Klára Machalická

Material properties of adhesives for shear bonded connections of structural glass

Thanks to intensive research in the field of polymer adhesives in the last few years, there is a possibility of using a glued joint with a real load bearing role. The reliability of adhesive in the connection during the lifetime of a structure is affected by many factors, but the initial choice of a proper adhesive material is the most crucial one. The article deals with the experimental analysis focused on the determination of material characteristics of adhesives in planar connections, it describes the effect of various factors on the behavior of an adhesive joint under increasing loads, its ultimate bearing capacity and its failure modes. The main investigated factors are the type of adhesive, the type of connected materials (material of substrate), surface treatment and the thickness of the adhesive layer. A special part of the article describes numerical models of a glued joint with respect to different types of adhesive.

Safety Design of Laminated Glass Regarding PVB Interlayer Stiffness for Large Glass Facades and Shop Windows

When looking at current architecture, we can notice large glass facades and shop windows. These elements are usually made of laminated glass panes with polymeric interlayer between and the task of shear forces transfer is the subject of a current survey especially in case of accidental load cases. It essentially depends on polymer material stiffness, which is temperature, load duration and loading rate dependent. A lot of different polymeric interlayers with different properties are available on a market but their experimentally determined material properties with respect to the load duration and temperature are not mostly specified. Structural engineers tend to design laminated glass structural elements on the safe side and do not take the interlayer stiffness into account. This leads to uneconomical and robust glass bearing members. In case of accidental load verification, shear stiffness of used interlayers plays a significant role. This paper is focused on two types of PVB (polyvinyl-buthyral interlayers) experimental investigation under various temperature and loading rate conditions.

Determination of PVB interlayer’s shear modulus and its effect on normal stress distribution in laminated glass panels

Noticing the current architecture, there are many examples of glass bearing members such as beams, panes, ribs stairs or even columns. Most of these elements are made of laminated glass from panes bonded by polymer interlayer so the task of transferring shear forces between the glass panes needs to be investigated due to the lack of knowledge. This transfer depends on stiffness of polymer material, which is affected by temperature and load duration. It is essential to catch the safe side with limit cases when designing these members if the exact material behaviour is not specified. There are lots of interlayers for structural laminated glass applications available on a market. Most of them exhibit different properties, which need to be experimentally verified. This paper is focused on tangent shear modulus of PVB (polyvinyl-buthyral) interlayer and its effect on the stress distribution in glass panes when loaded. This distribution may be determined experimentally or numerically, respectively. This enables to design structural laminated glass members more effectively regarding price and safety. Furthermore, this is the way, how to extend the use of laminated glass in architectural design.

Environmental Conditions Effect for Adhesive Connections in Glass Structures

Load-bearing joints of glass structures belong to the one of new applications of adhesive connections in civil engineering. They provide several important benefits particularly even stress distribution along the contact depending on geometry and stiffness of the glue joint, which is crucial for brittle glass. There is a lack of knowledge about semi-flexible or semi-rigid adhesive connections in the structural glass field and durability is one of the essential properties that have to be assessed during design-process of bonded connection. An extensive research focused on shear glued joints in glass structures was performed at CTU in Prague, which also comprised environmental effect simulation on the glued specimens in laboratory accelerated conditions. The paper is dedicated to impact of ageing to the specimens and their mechanical properties together with brief overview of available laboratory ageing methods.

Behavior of Glued Connections under Shear Loading

An intensive research in load-bearing glass structures leads to the requirement for performing glass-to-glass or glass-to-different material connections. Glued shear connection is suitable for these applications mainly due to its uniform stress distribution in larger area in comparison with bolted connections. The reliability of adhesive in the connection during the life time of a structure is affected by many factors, [1], [2], [3], [4]. The article deals with the experimental analysis focused on the determination of material characteristics of adhesives in planar connections, it describes the effect of various factors on the behavior of an adhesive joint under increasing shear loads, its ultimate load-bearing capacity and its failure modes. The main investigated factors are the type of adhesive, the type of connected materials (material of substrate), surface treatment and the thickness of the adhesive layer. Due to importance of adhesive layer thickness especially in rigid and semi-rigid glues, numerical models responding to the effect of thickness was carried out.