This thesis investigates the force transfer mechanisms between concrete substructures and steel pipe piles, specifically focusing on connections made using a concrete plug within the steel pipe pile. This thesis explores the mechanisms of force transfer in concrete plug connections within open-ended steel pipe piles, focusing on the viability of frictional (bond) transfer versus mechanical connections. The primary research objective was to determine the extent to which forces—both normal forces and bending moments—can be transferred through a concrete plug without the use of mechanical connections and to compare this with scenarios where mechanical connections, such as shear rings, are employed.

A comprehensive literature review revealed significant gaps in existing design codes and recommendations, which inadequately address concrete plug connections in steel pipe piles. Notably, regulations such as Rijkswaterstaat’s ROK V2.0 restrict the extent of force transfer through friction without clear justification. Existing standards like Eurocode 4 and the British Standard (BSI) offer bond strength values that vary widely and do not consider key parameters such as connection geometry and concrete shrinkage, potentially leading to inaccurate strength estimations. Although some models for grouted sleeve
connections might be applicable, their validation for concrete plug connections remains uncertain.

To address these gaps, a new analytical model was proposed to estimate the bond strength between
concrete and steel in plugged connections. The model incorporates factors including connection geometry, material properties, concrete shrinkage, surface irregularities, and the Coulomb friction coefficient. Push-out test results were used to update and validate the model, resulting in conservative bond strength values. Key parameters identified were the value for the surface and the Coulomb friction coefficient. The model’s predictions showed a Mean Average Error (MAE) of 0.589 MPa, primarily due to high variability in some test sets. However, the error was smaller for less variable data.

The findings indicate that connection geometry, particularly the diameter of the steel pipe pile, significantly affects bond strength. Smaller diameters exhibit higher bond strength due to better confinement and reduced concrete shrinkage effects. For larger diameter piles, where friction is insufficient to transfer normal forces, mechanical connections such as shear rings are recommended. These connections were evaluated using Eurocode 4 and CUR Recommendation 77 and found to provide substantially higher normal force resistance, enabling effective utilization of the geotechnical load-bearing capacity.

Regarding the transfer of bending moments, the study found that the wrenching mechanism between the concrete plug and steel pipe pile can manage the transfer through contact stresses. This stress distribution is linear along the plug height and sinusoidal around its circumference, provided it remains within allowable concrete compressive stress limits. The plug’s length should be designed to ensure these stresses do not exceed permissible values. A model for the interaction between bending moment and normal force was also developed, indicating that additional normal force resistance can be achieved under a certain bending moment, though this requires careful stress distribution verification.

In conclusion, while friction can achieve normal force transfer in concrete plug connections, it is often insufficient for larger piles. Mechanical connections such as shear rings offer a more effective solution, providing significantly higher normal force resistance and enabling efficient design. The wrenching mechanism can be used to transfer bending moments, but the ultimate bending moment resistance is governed by the concrete plug’s cross-sectional resistance. This is because the resistance of the concrete plug’s cross-section is lower than the wrenching resistance. This research provides a comprehensive framework for understanding and optimizing force transfer mechanisms in concrete plug connections within steel pipe piles, highlighting the importance of mechanical connections for effective and practical design.

