Consistent Time-to-Failure Tests and Analyses of Adhesive Anchor Systems

Abstract

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.

Creep rate based time-to-failure prediction of adhesive anchor systems under sustained load

“…After discussing basic features of time to failure tests in section 2 and introducing the formulation of the criterion in section 3, the application of the criterion is investigated using the authors own data only in section 4. Finally, following the Miyano approach [25], the stress versus time to failure curve is reconstructed in section 6, verifying the two domain curve that was introduced in [18,11] in a phenomenological manner. Therefore, an appropriate function relating the creep rate to the remote stress is necessary.…”

“…However, for more solid conclusions further tests at more temperature and stress levels are necessary in which all previously encountered influence factors such as loading rate [18] are properly controlled.…”

“…Nevertheless, no conclusion on the shape of the stress versus time to failure curve was made. Ninčević et al [18] followed the findings of Boumakis et al [11] and proposed a sigmoid stress versus time-to failure curve based asymptotic matching, i.e. imposing the physically reasonable behavior for high loads approaching the short-term capacity or low loads.…”

Einfluss unterschiedlicher Lastaufbringungsverfahren auf die Verschiebungsprognose von Verbunddübeln

“…Mittels einer Potenzfunktion kann daraus resultierend jenes Lastniveau abgeleitet werden, welches rechnerisch eine Standzeit von über 50 Jahren aufweist, vgl. hierzu beispielhaft [1, 4, 5, 7, 12].…”

“…Die Kenntnis dieses Langzeitverhaltens ist von essenzieller Bedeutung für die Bemessung solcher Befestigungen, da ein Überschreiten der kritischen Verschiebungen durch Kriechen zu einem abrupten Versagen der Befestigung während der Nutzungsdauer führen kann. Das Langzeitverschiebungsverhalten von Verbunddübeln ist daher Gegenstand intensiver Forschungen [1–8].…”