary structures, and, in case of failure, endanger the
fundamental stability of the building. The main structural
elements must have a safety and a reliability appropriate to their
design use and larger factor of safety than the one applicable to
the secondary structure or to the non structural infill elements.
These main structures are the reference structure and constitute
the point of reference for the coefficients determined hereafter.
3.4.2 secondary structure (e.g. glass fins)
Windows assembly frames, which are secondary structures
insofar as their stability is their own.
Note. A failure of these secondary structures only affects the
infill panels or the non-structural elements carried by this
secondary structure and in no case has any effects on the main
structure of the building. The secondary structures can be
replaced independently of the main structures.
3.4.3 infill panels
Elements placed in structures in order to close a building and which do not contribute in any
manner to the stability of the main structure.
Note.
3.4.4 classes of consequence
Classes which allow for the fact that the failure of the secondary structures or the infill panels
does not have the same economic and/or human consequences of that of the failure of the
main structures.
Note. A reduced factor of safety is thus acceptable on the actions. The coefficient of class of
consequence, kFI,expresses the reduction of safety applicable to the secondary structures and
infill panels compared to that applicable for the main structures according to the EN 1990
appendix B. This coefficient is integrated in the partial coefficients relating to the actions, Q
and G, except in the case where the action has a favourable effect in a combination of
actions. The coefficient of class of consequence does not apply to the partial coefficients
relating to materials.
Infill panel
Secondary structure
Main structure
Figure 1.
Identification of
structure
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3.5 unfactored load
an action as obtained from EN 1991 (e.g. wind load, snow load), including all the factors
relevant for determining the action, but before applying the partial factors for actions Q, G
and/or
4 Symbols and abbreviations
A Surface area of the pane ( = ax b)
a Shorter dimension of the pane
a* Characteristic length of an insulating glass unit
b Longer dimension of the pane
Cd Limiting design value of the relevant serviceability criterion
cH Coefficient for the effect of altitude change on isochore pressure (=0,12 kPa/m)
cprob Probability factor applied to the wind pressure for different return periods
cT Coefficient for the effect of cavity temperature change on isochore pressure(=0,34 kPa/K)
E Youngs modulus
Ed Effect of the action(s)
ESLS;d Serviceability limit state design value of the effect of the action(s)
EULS;d Ultimate limit state design value of the effect of the action(s)
E{FSLS;d}
Calculation of the effect of the serviceability limit state design value
E{FULS;d}
Calculation of the effect of the ultimate limit state design value
Fd Design value of the actionFd;1 Design value of the action on pane 1 of an insulating glass unit
Fd;2 Design value of the action on pane 2 of an insulating glass unit
FSLS;d Serviceability limit state design value of a single action or of a combination of
actions.
FULS;d Ultimate limit state design value of a single action or of a combination of actions.
fb;k Characteristic value of the bending strength of prestressed glass
fg;d Allowable maximum stress for the surface of glass panes
fg;k Characteristic value of the bending strength of annealed glass
G Value of self weight load
H Altitude
HP Altitude of production of insulating glass unith Nominal thickness of the pane
h1 Nominal thickness of pane 1 of an insulating glass unit or ply 1 of a laminated
glass
h2 Nominal thickness of pane 2 of an insulating glass unit or ply 2 of a laminated
glass
h3 Nominal thickness of pane 3 of an insulating glass unit or ply 3 of a laminated
glass
hef;w Effective thickness of a laminated glass for calculating out-of-plane bending
deflection
hef;;j Effective thickness of a laminated glass for calculating out-of-plane bending
stress of plyj
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hi Nominal thickness of pane i of an insulating glass unit or ply i of a laminated
glass
hj Nominal thickness of pane j of an insulating glass unit or ply j of a laminated
glass
hm;1 the distance of the mid-plane of the glass ply 1 from the mid-plane of the
laminated glass, ignoring the thickness of the interlayershm;2 the distance of the mid-plane of the glass ply 2 from the mid-plane of the
laminated glass, ignoring the thickness of the interlayers
hm;3 the distance of the mid-plane of the glass ply 3 from the mid-plane of the
laminated glass, ignoring the thickness of the interlayers
hm;j the distance of the mid-plane of the glass ply j from the mid-plane of the
laminated glass, ignoring the thickness of the interlayers
k1 Coefficient used in the calculation of large deflection stresses
k4 Coefficient used in the calculation of large deflection deflections
k5 Coefficient used in the calculation of large deflection volume changes
kFI Coefficient of class of consequence expressing the reduction of safety applicable
to the secondary structures and infill panels compared to that applicable for the
main structures
kmod Factor for the load duration
kmod;c Factor for the load duration when there are combined loads
ksp Factor for the glass surface profile
kv Factor for strengthening of prestressed glass
p Air pressure
p0 Isochore pressure for an insulating glass unit
pC;0 Isochore pressure due to the effect of change in cavity temperature and air
pressure
pH;0 Isochore pressure due to the effect of change in altitudepP Air pressure at the time of production of insulating glass unit
p* Non-dimensional uniformly distributed load
Qk,1 Value of the single action or dominant action
Qk,i Values of the actions which are not dominant
Rd Design value of the resistance to the actions
s Nominal cavity width of a double glazed insulating glass unit
T Insulating glass unit cavity temperature
TP Temperature of production of insulating glass unit
t Load duration (in hours)
V Volume change in an insulating glass unit cavity due to the deflection of one of
the paneswd Allowable deflection
wmax Maximum deflection calculated for the design load
z1 Coefficient used in the approximate calculation of k4
z2 Coefficient used in the approximate calculation of k1
z3 Coefficient used in the approximate calculation of k1
z4 Coefficient used in the approximate calculation of k1
1 Stiffness partition for pane 1 of an insulating glass unit
2 Stiffness partition for pane 2 of an insulating glass unit
G Partial factor for permanent actions, also accounting for model uncertainties and
dimensional variationsM Material partial factor
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M;A Material partial factor for annealed glass
M;v Material partial factor for surface prestress
Q Partial factor for variable actions, also accounting for model uncertainties and
dimensional variations
Insulating glass unit factor
Aspect ratio of the pane ( ba ) Poisson number
Glass density
max Maximum stress calculated for the design load
Coefficient for the shear transfer of an interlayer in laminated glass
Combination factors for the actions
0,i Combination factors for the actions which are not dominant
1 Partial factor for a frequent value of a variable action
Note. This value is determined - in so far as it can be fixed on statistical bases -
so that either the total time, within the reference period, during which it isexceeded is only a small given part of the reference period, or the frequency of it
being exceeded is limited to a given value. It may be expressed as a determined
part of the characteristic value by using a factor 11
2 Combination factor for a quasi-permanent value of a variable action
Note. This value is determined so that the total period of time for which it will be
exceeded is a large fraction of the reference period. It may be expressed as a
determined part of the characteristic value by using a factor 21
2,i Combination factor for a quasi-permanent value of a variable action
Note. This value is determined so that the total period of time for which it will be
exceeded is a large fraction of the reference period. It may be expressed as a
determined part of the characteristic value by using a factor 2;i1
5 Requirements
5.1 Basis of determination of glass strength
The process shall conform to EN 1990: Eurocode Basis of structural design.
The determination of actions shall be in accordance with the relevant parts of EN 1991:
Actions on structures. Where relevant or required, the following shall also be taken into
account.
EN 1997: Geotechnical design, and EN 1998: Design of structures for earthquake design.
