PSI - Issue 78

Enes Krasniqi et al. / Procedia Structural Integrity 78 (2026) 261–268

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1. Introduction Anchorage systems serve as pivotal load-transfer elements in precast reinforced concrete (RC) construction, particularly influencing structural ductility, robustness, and seismic resilience. In traditional design practice, anchorage of longitudinal reinforcement typically depends on sufficient embedment length to develop bond strength between steel and concrete. However, constraints in precast manufacturing, transportation, and assembly demand alternative strategies that ensure equivalent or superior structural performance with reduced embedment lengths. Mechanical anchorage systems offer a solution by incorporating mechanical interlock mechanisms such as headed bars, hooked ends, or the use of threaded bars with end nuts, which act to increase bearing resistance and engage concrete confinement effectively. The performance of anchorage zones is critical in resisting tensile forces, especially in regions of high seismic demand or structural irregularity where stress concentrations can lead to brittle failure if anchorage is insufficient. The development of mechanical anchorage systems is driven not only by mechanical efficiency but also by industrial trends in modular and accelerated construction. By reducing the required embedment length, threaded nut-bar systems facilitate more compact designs, enhanced construction tolerances, and fewer interference issues with other structural components such as transverse reinforcement, embedded ducts, or service conduits. Several experimental investigations have explored the structural benefits of mechanically anchored systems, noting significant improvements in ultimate tensile resistance, reduction in bond-dependent slip, and transformation of failure modes from brittle pull-out to more ductile yielding of the steel (Eligehausen et al. 1983), (Nishiyama et al. 2002) (Yalciner et al. 2012). These systems also demonstrate enhanced behaviour under cyclic loading conditions, as reported in studies addressing seismic retrofitting and performance-based rehabilitation strategies (Chiewanichakorn, et al. 2004), (Monti and Spacone 2000). From an analytical perspective, the complexity of stress transfer mechanisms—encompassing concrete cracking, bond degradation, plastic hinge formation, and confinement interaction—requires advanced simulation techniques. Traditional empirical formulas, such as those presented in ACI 318 or Eurocode 2, lack the resolution to account for the heterogeneous and nonlinear behaviour of concrete near failure. In response, the adoption of nonlinear finite element analysis (NLFEA), particularly with constitutive models that integrate fracture mechanics and plasticity theory, offers a higher-fidelity approach. Among the various platforms available, ATENA (Advanced Tool for Engineering Nonlinear Analysis) is widely used in academic and professional practice for simulating concrete structures, including post-installed anchors, lap splices, and mechanical terminations. Developed by Červenka Consulting (Červenka Consulting s.r.o. 2015), ATENA features an advanced concrete material model incorporating smeared cracks, tension softening, and compressive plasticity with damage evolution (Červenka and Papanikolaou 2008). This enables simulation of crack initiation, propagation, and coalescence with minimal mesh dependency, which is crucial for assessing failure modes and residual capacity. The fib Model Code 2010 recognises these advances and provides a structured framework for integrating nonlinear simulation into design and assessment workflows. Chapter 7.11 specifically endorses verification assisted by numerical simulations, outlining requirements for model validation, mesh sensitivity, and reliability-based safety formats. This shift aligns with the growing use of virtual testing for structural optimization, failure prediction, and robustness evaluation. In this paper, a comprehensive numerical study is conducted on a novel mechanical anchorage system utilising threaded bars with end nuts embedded in precast concrete (Dal Lago et al. 2025). The objective is to simulate and analyse their tensile performance under monotonic loading conditions using validated nonlinear FE techniques. The simulations replicate a series of experimental tests and aim to highlight the effect of embedment length, mechanical anchorage, and confinement detailing on structural performance metrics such as peak load, crack evolution, and failure mode. 2. Tested specimens Three distinct configurations of anchors were experimentally analysed, replicating previously tested experimental setups under axial tensile loading (full experimental results are available in Dal Lago et al. 2021). The models represent varying embedment lengths and anchorage types to assess the contribution of mechanical end nuts and confinement reinforcement:  TR01b: Reference specimen with medium embedment length and plain bar, without mechanical nut anchorage.