سيف عماد عكوبي

Concrete gravity dams, among the largest infrastructures, are already susceptible to failure, imposing daunting impulses particularly in seismically active areas. This is the specific objective of the present project, which aims to increase safety in these contexts thanks to a more accurate structural analysis of dam vulnerability. The main goal is to design a synergistic framework for seismic fragility assessment, incorporating aspects like epistemic uncertainties on dam modelling, fuzzy intervals on damage thresholds, and aleatory uncertainties on ground motions. The work is oriented to the seismic behaviour of gravity dams and their different types of foundation boundaries. Case study of the Koyna Gravity Dam reveals that three 2D finite element models were developed in the Abaqus software: a fixed-roller support model, an infinite element boundary model, and a viscous dashpot boundary model. A set of 40 ground motion records was used to create fragility curves for each model via Incremental Dynamic Analysis (IDA), which accounted for the maximum impacts of fuzzy intervals through polynomial membership functions. The findings indicate that the model with viscous dashpot boundaries suffers the least impact from fuzzy threshold conditions. This is because the boundaries tend to dampen the response and help absorb and dissipate the seismic energy differences in structural response. Also, the results show how fuzziness affects the probability of damage considerably. This paper highlights the importance of properly selecting the type of foundation for the design of a dam and the necessity of considering fuzzy thresholds in damage states during seismic risk assessments.

This study presents a comprehensive investigation into the axial performance of concrete-filled aluminum tubular (CFAT) columns externally confined with aramid fiber-reinforced polymer (AFRP) sheets, using an integrated finite element analysis (FEA) and machine learning (ML) framework. While CFAT columns offer significant advantages such as reduced weight, high corrosion resistance, and architectural appeal, their structural performance is often limited by the lower stiffness and yield strength of aluminum. To overcome these limitations, this research explores the use of AFRP confinement to enhance load-bearing capacity and ductility. A validated FEA model was developed in ABAQUS based on 23 experimental CFAT stub column tests, showing strong agreement with results (where PEXP/PFEA, the ratio of experimental to FEA-predicted load capacities, ranged from 0.85 to 1.14, confirming model accuracy). A detailed parametric analysis investigated the effects of AFRP layer count, concrete strength, and tube geometry (D/t ratio, the diameter-to-thickness ratio indicating slenderness), revealing that AFRP confinement significantly improves performance—particularly in thin-walled columns. Additionally, four ML models (SVR, RF, ANN, Meta-ANN) were trained on 113 datasets generated from numerical simulations to predict ultimate axial load capacity. The Meta-ANN model achieved the highest accuracy with a MAPE of 2.02% and R of 0.99. To interpret the predictions, SHAP (SHapley Additive exPlanations) analysis was used, identifying column diameter and concrete strength as the most influential parameters. This dual numerical–data-driven approach demonstrates the potential of combining AFRP confinement with AI-based prediction tools for the design and optimization of advanced composite columns.

This study investigates the influence of pile length, pile diameter, and undrained cohesion of end-bearing soil on the bearing capacity factor Nc* for bored piles under undrained conditions. A validated finite element model was developed and employed in a comprehensive parametric study to assess the effects of the key variables on Nc*. The findings demonstrate that increasing pile diameter significantly reduces Nc*, attributed to diminished failure zone development and reduced shear strength mobilization beneath the pile tip. It has also been noted that the Nc* increases with higher undrained cohesion due to enhanced shear resistance efficiency beneath the pile tip, while longer pile lengths lead to a reduction in mobilized Nc*. The results also showed that the existing equations yield poor predictions of Nc* because these equations do not consider the influence of pile diameter or pile length. The obtained results are used to propose a novel and accurate equation to estimate Nc* utilizing an evolutionary polynomial regression algorithm. The equation incorporates all critical influencing factors, offering a reliable tool for accurate estimation of Nc*.

