STRUCTURAL SILICONE JOINTS IN COLD-BENT SSG UNITS

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