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5.2 General requirements
Table 1: Table of requirements for the various limit states
Ultimate limit state Serviceability limit state
Requirement ddULS RE ; (1.a) ddSLS CE ; (1.b)where the effect of the
actions is:dULSdULS FEE ;; (2.a) dSLSdSLS FEE ;; (2.b)
in which: FULS;d is the Ultimate Limit
State design value of a single
action or of a combination of
actions.
FSLS;d is the Serviceability
Limit State design value of a
single action or of a
combination of actions.
and
where:
EULS;d is the design value of the effect of the action(s), expressed as
calculated stress, caused by the action(s).
Rd is the design value of the corresponding resistance, expressed
as maximum ultimate limit state allowable stress fg;d, takinginto account the material partial factor for the ultimate limit
state M(see 5.3).
ESLS;d is the design value of the effect of the action(s), expressed as
calculated stress or deflection, caused by the action(s).
Cd is the limiting design value of the relevant serviceability
criterion, expressed as maximum serviceability limit state
allowable stress fg;d, or limit on deflection, wd, taking into
account the material partial factor for the serviceability limit
state M(see 5.3).
5.3 Material partial factor
The recommended values of the material partial factor are given in table 2.
Table 2: Recommended values of the material partial factor
Ultimate limit state Serviceability limit state
Annealed glass(1) M;A= 1,8 M;A= 1,0
Surface prestress M;v= 1,2 M;v= 1,0
Note (1). The material partial factor for annealed glass is also applied to a
component of the strength of prestressed glass - see equation (7).
For specific National values, see Annex ZN.
5.4 Process of determining the load resistance of glass
For any calculation or test, the mechanical and physical properties of glass shall be
determined in accordance with clause 6.
The design value of the actions shall be determined in accordance with clause 7.
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The allowable stresses for the glass, for the ultimate limit state and for the serviceability limit
state (if required), shall be determined in accordance with clause 8.
Where a design deformation limit applies for the serviceability limit state, such a value shall
be determined in accordance with EN 1990. Where no other standard specifies a design
deformation limit, this shall be determined in accordance with 9.1.4.
For calculations, the principles and conditions shall be in accordance with clause 9.
Determination of load resistance by testing, or assisted by testing, shall be in accordance with
annex A.
6 Mechanical and physical properties of glass
6.1 Values
The values of the mechanical and physical properties needed for calculation, such as Young's
modulusE, the Poisson number , and the density of glass, are obtained from the following
product standards:
EN 572-1, EN 1748-1-1, EN 1748-2-1, EN 1863-1, EN 12150-1, EN 12337-1,
EN ISO 12543-1, EN 13024-1, EN 14178-1, EN 14179-1, EN 14321-1.
6.2 Approximate values
When (e.g. for assembling different glass materials) no distinction between the variousdifferences in mechanical and physical properties can be taken into account, or when it is not
necessary, the following values may be used:
glass density = 2 500 kg/m;
Youngs modulus E= 70 000 MPa;
Poisson number = 0,22;
These values are applicable approximations for glasses with:
a density between 2 250 and 2 750 kg/m; a Youngs modulus between 63 000 MPa and 77 000 MPa
a Poisson number between 0,20 and 0,25
These ranges cover the following glass materials (the list not exhaustive):
Basic soda lime silicate glass products conforming to EN 572 and processed glassproducts made from these basic glass products such as heat strengthened glass
conforming to EN 1863, chemically strengthened glass conforming to EN 12337,
thermally toughened soda lime silicate safety glass conforming to EN 12150 and heat
soaked thermally toughened soda lime silicate safety glass conforming to EN 14179.
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Basic borosilicate glass conforming to EN 1748-1, and processed glass products made ofthis basic glass such as thermally toughened borosilicate safety glass conforming to
EN 13024.
Basic glass ceramics conforming to EN 1748-2, and processed glass products made ofthis basic glass.
Basis alkaline earth silicate glass conforming to EN 14178-1, and processed glassproducts made of this basic glass such as thermally toughened alkaline earth silicate
safety glass in accordance with EN 14321.
Coated glass conforming to EN 1096 made using one of the above types of glass Mirror glass conforming to EN 1036 made using one of the above types of glass Assembled glass made of one or more of the glass types listed above such as laminated
glass and laminated safety glass conforming to EN 14449 and EN 12543.
Assembled glass made of one or more of the glass types listed above such as insulatingglass units conforming to EN 1279.
7 Actions
7.1 Assumptions related to the actions and combinations of actions
With regard to actions and combinations of actions in the service limit state, the frequent
combination applies. (see EN 1990 clauses 6.5.3 and 4.1.3)
With regard to the combination of the actions in an ultimate limit state, the fundamental
combination applies. (See EN 1990 clauses 6.5.3 and 4.1.3)
7.2 Combinations of actions
The values of the actions shall be determined in accordance with the appropriate parts of EN
1991.
The design value of the action (design load) shall be:
for ultimate limit state i
ikiQkQGd QQGF ,,01, ""."". (3.a)
for serviceability limit state i
ikikd QQGF ,,21,1 ""."" (3.b)
where:
Fdis the design value of the combination of actions;
Gis the value of permanent actions (e.g. self-weight load, permanent equipment);
Qk,1 is the characteristic value of the leading variable action (e.g. imposed load on
floor, wind, snow),
Qk,iis the characteristic value of the accompanying variable action (e.g. wind, snow)
0,iare factors for combination value of accompanying variable actions
1is the factor for frequent value of a variable action
2,i:is the factor for quasi-permanent value of a variable action
G is the partial factor for permanent actions, also accounting for model uncertainties
and dimensional variations
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Q: is the partial factor for variable actions, also accounting for model uncertainties
and dimensional variations
The recommended values of the partial load factors, , are given in table 3.
Table 3: Partial load factors
Type of element to be
calculatedG
(3)Q
favourable unfavourable
Main structure(1) see
Eurocodes
see
Eurocodes
see
Eurocodes
Secondary structure(1) 1,3 1,0 1,2
Infill panel(2) 1,1 1,0 1,1
Notes.
(1) Structural construction covered by Eurocodes(2) Non structural element not covered by Eurocodes
(3) The lower value is used when the permanent action has a
favourable effect in combination with other actions. The
higher value is used when the permanent action is
considered acting alone or has a unfavourable effect in
combination with other loads.
For specific National values, see Annex YN.
The recommended values of the partial factors, , are given in table 4.
Table 4: factors
Main structure(1) Secondary structure(1) Infill panel(2)
Wind 0 see Eurocodes 0,6 0,6
1 see Eurocodes 0,9 0,9
2 see Eurocodes 0,2 0,2
Snow 0 see Eurocodes 0,6 0,6
1 see Eurocodes 1,0 1,0
2 see Eurocodes 0,2 0,2
Other 01
2
See Eurocodes or national annexes
Notes.
(1) Structural construction covered by Eurocodes
(2) Non structural element not covered by Eurocodes
For specific National values, see Annex YN.
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7.3 Wind action
The wind actions calculated using EN 1991-1-4 are characteristic values (See EN 1990,
4.1.2). They are determined from the basic values of wind velocity or the velocity pressure.
In accordance with EN 1990 4.1.2 (7)P, the basic values are characteristic values which are
exceeded with an annual probability of 0,02, which is equivalent to a mean return period of50 years.
NOTE: All coefficients or models used to derive wind actions from basic values are chosen
so that the probability of the calculated wind actions does not exceed the probability of these
basic values.
A probability factor, cprob, can be applied to the design wind pressure allowing for a different
wind return period. Values are given in table 5.
