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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 –
The effect of moisture
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 –
The effect of moisture
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 –
The toughening process
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 –
The toughening process
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
reasonable foreseeable loading were to be applied to it.”Work at height regulations
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
Post-fracture performance:-
glass fracture patterns
-
glass & interlayer interaction-
ease of access
-
time to replacement-
need for total redundancy?
-
load case moderation?
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
Post-fracture performance:-
glass fracture patterns
-
glass & interlayer interaction-
ease of access
-
time to replacement-
need for total redundancy?
-
load case moderation?
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 –
the unanticipated event
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
reasonable foreseeable loading were to be applied to it.”Work at height regulations
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 –
the unanticipated event
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.
-
Typical laminates have a 1 or 5 year warranty
Damaged interlayer due to failure of weather seal
69
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
Setting block vs
silicone & pvb interlayer
70
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
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?