International Concrete Abstracts Portal

Scope of this study is to estimate the reliability of bonded anchor systems. Furthermore, the use of a factor K in order to account the effect of sustained loading on a fastening’s failure probability pf, is discussed. As a general standard in structural engineering, it was assumed that the extreme failure probability of pf = 10-6 per year applies to fastenings as well. By use of the factor K, which can be considered as an index of safety reserves as well, the sensitivity of the investigated system to variations of particular parameters can be captured. In order to define the range of K the input parameters were elaborated statistically considering their mean values, variations and types of distribution. Apart from that, the influence of different input parameters was determined through a parametric study. The statistic input of the study was obtained either from the Probabilistic Model Code (Joint Committee of Structural Safety) or from experimental measurements. Final aim was to find a value for the factor K that guarantees a failure probability of pf = 10-6.

The paper is related to basic understanding of curing and load performance of adhesive anchors with special focus on thermosetting systems cured at low base temperatures. Simulations of non-isothermal curing kinetics, vitrification and softening of the adhesives are compared to results of sustained load tests. Based on models for the reaction kinetics of thermosetting materials – considering the transition from mass to diffusion controlled curing regime – and a relation between glass transition temperature and chemical conversion the “curing-induced” vitrification was simulated for different temperature programs. The temperature programs are based on meteorological data and experimentally determined heating rates of concrete. In the simulations curing times, curing temperatures and heating rates were systematically varied. The simulated “vitrification” and “softening times” are compared to sustained load tests performed under the same conditions. The test results support the assumptions of our model which provide at least a qualitative prediction of the adhesive performance after different thermal or meteorological history. The behavior of thermosetting anchor systems cured at low base temperatures followed by fast heating is explained in terms of the competition between softening and post curing.

Adhesive and mechanical concrete anchor systems today are typically tested in concrete mix designs containing no fly ash. This paper investigates the influence of a certain amount of fly ash as a cement replacement on the short term resistance of common adhesive anchor systems. The result shows no significant influence for the tested conditions.

Bonded anchors are frequently used for connections between structural or non-structural elements to concrete members. These connections are loaded by long-term and short-term loads respectively. The evaluation of the long-term behavior in the current approval guidelines in the U.S. and Europe is established by sustained load tests having a minimum duration of 1,000 hours in the U.S. and 2,000 hours in Europe. The results of these tests are extrapolated to approximately 450,000 hours (50 years) for tests at standard temperature and to roughly 90,000 hours (10 years) for tests at elevated temperature. The extrapolation technique and the evaluation criteria are developed to allow for an evaluation on the safe side. The paper presents results of tests on anchors installed using a proprietary adhesive anchor system that were subjected to sustained loads for up to approximately 21,000 hours (2.4 years). In these tests not only the time of testing but also the load level were beyond the requirements of the current approval guidelines. Based on these results the current evaluation method is analyzed and the conservatism associated with several aspects of the testing and evaluation methods is discussed.

This paper describes an experimental investigation on the long-term creep behavior of adhesive anchors under sustained tensile loads in combination with different environmental exposures. The experimental program comprises of 36 pull-out test specimens. The specimens consist of a cylindrical shape concrete block of 300 mm (12 inch) in diameter and 200mm (8 inch) in depth, with 15M (No. 5) deformed steel bars post-installed to an embedment depth of six times the bar diameter or 125mm (5 inch). Three types of adhesives were used: Type A - Fast setting two component methyl methacrylate adhesive, Type B - Fast setting two part epoxy adhesive and Type C - Standard set two part epoxy adhesive. The study is divided into four phases. Phase I consists of static pullout tests to determine the yield strength (fy) and the maximum capacity of each anchor system. Phase II consists of sustained load tests under load levels of 40%fy at normal laboratory conditions. Phases III and IV are sustained load tests under load levels of 40%fy with moisture exposure and freeze/thaw cycling, respectively. All sustained load tests lasted for a period of at least 90 days. The results of the static pullout testing showed that specimens with epoxy based adhesive exhibited stronger bond strength, forcing the anchor to fail by rupture prior to bond failure. As for the sustained load test results, specimens with standard set epoxy based adhesive showed insignificant creep displacement under room conditions, however, when exposed to moisture noticeable creep displacements were recorded. Specimens with both fast setting epoxy and methyl methacrylate based adhesives showed higher creep displacements under environmental exposure versus those kept at room temperature.