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Embedded liquid-laminated connections for structural glass applications


Type

Thesis

Change log

Authors

Volakos, Efstratios 

Abstract

The structural use of glass in buildings and constructions has dramatically increased in recent years due to the ever-growing demand for architectural transparency. Indeed, the use of glass has evolved from simple infill panels for framed windows to large frameless facades and primary structural members (columns, beams). Given the brittle glass nature, one of the most critical issues in glass engineering is how to effectively connect structural glass components in a visually unobtrusive manner.

To date, bolted assemblies represent one of the most common methods for connecting glass. However, bolted glass connections are structurally inefficient because they generate high tensile stress concentrations which cannot be plastically redistributed due to the glass brittleness. Consequently, research has focused on adhesive connections which distribute the loads more evenly, thereby reducing the stress concentrations and simultaneously eliminating drilling of the glass. About a decade ago, a new type of adhesive connection emerged, known as embedded laminated glass connections, that has significantly improved the load-bearing capacity and appearance of glass connections. Typically, these connections consist of a metallic insert which is partially embedded within a glass laminate via solid foil interlayers and they are assembled in an autoclave. However, unfavourable residual stresses are set up in the embedded zone due to the differential thermal expansion between the glass and the metallic insert during the autoclaving fabrication process. To address this, this research aims to develop a novel variant of embedded laminated connections where lamination is achieved through a liquid resin interlayer. Unlike autoclave lamination, resin lamination is performed at much lower temperatures, thereby drastically reducing the undesirable residual stresses and the energy consumption required for lamination. To this aim, research has been undertaken to assess the structural performance of embedded resin-laminated connections under various loading and environmental conditions and to develop analytical/numerical tools capable of sufficiently predicting the connection mechanical response for engineering design purposes.

Specifically, in this thesis, the axial tensile load-carrying behaviour of embedded resin-laminated connections with thin steel inserts is investigated by means of experimental pull-out tests performed on physical connection prototypes. These tests are executed at varying displacement rates and temperatures in order to assess the effect of the time and temperature dependent behaviour of the polymeric resin interlayer on the strength, stiffness and failure mode of the connection. The resistance of the connection to humidity is also examined. Namely, as-new connection specimens are subjected to an artificial accelerated weathering schedule and then tested under pull-out loading in order to compare their mechanical response with that of their non-weathered counterparts.

To further interpret the experimental findings and better understand the connection mechanical behaviour, numerical finite element (FE) simulations of these tests are performed. The principal load-transfer/failure mechanisms of the connection are identified and the associated complex stress state within the connection is studied in order to quantify the resulting stress peaks. Alternative connection configurations are also numerically examined with the purpose of improving the connection structural performance.

Based on the experimental and numerical data, an analytical model is developed that captures the pull-out load-displacement response of the connection with less effort, time and cost compared to numerical modelling or experimental testing. Therefore, this analytical approach provides an insight of the connection response which is a useful aid for preliminary sizing of such connections during initial stages of design.

Finally, the benefits and viability of the embedded liquid laminated connection examined in this research are demonstrated by assembling a novel glass component (demonstrator). The successful completion of this component confirms that embedded resin-laminated connections are suitable for the development of robust and aesthetically appealing real-world glass applications.

Description

Date

2024-02-18

Advisors

McRobie, Allan

Keywords

analytical model, embedded liquid-laminated glass connections,, experimental tests, humidity, numerical (FE) analysis, strain rate, temperature

Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge