Aspects of Glass Handout

2

Institute of Structural Engineers, SE Counties Branch, 2010Institute of Structural Engineers, SE Counties Branch, 2010

Aspects of Structural GlassAspects of Structural Glass

Tim Morgan CEng Tim Morgan CEng MIMechEMIMechE

Technical Manager, Pilkington ArchitecturalTechnical Manager, Pilkington Architectural

3

Chemical Composition Soda Lime Silica Glass

Material

Symbol

mass, %

Silica sand

SiO2

69-74Lime (calcium oxide)

CaO

5-14

Soda

Na2

O

10-16Magnesia

MgO

0-6

Alumina

Al2

O3

0-3Others

0-5

Source: EN 572-1, 2004

4

Description of glass

-

Glass is a liquid that has cooled to a rigid state without crystallizing

-

Glass is not a super-cooled liquid but an inorganic solid with an amorphous non-

crystalline structure

Source: Glass in Building, Button & Pye & Structural Use of Glass, Haldimann, Luible, Overend

Viscosity

State

Temp(dPa

s)

(0C)

105

Working point

1040

108.6

Softening point

720

1014

Annealing point

540

1014.3

Transition temperature, Tg 530

1020

Room temperature

20

5

Structure of glass

Molecular modelling simulation by Dave Green, Pilkington

SiliconOxygenSodiumPotassium

6

Physical Properties of Soda Lime Silica Glass

Property

Symbol

Unit

Value

Density

ρ kg/m3

2,500

Young’s modulus

E MPa 70,000

Poisson’s ratio

ν

-

0.2Coeff. of thermal expansion

α

10-6K-1

9

Thermal conductivity

cp Jkg-1K-1

1

Average refractive index n -

1.5

Emissivity

ε

-

0.837

Source: EN 572-1, 2004

7

Aspects of Structural Glass:

1) Strength

2) Flexibility

3) Fragility

4) Durability

5) Connectivity

601 Lexington Avenue, Entrance, USA

8

1) Strength -

Theoretical Strength of Glass

The theoretical strength of glass can be determined, in a simpleway, by looking at the atomic bonding;

oth d

Eγσ =

Based on this, the strength of glass would be approx. 40 GPa !

do

where, σth

is the theoretical cleavage strength, E isYoung’s modulus (70GPa), γ

is the

surface energy (3.71Jm-2) and do is inter-atomic spacing (1.6Å)

9

1) Strength -

Practical Strength of Glass

BUT the practical strength of glass is only∼0.4% of the theoretical strength,

and typically lies between 35 - 350* MPa* based on 1ft diameter burst test data

Product # results Mean(Nmm-2)

Std Dev Highest value

Lowest value

Annealed 742 71.4 17.2 116 30

Practical demonstration:Results recorded for 742 “identical”

annealed glass test pieces

manufactured on the same day, on the same equipment and being visually indistinguishable from each other…

Expect a factor of 3 difference between the strongest and weakest!

10

1) Strength -

Practical Strength of Glass

-

Surface defects

-

Size of panel-

Stress concentrations

-

Rate of loading

-

Structure of glass

-

Surface condition

BUT the practical strength of glass is only∼0.4% of the theoretical strength,

and typically lies between 35 - 350* MPa* based on 1ft diameter burst test data

Reasons for the variability in strength –

Micro & Macroscopic

11

• For a plate with a circular hole, σtip

= 3σ• For a thread root, σtip

= 15σ• If c = 10μm & r = 1.6Å, then σtip

= 500σ

Inglis derived a generally applicable formulation for determining thesestress concentrations, where the fracture stress is governed by c and r,

⎟⎟⎠

⎞⎜⎜⎝

⎛+=

rc21σσ tip

2cr

σ

σ

σtip

1) Strength -

Work of Inglis

12

Griffith (1920) was the first person to postulate that low strengths were related to pre-existing defects, and that these defects gave rise to stress concentrations. He developed an equation to determine the stress required to cause fracture without the need for details of the crack tip.

