Publications at the division of Concrete Structures

Latest publications from the division of Concrete Structures

• Interaction dynamics of a cavitation bubble and an air bubble entrapped in a cavity

  In this study, a fully compressible, two-component, three-phase cavitation model was employed to investigate the interaction between cavitation bubbles and air bubbles confined within a finite-volume cavity. The focus was on understanding how an entrapped gas bubble influences cavitation dynamics, including bubble morphology, collapse intensity, the evolution of the secondary Bjerknes force, and the Kelvin impulse. Results show that at smaller wall-to-bubble distances (L), cavitation bubbles exhibit asymmetric growth due to interface intrusion into the air bubble, leading to earlier micro-jet formation and severe air bubble deformation. Rebound of the air bubble during collapse accelerates the micro-jet, enhancing jet velocity, though this effect weakens with increasing L. Larger cavity radius and depth reduce air bubble fragmentation and bottom pressure while maintaining collapse pressure. A power-law relationship was observed between the maximum collapse pressure and velocity and the dimensionless parameter ζ, highlighting the roles of cavity geometry and wall distance. Additionally, the secondary Bjerknes force exhibits significant fluctuations at smaller L, indicating strong mutual coupling between cavitation and air bubbles. These findings offer insights into optimizing gas-containing, cavitation-resistant structures through geometry control.

• Shear-type failure of deep, short and slender impact-loaded reinforced concrete beams

  Previous research on statically loaded reinforced concrete beams has shown a clear influence of the shear span-to-depth ratio on the resulting shear failure mode. Large shear spans relative to the depth typically lead to capacities governed by the breakdown of beam action, whereas low ratios result in capacities governed by the remaining or full arch. Experimental tests with static loading have determined limits for these ratios and the corresponding failure mode. However, no corresponding limits exist for reinforced concrete beams subjected to high strain rates. This is especially true for deep and short beams, for which test data remain scarce. Impact tests were conducted to study shear span-to-depth ratio limits and corresponding shear-type failure modes at high strain rates. Deep, short, and slender beams were tested to study differences in response. Crack development and deformations were analysed using high-speed photography and digital image correlation (DIC). The series consisted of 27 scaled beams tested under static and impact loading, with varying amounts of transverse reinforcement. Results indicated similar shear failure modes for static and impact-loaded beams across the tested shear span-to-depth ratios. For slender beams, inertial forces and undamaged direct struts dominated early, resulting in higher reaction and internal forces for impact-loaded beams. As deformation developed, the response during both load types was similar, with stiffness dominating and flexural and flexural-shear capacities governing the resistance. Strut and tie models generally aligned with the experimental results, while sectional models were over-conservative. A design procedure based on strut and tie modelling was proposed to capture both early transient and quasi-static phase capacities.

• Assessing the Effectiveness of Dowel Bars in Jointed Plain Concrete Pavements Using Finite Element Modelling

  Aggregate interlocking and dowel bar systems are the two primary mechanisms in a jointed plain concrete pavement for transferring the wheel loads from the loaded slab to the adjacent unloaded slab, avoiding critical stresses and excessive deformations across the joint. Aggregate interlocking is suitable for small joint openings, while the dowel bar provides effective load transmission for both smaller and wider joint openings. In this study, a three-dimensional finite element model was developed to investigate the structural performance of dowelled jointed plain concrete pavements. The developed model was compared with an analytical solution, i.e., Westergaard’s method. The current study investigated the effectiveness of the dowel bars in jointed plain concrete pavements considering the modulus of elasticity and the thickness of the base layer, as well as dowel bar diameter and length. Furthermore, the load transfer efficiency (LTE) of a rounded dowel bar was compared with that of plate dowel bars (i.e., rectangular and diamond-shaped dowel bars) of a similar cross-sectional area and length. This study showed that the LTE was enhanced by 4% when the base layer’s modulus of elasticity increased from 450 MPa to 6000 MPa, while the increase in stress was 23%. A 1.2% improvement in the LTE and a 2.1% reduction in flexural stress were observed as the base layer’s thickness increased from 100 to 250 mm. Moreover, increasing the dowel bar’s diameter from 20 mm to 38 mm enhanced the LTE by 4.3% and 3.8% for base layer moduli of 450 MPa and 4000 MPa, respectively. The corresponding rise in stresses was 10% and 5%. The diamond-shaped dowel bar of a 50 × 32 mm size showed a 0.48% increase in the LTE, while sizes of 100 × 16 mm and 200 × 8 mm reduced the stress 6.7% and 23.1%, respectively, compared to that in the rounded dowel bar. With rectangular dowel bars, a 4% rise in the stress was noted compared to that with the rounded dowel bar. Increasing the length of the diamond-shaped dowel bar slightly improved the LTE but had no impact on the stress in the concrete slab. The findings from this study can help highway engineers improve pavements’ durability, make cost-effective decisions, contribute to resource savings in large-scale concrete pavement projects, and enhance the overall quality of infrastructure.

• Dissolved Oxygen Modeling by a Bayesian-Optimized Explainable Artificial Intelligence Approach

  Dissolved oxygen (DO) is a vital water quality index influencing biological processes in aquatic environments. Accurate modeling of DO levels is crucial for maintaining ecosystem health and managing freshwater resources. To this end, the present study contributes a Bayesian-optimized explainable machine learning (ML) model to reveal DO dynamics and predict DO concentrations. Three ML models, support vector regression (SVR), regression tree (RT), and boosting ensemble, coupled with Bayesian optimization (BO), are employed to estimate DO levels in the Mississippi River. It is concluded that the BO-SVR model outperforms others, achieving a coefficient of determination (CD) of 0.97 and minimal error metrics (root mean square error = 0.395 mg/L, mean absolute error = 0.303 mg/L). Shapley Additive Explanation (SHAP) analysis identifies temperature, discharge, and gage height as the most dominant factors affecting DO levels. Sensitivity analysis confirms the robustness of the models under varying input conditions. With perturbations from 5% to 30%, the temperature sensitivity ranges from 1.0% to 6.1%, discharge from 0.9% to 5.2%, and gage height from 0.8% to 5.0%. Although the models experience reduced accuracy with extended prediction horizons, they still achieve satisfactory results (CD > 0.75) for forecasting periods of up to 30 days. The established models also exhibit higher accuracy than many prior approaches. This study highlights the potential of BO-optimized explainable ML models for reliable DO forecasting, offering valuable insights for water resource management.

• Effects of slab gaps, offsets, and underdrains on uplift forces in a stilling basin

  A stilling basin is a critical hydraulic structure designed to dissipate excess energy from high-velocity flow exiting a spillway, preventing erosion to downstream channels. Despite its significant role in dam safety, lining damage of stilling basins occurs frequently, due to gaps and offsets between slabs and undersized underdrains. This study employs a CFD approach to examine how these factors affect flow dynamics and uplift forces. Different scenarios are examined, combining varying gap widths, offset heights, and vent configurations, under three flow rates for each. Results reveal that gap width minimally influences uplift forces. Offset heights considerably enhance upliftpressures, with a 10% increase when offset height doubles from 1.5 cm to 3 cm. Venting reduces uplift pressures effectively by facilitating water escape beneath slabs, with larger vent sizes yielding negative uplift pressures. However, venting intensifies pressure fluctuations, with the pressure coefficient rising substantially, particularly at higher flow rates. This study contributes to a deeper understanding of damage mechanisms and offers valuable insights for upgrading and rehabilitating such structures.