PSI - Issue 78

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

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6. Conclusions

The key findings of the research can be summarised as follows:  The inclusion of mechanical nuts improved both tensile capacity and ductility of the anchorage systems. Specimens equipped with mechanical nuts (TR02a and TR02b) attained higher peak loads and exhibited more ductile post-peak behaviour compared to the configuration relying solely on bond (TR01). Notably, the TR02b specimen sustained a plateau in its load–displacement response, highlighting its higher ductility.  Distinct failure patterns emerged among the different configurations. While bonded-only anchors primarily failed due to sudden bond loss and pull-out, anchors fitted with mechanical nuts experienced conical breakout failures, which mobilised a larger volume of concrete, which delayed failure and enhanced ductility.  The nonlinear 3D finite element models developed using ATENA Science closely replicated key experimental observations, including initial stiffness, peak load, and crack patterns. The models successfully captured critical phenomena such as concrete cracking, bond–slip interactions, and steel yielding.  Some discrepancies emerged, particularly in the post-peak behavior. The numerical models tended to concentrate damage into fewer dominant cracks, which led to an underestimation of distributed microcracking and residual friction effects that help maintain load capacity in experimental specimens. Future refinements, such as implementing advanced post-cracking constitutive laws or more sophisticated modeling of aggregate interlock, could enhance the accuracy of post-peak predictions.  Incorporating mechanical nuts into anchorage systems enables significant reductions in required embedment lengths without compromising structural safety or ductility. This finding is particularly relevant for precast concrete design, where spatial constraints often play a crucial role. Although current design codes provide limited guidance for such systems, validated numerical models like those developed in this study offer a robust foundation for design verification and optimisation. ACI Committee 318, Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary, American Concrete Institute, Farmington Hills, MI, USA, 2019. Červenka Consulting s.r.o., ATENA Program Documentation—Theory and User’s Manual, 2015. Červenka, J., Papanikolaou, V.K., 2008. Three Dimensional Combined Fracture–Plastic Material Model for Concrete. International Journal of Plasticity 24, 2192–2220. Chiewanichakorn, M., Aref, A.J., Chen, W.F., 2004. Seismic Retrofit of Reinforced Concrete Bridge Columns Using Steel Jackets and Fiber Reinforced Polymer Wraps. Journal of Bridge Engineering 9(6), 527–535. Dal Lago, B., Del Galdo, M., Papa, E., Dal Lago, A., 2021. Tests on ductile short-length splice connections for precast concrete load-bearing elements. fib Symposium 2021: Concrete Structures: New Trends for Eco-Efficiency and Performance, Lisbon, Portugal, 14 th -16 th June, 1109-1118. Dal Lago, B., Krasniqi, E., Bartolac, M., Muhaxheri, M., Papa, E.A., Costa, P., 2025. Cyclic testing of precast column-to-foundation joints equipped with a novel ductile mechanical connection system. fib Symposium 2025: Concrete structures: extend lifespan, limit impacts, Antibes, France, 16 th -18 th June, 2628-2639. Eligehausen, R., E.P. Popov, and V. V Bertero, Local Bond Stress–Slip Relationships of Deformed Bars under Generalized Excitations , 1983. European Committee for Standardization (CEN), Eurocode 2: Design of Concrete Structures – Part 1-1: General Rules and Rules for Buildings, EN 1992-1-1, Brussels, Belgium, 2004. fib . Fib Model Code for Concrete Structures 2010, International Federation for Structural Concrete - Fédération Internationale du Béton (fib), Lausanne, Switzerland, 2013. Monti, G., Spacone, E., 2000. Reinforced Concrete Fiber Beam Element with Bond–Slip. Journal of Structural Engineering 126(6), 654–661. Nishiyama, M., Shiohara, H., Watanabe, F., 2002. Bond Splitting Failure of Reinforcing Bars in Concrete. Journal of Structural Engineering 128(7), 912–920. Yalciner, H., and others, 2012. Cyclic Performance of Headed Bar Anchorage in Reinforced Concrete. Engineering Structures 34, 408–417. References