2c

σ

σ

πcEγσf =

where,

E is Young’s modulus, γ

is the surface energy and c is size of the defect.

1) Strength -

Work of Griffith

13

In many materials, crack propagation prevention occurs by…

1) Strength –

The structure of glass

Grain boundary interactions 2nd

phase interactions Fibre interactions

In addition many materials exhibit crack tip shielding…

Phase transformation Micro-cracking Ductile 2nd

phase

THESE MECHANISMS ARE NOT PRESENT IN GLASS!!!

14

The strength of glass is dependent on its size…

You wannabet ...

I’m strongerthan you ..

1) Strength –

The size effect

The larger the sample, the more chance of finding a critical flaw.

15

1 MPa / Sec 1 MPa / Hour 1 MPa / Day

No problemsArrgggh

!!

The underlying cause of this is moisture levels…

1) Strength –

The effect of load rating

The strength of glass is dependent on the rate at which it is loaded…

16

1) Strength –

The effect of moisture

Glass is prone to stress corrosion -

a stress induced/accelerated reaction with water forming alkali solutions which attack the silica network…

Water vapourcauses corrosion

at crack tips

Sharpens thecrack tip

Leads to moresevere stressconcentrations

Increaseschancesof failure

Na+

+ H2

O = H+

+ NaOH

(glass) (atmosphere) (glass) (alkali)

The longer the glass is under tensile stress during testing, the more time available for stress corrosion to take place.

17

The severity of the effect is governed by the stress corrosion constant, n. A low value of n means more susceptibility to stress corrosion…

12-17

In water

16-22

In air (50%RH)

∞

In a vacuum

1) Strength –


Suggested values for n are…

n

tt

1

2

112 ⎟⎟

⎠

⎞⎜⎜⎝

⎛=σσ

18

Time to failure (mins)

1 10 100 1000 10000

Res

ulta

nt su

rface

stre

ss (M

Pa)

6

7

8

9

10

11

12

13

14

15

16

n

tt

1

2

112 ⎟⎟

⎠

⎞⎜⎜⎝

⎛=σσ

Graph showing the effect of stress corrosion (blue dots represent unbroken samples)

1) Strength –


19

The effect of ceramic frit:The strength of glass is reduced by the presence of ceramic inks. Glass printed with ceramic inks is weaker than unprinted glass. This is often made worse if there is more than one ink on top of another…

Glass

Black ceramicink

Silver ceramicink

Rule of thumb:1 ink -

strength 30%

2 inks -

strength 60%

1) Strength –

Surface effects

Source: Jon Williams, Pilkington

20

-

Glass is heated to about 650oC, and then rapidly quenched with air jets.

-

The surface cools quickly and the core more slowly. At ambient temperature, the core continues to cool and compressive stress develops in the surface, balanced by tension in the centre.

Heating Quenching

Annealed glass Tempered glass

1) Strength –

The toughening process

Toughening furnace, Pilkington

21

The tempering cycle gives rise to a parabolic stress profile within the glass,

Compression Tension

t

The compressive stress layer (20% of ‘t’) acts as a buffer to crack growth.Its magnitude at the surface is ≈2x that of the centre tensile region.

Notes –

Toughened Glass:BS EN 12150 quantifies stress by destructive particle count, however comparative tests have shown that the required compressive stress is80 to 90 MPa* (* source, Stress measurement & fragmentation, Schiavonato, GPD 2005)GANA recommendation for North America = 77.2MPa

1) Strength –


22

The tempering cycle gives rise to a parabolic stress profile within the glass,

Compression Tension

t

The compressive stress layer (20% of ‘t’) acts as a buffer to crack growth.Its magnitude at the surface is ≈2x that of the centre tensile region.

