mechanical behaviour of laminated hybrid adhesive point connections when exposed to humidity ...

106 Pages·2016·13.91 MB·English

by  Ninke Hanenberg

MSc Thesis

MECHANICAL BEHAVIOUR

OF LAMINATED HYBRID

ADHESIVE POINT

CONNECTIONS WHEN

EXPOSED TO HUMIDITY

CONDITIONS

N. Hanenberg, 11/08/2016

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Master Thesis
MECHANICAL BEHAVIOUR OF LAMINATED HYBRID ADHESIVE
POINT CONNECTIONS WHEN EXPOSED TO HUMIDITY
CONDITIONS

Student
Ninke Johanna Fransisca Hanenberg
1502700 (studentnumber)
Delft University of Technology
MSc Civil Engineering, track Building Engineering

Chair
Prof. ir. Rob Nijsse
Department: Civil Engineering
Section: Structural Design

Committee
Dr. ir. Christian Louter (daily supervisor)
Department: Architectural Engineering & Technology
Section: Structural Glass Design

Dr. ir. Fred Veer
Department: Architectural Engineering & Technology
Section: Material Science

Dr. ir. Manuel Santarsiero (external supervisor)
Company: Eckersley O’Callaghan

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Abstract

The use of structural glass has increased lately, due to the higher demands for transparency in modern
architecture. Therefore, the role of glass changes from a mere transparent function (used in windows only)
to a function in which the glass is contributing to the bearing structure as well. Because of the fragile nature
of glass, it is important to understand its behaviour. Due to the manufacturing process, the strength of glass
is decreased severely by small cracks that are present on the surface. Also, glass cannot redistribute stress
peaks very well. Stress peaks tend to occur near the connection between two (glass) components, making
this a critical part in glass design. A common way to joint glass elements is by a bolted connection. However,
this type of connection does not seem suitable for glass design. Due to the drilling process extra cracks will
occur, causing a reduced material resistance, and at the edge of the holes large stress intensifications arise.

Adhesive connections are more in line with the above stated problems of glass design. No drilling is needed,
so no extra cracks will occur. Also, forces are transferred over the entire surface of the connection, leading
to smaller stress peaks in the glass. However, adhesive connections know risks of their own. Problems are
(1) the sensitivity of some adhesives to aging affects like humidity, (2) the strongly non-linear behaviour of
the adhesive which causes stress peaks in the connection, and (3) the complex manufacturing process of
the joint, because some adhesives will liquefy and squeeze out during the lamination process. In this thesis
a concept for an adhesive connection is proposed that addresses these issues.

The concept proposes the use of two adhesives in order to reach the following effect. The first adhesive is
a rigid ionomer adhesive (SG) that is very sensitive for humidity and the second adhesive is a flexible silicone
adhesive (TSSA) which is not sensitive to aging effects. The first adhesive is used in the centre of the
connection and the second adhesive forms an external ring to protect the SG against moisture exposure.
Also, the non-linear behaviour of the rigid adhesive is leading to stress peaks at the edge of the connection.
By placing a less rigid adhesive at the edge, the overall stress distribution is more evenly divided. The
manufacturing process is enhanced because the TSSA remains solid during the lamination process, so it
can be used as a mould for the SG that will liquefy. The concept is called a hybrid adhesive connection.
The concept is tested for a circular point connection exposed to tensile loading. This is done by means of
an experimental and numerical analysis. The experimental analysis focusses on the deterioration of the
hybrid circular connection after exposure to either immersion or 100% relative humidity. The numerical
analysis concentrates on the stress distribution of the proposed connection. The following conclusions can
be drawn from this investigation. In the manufacturing process of the experimental analysis, also the TSSA
is squeezed out due to its softness. Therefore, extra measures should be taken to prevent this, which means
that the manufacturing process of hybrid connections is not improved in comparison to SG connections.
Deterioration of the connection due to humidity is still visible for a hybrid connection containing a ring of
TSSA with a width of 5mm. This effect is less visible when a width of 10mm TSSA is used. Unfortunately, due
to lamination problems, the samples suffered from poor SG bonding, which makes it difficult to give
substantial conclusions on the matter. The numerical analysis gave more clear results. The E-modulus of
TSSA is very low in comparison to that of SG. Therefore, the contribution of the TSSA to the bearing capacity
of the connection is negligible, so the stress distribution is not enhanced. On the other hand, due to the
external ring of TSSA, the stress peaks in the connection are moved inwards, from the perimeter of the
connection to the perimeter of the SG centre. This is a positive effect with regard to humidity exposure. The
strength of the hybrid circular point connection in comparison to the TSSA connections, is only slightly
increased, but the stiffness of the hybrid connection surely is enhanced. Treats of the hybrid connection
might be the risk of air bubbles in between the SG and TSSA and the absence of the whitening effect in the
TSSA.

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Acknowledgements

This thesis was written as part of the Civil Engineering MSc curriculum at the Delft University of Technology.
I would like to use this opportunity to express my gratitude to those who have helped me to complete this
MSc thesis.
First of all, I want to thank my graduation committee. My special thanks goes to Christian Louter, who was
the daily supervisor of this thesis. Thank you for the opportunity to write this thesis, for all your assistance
throughout the project and for keeping me on the right track. I am also very grateful to Fred Veer, not in
the least for helping me execute all the experiments of this research. Thank you for staying positive, even if
the results appeared to be disappointing at first. Thirdly, my gratitude goes to Manuel Santarsiero, who has
helped me from a distance. Your knowledge and experience on the subject was of great value to me. Finally,
I want to thank Rob Nijsse, who was the chair of the committee. Thank you for the clear and concise
meetings that helped me in the right direction. I am sincerely grateful for your valuable feedback.
Furthermore, I would like to express my gratitude to James O’Callaghan, for listening to the findings of this
thesis and for enlightening me with his extensive knowledge on the subject. My sincere gratitude goes out
to Kees Baardolf, who has helped me preparing the test set-up. His help was needed numerous times
during this project. Thank you for always making time in your busy schedule.
A final thanks goes to my friends and family who have supported me throughout this thesis. Whether it
was helping in this research, motivating me or helping me in any other way, I appreciated every bit of it.

N.J.F. Hanenberg
Delft, Augustus 2016

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Table of Content

Abstract 4
Acknowledgements 6
Table of Content 7
Symbols list 10
1. Introduction 11
1.1 Background 11
1.2 Problem definition 11
1.3 Scope 11
1.4 Objectives 12
1.5 Thesis outline 12
2. State of the art 14
2.1 Structural glass 14
2.2 Connections 16
2.3 SentryGlas® 18
2.4 TSSA 22
2.5 Norms and standards 25
3. Concept 28
3.1 Conventional adhesive connections 28
3.2 Concept of enhanced adhesive connection 29
3.3 Investigated geometry 29
4. Experimental Analysis 32
4.1 Introduction 32
4.2 Materials and methods 32
4.3 Test results 36
4.4 Test analysis and discussion 42
4.5 Conclusion 45
5. Numerical analysis 48
5.1 Introduction 48
5.2 Method 48
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5.3 Results 51
5.4 Analysis and discussion 55
5.5 Comparison with experimental results 57
5.6 Conclusion 59
6. Discussion 62
6.1 Hypothesis 62
6.2 Behaviour after exposure to humidity 62
6.3 Stress distribution in the hybrid connection. 63
6.4 The manufacturing process 65
6.5 Lamination process of SG 65
7. Conclusion 68
8. Recommendations 70
9. References 73
Appendix A 76
Appendix B 82
Appendix C 88
Appendix D 94
Appendix E 98
Appendix F 104

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