Table 5: cprob values
Years cprob Years cprob
1 0,241222 30 0,935845
5 0,702303 40 0,972028
10 0,795309 50 1
15 0,847782 60 1,022806
20 0,884522 65 1,032807
25 0,912822 70 1,042061
8 Strength and stress
8.1 Allowable stress for annealed glass
8.1.1 Formulae
The allowable stress for annealed glass material, whichever composition, is
AM
kgsp
dg
fkkf
;
;mod
;
(4)
where fg;k is the characteristic value of the bending strength (fg;k= 45 N/mm2).
M;A is the material partial factor for annealed glass (see 5.3 and Annex ZN).
ksp is the factor for the glass surface profile (see 8.1.2).
kmod is the factor for the load duration(see 8.1.3).
NOTE 1. CEN report CR rrr explains the origin of the value of fg;k.
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8.1.2 Glass surface profile factor
The factor for the glass surface profile is given in table 6.
Table 6: Factor for the glass surface profile
Glass material
(whichever glass composition)
Factor for the glass surface profile ksp
Float glass 1,0
Drawn sheet glass 1,0
Enamelled float or drawn sheet glass(1) (1,0)
Patterned glass 0,75
Enamelled patterned glass(1) (0,75)
Polished wired glass 0,75
Patterned wired glass 0,6
Note 1. These glass types are not generally available as annealed glass, but the values of kspare also required in the formulae for prestressed glass (see 8.2).
8.1.3 Factor for duration of load
The factor for the load duration of annealed glass is
16
1
mod 663,0
tk (5)
where tis the load duration in hours.
The factor kmodhas a maximum value of kmod= 1 and a minimum value of kmod= 0,25.
Typical values of kmodare given in table 7.
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Table 7: Factors for load duration
Action Load duration kmodpersonnel loads short, single(1) 0,85
wind short, multiple 0,74
snow intermediate(2) 0,44daily temperature variation
11 hours extreme peak duration
intermediate 0,57
barometric pressure variation intermediate 0,50
yearly temperature variation
6 month extreme mean value
duration
intermediate 0,39
dead load, self weight permanent 0,29
Notes: (1) The value of kmod=0,85 is based on a personnel load of 1 minute duration.
Other values may be considered depending on the type of personnel load being
evaluated and also the building use.(2) kmod=0,44 can be considered representative for snow loads lasting between
1 week (kmod=0,48) and 3 months (kmod=0,41). Other values of kmodmay be
appropriate depending on local climate.
Where loads with different durations need to be treated in combination, the appropriate factor
for load duration for the combined loads, kmod;c, is determined from the following equation.
i i
iULSULS
G
GULS
i
iULSULSGULS
c
k
E
k
E
k
E
EEE
k
mod;
;
1mod;
1;
mod;
;
;1;;
mod; (6)
8.2 Allowable stress of prestressed glass
8.2.1 Formula
The allowable stress of prestressed glass material, whichever composition is
vM
kgkbv
AM
kgsp
dg
ffkfkk
f;
;;
;
;mod
;
(7)
where fg;k, M;A, kmodand kspare described in 8.1.
M;v is the material partial factor for surface prestress (see 5.3 and Annex ZN).
fb;k is the characteristic value of the bending strength of prestressed glass (see
8.2.2).
kv is the factor for strengthening of prestressed glass (see 8.2.3).
8.2.2 Characteristic bending strength
The values of characteristic bending strength for prestressed glass are given in table 9.
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Table 9: Values of characteristic strength and strengthening factors
for prestressed glass
Values for characteristic bending strengthfb;k
for prestressed glass processed from:
Glass
material per
product(whichever
composition)
thermally toughened safety glass,and
heat soaked thermally toughened
safety glass
heat strengthenedglass
chemicallystrengthened glass
float glass or
drawn sheet
glass
120 N/mm2 70 N/mm2 150 N/mm2
patterned
glass 90 N/mm2 55 N/mm2 150 N/mm2
enamelledfloat or
drawn sheet
glass
75 N/mm2 45 N/mm2
enamelled
patterned
glass
75 N/mm2 45 N/mm2
8.2.3 Strengthening factor
The presence of tong marks in vertically toughened glass reduces the effectiveness of the
prestressing locally compared with horizontally toughened glass which has no tong marks.The strengthening factor for method of manufacture is given in table 10.
Table 10: Strengthening factor
Manufacturing process Strengthening factor, kv
Horizontal toughening
(or other process without the use of tongs or
other devices to hold the glass)
1,0
Vertical toughening
(or other process using tongs or other devices
to hold the glass)
0,6
9 Calculation principles and conditions
9.1 General method of calculation
9.1.1 Design load
The characteristic value of the design load,Fd, shall be determined in accordance with clause
7.
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Note: If glass is used in an application where there is no specific design load from
standards or regulations, consideration should be given to using a glass thickness
sufficient to resist an unfactored short duration uniformly distributed load of
500 N/m2.
9.1.2 Stress and deflection calculation
The design load shall be used for calculating the tensile or tensile bending stress in the glass
and the deflection of the glass.
The method used for the determination shall be an engineering formula or method
appropriate to the load distribution, the shape of the glass and the support conditions. For
common applications of glass, Part 1 and Part 2 of this European Standard give simple
methods.
In general, the maximum stress and the maximum deflection, wmax, shall be calculated
according to linear theory. Where the deflection induced by the actions exceeds half theglass thickness, linear theory of plate bending may excessively overestimate the stresses and
maximum deflection. In this case the stress distribution and maximum deflection can be
calculated according to non-linear plate theory. Annex B gives formulae for non-linear
calculations for four-edge supported rectangular panes.
Note: For fenestration, Part 1 of this European Standard gives an approximate
method using glass factors to compensate for the use of linear plate bending theory in
fenestration, where the effect of actions is generally non-linear. The derivation of this
is given in Annex C.
For laminated glass, the stress in each ply shall be calculated. For insulating glass units, the
stress in each pane shall be calculated. A method for determining the loads applied to each
pane of an insulating glass unit is given in Annex D.
9.1.3 Allowable stress
The allowable stress, fg;d, shall be determined according to clause 8. The value of the load
duration factor used to calculate the allowable stress shall be appropriate to the anticipated
duration of the single load (or the dominant load where there are combined loads).
9.1.4 Allowable deflection
There is no specific requirement of glass to limit the deflection of the glass under load. Other
standards or regulations may require deflection limits for particular applications.
If required, the allowable deflection, wd, shall be in accordance with the appropriate standard
or regulation.
Consideration should be given to ensuring the glass is not excessively flexible when
subjected to applied loads, as this can cause alarm to building users. In the absence of any
specific requirement, deflections shall be limited to Span/65 or 50 mm, whichever is the
lower value.
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9.1.5 Comparisons of stress and deflection
The maximum stress calculated for the design load shall not exceed the allowable stress:
max fg;d (8)
If there is a requirement for limitation of the glass deflection, the maximum deflectioncalculated for the most onerous load condition shall not exceed the allowable deflection:
wmax wd (9)
If there are combinations of loads to be considered, it may be necessary to perform the
procedures in 9.1.1 to 9.1.5 more than once, taking alternative loads as the dominant load, in
order to determine the most onerous condition. The most onerous condition is either:
- the highest value of the effective stress, in relation to the allowable stress based on
the duration of the dominant load; or
- the largest value of maximum deflection.
Note: The most onerous condition may differ for stress and deflection.
9.2 Calculation method for laminated glass and laminated safety glass
9.2.1 Calculation method
In cases where shear stress is developed in laminated glass parallel with the interlayer, the
interlayer can be considered as having some shear resistance. This can be taken into account
in evaluating resistance to bending of the laminated glass using a suitable engineeringformula in combination with the shear resistance of the interlayer.