Notes –

Heat Strengthened Glass:BS EN 1863 quantifies stress by destructive particle count, however comparative tests have shown that the required compressive stress is35 to 60 MPa* (* source, Stress measurement & fragmentation, Schiavonato, GPD 2005)GANA recommendation for North America = 38.6MPa

1) Strength –


23Source : Wymond

& Arumugam, Meinhart

Façade Technology PTY, GPD India 2008 (updated)

Country USA - Code

USA - Industry

UK PRC Australia

Code ASTM E1300-09

GANA 2004

BS6262-2 2005

JGJ 102- 2003

AS1288

Permissible/ Limit State

P P L L L

Wind Load Duration

3 sec 60 sec 60 min 10 min 3 sec

Annealed Stress Limit

23.3 MPa - - 19.5 MPa 33.0 MPa

HS Stress Limit

46.6 MPa - - - 58.0 MPa

FT Stress Limit

93.1 MPa - - 58.8 MPa 82.0 MPa

1) Strength –

Existing design codes

24Source : Wymond

& Arumugam, Meinhart

Façade Technology PTY, GPD India 2008 (updated)

Country USA UK/EU PRC India Australia

Code ASCE7 1995

EN 1991-4 2005

GB5009- 2001

IS875.3 2004

AS1170.2- 2002

Permissible/ Limit State

L L L P L

Return Period

50 yrs 50 yrs 50 yrs 50 yrs 50 to 1000 yrs

Gust Duration

3 sec 10 min 10 min 3 sec 3 sec

1) Strength –

Corresponding loading codes

25Source : Pilkington Glass Consultants, for UK loads and glass product standards

1) Strength –

Manufacturer’s data

Glass type Body stress (MPa) Edge Stress (MPa)Annealed (≤6mm) 41 28

Annealed (10≥mm) 28 17.8Patterned Glass 27 27

Wired Glass 21 21Toughened Glass 59 59

Permissible stress for short load duration:

Load type Annealed (Nmm-2) Toughened (Nmm-2)Snow Short dur/2.6 Short dur/2.6

Water & Shelves 7 35Floor 8.4 35

Self Weight As per load type As per load type

Permissible stress for long load duration:

26

Notes :

Comparison for interest onlyAllowable stress values are for short term loadingprEN13474 are personal calculations –

code not yet complete to publish

Body/Code type

USA(prod)

USA(design)

EU(product)Approx.

EU(design)draft

Planar(prod)

Planar(design)

Code GANA 2004

ASTM E1300-09

en12150en1863

prEN13474

- -

Annealed 19.3MPa

23.3 MPa - - - -

Heat strengthn

38.6 MPa

46.6 MPa - - 45-55 MPa

45 MPa

Toughen 77.2 MPa

93.1 MPa - - 113 MPa

90 MPa

1) Strength –

Comparison of codes

Comparison of product standards and allowable stress:

27

1) Strength –

Code Work

Expectation for new structural design codes :

EuroNorm, prEN13474-3, CEN/TC129/WG8Title:

Glass in Building, Determination of the strength of glass panes

Scope:

Fenestrations, facades & infil

panelsStatus:

To be issued for public comment in 1st

quarter 2010

EuroNorm, Eurocode for Structural Glass, CEN/TC250/WG3Title :

Eurocode

for Structural Glass

Scope:

Limit State approach for structural

glazed elements Status:

Resolution 258 has agreed the formation of working group 3First meeting expected within the next few months

28

2) Flexibility –

Current design limits

Document Deflection limit Notes

BS 6262 L/125 (single)L/175 (insulated)

Allowable deflections of edges for 4 edge full supported glass

BS 5516 Single, (S2x1000)/180 or 50mm (whichever less)

2 edge supported glass, where S=span [m] between supports

BS 5516 IGU, (S2x1000)/540 or 20mm (whichever less)

2 edge supported glass, where S=span [m] between supports

ASTM E- 1300-04

19mm Deflection of supported edges less than L/175, L=length

AS1288- 94

L/60 Deflection of unframed toughened glass, L=length

Pilkington Planar

b/50 Deflection of unframed Planar system, b=width of panel

Source : Extract of table 6.4, IStructE

Structural use of glass in buildings, 1999

29

2) Flexibility –

Glass is flexible!

