Wooden constructions are on the rise again – encouraged by a strong trend towards sustainable and resource efficient buildings. Load-bearing timber-glass composite elements – a novel concept to use the in-plane loadbearing potential of glass – could contribute to a more efficient use of materials in façades. The current study relates to the adhesive bond between the glass pane and the timber substructure. The applicability of structural sealants such as silicones is limited due to their distinct flexibility which leads to large deformations of the joint. Further potential arises from the use of adhesives of medium and high stiffness. Their general performance as well as their durability have not yet been evaluated with respect to the proposed use in building constructions. This paper draws attention to the ageing stability of two promising adhesives. Small-scale adhesively bonded specimens which are composed of a wooden and a glass piece are exposed to different ageing scenarios which relate to the impacts typically encountered in façades. Based on the results it can be concluded that the considered high-modules adhesives enable an increase of characteristic failure loads and a reduction of joint deformation, but also reveal shortcomings regarding their ageing stability.
Research has repeatedly pointed out the suitability of adhesive bonding to substitute to “traditional” joining techniques for numerous materials and loads, including timber to glass. Practitioners, however, are still reluctant to implement them into their designs. Adhesion as a method of joining, particularly in the context of hybrid structures, presupposes knowledge of all involved materials, including codes and procedures; most practitioners however tend to be focused on just a subset of materials. While such specialization is not unusual, it makes it challenging to implement novelty (i.e. new materials or techniques). Additionally, when it comes to adhesion where most of the knowledge has been generated by chemists, the lines become even more blurred. Taking the example of a pedestrian timber-glass bridge, this research shows how design and dimensioning of complex bonded hybrid structures can be performed in accordance with “traditional” engineering practice. The paper guides through every step, from the first concepts to the final design, including the manufacturing, of a relatively complex structure, in which timber and glass act together as equivalent members. The compliance of this process with engineering models is emphasized, and the embedment into existing codes and standards is sought after to ensure acceptancy by practitioners.
The paper presents results from the experimental testing of load-bearing timber–glass composite shear walls and beams. Shear wall specimens measuring 1200 × 2400 mm2 manufactured with three adhesives of varying stiffness were tested. Twelve specimens with a single 10 mm thick glass pane and one specimen with an additional insulating glass unit were produced. The testing procedures involved various loading conditions: pure vertical load and different combinations of shear and vertical loading. The test results showed that the adhesive had only a minor influence on the buckling load which was the main failure mechanism. 240 mm high and 4800 mm long timber–glass beams manufactured with adhesives of different stiffness were tested. For the webs, two types of glass were used: annealed float and heat-strengthened glass, in both cases 8 mm thick panes were used. In total, 12 beams were tested in four-point bending until failure. Despite the considerable difference in adhesive stiffness, beam bending stiffness was similar. Concerning load-bearing capacity, the beams with heat-strengthened glass were approximately 50% stronger than the beams made using annealed float glass.
Fulfilment of conditions given by European design codes for structures in seismic regions presents a problem during the design of new and repairing of existing structures. Although there are various options, obvious choices are solutions which provide increase of rigidity and seismic capacity with minimal increase of structural mass. Current research at the University of Zagreb, performed in cooperation with the University of Ljubljana, is leading to the development of special kind of high-ductility hybrid panel made of timber frame with supporting laminated glass infill, which, in addition to strength and stiffness, is also characterized by high level of seismic energy dissipation. This paper objective is to give preliminary assessment of application of hybrid panel as seismic reinforcement in concrete, steel and timber frame structures. Finally, to provide more accurate input data, numerical results are compared for the structures tested in full-scale shaking table test.
CLT frames infilled with load-bearing glass sheets represent an innovative, hybrid structural element that can serve as load-bearing panel carrying load in both vertical and lateral direction. It can be used as a part of the prefabricated timber house or as a strengthening structural element in an existing timber building or the supporting...
Fulfilment of conditions given by European design codes for structures in seismic regions presents a problem during the design of new and repairing of existing structures. Although there are various options, obvious choices are solutions which provide increase of rigidity and seismic capacity with minimal increase of structural mass. Current research at the University of Zagreb, performed in cooperation with the University of Ljubljana, is leading to the development of special kind of high-ductility hybrid panel made of timber frame with supporting laminated glass infill, which, in addition to strength and stiffness, is also characterized by high level of seismic energy dissipation. This paper objective is to give preliminary assessment of application of hybrid panel as seismic reinforcement in concrete, steel and timber frame structures. Finally, to provide more accurate input data, numerical results are compared for the structures tested in full-scale shaking table test.