The following approach, using the concept of effective thickness can be used.
The effective thickness for calculating bending deflection is:
3 33; 1 i ii iwef hhh (10)
and the effective thickness for calculating the stress of glass ply numberjis:
jmj
wef
jefhh
hh
;
3
;
;;2
(11)
where is a coefficient between 0 and 1 representing no shear transfer (0) and full shear
transfer (1),
hi, hjare the thicknesses of the glass plies (see figure 2), and
hm;j is the distance of the mid-plane of the glass ply j from the mid-plane of the
laminated glass, ignoring the thickness of the interlayers (see figure 2).
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The effective thicknesses for calculating stresses and deflection in laminated glass
comprising two plies of the same thickness using a value of = 0.25 are given in table 11.
Table 11. Effective thicknesses of laminated glass
with two plies of the same thickness and = 0.25
Short duration loads (= 0.25) Long duration loads (= 0.05)Glass thickness
mm hef;wmm hef;;jmm hef;wmm hef;;jmm
3 + 3 4.55 5.02 3.96 4.44
4 + 4 6.07 6.69 5.28 5.92
5 + 5 7.59 8.37 6.60 7.40
6 + 6 9.11 10.04 7.92 8.88
8 + 8 12.15 13.39 10.56 11.84
10 + 10 15.18 16.73 13.20 14.80
9.2.2 Determination of
The value of to be used for a specific interlayer and a particular load case depends on the
interlayer stiffness family to which the interlayer belongs for that particular load case.
The interlayer stiffness families and the equivalent values of are given in table 12.
Table 12. Value of associated with interlayer stiffness family
Interlayer stiffness family Value of
3 0.6 ?
2 0.25 ?
1 0.1 ?
0 0
1
2
h1
h2
h3
hm;1
hm;2
hm;3
1 Mid-plane of each glass ply
2 Mid-plane of laminated glass
Figure 2. Example of laminated glass thickness dimensions
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Each interlayer has its interlayer stiffness family assigned for a number of different load
cases according to the test method and evaluation from EN vwxyz. The load cases are given
in table 13.
Table 13. Load cases
Load case Load duration Temperature range
Wind load 3 seconds 0 oC < < 20 oCPersonnel loads - normal duty 30 seconds 0 oC < < 30 oCPersonnel loads - crowds 5 minutes 0 oC < < 30 oCSnow load - external canopies 3 weeks -20 oC < < 0 oCSnow load - roofs 3 weeks -20 oC < < 20 oCPermanent 50 years -20 oC < < 40 oC
Editorial note: The above are examples. The load cases, durations and temperature ranges
are to be determined by the CEN/TC129/WG8 full committee.
9.3 Calculation method for insulating glass units
The calculation method for insulating glass units conforming to EN 1279 shall take into
account the consequences arising from the presence of the hermetically sealed and fixed
quantity of gas within the cavity or cavities of the insulating glass unit. This shall take into
account:
the presence of the fixed quantity of gas causing actions which are applied to only one
pane to develop effects in all the panes in the insulating glass unit (a phenomenon alsoknown as load sharing);
changes in ambient barometric pressure conditions relative to the barometric pressure atthe time of sealing the insulating glass unit causing actions (internal actions) which
develop effects in all the panes;
changes in the temperature of the gas in the cavity causing actions (internal actions)which develop effects in all the panes.
A method is given in Annex D for determining the proportions of the loads applied to the
individual panes of a double glazed insulating glass unit.
If insulating glass units conform to EN 1279-5, then the stresses generated in the seal whenthe units are subjected to normally expected loads in service - e.g. wind, snow, self-weight,
personnel, or climatic, but excluding exceptional loads such as explosion pressures - will not
cause premature failure of the hermetic seal, provided the deflection of the glass is not
excessive.
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Annex A (normative)
Principles of determining the load resistance of glass by testing
A.1 General
Testing of glass as a construction element or part thereof shall preferably be performed on
full scale models. Where models different from full scale are used, appropriate techniques
shall be used to:
verify that calculated and measured values for the model used do not differ significantly; evaluate the expected deformations and stresses for the considered construction element
with a reliable degree of accuracy and confidence.
For the ultimate limit state the following requirement applies.
dd RE (A.1)
where Edis the effect of the action(s), expressed:
as measured stress;
or as an evaluated stress on the basis of the measured stress when no 1 to 1
scale model has been used;
caused by the action(s), which shall be determined in accordance with clause 7 of this
European Standard.
Rdis the design value of the corresponding resistance, expressed;
as the maximum allowable stress, fg;d, determined in accordance with this
European Standard.
For the serviceability limit state the following requirement applies
dd CE (A.2)
where Edis the effect of the action(s), expressed:
as measured stress;
or as an evaluated stress on the basis of the measured stress when no 1 to 1
scale model has been used;
or as deformation;caused by the action(s), which shall be determined in accordance with clause 7 of this
European Standard.
Cdis the limiting design value, expressed;
as the maximum allowable stress, fg;d, determined in accordance with this
European Standard;
or as the maximum allowable deformation in accordance with this European
Standard.
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A.2 Factors affecting load resistance
Glass is a homogeneous isotropic material having almost perfect linear-elastic behaviour over its
tensile strength range.
Glass has a very high compressive strength and theoretically a very high tensile strength, but thesurface of the glass has many irregularities which act as weaknesses when glass is subjected to
tensile stress. These irregularities are caused by attack from moisture and by contact with hard
materials (e.g. grit) and are continually modified by moisture which is always present in the air.
Tensile strengths of around 10 000 N/mm2can be predicted from the molecular structure, but
bulk glass normally fails at stresses considerably below 100 N/mm2.
The presence of the irregularities and their modification by moisture contributes to the properties
of glass which need consideration when performing tests of strength.
Because of the very high compressive strength, glass always fails under tensile stress. Since
glass in buildings is very rarely used in direct tension, the most important property for load
resistance is the tensile bending strength.
The major influences on the bending strength and load resistance of glass are the following
factors:
a) rate and duration of loading;
b) area of surface stressed in tension;
c) the surface condition.
The bending strength and load resistance of laminated glass is also influenced by the following
factors affecting the interlayer properties:
d) rate and duration of loading giving rise to creep of the interlayer;
e) temperature affecting the stiffness of the interlayer.
The influence exerted by factors a) to e) on bending strength and load resistance should be taken
into account in the testing method and/or subsequent analysis.
A.3 Effect of rate and duration of loading
Since glass is linearly elastic, altering the rate or duration of load does not affect stresses or
deflections if all the other components are also linearly elastic. However the duration of the
load has a significant effect on the ultimate strength. In particular, if the design load is long
duration, it is not sensible to test to ultimate failure in a short duration test. Better is to
measure the induced stress (e.g. by the use of strain gauges) and compare it with the
allowable long duration stress.
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For laminated glass there is no simple way to measure the stresses in a short duration test to
obtain an estimate of long duration stresses, since the greater shear transfer over short
duration can develop significantly different stresses in the glass plies. The test and the
analysis model need to take this into account.
A.4 Effect of stressed surface area
There is an area effect on glass strength depending on the specimen size. On average,
smaller sizes will break at higher stresses than larger sizes. This can be overcome by using
test specimens of sizes representative of the application. It affects only the breakage stress,
not the stress generated by a specific load.
The interlaminar shear transfer in laminated glass is size dependent. Larger pane sizes have
greater shear transfer than smaller pane sizes. The test specimen sizes should be
representative of the application.