There is often a design to attach glass to an “ultra-flexible” host Structure, but what is acceptable?

Centre Square Vestibule, USA

Single tension cable detail

Normal deflection limit for Planar, b/50 = 46mm

Max. deflection of cable at centre span = 150mm

Cable deflection at first hor. glass joint = 100mm

30

2) Flexibility –

Glass is flexible!

1.6x2.3m puck support panel : make up, 10/16/6 Test Load, 1054Pa : Cable deflection, 118mm

(Video clip)City Creek Centre test panel, Pilkington, UK

31

2) Flexibility –

Glass is flexible!

1.8x1.8m Intrafix concept panel : make up, 6/16/12 Test Load, 5kPa : Deflection, 120mm

(Video clip)Displacement investigation test panel, Pilkington, UK

32

2) Flexibility –

Horizontal applications

Skylight, Rolex HQ, Geneva

Project details:-

insulated laminated panels

-

make-up, 10/16/6-1.52pvb-6-

tension support system

-

horizontal

Issues:-

standing water leaches soda from the glass surface quickly

-

the resulting staining is permanent-

Pilkington specify a minimum 3 degree pitch for “horizontal” glass

-

Ready access for cleaning or self- cleaning glass (e.g. ActivTM) are

advisable for near hor. pitches

33

2) Flexibility –

Key points, Glass panels

-

Toughened and heat strengthened glass are capable of coping with extreme deflection! The average member of the public cannot cope with the idea the glass is flexible!

-

Where deflection is not limited by code (e.g. BS 6180) Pilkington have successfully adopted an aesthetic limit of b/50 for PlanarTM, where b is the shorter dim. of the panel

-

The implications of large centre span deflections need to be designed for at the support locations!

-

Standing water will damage glass permanently! For horizontal panels Pilkington insist on a slope of 3 degrees

34

-

Cantilevered toughened glass fin (friction connected)

-

530mm x 3500mm x 19mm

-

Typical max. design moment, 40kNm

-

Design often limited by lateral torsional

buckling

2) Flexibility –

Glass fins (in-plane)

Cantilevered fin performance tests, Pilkington, UK

Friction connection

35

2) Flexibility –

Glass fins (out-of-plane)

4.8m long, 19mm thk

toughened cantilevered fin65kNm bending moment

(Video clip)Cantilevered fin buckling validation tests, Pilkington, UK

36

2) Flexibility –

Key points, Glass fins

-

Toughened fins are extremely rigid in-plane. The structure to which they are attached is sometimes not so rigid!

-

Historically, Pilkington have used the following moment limits to guard against lateral torsional

buckling:

Thickness

Full height fins

Cantilevered fins19mm

69kNm

40kNm

15mm

33kNm

19kNm12mm

17kNm

13kNm

-

When providing additional lateral restraint to glass fins, Appendix H4, AS1288:1989 accurately predicts buckling loads (but with no safety factors!)

-

Toughening bow can significant reduce the lateral stability of fins unless the façade design accommodates this.

37

3) Fragility –

Is toughened glass fragile?“A surface or material which would be liable to fail if any

reasonable foreseeable loading were to be applied to it.”Work at height regulations

Typical requirements:BS EN 12600

-

50kg twin tyre impactor

-

450, 900, & 1200mm drop

BS EN 356-

4.11 kg steel ball

-

1.5m to 9m drop height

10*/16/6 bolted unit, impactor

height 1200mm

38

3) Fragility –

Is toughened glass fragile?

BB

C s

pons

ored

tria

ls, 2

006

“Wha

t the

20t

hC

entu

ry d

id fo

r us.

