prEN 13474-3 June2008

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CEN/TC129/WG8 N252E

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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CEN/TC129/WG8 - N252E

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)


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


glass


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


hm;j the distance of the mid-plane of the glass ply j from the mid-plane of the


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




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


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


Snow 0 see Eurocodes 0,6 0,6



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


(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


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:


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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CEN/TC129/WG8 - NxxxE

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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Page 2


2

Contents

Foreword

Introduction

1 Scope


3 Definitions

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Foreword

To be completed later

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Page 4


4

1 Scope

To be added later.

2 References

EN 410

EN 673


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.


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

Documents

prEN 13474-3 June2008