A.5 Surface condition
The variation in microscopic flaws in glass surfaces means that the load resistance obtained
in a test to ultimate failure of nominally identical glass specimens can vary by a factor of 4.
Caution should be used in assessing factors of safety related to ultimate strength tests unless a
large number have been performed (more than 10 to obtain a reliable mean strength and more
than 20 in order to obtain a reliable characteristic strength).
A.6 Temperature
Variations of temperature within the range normally obtained in buildings have negligibleeffect on the reaction of glass to load and stress. Temperature can have a major effect on the
properties of laminated glass interlayers. Where possible tests on laminated glass should be
conducted at a temperature representative of service.
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Annex B (informative)
Calculation formulae for stress and deflection for large deflections of
rectangular panes supported on all edges.
Of the dimensions aand bof the pane, ashall be taken as the shorter dimension. The aspect
ratio is given by = a/band the area is given byA= ab
For practical determination of the stress, the deflection and the change in volume (for the
cavity of insulating glass units), formulae are given as follows:
Maximum tensile bending stress dFh
Ak
21max (B1)
Deflection E
F
h
A
kwd
3
2
4max (B2)
VolumeE
F
h
AkV d
3
3
5 (B3)
The values of the coefficients are given in tables B.1 to B.3.
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In case of four-edge supported panes, the dimensionless coefficients k1and k4, depend on the
aspect ratio, , and the non-dimensional load.
Non-dimensional loadE
F
h
Ap d
2
24*
(B4)
The coefficients in tables B.1 to B.3 are valid for a Poisson number in the range 0,20 to 0,24.
They can be interpolated linearly. For small deflections (linear theory) the values for p* = 0
apply.
Table B.1: Coefficient k1for calculation of the maximum stress
p*
=a/b 0 1 2 3 5 10 20 50 100 200 300
1,0 0.268 0.261 0.244 0.223 0.190 0.152 0.135 0.130 0.129 0.128 0.128
0,9 0.287 0.278 0.258 0.234 0.197 0.155 0.137 0.131 0.130 0.129 0.129
0,8 0.304 0.295 0.273 0.247 0.205 0.159 0.138 0.131 0.130 0.130 0.130
0,7 0.314 0.306 0.285 0.261 0.218 0.165 0.140 0.130 0.129 0.129 0.1290,6 0.314 0.309 0.294 0.274 0.235 0.176 0.143 0.129 0.127 0.126 0.126
0,5 0.300 0.298 0.290 0.279 0.253 0.197 0.151 0.128 0.124 0.123 0.122
0,4 0.268 0.268 0.266 0.262 0.252 0.221 0.171 0.129 0.119 0.116 0.116
0,3 0.217 0.217 0.217 0.216 0.215 0.208 0.189 0.141 0.116 0.107 0.105
0,2 0.149 0.149 0.149 0.149 0.149 0.149 0.148 0.140 0.123 0.100 0.091
0,1 0.075 0.075 0.075 0.075 0.075 0.075 0.075 0.075 0.075 0.074 0.073
For the purposes of calculation:
5.0
2
4
2
3
2
2
2
1
*
*14
1
pzz
p
z
k
where
073.1
2 11
17.1exp10803.00447.024
z
5.411
5.4
2
3
z
11
05.0585.04
z
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Table B.2: Coefficient k4for calculation of the maximum deflection
p*
=a/b 0 1 2 3 5 10 20 50 100 200 300
1,0 0.0461 0.0414 0.0354 0.0310 0.0255 0.0189 0.0137 0.0088 0.0062 0.0044 0.0036
0,9 0.0452 0.0409 0.0351 0.0309 0.0254 0.0188 0.0136 0.0088 0.0062 0.0044 0.0036
0,8 0.0437 0.0399 0.0346 0.0305 0.0253 0.0188 0.0136 0.0087 0.0062 0.0044 0.0036
0,7 0.0404 0.0377 0.0333 0.0297 0.0248 0.0186 0.0136 0.0087 0.0062 0.0044 0.0036
0,6 0.0354 0.0339 0.0309 0.0281 0.0240 0.0183 0.0134 0.0087 0.0062 0.0044 0.0036
0,5 0.0287 0.0281 0.0267 0.0251 0.0222 0.0176 0.0132 0.0086 0.0062 0.0044 0.0036
0,4 0.0208 0.0207 0.0204 0.0199 0.0187 0.0159 0.0125 0.0085 0.0061 0.0044 0.0036
0,3 0.0128 0.0128 0.0127 0.0127 0.0125 0.0119 0.0105 0.0079 0.0059 0.0043 0.0035
0,2 0.0059 0.0059 0.0059 0.0059 0.0059 0.0059 0.0058 0.0055 0.0048 0.0038 0.0033
0,1 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015
For the purposes of calculation:
*16
2
1
*4
15.0
21
5.0
2
41
4p
zpz
k
where 1.097
2 2
1
1192 1 0.00406 0.00896 1 exp 1.123 1z
Note: For p*=0,16
14
zk
Table B.3: Coefficient k5 for calculation of the volume change
=a/b 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1
k5 0,0190 0,0186 0,0181 0,0169 0,0150 0,0124 0,0094 0,0061 0,0031 0,00086
E.
Dupont 0,0196 0,0192 0,0186 0,0174 0,0153 0,0126 0,0094 0,0061 0,0031 0,00086
For the purposes of calculation :-
33.1
15 8.6exp22.04198.016 z
k
where z1is given in table B.2
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Annex C (Informative)
Procedure for obtaining the simplified method used in prEN 13474-1 from
the four edge supported non-linear method given in prEN 13474-3
Proposed to insert the contents of document CEN/TC129/WG8 - N186 (to be revised) here
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Annex D (Informative)
Calculation process for insulating glass units
D.1 General
In case of double glazing, with panes of thickness h1and h2, the distribution (partition) of
external uniformly distributed loads (e.g. wind, snow, self weight) is essentially determined
by the distribution (partition) of the stiffness of the panes, that is:
Stiffness partition for pane 1 with thickness h1: 32
3
1
3
11
hh
h
(D1)
Stiffness partition for pane 2 with thickness h2: 132
3
1
3
22 1
hh
h (D2)
Additionally, the distribution (partition) of external loads as well as the effect of internal
loads is determined by theinsulating unit factor :
4*)/(1
1
aa (D3)
The length a gives the actual dimension of the unit (e.g. in case of a rectangular unit the
length of the short edge) while a* is the characteristic length of the unit, depending on the
thickness of the glass panes and the gas space,s, and the shape of the unit.
25,0
5
3
2
3
1
3
2
3
19,28*
khh
hsha (D4)
The coefficient of volume, k5, depends on the shape of the unit (see table B.3 in Annex B)
D.2 Distribution (partition) of external loads (load sharing)
By means of the internal pressure the external loads (e.g. wind on pane 1) are distributed to
both panes.
Table D.1: Load partition for external loads
Load Partition of load carried
by pane 1
Partition ofload carried
by pane 2
External loadFdacting on pane 1 dd FF 211; dd FF 22; 1
External loadFdacting on pane 2 dd FF 11; 1 dd FF 212;
D.3 Effect of internal loads
D.3.1 Internal loads applied to the panes
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The internal loads given by the isochore pressure are reduced by the flexibility of the panes
described by the insulating glass unit factor, .