This study discusses the development of data-driven models to predict the shaft resistance and lateral displacement of tapered piles subjected to seismic loads. A comprehensive database of 3600 data points, derived from validated finite element analyses, was utilized to train and test evolutionary computing–based models. The proposed equations demonstrate high predictive accuracy, with coefficients of determination of 0.98 for shaft resistance and maximum lateral displacement. Statistical metrics, including mean absolute error and root mean square error (RMSE), and frequency of error analysis confirm the robustness of the models. Also, parametric analyses were carried out to understand the seismic response of tapered piles, where it was found that increasing pile taper angle increases shaft resistance and decreases lateral displacement. The findings of this research provide practical tools for engineers to optimize tapered pile designs in seismic-prone regions, bridging the gap between theoretical research and routine engineering practice. This study underscores the potential of tapered piles in improving seismic resilience while highlighting the need for further validation in field conditions.

This research investigates the impact of embedment depth, footing width, and undrained cohesion on the mobilized Nc in undrained conditions for rough strip footings. The research was carried out using a verified Plaxis 2D model. It has been noted that the Nc factor initially upsurges with the rise of the footing depth but declines beyond a certain normalized footing depth due to the change of the failure mechanism from general shear failure to punching shear failure. In addition, it has been observed that the footing width significantly influences the mobilized Nc due to reduced shear strength mobilization efficiency along failure surfaces, confirming the presence of scale effect for footings on undrained soils. Also, it has been noted that the Nc values proposed in past seminal studies (e.g., Terzaghi, Meyerhof, Skempton, Salgado et al.) are inadequate, as they either neglected embedment depth and footing width effects or failed to account for failure mode transition at deeper embedment. On the other hand, it has been shown that the undrained cohesion does not have a noticeable impact on the mobilized Nc, suggesting that failure wedge geometry governs behavior rather than soil shear strength. Finally, a new predictive model of the Nc factor in undrained condition is introduced. The new model takes into account the effect of the footing width and embedment depth. This model scored high prediction accuracy with a mean absolute error of 0.075, root mean square error of 0.107, mean of 1.00, and coefficient of determination of 0.983. Thus, this model offers a reliable tool for geotechnical design, addressing gaps in current theoretical frameworks.

This study employs two-dimensional finite element analysis to investigate the influence of tire-derived aggregate (TDA) placement and backfill height on the structural performance of buried concrete pipes, with a focus on reducing maximum bending moments in the pipe wall. The analysis considers a 1.5-m diameter concrete pipe under varying backfill heights (2.0 to 10.0 m) and evaluates the effectiveness of TDA in inducing positive arching, as well as its impact on bedding factors. Key findings demonstrate that optimal TDA performance is achieved when positioned directly above the pipe crown, maximizing load redistribution through positive soil arching. The results indicate that increasing backfill height significantly enhances the beneficial effects of TDA in AASHTO type 2 and type 4 installations. For a 0.5-m-thick TDA layer in type 2 installations, the percentage reduction in maximum bending moment rises from 31% at 2.0-m backfill height to 42% at 10.0 m. Furthermore, greater TDA thickness substantially improves load attenuation—for instance, in type 4 installations with an 8.0-m backfill height, bending moment reductions increase from 36% (0.5-m TDA thickness) to 60% (2.0 m TDA thickness). The results also showed that the TDA performed better in the type 2 installation, as it achieved a higher percentage of bending moment reduction. Finally, new bedding factors have been proposed for different backfill heights and TDA layer thicknesses. These factors implicitly consider the positive soil arching and thus could be easily utilized by the pipeline designers.

Expansive soil is treated with lime to a certain depth before construction to stabilise the soil under the action of a pozzolanic reaction. However, there is a need to evaluate the required depth of treatment based on the swelling characteristics of soil, the percentage of lime used for stabilisation, and the span or width of treatment required. This study attempts to find the effective depth of lime treatment using a combination of experimental and numerical approaches. The experimental phase involves determining soil properties and using them in the numerical model, consisting of the heave evaluation of expansive soil. The linear finite element analysis has been carried out using Plaxis 2D, considering the depth of lime treatment as d = 250–2000 mm, the swelling pressure as p = 10–200 kPa, the length of soil deposit representing plan area as B = 5, 10, and 15 m, and the degree of lime treatment by weight as 0%, 2%, 4%, 6%, and 8%. The results of the finite element analysis are presented in the form of design charts, which can be used to find out the effective depth of lime treatment considering the design heave of swelling soils.