”5f

t min

i dro

p

39

3) Fragility –

Toughened glass

Nickel Sulphide inclusion

α-NiSHexagonal (high temp) form

Nickel Sulphide (NiS)Sudden fracture may result from

the transformation of:

β-NiSRhombohedral (low temp) form

40

3) Fragility –

Toughened glass

Nickel Sulphide inclusion

(NiS) Key issues:-

NiS

only affects toughened glass

by transforming in the tensile zone

-

Stones can be between 50μm and 800μm and not all stones cause spontaneous fracture

-

EN14179 quotes a 1 in 400 ton frequency in heat soaked glass but this is an average!-

Not all stones that cause spontaneous fracture are NiS

(silicone formed by redox

reaction with Al can also occur)-

“Spontaneous”

fracture is more often caused by impact, in-

service damage and installation issues

41

3) Fragility –

Managing edge damage

Edge ‘Bright’ Edge ‘Fire’ Pre-toughening work

Edge ‘Splinter’ Edge ‘Chip’ Surface ‘Shell’

42

3) Fragility –

Managing edge damage

Description Cause Effect Acceptability

Edge “bright” Arris not removed all edge break out

Aesthetic only if <5mm (2off)

Edge “fire” Low coolant level at finisher post

Aesthetic only Can be removed with light dressing

Pre-toughening dressing

Edge damage corrected before toughening

Aesthetic only -

Edge “splinter” Handling, transport, installation

Aesthetic with low structural risk

if <1mm deep & <25mm long

Edge “chip” Handling, transport, installation

Aesthetic only If <3mm deep& <3mm long

Surface “shell” Surface breakout damage not removed by arris

Aesthetic with medium structural risk

Not acceptable

Pilkington recommendations for edge damage acceptability with Planar Glazing

43

3) Fragility –

Toughened glass“A surface or material which would be liable to fail if any


Key issues:-

Toughened glass is durable and resistant to impact when the impact is understood and has been anticipated in design!

-

The risk of breakage due of toughened glass due to Nickel Sulphide can be reduced (EN14179) but not eradicated.

-

Toughened glass is vulnerable to edge damage and scratches and the effect of damage is difficult to quantify

-

Designing with monolithic toughened glass requires the engineer to ask, “What happens when this glass breaks?”

44

3) Fragility –

the unanticipated event

CPN

I tria

ls, 2

010

Bla

st re

sist

ance

of t

ough

ened

Pl

anar

TMfa

çade

–te

nsio

n ro

ds

45

3) Fragility –

Laminated glassTypes of interlayer:(1) Polyvinyl butyral (PVB)

-

most commonly available in industry-

manufactured in autoclave at elevated Temp and pressure

-

available in coloured and printed form-

Glass transition temperature, 230C

(2) Ethylene Vinyl Acetate (EVA)-

cured at elevated Temp but no requirement for autoclave

-

good durability and edge stability-

increased stiffness for load sharing & security

(3) Cast-in-Place (CIP)-

2 part liquid pour interlayer

-

suited to small volume and specialist artwork type applications-

better able to cope with toughened and curved glass

(4) Structural Ionomer interlayers – e.g. Sentry Glas

46

σLc

σLt

σc = compressive stress

σc

σt

σt

σc

σt = tensile stress

3) Fragility –

Laminated glassThe great “strength of laminated glass”

debate:

Can the interlayer material transfer shear and increase the equivalent thickness of the complete laminate over and above the sum of the strength of the individual panels?

Relevant factors:- interlayer material type- temperature- load duration- load rate

47

-10 0 10 20 30 40 50 60

Temperature oC

100

101

102

103

Sto

rage

You

ng's

Mod

ulus

(M

Pa)

1 Hz

SentryGlas(R) PlusButacite(R)

-

stiffer than PVB over wide range of temperatures-

higher tear energy (5 x PVB)

-

improved edge durability and transparency

Engineering Strain, e

0 1 2 3 4 5

Engi

neer

ing

Stre

ss, σ

a (M

Pa)

0

10

20

30

40

PVB LaminateIonoplast (SentryGlas(R) Plus) Laminate

Strain Rate ~ 0.1/s

3) Fragility –

Laminated glassStructural benefits SentryGlas® interlayer:

48

Integral

Planar SGP

Planar PVB

3) Fragility –

Laminated glass

Post-fracture performance of various configurations & interlayersBreak 3 – post-fracture loading

