## 1 Introduction  
Fastenings are crucial for the construction industry. They facilitate the use of pre-manufactured elements in new structures and allow the attachment of load bearing structural components and equipment to existing structural elements. Typically, they are used in modular construction, renovations or retrofit projects to increase the ultimate strength or control deformations [1; 2; 3]. Some applications require temporary solutions for a relatively short period of time (e.g., to restrain scaffolds). Other problems require long-term solutions, and increasingly more often a 50-100 year service lifetime is demanded for infrastructure projects (e.g., ventilation systems, suspended ceiling panels,...). Various types of fasteners can be found on the market that differ significantly in working mechanisms and/or installation time [1]. This contribution focuses on bonded anchors/adhesive anchors only. In general, bonded anchor systems are typically steel connectors such as threaded bars that are installed in holes, drilled or cored into a base material, and then filled with an adhesive. These types of post-installed fasteners transfer loads mainly by adhesion/bond between the connection element (typically steel rebar, threaded bar, or anchor) and the base material [1]. In the recent past, two accidents [4; 5] caused by the failure of adhesive fasteners under sustained load triggered a critical review of the respective approval and design procedures even though, ultimately, investigations showed that the main reason for both accidents was a wrong choice of adhesive in combination with bad installation. Obviously, limited \"short-time\" testing is the only solution to satisfy modern building demands and to ensure the safe use of products on the market. The engineering community has to rely on fundamental concepts and assumptions concerning the time-dependent material behavior, structural response, and failure mechanisms since only short-term tests to investigate and ultimately predict the multi-decade behavior of building products are feasible. Considering the complexity of the problem and the large number of influence factors including concrete aging, post-curing of the adhesives, non-constant boundary conditions, large variability in anchor types and geometries, it is obvious that reliable and accurate lifetime predictions remain a quite challenging task. Over the last few decades, different research was conducted and several standards have been established to predict the service life of adhesive anchors under sustained load [6; 7; 8; 9]. The currently established approach is based on a pass/fail method using a displacement criterion applied to extrapolated relatively short sustained load tests [10; 11]. The displacement criterion is derived from so-called confined tests, i.e., short-term pull-out tests with close support, and is defined as the displacement at maximum load. The sustained load tests are performed in the same configuration by applying a percentage of the short-term ultimate capacity and by maintaining the load for a hold period of about 2000 h. The obtained displacements for different load levels are then extrapolated in time to 50 years using either a logarithmic function [8; 9], or a power-law function [6; 12]. [PERSON] et al. proposed even the use of a third degree polynomial function [13] without physical justification. In general, this pass/fail method is assumed to provide a conservative time-to-failure prediction. One reason is the conservative choice of the displacement criterion, i.e., the displacement at loss of adhesion (peak load) while the actual displacement at creep failure follows approximately the post-peak softening branch of short-term pull-out tests as shown by [14; 15]. [PERSON] et al. [10; 11] and [PERSON] [16] showed that the main disadvantage of this method is the high dependence on the chosen creep function, and the inability to predict failure times for other anchor geometries or boundary conditions than the tested one.