Creep and shrinkage in fastening systems

The efficient and permanently safe design of fastening systems requires a thorough understanding of all involved load carrying mechanisms and their potential change in course of time due to deterioration and material aging. The latter are determined by the involved materials - concrete, steel, and, depending on the system, the mortars. In this contribution we focus on concrete cone failure, the critical failure mechanism for bonded as well as mechanical anchors under pre-dominant tension loading. Both mechanical as well as chemical anchors undergo an approval process during which their performance is certified. These tests are performed according to strict guidelines and for concretes of a specified composition and age range. Nonetheless, differences between laboratories, the age of concrete at testing, the storage conditions, the coarse aggregate type exist. In this contribution we attempt to quantify the effect of testing age in combination with storage conditions on obtained pull-out loads. We will present the numerical framework that is able to model the coupled problem of heat and moisture transport, hydration, aging of material properties, shrinkage and creep in a rate-type, point-wise form. The framework will be calibrated based on an experimental study of creep and shrinkage on a typical C25/30. The mechanical model is calibrated and validated on standard tests for uniaxial compression, three point bending as well as pull-out tests. Afterwards, the calibrated framework is applied in a purely predictive way to fastenings under sustained loads