Recent advancements at TU Delft have investigated the potential of geometrically enhanced profiles to improve the performance of concrete-to-concrete interfaces, with one study focusing on the tensile behavior of single-tab Strain Hardening Cementitious Composites (SHCC)-to-SHCC interfaces through experimental testing. SHCC, an advanced fiber-reinforced cement-based material, is known for its distributed cracking and strain-hardening capabilities, offering superior ductility and crack control compared to traditional concrete. Building on this foundation, this thesis models the tensile behavior of geometrically profiled SHCC-to-SHCC interfaces using a continuum smeared cracking model in Abaqus and a lattice discrete cracking model.
The research aims to assess the predictive capability of these numerical models in capturing the behavior of geometrically profiled SHCC-to-SHCC interfaces. It focuses on understanding how interface parameters, such as strength and geometric profiles, influence tensile performance, particularly in enhancing ductility, controlling fracture response, and shifting failure modes from brittle interface failure to ductile SHCC material failure.

To evaluate the ability of numerical models to represent the tensile behavior of geometrically profiled SHCC-to-SHCC interfaces and assess the benefits of geometric enhancements for improving tensile performance, a systematic methodology was adopted. This included an analytical analysis to identify underlying failure mechanisms and develop a simplified model for quantifying their force-displacement response. A continuum smeared cracking model in Abaqus was employed to replicate experimental behaviors and investigate the influence of interface parameters through a parametric study. Finally, a lattice model was implemented to capture fracture responses in detail, enabling an in-depth analysis of the effects of interface strength and interface geometry on strength, ductility and fracture response.

The numerical models provided insights into the tensile behavior of geometrically profiled SHCC-to-SHCC interfaces, revealing the influence of interface parameters and geometric characteristics on failure mechanisms. The continuum smeared cracking model demonstrated the ability to simulate various failure mechanisms by adjusting interface parameters, but it underestimated SHCC’s strain-hardening behavior during local material-dominated failure due to the delayed introduction of damage. Conversely, the lattice discrete cracking model effectively captured distributed cracking patterns but exhibited overly brittle responses in interface-dominated failure mechanisms due to assumptions of brittle interface elements and the neglect of frictional resistance. Parametric studies confirmed that changing interface geometry and optimizing interface strength could shift failure modes from brittle, interface-dominated failure to ductile SHCC material-dominated failure.

This study highlights the capabilities and limitations of numerical models in optimizing the tensile behavior of geometrically profiled SHCC-to-SHCC interfaces. The continuum smeared cracking model in Abaqus identified critical parameters, such as tensile strength and fracture energy, influencing failure mechanisms. However, it underestimated SHCC hardening during tab failure due to delayed damage initiation, which should occur immediately after the elastic limit to accurately capture distributed cracking behavior.
The lattice discrete cracking model effectively simulated distributed cracking but exhibited overly brittle responses in interface-dominated failure mechanisms. This limitation stemmed from brittle interface assumptions and the omission of friction, resulting in a significant underestimation of displacement capacity.

Parametric studies using the analytical and lattice models revealed that modifying the interface geometry significantly reduces the interface strength required for ductile failure. For instance, the analytical model demonstrated that adjusting the geometry reduced the interface strength needed to transition from interface-dominated to material-dominated failure from 20% to 7%. In the lattice model, at low interface strengths (≤ 25%), a change in geometry of 1% enhanced SHCC damage by 3% to 6%. At higher strengths (≥ 30%), interface-dominated failure mechanisms diminished, with full SHCC material activation observed beyond 150% strength, ensuring global rather than localized failure.

These findings confirm that optimizing interface strength and geometry enables the transition from brittle, interface-driven failure to ductile, material-driven failure. Nonetheless, the models' limitations must be addressed, particularly the insufficient representation of strength-geometry-friction interactions in the analytical model and the lack of interface ductility and friction in the lattice model. Despite these challenges, the results provide a valuable foundation for refining numerical models and guiding experimental validation to optimize SHCC-to-SHCC interfaces.

The thixotropic properties of contemporary mortars allow the insertion of mortar in small vertical seams by using a mortar pump without the need for traditional formwork. In such a seam, a vertical mortar connection for the transfer of shear forces can be created by simply adding a profile to the mortar-to-concrete interfaces. In this way a constructible continious vertical shear connection can be constructed between storey-high precast concrete wall elements. In this investigation, narrow vertical mortar connections are developed for the transfer of shear forces in precast concrete shear walls with tying reinforcement in the slabs. The shear behaviour of five versions with differently shaped mortar-to-concrete interfaces is obtained from shear tests. All experimental results are presented and discussed, while the shear behaviour of the Staggered shear key connection is analysed in detail. Also, the shear behaviour of the five mortar connections are mutually compared and assessed on their performance for functioning as a vertical mortar connection. A diagonal bar model is proposed for simulating the shear behaviour of the Staggered shear key connection, which is called the “inclined compression strut model”. Also, an equation for predicting the shear capacity is proposed. The functioning of the model and equation are investigated by applying them in case studies with cantilever shear walls in versions with and without window openings.@en