Publikationer vid avdelningen för Betongbyggnad

Senast publicerade artiklar från avdelningen för Betongbyggnad

• 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.

• Mesoscopic modeling the interaction of two attached-wall cavitation bubbles

  A hybrid thermal lattice Boltzmann cavitation model based on a nonorthogonal framework is developed to investigate the interaction of two attached-wall cavitation bubbles. The interaction modes are systematically analyzed, with an emphasis on how varying contact angles influence the flow and temperature distributions, as well as the evolution of wall heat flux under strong and weak interaction conditions. Bubbles formed on the hydrophobic surface display increased contact radius and greater curvature radii compared to those on the hydrophilic wall, leading to greater volumes but weaker collapse intensity. The growth rate of the bubble equivalent radius for the weak interaction modes consistently follows the relation U∝2p∞/3ρl. Additionally, bubble coalescence occurs at the interface regions along the hydrophobic surface, altering the final collapse dynamics and resulting in distinct temperature and velocity distributions. Finally, the instantaneous heat flux characteristics are explored. Due to differences in the contact points motion rate and microjet angle with the solid wall, the peak value and number of heat flux peaks vary on walls with different wettability.

• Kinematic responses of pipe piles considering the effects of soil plugs and underlying strata subjected to P-waves

  An innovative semi-analytical approach is devised to evaluate the dynamic characteristic of a friction-type pipe pile partially packed with soil plugs, subjected to time-harmonic seismic P-waves in a homogeneous soil medium. In this model, the shaft is conceptualized as a hollow structure with inner soil acting as continuum. The soil beneath the pile's vertical projection is viewed as a distinct soil pillar, while the surrounding soil and the column are collectively modeled as a uniform continuum. By examining the energy interactions between the inner soil and the pile-soil system and leveraging the Hamilton’s variational principle, the governing equations for both the shaft and the soil pillar, along with the interface contact requirements, are established. The attenuation characteristics of the surrounding soil are also derived. The solution employs variable separation techniques and an iteration methodology to resolve the coupled equations, satisfying the pile-soil system’s boundary and continuity constraints. This leads to a frequency-domain semi-analytical formulation for the seismic responses of the system. The accuracy of the developed solution is substantiated by comparing it with established results. Subsequently, numerical analyses are conducted to explore how varying material and geometric parameters impact the seismic interactions between the pile and soil.

• Stilling basin damages at low heads - Experimental investigation

  Structural integrity for energy dissipation of spillways is essential to maintain a high dam safety level. In some Swedish low-head facilities (< 15 m), damages appear also where flow velocities are expected to be too low to cause cavitation. To better understand the reason for damages a study including desktop survey, hydraulic scale model tests and numerical modelling with CFD has been initiated at Vattenfall R&D. Most common damages found in an inventory were erosion of bedrock in stilling basins, often in or adjacent to weak zones (clay filled cracks or crushed rock). Sometimes the damages progressed under concrete structures. A flow velocity above 15 m/s atthe end of the crest or at the intersection with the downstream water level seems to be a limit for when damages occur in the studied spillways. Scale model tests (1:17.5) of a case with damages has been performed to study the energy dissipation and potential causes for initiation of the damages. A CFD-model (OpenFOAM) of the same case, in model scale, has been set up to make a comparison. Measurements of flow velocities give that the tested scenario could cause flow velocities above 15 m/s in prototype scale. The pressures given by the CFD-model where in line with the ones from the model tests. From the model test the pressures, near the transition from the crest to the stilling basin, were low but not sub atmospheric. In the CFD-model the indicated risk for cavitation was high and in the same area as the real damages. Excluded from both model tests and CFD-model is the fact that cracks where visible in the real structure. Therefore, it cannot be ruled out that the initiation of damages also was stagnation pressure in the cracks. The study will continue with further tests with more pressure gauges and simulations. and the validation of the numerical model and conclusions presented are therefore preliminary.