Glued glass fronts are extensively applied and meet the highest standards. The objective of several research projects was the development of stiffening glass fronts to replace expansive frameworks or wind bracings. Furthermore, the use of timber-glass composite (TGC) beams was investigated. Within the research project "Load Bearing TimberGlass Composite Structures” (LBTGC) within the framework WoodWisdom-Net the short-term behavior of TGC-beams was investigated. Therefore, the Department of Structural Design and Timber Engineering (ITI) developed a beam-setup to test the load-bearing capacity of such elements under a four point bending test. Two different adhesives, silicone and epoxy, were used to connect timber and glass. The two adhesives vary in their strength and their stiffness. This has an immense influence on the behavior of the beams. This paper illustrates the results of various applications.
Up to now, structural sealant glazing façades have been extensively applied. They are at the cutting edge of technology and meet the highest standards. The objective of several research projects was to develop stiffening glass fronts, which replace expensive frameworks or wind bracings behind the large glass windows. Thus, potential applications of timber-glass composites (TGC) as alternative stiffening constructions for multi-story façades were investigated. Based on the results of those previous research projects the Department of Structural Design and Timber Engineering (ITI) coordinated the follow-up international research project “Load bearing timber-glass composites (LBTGC)” within the framework WoodWisdom-Net. In consideration of long-term behavior and practical application, the objective of the joint research project LBTGC was to develop load-bearing and stiffening TGC structures. With the purpose to meet the highest standards of cost effectiveness and environmental compatibility, alternative stiffening TGC constructions for multi-story facades were investigated. This paper illustrates these developments and application of TGC multi-story façades.
Glued glass front constructions have long been in use and are generally considered the state of the art. However, with these solutions the glass serves no stiffening or bearing function, but merely functions as an outer cover. The objective of several research projects was to investigate alternative constructions of stiffening glass fronts, which replace St. Andrew’s cross wind bracings and costly frameworks. To this end, the Department of Structural Design and Timber Engineering (ITI) studied and optimized the load-bearing capacity of these existing construction components and subsequently developed simple calculation and sizing concepts. Based on the results of the research project „Timberglass composites: calculation and sizing concept (HGV III)“ the ITI coordinated the follow-up international research project “Load bearing timber-glass composites (LBTGC)” within the framework WoodWisdom-Net. In consideration of its long-term behavior and practical application, the objective of the research project LBTGC was to develop “stiffening timber-glass composite (TGC) structures”. With the purpose to meet the highest standards of cost effectiveness, alternative stiffening TGC constructions for multi-story buildings were investigated. This paper illustrates these developments.
The architectural need for more transparent building envelopes not only changed the appearance of the buildings, but also their structural behaviour. Walls do not only have a vertical load-bearing function any more, they are also used for the transfer of wind and earthquake induced loads. Structural sealant glazing structures have been used for a long time and are nowadays state of the art technology. In these applications, however, the glass has not got a load bearing function. It only serves as a pure building envelope. Research projects carried out at Holzforschung Austria over more than ten years have shown that timber-glass composites can be used as load-bearing elements in wooden frame houses. A construction system was developed, which allows for a very cost-efficient use of prefabricated timberglass-composite elements on building site. The principle suitability of several adhesives considering different loadings was investigated by means of small scale experiments. Thereafter, the load bearing capacity of such elements was investigated by means of large-scale fracture tests of prototypes providing insight into the load transfer and failure mechanisms. Long-term aspects such as the durability and the robustness of the composite elements were also investigated, as well as questions regarding building physics. The conclusions gained from these research activities were also applied in timber-glass-composite prototypes which have been installed in real buildings. They allowed for a long-term monitoring of such composite structures. A research project at the Vienna University of Technology, Department Structural Design and Timber Engineering, which was finished in 2015, has led to a comprehensive design concept, which allows for an analysis and design of timber-glass-composite constructions. It is based on the combination of spring models and deals with the incorporation of the shear wall- and the compression diagonal-theory in the glass. Numerous applications of the timber-glass-composite system developed by Holzforschung Austria in real buildings, from single-family houses to large facades, have proved the advantages of this system.