Concrete is the second most used material in the world after water and recent trends show no slowing down of the concrete use around the world. Concrete is also a huge contributor to CO2 emissions as it makes up 8% of emissions. This study investigates the optimization of concrete structures to reduce environmental impact while maintaining structural integrity and cost-effectiveness, e.g. how to make a concrete structure more sustainable. A previous report where quay wall designs of different materials were compared in regard to the CO2-emissions and life cycle assessment found that a concrete quay wall had 43% more emissions than a steel quay wall. The goal of this study is to reduce the overall CO2 equivalent emissions related to a concrete structure by 50% and make the design more sustainable.
A concrete ship lock chamber as part of the Delta21 project is used as a case study. To measure the positive effect of sustainability two chambers are designed; a base case chamber designed based on what is most commonly done in practice in the structural engineering field, and an alternative chamber design with the aim of making the concrete lock chamber more sustainable. A partial life cycle assessment (LCA) is performed on both of the two design alternatives. The optimization of the alternative chamber design focused on minimizing global warming potential (GWP) by adjusting the reinforcement-to-concrete ratio and incorporating structural elements such as plated steel anchors. The two alternatives are analysed comparably as they are designed under the exact same conditions, in the same environment and with the same functionality aspects.
The base case structure is a U-basin concrete chamber with tapered walls. The alternative optimised structure enhances the structural behaviour of the chamber wall by adding anchors. This reduces the moments by 88% and the shear force by 56% compared to the base case design. By changing the structural wall type in the chamber by adding anchors, the concrete volume could be reduced by 47% between the base case design and the optimised design. This also allows for a reduction of concrete strength class, reinforcement volume, underwater concrete floor thickness and the number of tension piles for the construction pit. The LCA reveals a 55% reduction in the GWP for the alternative concrete chamber design, compared to the base case design. An optimum reinforcement ratio for the alternative concrete chamber anchored wall of 2.3% is identified, resulting in a balance between structural performance and environmental sustainability without increasing material costs. This ratio doesn’t incorporate labour cost which might affect this optimum ratio by lowering it. This demonstrates the potential for achieving environmentally responsible solutions without compromising the structural integrity of a structure or incurring additional costs.
The study highlights the potential for integrating sustainability objectives into concrete structure design, with recommendations for further research including exploring alternative materials and advanced optimization techniques.

To align with the objective of the European Green Deal [46] policy of achieving net-zero greenhouse gas emissions by 2050, the construction sector must transition to a circular built environment. Most of the waste in the Netherlands is related to construction and demolition waste, with the industry accounting for approximately 35% of CO₂ emissions [89]. The goal of the circular built environment is to minimise waste by reducing, reusing, recycling, and recovering materials throughout the life cycle of a product [66]. Therefore, making an impact in the construction industry can lead to a significant reduction in CO₂ emissions and contribute to the achievement of the European Green Deal [46].

This research contributes to the "reuse" component of the aforementioned circular built environment goals. Specifically, the focus is on developing a reusable connection between hollow core slabs and steel frames by implementing increased execution tolerances. Increased tolerances are necessary to allow reuse, as alignment-related problems often occur. The research consists of several parts: the design process, structural verification, experimental research on demountability, and environmental impact assessment. The design process comprises a tolerance analysis supported by a Monte Carlo simulation, variant studies, and a comprehensive qualitative trade-off analysis. After the best scoring alternative is determined, the verification part assesses the structural behaviour of the connection in terms of strength and stiffness. This is done using a combination of analytical and numerical calculations. The purpose of the experimental research is to investigate the demountability potential of the reusable connection. The final part of the research investigates the impact of the reusable connection compared to conventional connections for different lifecycle scenarios.

The research demonstrated that incorporating additional tolerances in the connection between the hollow core slab and steel frame is crucial to achieve a reusable construction. Three connection alternatives were generated that can incorporate these tolerances based on a literature review and meetings with experts in the field of building construction. The alternatives were weighted on tolerance inclusion, ease of installation, demountability potential, and costs. The best option was identified as a connection consisting of a square hollow section and a bolted shear stud encased in mortar. This alternative outperformed competitors in terms of tolerances, installation, and costs. However, the demountability potential was identified as a critical part of the connection and, therefore, was further investigated experimentally. The experiments showed an increased demountability potential in situations that include pre-treatment. Vaseline-treated specimens showed no signs of chemical bonding and better lubrication compared to oil-treated specimens, resulting in the lowest resistance and, therefore, the best demountability. The last step of the research investigated the environmental impact of the reusable connection and compared it with the conventional construction technique. Results showed that a marginal addition of 1.3% to the initial environmental impact of the superstructure results in a significant reduction over the full lifespan of the structural elements. This was attributed to the reusability of the connection and the ability to reuse structural elements in another building in a second life cycle.