49

3) Fragility –

Laminated glass

Considerations for “intact”

performance:-

load duration & application rate

-

interlayer Temp. per load case-

durability and compatibility

-

need for sacrificial components

Willis Tower, Chicago, 1353ftDesigned by Yolles

Halcrow3 ply laminate 12mm toughened heat soaked glassRated for 125psf with redundancy

50

3) Fragility –

Laminated glass

Post-fracture performance:-

glass fracture patterns

-

glass & interlayer interaction-

ease of access

-

time to replacement-

need for total redundancy?

-

load case moderation?

Apple Store, Japan, OsakaDesigned by Eckersley O’Callaghan

Project details:-

glass treads comprise of annealed laminated glass

-

glass stringer is curved, chemically toughened laminated glass

-

designed for seismic loading

51

3) Fragility –

Laminated glass



-


ease of access

-



-


Apple Store, 14th

Street, New YorkDesigned by Eckersley O’Callaghan

Project details:-

first twin storey glass staircase

-

central glass core supporting cantilevered glass treads supporting stringers

-

outer stringer comprises 3ply chemically toughened laminate

52

3) Fragility –

Laminated glass



-


ease of access

-



-


Apple Store, Upper West Side, NYDesigned by Eckersley O’Callaghan

Project details:-

glass fins laminated from 5ply 19mm low iron glass

-

fins spliced together with interlayer to create 35ft tool single span beams

53

“A surface or material which would be liable to fail if any reasonable foreseeable loading were to be applied to it.”

Work at height regulations

Typical requirements:BS EN 12600

-

50kg twin tyre impactor

-

450, 900, & 1200mm drop

BS EN 356-

4.11 kg steel ball

-

1.5m to 9m drop height

10/2.28sgp/6, EN356 test, 4.11kg ball at 9m (2nd

impact)

3) Fragility –

Laminated glass

54

“A surface or material which would be liable to fail if any reasonable foreseeable loading were to be applied to it.”

Work at height regulations

Cycling requirements:+20 to +50psf

3500x

+0 to +60psf

300x+50 to +80psf

600x

+30 to +100psf

100x-30 to -100psf

50x

-50 to -80psf

1050x-0 to -60psf

50x

-20 to -50psf

3350x

Various broken laminates on hurricane cycling

3) Fragility –

Laminated glass

55

3) Fragility –


Com

blas

ttria

ls, 2

004

Bla

st re

sist

ance

of P

lana

r usi

ng

pvb

and

Sent

ry G

lass

inte

rlaye

r

Prod

uct 1

(Sen

try

Gla

ss)

Prod

uct 2

(PVB

)

56

3) Fragility –

Laminated glass“A surface or material which would be liable to fail if any


Key issues:-

Laminated glass is generally more expensive & can add significant weight

-

The use of laminates will considerably improve post-fracture behaviour in most cases but is not the “automatic”

answer it

has become in some quarters-

The performance of laminated glass is temperature and load duration dependent

-

Laminated glass will be significantly less durable-

Laminated glass has a limit too!

57

3) Fragility –


Proj

ect P

erfo

rman

ce T

est,

2005

Lam

inat

ed p

anel

s to

cab

le s

uppo

rtPr

ojec

t ove

rload

, 2.3

9kPa

58

3) Fragility –

Toughened or laminated?BS 5516-2:2004, Code of practice for sloped glazing:Section 8.3.2 –

Roof or canopy glazing

Glazing at a height up to 5m-

toughened, toughened & heatsoaked, laminated or wired

Glazing at a height over 5m and up to 13m-

laminated or wired, or toughened and toughened & heatsoaked not more than 6mm thick and 3m2

in area

Glazing above 13m-

laminated glass or wired glass

Note

: Advice related to single glazing and the lower component of insulated glazing

Note

: Advice does not relate to vertical facades where toughened glass will often remain in place

