Nomenclature

ETAG = European Technical Approval Guideline

Introduction

Structural sealant glazing based on silicone adhesives is a well-known and powerful design concept with respect to line-type bonding geometries of rectan­gular cross sections. On the one hand, over 40 years of experience exists for such kinds of applications, especially in the United States. On the other hand, gaining a systematic and profound knowledge of the mechanical properties of the adhesive material for varying operating conditions during its service life and from a fatigue and durability point of view is still a challenging task today. A comprehensive knowledge of the mechanical properties of the bonding adhesive for different loads is the key point in order to assess the structural integrity of glass facades. This is also important from a durability point of view. This paper intends to provide insight into selected issues linked to the mechanical proper­ties of the silicone material.

Up to the present, the use of advanced bonded design solutions beyond the applications covered by ETAG 002 [1] is significantly limited by the lack of full acceptance of the approving authorities. Even in the case of ETAG 002, only a sub-set of potential applications is approved in Germany, i. e., Type 1 and Type 2 designs. The main reason behind this attitude is the missing confidence in the durability aspects of bonded designs. Authorities claim a lack of knowledge with respect to durability, especially in the case of novel designs and assume in­field problems that are not reproduced by the range of standard laboratory con­ditions. Thus, this paper compiles the initial results of various aspects which might impact the durability of bonded point supports in order to identify topics which need more attention in future research.

In principle, the paper is organized in two sections: in the first part, focus is given to mixing issues of the two components of the adhesive, while in the sec­ond part, the behavior under tensile loading for structural applications is addressed. In order to study the effects of the mixing quality, conventional ma­terial tests are considered, such as tensile tests of dog-bone specimens and shear tests of H-type specimens similar in adhesive geometry as described in ETAG 002 [1]. In addition, the behavior under cyclic load schemes was investigated for circular point supports. Furthermore, an attempt is made to link the quality of the bonding to the mechanical characteristics for the investigated specimens as a first step, based on monotonically increasing loads. Mixing aspects dis­cussed in this paper focus, on the one hand, on the variation of the mixing ratios and, on the other hand, on incomplete mixing procedures; both aspects are investigated with respect to their impact on basic material characteristics. Regarding the cyclic loading schemes, the mechanical behavior during the load

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cycles and the post-cycle failure characteristics are of special interest in order to gain insight into the mechanical performance of the adhesive.