Table D.2: Internal loads
Load carried by pane 1 Load carried by pane 2Isochore pressurep0 0p 0p
D.3.2 Isochore pressure
The isochore pressure generated by a difference of altitude is:
)(0; PHH HHcp (D5)
where 012,0Hc kPa/m
Isochore pressure generated by a difference of temperature and/or air pressure is:
)()(0; PPTC ppTTcp (D6)
where 34,0Tc kPa/K
The isochore pressure is:
0;0;0 CH
ppp (D7)
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Annex YN (informative)
Proposal for a model of a National Annex (informative)
The values of the partial load factors for glass to be used on the territory of [Member State]
are:
Table YN1. partial factors
Type of element to be
calculatedG
(3)
Q
favourable unfavourable
Main structure(1)
Secondary structure(1)
Infill panel(2)
Notes.(1) Structural construction covered by Eurocodes
(2) Non structural element not covered by Eurocodes
(3) The lower value is used when the permanent action has a
favourable effect in combination with other actions. The
higher value is used when the permanent action is
considered acting alone or has a unfavourable effect in
combination with other loads.
Table YN2. partial factors
Main structure(1) Secondary structure(1) Infill panel(2)
Wind 0
1
2
Snow 0
1
2
Other 0
1
2
See Eurocodes or national annexes
Notes.
(1) Structural construction covered by Eurocodes
(2) Non structural element not covered by Eurocodes
When not filled in, the recommended values in this European Standard should be used (see
7.2).
Probability factor for wind return period: cprob = 1,0.
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Annex ZN (informative)
Proposal for a model of a National Annex (informative)
Nationally determined material partial factors by [Member State]
The values of the material partial factor for glass to be used on the territory of [Member
State] are:
Ultimate limit state Serviceability limit state
Annealed glass(1)
M;A= . M;A= .
Surface prestress M;v= . M;v= .
Note (1). The material partial factor for annealed glass is also applied to a
component of the strength of prestressed glass - see equation (7).
When not filled in, the recommended values in this European Standard should be used (see5.3).
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EUROPEAN STANDARD prENthstrNORME EUROPENNE
EUROPISCHE NORM October 2007_____________________________________________________________________ICS
Descriptors :
English version
Glass in building - Thermal Stress Calculation Method
Verre dans la construction - Glas im Bauwesen -
This draft European Standard is submitted to the CEN members for CEN enquiry. It has been drawn up
by Technical Committee CEN/TC129.
If this draft becomes a European Standard. CEN members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a
national standard without any alteration.
This draft European Standard was established by CEN in three official versions (English, French,
German). A version in any other language made by translation under the responsibility of a CEN member
into its own language and notified to the Central Secretariat has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France,
Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden,
Switzerland and United Kingdom.
CEN
European Committee for StandardisationComit Europen de NormalisationEuropisches Komitee fr Normung
Central Secretariat: rue de Stassart 36, B-1050 Brussels
__________________________________________________________________________________
c CEN 2007. Copyright reserved to CEN members
Ref. No. prEN thstr: 2007
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2
Contents
Foreword
Introduction
1 Scope
2 Normative references
3 Definitions
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Foreword
To be completed later
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4
1 Scope
To be added later.
2 References
EN 410
EN 673
To be completed later
3 Definitions
Backup: an area of solid material, behind and in close proximity to the glass, which will
reflect heat back into the glass and / or trap hot air behind the glass and / or insulate the rear
surface of the glass.
Thermally safe: the risk of thermal stress cracks originating from a good quality glass edge
is sufficiently low to be acceptable.
To be completed later
4 Symbols
To be added later
5 Calculation Method
5.1 General
Thermal stress in glass panes in buildings is caused by the central area of the glass heating
up, when the sun shines on it and when ambient temperatures rise, more quickly and to a
higher temperature than the edges of the glass, which are concealed within a frame, and maybe subjected to a shadow from its direct environment. The warmer central area expands
relative to the cooler edges and causes tensile stress to be developed in the edges of the glass.
If the temperature difference between the warmer centre and the cooler edges is sufficiently
high, the stress can cause cracks to develop from the edges of the glass.
For each pane submitted to a cast shadow, three zones are considered:
- the central zone directly hit by the sun
- the shaded part of the central zone
- the edges of the pane in the shaded part.
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The calculation of the edges temperature takes into account the effect of the inertia of the
rebate, together with the influence of the spacer between the panes, generally metallic, that
tends to equalize the temperatures of the two adjacent glass panes edges.
The temperature difference to be considered for each pane is the greater difference between
the first, and alternatively the second or third zone temperatures.
5.2 Principles
It is stated in the following that any glazing in a building shall be able to withstand the effect
of a cast shadow, resulting from permanent or temporary external obstacles, for all possible
climatic conditions of the site.
Thus the instantaneous temperature difference for each glass shall be calculated in the worst
condition for that glass.
The temperature differences between two points of one glass depend on:
- climatic conditions of the site (solar flow, daily amplitude, faade orientation,
altitude, season)
- Nature and constitution of the glazing (number of panes, solar characteristics, U
value)
- Thermal inertia of the framing
- Presence and nature of a blind or a backup, or eventually of a radiator
In the case of mobile blinds or awnings, the temperature difference shall be calculated taking
into account different positions of the blind (Retracted, half retracted, extended), or of thelathes of a venetian blind (closed, open at 45, open).
The value of the thermal stress is proportional to the temperature difference.
The calculated thermal stress shall be less than the allowable thermal stress.
The allowable thermal stress depends on the nature of the glass and its treatment, but also of
its position and settlement: if the edges of the glass may be subjected to mechanical stresses,
the allowable thermal stress is reduced.
Due to the probabilistic character of thermal breakage, the allowable thermal stress
considered is higher for non permanent shadow risks (e.g. smooth faade) than for permanent
shadowing condition (window masonry framing, balconies, etc)
6 Characteristics of the glazing
6.1 General
The sides of the panes in a glazing are numbered from exterior to interior.
The slope of the glazing shall be specified.
The treatment of the edges of the glass is defined in Annex.
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6.2 Solar characteristics
Each glass, monolithic or laminated, is defined by its solar characteristics (transmission,
absorption, reflection) calculated according to EN 410, for each side.
For an insulating glazing, the characteristics have to be known for each component
individually.
The global characteristics of the glazing, with or without a blind, are calculated from those of
each component, according to EN 13363.
Note: The use of the solar characteristics of the component constitutes an admissible
simplification, which generally overestimates the absorptions and thus is on the safe side
concerning glass warming up under the sun.
If the spectral characteristics of the components are known, they can be used in a more
precise calculation.
6.3 Glass with high thermal resistance
The glass products offering a high resistance to thermal shock are:
- heat strengthened soda lime silicate glass (EN 1863) or toughened (EN 12150 or EN
14179) or chemically strengthened (EN 12337)
- glass with low expansion coefficient, such as borosilicate that are generally thermally
toughened, or glass ceramics (EN 1748-2), or alkaline earth silicate glass (EN 14178).
6.4 Treatment of edges
Treatments of glass edges increasing the thermal shock resistance are described in Annex 1.
7 Surrounding of the glazing
7.1 Rebates
Three types of rebates are considered, from their thermal inertia.
7.1.1 Light inertia rebates
Enter in this category: (sketches to be given)- Wood or PVC frames
- Aluminium frames, with or without thermal break
- Thin steel frames, in openings or without contact to the structure
- Mix frames using wood and aluminium or PVC.
- Structural sealant glazing
- Point fixed glazing
7.1.2 Medium inertia rebates
Enter in this category: (sketches to be given)
- Heavy steel framings (hot laminated)
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- Fixed frames of aluminium of steel in direct contact to a masonry or a heavy metal
structure, even on one side only
- Mix frames using steel and aluminium
7.1.3 High inertia rebates
Enter in this category: (sketches to be given)
- Mineral rebates
- Metallic rebates engraved in masonry
This is mainly the cases of showroom glazing.