59

4) Durability –

the easily forgotten issue

Glass:-

extremely durable with a track

record of 100s of years

1320s Crown Glass invented in France (nr Rouen)

1678 Crown Glass made in London

1851 Crystal Palace made by ‘Cylinder’ method

1920s Rolled Glass commonly used

1960 Float Process introduced by Pilkington

Crown Glass

60

4) Durability –

the issue

Glass:-

extremely durable with a track

record spanning hundreds of yrs

Associated components:-

Poly Vinyl Butyral

(PVB) sheet

invented in 1930s-

Poly Iso

Butylene

(PIB)

invented in 1950s & 60s-

Silicone weather seals invented

1950s-

Polyamides (Nylon) invented in

1930s [but most plastics used today are <10yrs old and acceleration factor <10!

US Steelworkers Union Building, Pittsburgh, 1958

61

4) Durability –

Insulated units

Issues:-

water ingress (typical units have a 5 or 10 year warranty)

-

compatibility issues between adjacent sealants-

transportation and installation at height

-

UV stability of unit components (e.g. polysulphide)-

Gas leakage & unit “pillowing”

-

Sputter coatings are often vulnerable to processing damage and corrosion

62

4) Durability –

Insulated units

Edge seal components

A

Secondary Seal

Hollow Spacer

Edge seal construction:

C

B

DE

Key:

A) Secondary seal depth

B) Primary seal depth

C) Unit site line

D) Cavity with

E) Overall unit width

63

4) Durability –

Insulated units

Edge seal components

A

Secondary Seal

Hollow Spacer

Edge seal construction:

C

B

DE

Durability testing:BS EN 1279Glass in buildingsInsulated Glass Units

Part 2 –

Long term test method for moisture penetr.

Part 3 –

Long term test method for gas leakage

Part 6 –

Factory production control test (3 week)

64

4) Durability –

Insulated units

BS EN 1279 : Glass in buildings -

Insulated Glass Units:Part 2 –

Long term test method for moisture penetration.

4 weeks cycling between -180C & +530C (every 12 hours)7 weeks at constant +580Crelative humidity ≥

95 %

Part 6 –

Factory production control & short climate test3 weeks at +580Crelative humidity ≥

95 %

multiple component quality tests

PILKINGTON : ln-house “long life” unit testing:2000 hours UV (84 days) (as EN 1093-3:2001)35/750C, 4 cycles per day, 500 cycles, (125 days)Relative humidity 100%

65

4) Durability –

Insulated units

Insulated units : make up, 10/16/6 Both units subject to EN 1279-6 : starting width, 32.5mm

Competitor unit performance comparison, Pilkington, UK

36.7

5mm

33.1

6mm

66

4) Durability –

Insulated units -

faults

Voids in PIB seal Condensation formation

Total rupture of PIB seal

67

4) Durability –

Laminated glassIssues:- manufacturing issues-

water damage

-

compatibility issues-

loss of plasticizers at edges

-

UV stability -

Discoloration at high temp.

-

Haze growth at high temp.-

Typical laminates have a 1 or 5 year warranty

Finger delamination indicating interlayer depletion bdue

to over compression

68

4) Durability –

Laminated glassIssues:-

manufacturing issues

- water damage-

compatibility issues

-

loss of plasticizers at edges -

UV stability

-

Discoloration at high temp.-

Haze growth at high temp.

-


Damaged interlayer due to failure of weather seal

69

4) Durability –



-

water damage- compatibility issues-

loss of plasticizers at edges

-

UV stability -

Discoloration at high temp.

-

Haze growth at high temp.-


Setting block vs

silicone & pvb interlayer

70

4) Durability –



-

water damage-

compatibility issues

- loss of plasticizers at edges-

UV stability

-

Discoloration at high temp.-

Haze growth at high temp.

-


Edge delamination -

Orlando

71

5) Connectivity -

facades

Cable clamp to laminateProject,

(Julliard)

Spring plate to IGUProject, (Kangnam)

Tension rod to toughenedProject, (Centre Sq)

72

Planar Fixing(inventor : Pilkington, 1982)

Rotule FixingDutton & Martin (RFR), 1986)

18

5) Connectivity -

facadesPoint fixed systems:

Fixed or articulated?

