VILNIUS TECH Library invites you to follow the published new dissertations. The dissertation „Numerical bond modelling of reinforcement bars and concrete“ prepared by VILNIUS TECH, Domas Valiukas. The dissertation was prepared in 2020–2025. Scientific Consultant – Prof. Dr Habil. Gintaris Kaklauskas.
The dissertation was defended at the public meeting of the Dissertation Defence Council of the Scientific Field of Civil Engineering in the Aula Doctoralis Meeting Hall of Vilnius Gediminas Technical University at 9 a.m. on 16 May 2025.
Reinforced concrete is the most widely used building material in the world. Combining materials with fundamentally different mechanical properties creates a composite that benefits from both strengths. The surface interaction, or bonding, between these materials is crucial for the overall performance of reinforced concrete structures, affecting both safety and serviceability. In engineering calculations, the ideal bond between concrete and reinforcing bars is often assumed, meaning that under load, their deformations and displacements are equal, thus resulting in zero slip value. This simplification works well for assessing the bearing capacity of structures (when reinforcement pull-out failure mode from the concrete is considered). However, it poorly predicts crack widths and distances between cracks in serviceability limit states, leading to significant errors in calculating deflections and deformations. One approach to modelling the cracking and deformation of structures is the stress transfer mechanism. This mechanism considers the local interaction between reinforcement and concrete, where forces are transmitted through mechanical resistance, internal friction, and initial adhesion due to the concrete matrix bonding to the reinforcement’s rough surface. While the stress transfer mechanism can model creep, concrete failure, and crack distances, it suffers from uncertainties in the bond-slip law. No universal bond stress-slip law currently exists, and existing laws have narrow application limits, leading to large errors in calculating crack distances and widths. This work examines the stress transfer mechanism numerically, at the microscopic level, to better understand the interaction between concrete and reinforcement. An accurate numerical model, calibrated by double pull-out tests, allows the study of concrete deformation at various levels, propagation of secondary cracks from the tips of reinforcement ribs, and displacement between reinforcement and concrete (or simply slip) along structural elements. This model enables the study of the bond stress–displacement law through virtual experiments. With this new numerical model, it is possible to analyse concrete behaviour under various load levels (serviceability and ultimate limit states), study cracking and deformations in structures, and derive simplified interaction laws between concrete and reinforcing bars for practical engineering calculations.
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