7.2 Openings
The type of opening shall be precised (side-hung casement, sliding sash, galandage).
As a general case, the window will be considered in its closed position.For sliding sashes, the opened position shall also be considered. This type of opening may
lead to the total or partial superposition of two double glazings, and thus a greater
temperature rise in the space between the two glazings, with increased breakage risks if this
space is not ventilated, and moreover if there is a cast shadow from the reveal wall.
7.3 Cast shadows
The presence of solar screens, top boards, loggias, reveals, or any masks, may induce
temporarily or permanently a cast shadow on the glazing. Presence of one or more of these
elements shall be indicated by the building owner.
Glazing set at the inner side of the wall present systematically a cast shadow.Glazing at the outer side of the faade or of the roofing, and not subjected usually to the
shadow of a neighbour obstacle are termed without cast shadow.
Vertical or horizontal pivot casements are systematically subjected to cast shadows.
7.4 Blinds or solar protections, shutters
7.4.1 Characteristics
The blind characteristics are defined according to EN 14501, from:
- its type (fabric, Venetian blind)
- its solar characteristics (transmission, reflexion, absorption)- its permeability, or openness factor
The characteristics of shutters are defined according to Annex H of EN ISO 10077-1.
The position of the solar protection or shutter (interior, exterior or incorporated into the
glazing) shall be indicated.
In the case of glazing equipped with blinds of mobile solar protections (interior, exterior or
incorporated into the glazing), the solar protection is supposed to be half extended.
Calculation shall then be performed, for the central part, for shaded and not shaded zones,
alternatively with and without the solar protection.
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When incorporated in a glazing, a Venetian blind shall be considered successively as closed,
then opened at 45.
7.4.2 Ventilation
A blind or a solar protection may be ventilated or not, and partially permeable to infra-red
radiation.
Ventilation of the space between blind or shutter and the glass results from several factors:
- porosity of current part
- ventilation through the peripheral gaps between the blind and wall or window.
(see sketch)
Provision should be taken so that the blind do not remain in direct contact with the glass.
If the interior blind in retracted position does not escape completely the glazing light, it has to
be considered as an opaque backup if it meets the conditions explained in paragraph 7.5.
Blind or
shutterOutdoors Indoors
Outdoors
Indoors
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7.5 Opaque backups
7.5.1 Dimensions and geometry
The figures xx and xy below define the conditions where a glazing is considered as in front ofan opaque backup.
On a vertical cross section, the glazing is in front of a backup if :
d1 < 0,80 m and h1 0.5 d1 + 0.10 (m)or
d2 < h2 and h2 0.10 m
On a horizontal cross section, the glazing is in front of a backup if:
d3 < h3 and h3 0.10 m
Glazing Wall or
opaque parts
Wall or
opaque parts
Wall or
opaque parts
Glazing
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For a glazing located partially in front of a backup, the calculation of the temperatures
includes the following steps:
- Higher temperature: in frond of the backup, not shaded
- Lower temperatures central zone far from backup, shaded
glass edges far from backup, shaded
7.5.2 Solar and thermal characteristics
The opaque backup is defined through its thermal resistance, as a function of the thickness
and thermal conductivity of the constitutive material(s), and of its solar absorption or
reflexion.
In the case of a concrete floor abutment, or of a thick mullion, the thermal resistance of the
obstacle is evaluated grossly considering a backup thickness equal to its width.
Examples of backup characteristics are given in Annex 2.
7.6 Glazing in front of a radiator
The glazing should not be exposed to a local concentrated energy flow.
If the glazing is submitted to thermal flows from radiating or air pulsating systems (high
intensity spotlights, radiating heater, radiator, pulsed air convector), it is necessary:
- either to use a high thermal shock resistance product (defined in 6.2)
- or to make sure that the radiator is distant at least of 20 cm from the glass
In this latter case, a verification of the temperature difference between:
- the zone of the glazing facing the radiator, and hit by the sun,- a zone far from the radiator, shaded
- the glass edges in this shaded zone
The surface temperature of the radiator can be estimated as 70C during the colder seasons.
In summer, the radiator is to be considered as a static backup.
8 Climatic data
8.1 General
The temperature difference on the panes of insulating glazing depends on the external
temperature, mainly because of the thermal coupling of the edge temperatures by the spacer.
For a given orientation and slope of the glazing, the maximal incident solar flow and
associated temperature conditions depend on the season.
For these reasons the calculations will be performed in the four seasons :
- Winter, cold temperature, higher solar flow on south faades
- Spring, with high solar flow on South-East and South-West faades, supposed low
temperatures
- Summer, high temperatures, high solar flow on East and West faades
- Autumn, with high solar flow on South-East and South-West faades, supposed warm
temperatures
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This satisfies the requirement of all year round verification towards thermal shock.
Common sense considerations apply naturally to some cases:
- a radiator will be supposed turned off in summer and autumn
- Sliding sashes are not supposed to be completely open in winter
8.2 Temperatures
A given geographic site is characterized by:
- the maximum temperature in summer
- the minimum daily temperature in winter
- the maximal temperature amplitude on clear days.
These figures can be obtained from available meteorological data using the following rules.
8.2.1 Meteorological data
For a given location, the following data are generally available:
- Record maximum temperature
- Record minimum temperature
- Mean monthly maximum temperature
- Mean monthly minimum temperature
Rules :
- maximum temperature in summer Tmax,s= record maximum temperature less 2
- minimum daily temperature in winter Tmin,w= record minimum temperature plus 5
- maximal amplitude is obtained from the difference between mean maximum and
mean minimum temperatures, plus 5.
8.2.2 Basic outdoor temperatures for each season
Basic values of outdoor temperatures are obtained as:
- Te,summer = Tmax,s
- Te,autumn = 2/3.Tmax.s + 1/3.Tmin,w + Amplitude
- Te,winter = Tmin,w
- Te,spring = 1/3.Tmax,s + 2/3.Tmin,w
A more refined temperature analysis taking into account the faade orientation is given in
Annex 3.
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8.2.3 Indoor temperatures
The indoor temperature of building zones in exploitation is supposed constant and given in
table 1 below.
Table 1 Indoor temperatures
Vertical glazing
(60)Sloping glazing
(< 60)Summer air conditioned zone Ti = 25C 30C
Summer non air conditioned Ti = 25C Ti = Tmax,s 35COther seasons Ti = 20C Ti = 20C
Winter, no heating Ti = 5C Ti = 5C
8.3 Solar radiation intensity
8.3.1 General
The maximum solar radiation intensity, I, which may be incident on the glass can be
calculated using any appropriate method which takes into account:
the latitude of the site, the orientation of the glazing, the slope of the glazing, the altitude of the site, the haze factor, the ground reflectance, and the time of year.
Detailed solar radiation data may be obtained for each European city from the website:
re.jrc.ec.europa.eu/pvgis
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8.3.2 Maximal solar radiation on vertical glazing
Figure 1 - Maximal solar irradiation on vertical walls at sea level
(to be discussed)
The above figure shows the maximum solar radiation intensity on vertical wall for Europe:
- in regions with altitude
500 m- in the open land
Corrections for urban situation and altitude are introduced according to the following table.
Let Io be the solar radiation intensity at low altitude in the open land from the above map.
