Characterization of Adhesive Joints for Hybrid Steel-Glass Beams by Means of Simplified Small Scale Tests

In the recent past there have been calls for transparent and filigree structures in the building industry. Therefore, glass plays an increasing role not only in a classic way, as a space enclosing element, but also more and more in terms of offering load carrying functions. Glass beams for facade elements or floor girders, glass columns, or bracing facade elements are examples of this. To realize such architecturally attractive structures, bonded hybrid steel-glass elements have been developed in which each material is used in an optimized way according to its material properties. Promising examples for such bonded structures are I-beams in which steel flanges and glass webs are connected by linear adhesive bonds. The shear force is carried by the glass web, whereas the bending capacity of the hybrid beam is significantly increased by slender steel flanges compared to the pure glass pane. The shear forces between steel and glass are sustained only by the adhesive between them. In order to maximize the exploitation of both steel and glass, the adhesive on the one hand has to ensure an adequate stiffness but on the other hand has to be flexible enough to allow for a reduction or redistribution of local stress peaks, as well as other constraints such as thermal dilatation. However, the load-bearing capacity of such beams is governed, besides by the mechanical and geometrical characteristics of the adhesive joint, by aging, temperature, and creeping. In this contribution, an approach is shown for characterizing the adhesive joints for hybrid steel-glass beams by means of simplified small-scale tests. Standardized specimens (block shear and tension bulk specimens) and small-scale push-out tests are used to derive adequate mechanical values for analytical and numerical calculations, allowing one to draw conclusions regarding the general load carrying behavior of large-scale hybrid steel-glass beams. The results show that full-scale hybrid steel-glass beams, especially those with butt splice bonded and U-bonded geometries, are feasible using new structural adhesives, predominantly elasto-plastics such as polyurethanes or epoxy resins.