Aggregate effect on the concrete cone capacity of an undercut anchor under quasi-static tensile load

In the last decades, fastening systems have become an essential part of the construction industry. Post-installed mechanical anchors are frequently used in concrete members to connect them with other load bearing structural members, or to attach appliances. Their performance is limited by the concrete related failure modes which are highly influenced by the concrete mix design. This paper aims at investigating the effect that different aggregates used in the concrete mix have on the capacity of an undercut anchor under tensile quasi-static loading. Three concrete batches were cast utilising three different aggregate types. For two concrete ages (28 and 70 days), anchor tensile capacity and concrete properties were obtained. Concrete compressive strength, fracture energy and elastic modulus are used to normalize and compare the undercut anchor concrete tensile capacity employing some of the most widely used prediction models. For a more insightful comparison, a statistical method that yields also scatter information is introduced. Finally, the height and shape of the concrete cones are compared by highly precise and objective photogrammetric means

Consistent time-to-failure tests and analyses of adhesive anchor systems

Motivated by tunnel accidents in the recent past, several investigations into the sustained load behavior of adhesive anchors have been initiated. Nevertheless, the reliable lifetime prediction of bonded anchor systems based on a relatively short testing period still represents an unsolved challenge due to the complex nonlinear viscoelastic behavior 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 are presented with the main goal to (i) provide guidance for the analysis of load versus time-to-failure test data, and (ii) to derive a set of recommendations for efficient time-to-failure tests having in mind the needs associated with different analysis techniques. Finally, a new approach based on a sigmoid function, previously used only for concrete, is for the first time applied to bonded anchors systems and compared to the established regression models

Numerical investigation of factors influencing the experimental determination of concrete fracture energy

The fracture energy is one of the most crucial parameters for the numerical investigation of damage propagation and failure in reinforced concrete members. The correct characterization of concrete fracture properties can be compromised by different laboratory limitations, such as specimens size, mode of control, loading rate and the test apparatus. Nowadays limited recommendations exist concerning the experimental evaluation of fracture energy for normal and high strength concrete. In order to investigate the differences between different specimen sizes, evaluate the effect of mode of control and analyze the influence of different set-up on the fracture test, a numerical analysis supported by an experimental campaign is presented. The Lattice Discrete Particle Model (LDPM) has been used to simulate concrete and to provide realistic crack patterns and crack widths. In the first part of the study the position of the traveling crack tip is identified with two approaches and then used to investigate the strain rate distribution along the ligament. It is well-known that concrete is a visco-elastic material with strain-rate dependent fracture properties. For this reason in the second part of the study the potential influence of differences in loading rate on the effective fracture energy determined by the work of fracture method is investigated with simulated three-point bending tests of differently sized specimens and two notch depths

Comprehensive data collection for the development of anchorage lifetime prediction models

Nowadays, fastening systems represent a very important part of the construction industry due to their versatility and use in reconstruction. Therefore, it is essential to study and understand phenomena and effects influencing the lifetime of a fastening system. However, the mechanisms are complex and not yet fully understood. As a result, numerical models, which are reliable and are able to capture all involved effects, are needed. The basis of these models is a wide range of high quality data, for model development, calibration, and validation purposes. Within the 7‐year Christian Doppler Laboratory (CDL) of Life Cycle Robustness, an extensive concrete data base, consisting of short‐term mechanical properties of concrete, time‐dependent measurements as well as tests on full fastening systems, was generated. The material tests reach from compression, indirect tensile, and fracture tests to long‐term creep and shrinkage tests. Shear and pull‐out tests were carried out on bonded and mechanical anchors. In order to characterize the long‐term performance, sustained load and time to failure tests were conducted at a system level. In total, 12 concrete mixes were tested. This contribution will give an overview of the performed tests and will highlight the importance of sound experimental data

Discrete element framework for modeling tertiary creep of concrete in tension and compression

In this contribution, a computational framework for the analysis of tertiary concrete creep is presented, combining a discrete element framework with linear visco-elasticity and rate-dependency of damage. The Lattice Discrete Particle Model (LDPM) serves as constitutive model. Aging visco-elasticity is implemented based on the Micro-Prestress-Solidification (MPS) theory, linking the mechanical response to the underlying physical and chemical processes of hydration, heat transfer and moisture transport through a multi-physics approach. The numerical framework is calibrated on literature data, which include tensile and compressive creep tests, and tests at various loading rates. Afterwards, the framework is validated on time-to-failure tests, both for flexure and compression. It is shown that the numerical framework is capable of predicting the time-dependent evolution of concrete creep deformations in the primary, secondary but also tertiary domains, including very accurate estimates of times to failure. Finally, a predictive numerical study on the time-to-failure response is presented for load levels that are difficult to test experimentally, showing a deviation from the simple linear trend that is commonly assumed. Ultimately, two alternative functions for time-to-failure curves are proposed that are mechanically justified and in good agreement with both, experimental data and numerical simulations