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

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

Investigation of fracture based on sequentially linear analysis

There are different mathematical models describing the complex fracture behavior of quasi-brittle materials. In particular, the discrete and smeared crack models stand out in their ability to represent the gradually softening response of these materials. Their application requires the knowledge of experimentally determined fracture properties, such as the tensile strength and the fracture energy. Therefore, two different approaches are introduced in this paper to determine these material properties from a large set of standard notched three point bending tests. More specifically, the recently introduced inverse analysis based on a sequentially linear approach is compared with the commonly used work of fracture method and the main differences are highlighted

Age and cure dependence of concrete cone capacity in tension

A large experimental campaign was completed with the objective to determine how concrete composition and age affect the tensile load capacity of mechanical anchors with concrete cone breakout, tested in three different normal-strength concretes. Structural tests for cast-in headed stud anchors were performed at 28 and 70 days and compared to results obtained on post-installed undercut anchors. The concretes were fully characterized in terms of Young's modulus, compressive and tensile strength, and fracture energy. The evolution of the concrete compressive strength is consistent with the aging function proposed in codes. Because the history of environmental conditions influences the development of material properties with age, three different curing conditions are considered for the material characterization, including indoor moist-curing and outdoor storage with the slabs. The structural data clearly show a pronounced aging effect, even after normalization by compressive strength, regardless of the curing protocol considered

Concrete creep and shrinkage effect in adhesive anchors subjected to sustained loads

The safe design of fastening systems requires an accurate understanding of all time-dependent phenomena that may lead to damage or even failure during its service life of typically 50 years. Generally, safety and serviceability requirements are ensured through rigorous experimental testing during the approval phase. In the case of time-dependent phenomena, or more specifically the behavior under sustained load, the common practice of directly testing all critical service conditions fails. The long-term response can only be approximated e.g. by short-term structural system tests that are extrapolated to the full life-time utilising empirical models as required by current guidelines. These are based on the assumption of uniformly distributed bond stress along the anchor, attribute all creep deformations to the adhesive mortar, neglect the concrete creep contribution, and assume a stationary creep process represented by a power-law. Generally, it can be assumed that reliable predictions of the time-dependent behavior of complex systems can only be obtained by models that are derived from a systematic investigation of all involved factors and their interaction. In this study, specifically the effect of concrete creep and shrinkage on the long-term behavior of adhesive anchor systems, based on extensive experimental data and numerical analyses, is investigated. A state-of-the-art computational framework is applied which can explicitly model the underlying physical and chemical mechanisms at early age and beyond. The well-established Lattice Discrete Particle Model (LDPM) describes the time-dependent mechanical response of the structure considering the local maturity of concrete, temperature, and moisture content. After calibration and validation of the numerical framework, structural deformations owing to concrete creep, bond stress redistributions over time, and the gradual development of damage at higher load levels are discussed

Evolution of creep and shrinkage models for concrete structures in Austria and Germany : evaluation of the current models regarding the sensitivity of the input parameter

Evolution of creep and shrinkage models for concrete structures in Austria and Germany - Evaluation of the current models regarding the sensitivity of the input parameter Concrete is one of the most important materials in civil engineering structures and finds its application in the building of bridges, ground engineering and building construction. As widely known, concrete is a material which changes its behavior with time in dependency of the environmental conditions. Especially the long-term deformations caused by creep and shrinkage processes are of great interest regarding the durability and sustainability of infrastructures. Early versions of design codes gave some guidelines on how to treat deformations caused by these sources. In the beginning, these deformations were taken into account by an additional temperature drop. The first sophisticated approaches on how to deal with these long-term processes were published in the standards for prestressed concrete structures. These early models were updated and improved to today's prevailing documents such as the Eurocode 2 and the fib Model Code. The first part of this paper gives an overview of the historical development of creep and shrinkage models in Austria and Germany until today's guidelines. The second part presents a sensitivity study of the current models regarding the input parameters for some given scenarios. Lastly, the differences between the models are highlighted based on an application example taken from literature

Analysis of time dependent cohesive laws for high and normal strength concretes based on Sequentially Linear Analysis (SLA)

In earlier research it was found that the fracture energy can be obtained from incomplete load-opening curves utilizing Sequentially Linear Analysis (SLA) (Czernuschka et al., 2018; Vorel et al., 2019). This method has the advantage that the traction-separation diagram (TS) becomes accessible without prior assumptions concerning its shape, which is an important feature for the evaluation of the fracture behavior. This contribution employs the introduced SLA to study the evolution of fracture properties with age based on notched three-point bending tests. The results confirm that the TS-diagrams can be approximated by a bilinear or trilinear softening law. Furthermore, the tensile characteristic length, as defined by Hillerborg et al. (1976), is chosen for the description of aging fracture properties