This document discusses the use of structural silicone joints in cold-bent insulating glass units. Cold-bending glass introduces permanent tensile forces and shear movements that affect the joints. Verification of joints per existing standards may not fully account for these effects. The document recommends optimizing systems to reduce shear displacements, such as using leaner frame designs or optimized bending. It concludes that while cold-bent glass is increasingly used, more extensive guidelines are needed to properly evaluate joints subjected to forces from cold-bending.

1. 30 JUNE 2017
VIVIANA NARDINI
MARKET FIELD ENGINEER FAÇADE / INSULATING GLASS
SIKA SERVICES AG
STRUCTURAL SILICONE JOINTS
IN COLD-BENT SSG UNITS

2. STRUCTURAL SEALANT GLAZING
LEADING FACADE TECHNOLOGY
High-strength,
but low-stress connections
Flexible joining technique
Simple and economical
system design
High technical and esthetical demands on facades
ELASTIC BONDING
2 Structural Silicone Joints in Cold-Bent SSG Units

3. IG sealant
Structural silicone
SSG adhesive
Structural silicone
Weather sealing
Silicone sealant
Assembling
Spacer Tape, gasket
STRUCTURAL SEALANT GLAZING
TRADITIONAL APPLICATIONS
3 Structural Silicone Joints in Cold-Bent SSG Units

4. STRUCTURAL SEALANT GLAZING
CHANGE OF ARCHITECTURAL DEMANDS
4 Structural Silicone Joints in Cold-Bent SSG Units

5. COLD-BENT UNITS
DIFFERENTIATION OF CURVED GLASS PRODUCTS
CRITERIA HOT-BENDING COLD-BENDING BENDING BY LAMINATION
Shaping / curvature
optional within the limits
of technical restrictions
hyperbolic paraboloid or quasi-
cylindrical / natural bending shape
cylindrically and spherically /
limited by natural bending shape
Bending radii heavily and slightly curved slightly curved slightly curved
Tolerance
significant / depending on geometry
and process
no / precisely adjustable
in the final state
back flipping / precisely
adjustable in the final state
Glass properties differing from flat state analogous to flat glass products analogous to flat glass products
Film-coating only if suitable for heat-treating analogous to flat glass products analogous flat glass products
Frit-coating not feasible analogous flat glass products analogous flat glass products
Stress glass
(installed)
stress-free in installed condition permanent stress permanent stress
Stress interlayer stress-free in installed condition permanent stress permanent stress
Stress glass supports stress-free in installed condition high permanent reaction forces reduced permanent reaction forces
Stress IGU’s
edge seal
stress-free in the installed
condition / increased
climatic effects
high permanent reaction
forces / increased
climatic effects
reduced permanent reaction
forces / increased
climatic effects
5 Structural Silicone Joints in Cold-Bent SSG Units

6. COLD-BENT UNITS
«STATE-OF-THE-ART» ???
6 Structural Silicone Joints in Cold-Bent SSG Units

7. COLD-BENT UNITS
EFFECTS ON STRUCTURAL SILICONE JOINTS
▪ Permanent tensile forces
→ restoring forces (flipping back) of displacements elastically applied
▪ Permanent shear movements
→ differential displacements imposed to bonded elements
SG joint
IG joint
Frame
7 Structural Silicone Joints in Cold-Bent SSG Units

8. COLD-BENT UNITS
EFFECT OF RETENTION FORCES
▪ Installation = short-term effects (quasi dynamic)
▪ Life cycle = permanent loading
▪ Numerical simulation shows significant stress peaks in the element corners
▪ Uniform load reactions after interaction with dynamic loads
8 Structural Silicone Joints in Cold-Bent SSG Units

9. COLD-BENT UNITS
EFFECT OF RETENTION FORCES – MULLINS EFFECT
9 Structural Silicone Joints in Cold-Bent SSG Units
Strain [% ]
Strain [% ]
Stress
[MPa
]
Stress
[MPa
]

10. COLD-BENT UNITS
EFFECT OF SHEAR MOVEMENT
▪ Permanent displacement between bonded edges in a curved shape
▪ Geometrical effect (shortening of secant, rotation of cross section)
▪ Maximum displacement in the corners of the units
10 Structural Silicone Joints in Cold-Bent SSG Units

11. COLD-BENT UNITS
VERIFICATION OF STRUCTURAL SILICONE JOINTS
Product EOTA ETAG 002
σdes
[MPa]
τdes
[MPa]
τ∞
[MPa]
G
[MPa]
Sikasil® SG-500 0.14 0.105 0.0105 0.50
Sikasil® SG-550 0.20 0.13 0.013 0.63
Sikasil® IG-25 0.14 0.101 0.010 0.73
Sikasil® IG-25 HM Plus 0.19 0.13 0.011 0.86
Wind = dynamic tensile
Dead load = permanent shear
Thermal dilatation = dynamic shear
11 Structural Silicone Joints in Cold-Bent SSG Units

12. COLD-BENT UNITS
VERIFICATION OF STRUCTURAL SILICONE JOINTS
EOTA ETAG 002, 5.1.4.6.8
s∞ = sdes / 10
PERMANENT TENSILE STRESS
12 Structural Silicone Joints in Cold-Bent SSG Units

