  Motivated by tunnel accidents in the recent past several investigations into
the sustained load behavior of adhesive anchors have been initiated.
Nevertheless, the reliable life-time prediction of bonded anchor systems based
on a relatively short period of testing still represents an unsolved challenge
due to the complex non-liner viscoelastic behaviour of concrete and adhesives
alike. This contribution summarizes the results of a comprehensive experimental
investigation and systematically carried out time-to-failure analysis performed
on bonded anchors under sustained tensile load. Two different adhesive
materials that find widespread application in the building industry were used,
one epoxy and one vinylester based. Performed experiments include full material
characterizations of concrete and the adhesives, bonded anchor pull-out tests
at different loading rates, and time-to-failure sustained load tests. All
anchor tests are performed in a confined configuration with close support.
After a thorough review of available experimental data and analysis methods in
the literature the experimental data is presented with the main goals to (i)
derive a set of recommendations for efficient time to failure tests, and (ii)
to provide guidance for the analysis of load versus time-to-failure test data.
Finally,a new approach based on a sigmoid function is proposed and compared to
the established regression models. The analyses indicate a better agreement
with the physics of the problem and, thus, more reliable extrapolations.
