Summary and Conclusions
This paper outlines two topics of high importance for structural joint durability. First, the jointing material itself was in the focus of research activities. Tensile and shear tests were performed for unaged and artificially aged specimens. Furthermore, corresponding tests were performed for unaged specimens at different temperatures. Finally, creep behavior was also tested within the
FIG. 21—Maximum principal stress distribution in E-type bonding, Lf=22 mm (1 N/mm2=1 MPa).
framework of the tensile tests. The experimental results are summarized as follows:
• Regarding tension tests, aging leads to increased flexibility but no significant changes in strength are visible.
• Regarding shear tests, aging leads to increased flexibility and to reduced strength.
• Regarding tension tests, increasing temperatures lead to increased flexibility, but no clear trend is visible for strength.
• Regarding shear tests, increasing temperatures lead to increased flexibility and to reduced strength.
• Regarding tension tests, creep does not show significant impact on flexibility and strength at higher loads.
As not all experimental results show unique trends, additional test activities in this field are recommended. In addition, other adhesive materials should be investigated as well in order to broaden the experimental database.
As a second step, different bonding geometries were analyzed with respect to durability issues, working with the hypothesis that the maximum principal stress level in the vicinity of the exposed bonding surface is a measure for durability. This assumption is based on the concept that the environmental impact of aggressive media and solar radiation is related to the penetration depths into the adhesive. The highest impact of environmental effects is expected at the exposed bonding surface. In addition, it is supposed that an attenuation of these effects appears with increasing depth from this surface. For aggressive media, this assumption is guided by the physical principles of diffusion into the adhesive, while for radiation, physical principles of absorption of the radiation seem applicable for the adhesive. Although it is quite difficult to quantify the impact of these mechanisms on material strength in terms of exact numbers, this approach allows the derivation of design rules for different bonding geometries such as U-type, T-type, L-type, and E-type bonding designs which were numerically and, in part, also experimentally analyzed. Furthermore, the design considerations can be generalized to a class of bonding geometries with planes parallel and perpendicular to the tensile load axis. Regarding durability it can be concluded that:
• Bonding geometries with all exposed surfaces located only at the end of side regions are expected to show good durability properties in the context of applied stress. Examples are U-type bonding geometries and E-type bonding geometries.
• Bonding geometries with at least one free surface located at a front region are expected to show lower durability properties in the context of applied stress. Examples are T-type bonding geometries and L-type bonding geometries. One should note that these statements hold true for
the fully operative bonding. The situation of post-failure behavior is not treated in this paper with the exception of the presentation and discussion of experimental results for degraded bonding geometries.
The author would like to thank the building owner—Erzdiozese Munchen und Freising, Erzbischofliches Baureferat—for unconditional support of the advanced design of the Herz-Jesu Church, Munich. Furthermore, the author would like to thank Dow Corning GmbH for their outstanding technical support provided during the design of the facade as well as in the related research phase.