From the results, it is concluded that a reusable and structurally feasible connection between hollow core slabs and integrated steel beams can be created with a small additional investment upfront, resulting in a substantially reduced environmental impact. The purpose of this study is to provide guidance and persuade decision makers, such as project developers, building owners, and government organisations, to consider implementing reusable construction methods in their real estate projects. By doing so, they can contribute to the objective of the European Green Deal [46] policies and the goal of achieving net-zero greenhouse gas emissions by 2050.

Flexural shear failure is a brittle failure mode that can occur in reinforced concrete (RC) beams without stirrups due to the combination of flexural and shear stresses. The failure mode begins with vertical flexural cracks at the bottom of the RC beam central span area due to flexural tensile stresses, followed by diagonal cracks. During stabilization, a diagonal crack enlarges, leading to flexural shear failure. The failure mode is brittle due to the significant bearing capacity reduction making it more difficult to predict.

Accurately predicting the capacity of concrete structures is important for ensuring their safety, especially in the case of brittle failures. Various design codes are available to design and assess such structures, but an advanced numerical method called the Non-Linear Finite Element Analysis (NLFEA) is an alternative to these codes. NLFEA allows for more detailed and accurate modeling of the structure behavior by considering material, geometry, and boundary conditions nonlinearity. By using NLFEA, engineers can optimize their design and gain a deeper understanding of the behavior of RC beams without stirrups. The NLFEA model requires several modeling decisions to accurately simulate the structures’ behavior.

Sensitivity analysis on different modeling aspects is crucial to obtain a numerical model that can accurately simulate the RC beam. To be considered accurate, the numerical model should simulate approximately the same damage progression, failure mode, and failure load compared to the experiments. The sensitivity analysis is performed to modeling aspects with uncertainties identified during the literature review. These uncertainties are in the constitutive model, finite element discretization, and analysis procedure modeling aspects. Sensitivity analysis on various modeling aspects is per-formed using four experimental beams with distinct geometrical sizes, while some material configura-tions differ. This research investigates whether, using sensitivity analysis, a numerical model can be obtained that accurately simulates flexural shear failure for RC beams without stirrups.

The total strain crack models’ crack orientation sensitivity analysis shows that the rotating crack orientation can suffer from over-rotation, which causes delamination of the concrete cover. Over-rotation also shows a strong correlation with many non-converged steps. In addition, the fixed crack orientation simulates a more realistic representation of the experimental failure mode. The compression-compression confinement sensitivity analysis shows that this modeling aspect does not influence simulations for cases with flexural shear failure much and can thus be excluded. A slightly lower failure load is simulated with the confined numerical model for one of the four cases. The sensitivity analysis on the FIB bond-slip relation and Shima bond-slip relation reveals that the former has a lower initial stiffness when using the same material configurations for their modeling assumptions. Due to the lower initial stiffness, there is a higher relative displacement between the concrete and reinforcement. In some cases, this results in either increased convergence problems, a higher possibility of dowel failure, a lower failure load, or a combination of them.

For the fourth sensitivity analysis modeling aspect, the full Newton-Raphson (NR) iteration scheme simulations are slightly more representative of the experiment than the Secant iteration scheme. This result is obtained despite the full NR scheme having more convergence problems during the initial crack. In addition, for a few cases, the Secant iteration scheme simulates symmetrical flexural shear failure due to failing to include material nonlinearity.

Sensitivity analysis of the reinforcement elements shows that simulations with truss elements are more accurate than beam elements. The beam elements models show compatibility issues when combined with plane stress elements. The interface elements fail to correctly tie the beam elements’ extra rotational degree of freedom to the transitional degree of freedom. This incompatibility results in convergence problems. Also, higher relative displacements and a higher stiffness after the initial crack is noticed in some cases compared to the experiment. The final sensitivity analysis reveals that the element size sensitivity increases with an increase in the geometrical beam size. Too-large element sizes decrease the accuracy of simulations. In contrast, too-small element sizes increase the computational cost but can also simulate irregular crack patterns not representative of the experiment. A formula is introduced from the sensitivity analysis for beams up to a depth of 1200 mm to predict an appropriate element size.