Table 2 Corrections for altitude and urban zones
Radiation intensity (W/m)Altitude (m)
Rural zone Urban zone
0 - 500 Io Io-50
500 - 1000 Io + 50 Io> 1000 Io + 150 Io + 100
Note: provision shall be made for temporary or local increase of the solar radiation due to
reflecting surfaces (snow, reflective glass roofing below a part of the building,etc)
8.3.3 Sloping glazing
For sloping glazing, the above values are to be multiplied by a coefficient Ci, depending on
the slope of the glazing to horizontal, and given by table
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Table 3 - Factors for maximal solar radiation on sloping glazing
(Latitude 42 to 48N)
Slope 90 75 60 45 30 15 0
Ci summer 1,00 1,15 1,20 1,25 1,25 1,25 1,20
Ci winter 1,00 1,15 1,15 1,05 0,95 0,75 0,50
Note: these coefficients depend on latitude
8.3.4 Diffuse and reflected radiation
The shaded zones of the glazing receive however the diffused and reflected parts of the solar
radiation.
These are estimated at 10% of the global incident radiation, without being less than 75 W/m.
9 Heat transfer coefficients
9.1 External heat transfer coefficient
The value of the external heat transfer coefficient, he, shall be obtained from table 4.
Table 4 -. External heat transfer coefficient
External heat transfer
coefficient, he (W/m.K)
Slope
Winter,
Spring
Summer,
Autumn
90o(vertical) 11 13
0o(horizontal) 12 14
For slopes between vertical and horizontal, the external heat transfer coefficient can be
estimated by linear interpolation.
9.2 Internal heat transfer coefficient
The value of the internal heat transfer coefficient, hi, shall be obtained from table 5.
Table 5. Internal heat transfer coefficient
Slope Internal heat transfer
coefficient, hi
90o(vertical) 8 W/m2K
0o(horizontal) 6,7 W/m2K
For slopes between vertical and horizontal, the internal heat transfer coefficient can be
estimated by linear interpolation.
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9.3 Cavity heat transfer coefficient
The value used for the cavity (gas space) heat transfer coefficient, hs, shall be calculated
according to EN 673 for vertical glazing. Calculation of hs proceeds normally using the
calculated values of the adjacent pane temperatures
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10 Allowable temperature difference
10.1 Principle
The allowable temperature difference for a glass is obtained from the comparison between
the thermal stress thresulting from a temperature difference on a glass, and the allowablethermal stress adm:
adm= kv.ka.vmth= kt.E.. < adm
10.2 Coefficient kt
The shadow coefficient, kt, represents the fact that the glazing is submitted or not to a cast
shadow, together as the rebate inertia: if the rebate inertia is high, the peripheral zone of the
glazing may remain cold on the four sides, increasing the thermal stress.
The values of ktare given in the table 6.
Table 6 Values of kt
Low inertia,
Structural sealant
Medium inertia High inertia
With cast shadow 0.90 1.00 1.10
Without cast shadow 0.80 0.95 1.10
10.3 Working stress of glass , vm
The table 7 gives, as a function of the glass nature, the allowable working stress for glass in
vertical position towards thermal stresses.
Table 7 Working stress vmGlass type vm
(MPa)
Float or sheet glass 20Patterned glass 18
Wired patterned glass or polished wired glass 16
Heat strengthened glass (all types) 35
Toughened glass (all types) 50
Laminated glass Smallest
value of the
component
panes
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10.4 Coefficient kv
The coefficient kvrepresents the sensitivity of the glass to thermal shocks. It depends on the
nature of the glass and on its transformation. It applies to monolithic and laminates, with
edges worked as defined in XXX.
Table 8 Values of coefficient kv
Nature Sawed glass As cut or arrissed Smooth ground or
polished
Monolithic glass 12 mm15 or 19 mm
25 mm
- 1.00
0.85
0.75
1.20
Symmetric laminate 0.75 1.00 1.20
Non symmetric laminate 0.70 0.75 1.00
Wired glass - 0.80 -
Patterned glass - 1.00 1.00
10.5 Coefficient ka
The coefficient kadepends on the slope of the glazing and on its setting conditions.
Stresses due to the self weight of the glass may develop at the edges and be added to the
thermal stresses, and particularly if the glass is not settled on its whole periphery.
Table 9 gives the values of the coefficient ka.
Table 9 Values of coefficient ka
Glazing settled on Angle with horizontal
60 60 > 30 < 30All sides 1.00 0.90 0.80
Other cases 0.90 0.8 0.70
10.6 Values of allowable temperature difference
The allowable temperature difference for a glass is given by :
adm=
..
..
Ekt
vmkakv
Some typical cases for adm are given below.
Example : For a vertical glass 12 mm settled on 4 sides, as cut, in aluminium rebate
adm=69.0*70000*9.0
20*1*1
e= 35
(To be completed)
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11 Temperature difference calculations
11.1 General process
a) Calculate the maximal temperatures of the sunlit panes
If there is presence of movable blind, backup, radiator, etc the temperatures are calculated
with it.
b) Calculate the temperatures of the shaded panes
If there is presence of movable blind, backup, radiator, etc the temperatures are calculated
without it.
c) Take into account the cold bridge effect
The cold bridge effect due to the metallic spacer has to be taken into account.
The temperatures of the two pane edges in rebate are equalized to a value To.
For glass panes in a metallic rebate: T0 #2
2010 TT
d) Select the worst case of temperature difference for each pane
Tb1 = Max{(T1 T10), (T1-T0)} = (T1-T10) + Max{T10-T0, 0}Tb2 = Max{(T2 T20), (T2-T0)} = (T2-T20) + Max {T20-T0, 0)
tot
T1 T2
dif
T20T10
T10 T20
T0T0
dif
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11.2 Example of a double glazing without blind or backup
a) Temperatures in the sunlit part
T1 =)...(
)1..).(()2...(
hshehshihehi
eITehehshieITihihs
T2 =)...(
)2..).(()1...(
hshehshihehi
eITihihsheeITehehs
b) Temperatures of the shaded part
T10 =
)...(
)1.1.0.).(()2.1.0..(
hshehshihehi
eITehehshieITihihs
T20 =)...(
)2.1.0.).(()1.1.0..(
hshehshihehi
eITihihsheeITehehs
c) Cold bridge effect
T0 =)...(2
))2.(2)2.(1.(1.0)...(2).(.
hshehshihehi
hshehshiITeheTihihsTeTihehi
The temperature differences may be expressed in a simpler form as :
Outer pane:
siseie
aesieb
hhhhhh
hIhhITTT
211; 9.0101
(2)
Inner pane:
siseie
seeseb
hhhhhh
hhIhITTT
212; 9.0202
(3)
Cold bridge effect
T10-T0 =)...(2
].)[(
hihehshihshe
hiheTiTe
>0 if Te>Ti (summer)
T20-T0 =)...(2
].)[(
hihehshihshe
hiheTeTi
>0 if Ti>Te (winter)
.
d) Worst case :Tb1 = Max{(T1 T10), (T1-T0)} = (T1-T10) + Max{T10-T0, 0}Tb2 = Max{(T2 T20), (T2-T0)} = (T2-T20) + Max {T20-T0, 0)
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11.3 General equations
For any case, the temperatures in the components of a glazing can be obtained by solving a
system of equations, for both situations (sunlit and shaded part of the glazing), following the
principles described in chapter 11.1.
The components considered may be a glass pane, a blind, a backup, a gas layer ventilated or
not.
The corresponding systems of equations are given in Annex 5. Other cases may be easily
derived from those given.
11.4 Influence of rebate inertia
For medium and high inertia framing, the effect of increased inertia is taken into account by
increasing the temperature
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