13. COLD-BENT UNITS
VERIFICATION OF STRUCTURAL SILICONE JOINTS
PERMANENT SHEAR MOVEMENT
EOTA ETAG 002, Annex 2
sjoint = 0.5mm (example)
e = G x D / t∞
Sikasil® SG-500: G = 0.5MPa; t∞ = 0.0105MPa
e = 23.8mm ???
13 Structural Silicone Joints in Cold-Bent SSG Units

14. COLD-BENT UNITS
VERIFICATION OF STRUCTURAL SILICONE JOINTS
PERMANENT SHEAR MOVEMENT
Load steps Stabilized joint movement
after 91d @ 55°C / 95% r.h.
Xmean;∞ / Xmean;+23°C
1) 100% Design Load NO! 0.77
2) 60% Design Load NO! 0.77
3) 40% Design Load NO! 0.79
4) 30% Design Load YES 1.02
5) 20% Design Load YES 1.00
6) 10% Design Load YES 1.04
14 Structural Silicone Joints in Cold-Bent SSG Units

15. COLD-BENT UNITS
VERIFICATION OF STRUCTURAL SILICONE JOINTS
PERMANENT SHEAR MOVEMENT
15 Structural Silicone Joints in Cold-Bent SSG Units

16. COLD-BENT UNITS
VERIFICATION OF STRUCTURAL SILICONE JOINT
PERMANENT SHEAR MOVEMENT
sjoint = 0.5mm (example)
e = G x D / t∞,Movem
Sikasil® SG-500: G = 0.5MPa; t∞,Movem = 0.0315MPa
e = 8mm
For Sikasil® SG-500:
30% Design load: t∞,Movem = 0.30 x 0.105MPa = 0.0315MPa or 3 x t∞
From ETAG test: t∞,Movem = 0.36mm x 0.5MPa / 6mm = 0.030MPa
16 Structural Silicone Joints in Cold-Bent SSG Units

17. COLD-BENT UNITS
VERIFICATION OF STRUCTURAL SILICONE JOINTS
EXTENDED RANGE OF DESIGN VALUES
Product EOTA ETAG 002
σdes
[MPa]
τdes
[MPa]
τ∞
[MPa]
G
[MPa]
σ∞
[MPa]
τ∞, Movem
[MPa]
Sikasil® SG-500 0.14 0.105 0.0105 0.50 0.014 0.0315
Sikasil® SG-550 0.20 0.13 0.013 0.63 0.020 0.039
Sikasil® IG-25 0.14 0.101 0.010 0.73 0.014 0.030
Sikasil® IG-25 HM Plus 0.19 0.13 0.011 0.86 0.019 0.033
17 Structural Silicone Joints in Cold-Bent SSG Units

18. COLD-BENT UNITS
VERIFICATION OF STRUCTURAL SILICONE JOINTS
COMBINED LOADING
Combination of long-term / permanent effects with design values for permanent loading:
µshear, ∞ = tperm / t∞ + … ≤ 1.0
µtensile,∞ = sperm / s∞ + … ≤ 1.0
µperm = µtensile,∞ / 2 + [(µtensile,∞ / 2)2 + (µshear,∞)2]0.5 ≤ 1.0
Combination of all long-term and short-term with design values for dynamic loading:
µshear = tdyn / tdes + tperm / tdes + … ≤ 1.0
µtensile = sdyn / sdes + sperm / sdes + … ≤ 1.0
µdyn = µtensile / 2 + [(µtensile / 2)2 + (µshear)2]0.5 ≤ 1.0
18 Structural Silicone Joints in Cold-Bent SSG Units

19. COLD-BENT UNITS
SYSTEM OPTIMIZATION
▪ Reduction of glass stiffness (glass thickness, glass dimension, elastic / viscous-
and thermo-elastic interlayers)
▪ «Hot-bending» of the carrier frame, cold-bending of the glass unit
▪ Bonding of glass and frame in the final curved shape
▪ Mechanical retention of permanent loads
19 Structural Silicone Joints in Cold-Bent SSG Units

20. COLD-BENT UNITS
SYSTEM OPTIMIZATION
L
w
α
▪ Degree of shear deformation is significantly influenced by the cross-sectional
height of the bonded components
▪ Increase of joint thickness
▪ Reduction of the cross-sectional height of the bonded components
D = ∝ [rad] ×
hf+ hg
2
+ e
20 Structural Silicone Joints in Cold-Bent SSG Units

21. COLD-BENT UNITS
SYSTEM OPTIMIZATION
L
w
α
▪ Degree of shear deformation is significantly influenced by the cross-sectional
height of the bonded components
▪ Increase of joint thickness
▪ Reduction of the cross-sectional height of the bonded components
D = ∝ [rad] ×
hf+ hg
2
+ e
21 Structural Silicone Joints in Cold-Bent SSG Units
Glass
Structural
Silicone
Slim adapter
frame free to
slide
Load bearing
frame

22. COLD-BENT SSG UNITS
CONCLUSIONS
22 Structural Silicone Joints in Cold-Bent SSG Units
▪ Use of cold-bent glass elements is a global trend
▪ Effects of cold-bending procedure on structural silicone joints must be
properly accounted for
→ permanent tensile forces and permanent shear movements
▪ Options to limit shear displacements exist
→ leaner adapter frame or optimized cold-bending procedure
▪ Existing Standards for SSG systems can be consulted only to a limited extent
when cold-bent elements are involved
▪ More extensive guidelines are needed for evaluation and calculation
method of cold-bent elements, as well as definition of meaningful allowable
strength.

23. THANK YOU