The sensitivity analysis reveals that the most accurate numerical model is a fixed crack orientation and the Shima bond-slip relation combined with truss elements using the full NR iteration scheme. The sensitivity analysis is followed by a quantitative analysis of 76 experimental cases to verify the accuracy of the obtained numerical model for a broad range of differently configured experimental cases. Analysis shows that dowel failure can get captured due to an excessive change in the dam-age-based shear retention factor using the obtained numerical model. However, decreasing sensitive load step sizes to very small ones results in flexural shear failure. Also, the quantitative simulations show that the numerical model simulations are largely accurate, with 62 simulated cases below a failure load percentage difference of 10 % compared to the experiment. The average percentage difference is 6 % between the simulations and the experiment.

Analysis shows that this research successfully obtains a numerical model that accurately simulates flexural shear failure for RC beams without stirrups. The information obtained from this research can be used to make modeling choices. In addition, some uncertainties for other modeling aspects are introduced for future research. These modeling aspects are the shear retention model, concrete elements compatibility with the reinforcements beam elements, and the global element size for beams deeper than 1200 mm.

The use of precast Reinforced Concrete has been the norm for the construction of tunnel linings for decades. However, the use of Steel Fiber Reinforced Concrete is gaining popularity due to its beneficial mechanical properties, improved sustainability, improved durability, and lowered costs compared to traditional Reinforced Concrete (RC). The amount of reinforcing steel can be reduced significantly, lowering the costs and carbon footprint of a project making it an appealing alternative. One application of SFRC is found in tunnels making use of precasted concrete segments, typically built with a Tunnel Boring Machine (TBM). This type of tunnel is found in Amsterdam, namely the
Noord/Zuidlijn: a metro line linking the north and south of the city. This project is used as a reference to perform a feasibility study on the use of SFRC and investigate its benefits.

The research involves a structural analysis of an SFRC design considering the loads and boundary conditions of the original Noord/Zuidlijn. The loads occur at different phases in the realization of the tunnel: transient, construction, and service phase. These loads can lead to various failure mechanisms, with the primary concern being tensile splitting of the concrete. Each phase is defined by a dominant component that governs its behaviour. During the transient stage, involving demoulding, stacking, and handling of the segments, the bending stresses inside the segment need to be checked. During the construction stage, the ring joints of the segments presents a weakness and need to be checked for
spalling and/or splitting of the concrete. During the service stage, the longitudinal joint needs to be checked for splitting of the concrete and the global cross sectional stresses of the lining need to be examined.

Numerical models are created to assess SFRC’s performance in the governing parts of the tunnel during the three phases, with the addition of identical RC models as a basis for comparison. The general bending and shear stresses, as well as localised splitting and spalling stresses, are investigated in both the Serviceability Limit State and Ultimate Limit State. The structural behaviour of SFRC corresponded with the characteristics found in literature, with a higher initial cracking load than RC and a more stable crack propagation due to its residual tensile strength. The peak strength of SFRC is found to be lower, but still passes all the checks. The results show that an SFRC design with the
minimum fiber content of 30 kg/m3 is sufficient for the transient and construction phases, but 40 kg/m3 is needed for the service phase. The benefits of implementing SFRC in the Noord/Zuidlijn can be quantified in a steel reduction of 60%, which would mean a decrease in steel consumption of 3050
tons. The CO2 emissions would decrease with 5500 tons, equivalent to the amount absorbed by 220.000 trees over the course of one year.

The concluding results can be used as guidance when opting for SFRC in a new bored tunnel project. The performed design checks show a governing load situation in both the construction phase and the service phase. The sufficiency of SFRC for the ring joint check during construction is governed by the
splitting force between the loading shoes of the TBM. The magnitude of this splitting force depends on the size of the TBM, the characteristics of the soil, and the depth of the tunnel. A large diameter tunnel, high-friction soil, or deep tunnel will decrease the likelihood of a design with solely fibers. The same unfavorable conditions cause large internal bending moments which could pose problems for the longitudinal joint and global cross section check. A small diameter tunnel and a tunnel constructed in stiffer soil will increase the feasibility of a design making use of solely fibers