73

(Pilkington video)

1.8x1.8m Intrafix concept panel : make up, 6/16/12 Test Load, 5kPa : Deflection, 120mm

Displacement investigation test panel, Pilkington, UK

5) Connectivity -

facades

7418

5) Connectivity -

facadesPoint fixed systems:Fixed: Articulated:- smaller

- larger

-

‘articulated’ at support

-

articulated at glass-

rotation stiffness is difficult

-

more straightforward to

to model by FEA

model-

reduced size can mean

-

articulation needed by design

less site tolerance

often misused to provideadded site tolerance

-

smaller sizes requires better

-

larger pullout strengthsunderstanding of stresses

7518

5) Connectivity -

facadesFaçade connections in general:-

glass dead load -

as high as 600kg per panel

-

wind load reaction-

often as high as 10kN per fixing

-

provide movement capacity-

thermal, seismic, support structure

-

no glass to metal contact-

no tight clamping of IGUs

or laminates

-

corrosion resistant-

vibration resistant

-

UV & moisture resistance plastics Corner patch to laminated glassPilkington 2009, Julliard College

76

5) Connectivity –

glass mullions

Kensington Marriot, Pilkington, 200524m long, 19mm toughened & spliced mullions

Friction connection:-

historically the connection of choice

-

HSFG bolts can apply shank tension of 90kN without breakage

-

A friction connection avoids the issue of glass strength variability

-

Gasket material is absolutely critical (natural aluminium is an issue)

-

Torque to shank tension relationship is critical

-

Has proved unsuitable for connections in roof beams under constant load

77

5) Connectivity –

glass mullions

Bishop’s Avenue London, Pilkington, 2008Vertical & horizontal spliced fins

“Holes in bearing” connection:-

reliant upon glass strength and induced stresses at holes

-

beams will generally be deeper or thicker when compared to friction type

-

holes must be isolated by suitable plastic or aluminium bushes

-

hole connections often injected with epoxy resin or fitted with tight bushes and then drilled on site

-

edge & hole strengths from different processors will be different

-

Pilkington have observed that an edge chip will reduce strength by av. 26%

78

5) Connectivity –

glass mullions

Load tests –

15mm csk hole -

negative

Summary:

-

# samples, 14

-

95/95 characteristic strength (3s gust) = 12.1kN

-

95/95 characteristic strength (60s gust) = 8.1kN

-

results based upon Weibull

statistics

79

5) Connectivity –

glass mullions

Apple Store, 5th

Avenue, NY, May 2006Designed by Eckersley O’Callaghan

Interlayer connections:-

highly specialised and often protected by patents

-

possible to splice annealed glass and laminate to create multi-ply single span beams 10m long

-

possible to adhere metallic inserts into the interlayer for strength/robustness

Stair tread connection utilising titanium inserts as patent US D478,999 S

80

5) Connectivity –

glass mullions

55 Water Street, USA, 2006Cantilevered 2 part epoxy adhered fins

Adhesive connections to glass:-

not to be confused with the use of water based adhesives to increase μ

-

experience with SSGS is widespread, but the strength of silicone is limiting(σshort

= 0.14MPa, σlong

= 0.014MPa)-

limited tests have been conducted with acrylics & epoxies –

and research

continues at Cambridge & Delft-

short tack times and installation on a construction site are a major issue

-

simulating long term durability will be a challenge

81

Tim Morgan CEng Tim Morgan CEng MIMechEMIMechE

Technical Manager, Pilkington ArchitecturalTechnical Manager, Pilkington Architectural

Institute of Structural Engineers, SE Counties Branch, 2010Institute of Structural Engineers, SE Counties Branch, 2010

Aspects of Structural GlassAspects of Structural Glass

Thank you & Any questions?Thank you & Any questions?

Aspects of Glass Handout

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