Glass in Building

Structural Adhesive Joints with UV – and Light-Curing Acrylates

Adhesive joints can be designed with different forms: point, linear or planar. In structural glass designs, load bearing adhesive joints have so far been mainly

FIG. 9—Adhesive strengths (cylinder tensile test) for various adhesives and different testing temperatures.

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planar or linear [43]. The planar joints include the laminating of panes of glass to form laminated or laminated safety glass. The linear joints, beside the edge seals around insulating glass units, include structural sealant glazing (SSG) sys­tems according to ETAG 002-1 [23].

Load bearing point adhesive joints with transparent adhesives are being investigated in order to increase the benefits of using glass in buildings. The UV – and light-curing acrylates are particularly interesting because in contrast to silicone adhesives they exhibit much higher initial strengths although applied in much thinner layers. The adhesives investigated are completely transparent and hardly visible to the naked eye. Curing is carried out with a special lamp, pref­erably using ultraviolet radiation. The adhesive is fully cured after exposure to the radiation for a length of time ranging from a few seconds to a few minutes, and the joint can be loaded immediately. The aging resistance of acrylate adhe­sives has been investigated and described in detail in Ref. [44].

Verification of load bearing and residual load bearing capacities has also been carried out on bonded component models, also punctually bonded glass panes in the form of a canopy system stored outdoors in order to be able to assess durability under natural weathering conditions [37,42]. The panes of glass were stored either suspended from above or supported from below depending on the options presented by the system (Fig. 10). Visual inspections of the adhesive joints were carried out at regular intervals to see if any changes had taken place. After a period of three years outdoors, various changes are visi­ble: the volume of small air bubbles, caused by the manual method of producing the joint, increased at some points. In the case of the overhead glazing sup­ported from below, restraint stresses were detected in the adhesive joint due to the extremely stiff construction of the components, and this had led to delami­nation. On the basis of this experience, a structural determinate system is rec­ommended which supports without restraint in the plane of the glass pane.

FIG. 10—Outdoor overhead glazing test: in the foreground the suspended pane, in the background the supported pane.

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Rochester Institute Of Technology pursuant to License Agreement. No further reproductions authorized.