Teaching Documents by George Markou
Research software manual with detailed examples on how to use Reconan FEA.
Papers by George Markou
COMPDYN Proceedings, Dec 31, 2022
As a result of shopping centres closing and being converted into either accommodation or factorie... more As a result of shopping centres closing and being converted into either accommodation or factories, engineers have been needing to come up with new and innovative solutions to help increase the strength and decrease the deflection of already built concrete structures. If the structure's purpose was to change, then the building would need to be redesigned to ensure its structural integrity. The objective of this study is to investigate the effects that retrofitted Carbon Fibre Reinforced Polymer (CRFP) plates have on the strength of healthy and corroded waffle slabs. 3D state-of-the-art finite element modeling software will be used to create accurate models that can be used to perform nonlinear analyses. Within these models, factors such as deteriorated concrete and corroded steel will also be modelled to investigate the effects of using CFRP plates as a strengthening approach to deteriorated Reinforced Concrete (RC) structures, and in this case with waffle slabs.
COMPDYN Proceedings, Dec 31, 2022
The high complexity of investigating the mechanical response of reinforced concrete pile foundati... more The high complexity of investigating the mechanical response of reinforced concrete pile foundations embedded in different soil domains is well known, thus not allowing a deep understanding of the overall structural and geotechnical response of the foundation system. This study investigates the Soil-Structure-Interactions (SSI) and the development of stress levels for different pile configurations under different imposed lateral displacements and superstructural loads. SSI has a significant effect on the lateral resistance of pile groupings that assume two or more piles. The state-of-the-art 3D detailed numerical investigation performed in this research work foresaw an investigation of the effects that pile groupings under imposed lateral displacement have on soil stresses and the overall response of the soil and foundation system. An in-depth study of the resulting stress regions and levels in the soil medium was performed for different loading configurations. The study concluded that the base reaction is proportional to the imposed displacement and the number of piles in the grouping, while the geometry of the foundation system significantly affects the soil stress development. Finally, when torsion is developed at the level of the foundation system, a significantly complicated deformation field derives that requires an advanced modelling approach to objectively and accurately investigate the overall mechanical response of the soil and foundation domains.
COMPDYN Proceedings, Dec 31, 2022
Currently, there is no standardized method nor a reliable and easy to implement analytical relati... more Currently, there is no standardized method nor a reliable and easy to implement analytical relationship for obtaining the section rotations of horizontally curved steel I-beams that could be specified in design guides and used by practicing engineers. Analysis of horizontally curved I-beams is especially difficult to perform using traditional methods because, even under the influence of gravitational loads, the beams experience a combination of primary flexure and non-uniform torsion that result in vertical deflections that are coupled with twist rotations. This research work proposes a systematic approach that was used to develop a simple analytical formula that could predict the sectional rotation of horizontally curved steel I-beams that were fully fixed at each end and subject to a vertical point load at their midspan. The development of such a formula had never been attempted before in international literature yet by combining data derived from 3D finite element analysis with a machine learning algorithm that makes use of higher-order nonlinear regression, a predictive formula was developed that could calculate the section's rotation of horizontally curved steel I-beams with a mean absolute error of just 1.44%.
South African Dental Journal
Minimally invasive endodontics' specific focus on dentine preservation is gaining popularity.... more Minimally invasive endodontics' specific focus on dentine preservation is gaining popularity. Before deciding on the appropriate endodontic access cavity design, clinicians should investigate the advantages and disadvantages associated with different treatment modalities. The purpose of this article is to provide a summary of possible advantages and disadvantages of different endodontic access cavity designs with the focus on traditional, conservative and ultra-conservative endodontic access cavities, specifically in molar teeth. No conclusive evidence is found in the literature favouring one access cavity design above another and clinicians are advised to evaluate each case individually when deciding on the appropriate access cavity design for that specific case. Fracture resistance, proper shaping in order to facilitate irrigation and disinfection, as well as canal location and orifice detection are some of the contributing factors in selecting an appropriate access cavity des...
Computational Mechanics, Jan 8, 2024
Data-driven models utilizing powerful artificial intelligence (AI) algorithms have been implement... more Data-driven models utilizing powerful artificial intelligence (AI) algorithms have been implemented over the past two decades in different fields of simulation-based engineering science. Most numerical procedures involve processing data sets developed from physical or numerical experiments to create closed-form formulae to predict the corresponding systems' mechanical response. Efficient AI methodologies that will allow the development and use of accurate predictive models for solving computational intensive engineering problems remain an open issue. In this research work, high-performance machine learning (ML) algorithms are proposed for modeling structural mechanics-related problems, which are implemented in parallel and distributed computing environments to address extremely computationally demanding problems. Four machine learning algorithms are proposed in this work and their performance is investigated in three different structural engineering problems. According to the parametric investigation of the prediction accuracy, the extreme gradient boosting with extended hyperparameter optimization (XGBoost-HYT-CV) was found to be more efficient regarding the generalization errors deriving a 4.54% residual error for all test cases considered. Furthermore, a comprehensive statistical analysis of the residual errors and a sensitivity analysis of the predictors concerning the target variable are reported. Overall, the proposed models were found to outperform the existing ML methods, where in one case the residual error was decreased by 3-fold. Furthermore, the proposed algorithms demonstrated the generic characteristic of the proposed ML framework for structural mechanics problems.
COMPDYN Proceedings, Dec 31, 2022
This research study presents a novel energy-based constitutive model of concrete in the framework... more This research study presents a novel energy-based constitutive model of concrete in the framework of the smeared crack approach. The proposed model constitutes an extension to a previous numerical model [1,2] with an addition of a fracture energy-based algorithmic approach developed by [3]. The uncracked behavior of concrete is based on the experimental evidence of the triaxial behavior of concrete described in the literature [4]. The cracked behavior of concrete is modelled with a fracturing approach while cracking is treated with the smeared crack approach. The proposed modelling approach manages to capture the behavior of reinforced concrete (RC) structures with computational efficiency and numerical accuracy as it combines the experimental triaxial behavior of concrete in an algorithmic framework that can alleviate numerical issues of nonlinear concrete behavior such as cracking. The numerical simulation is implemented by using hexahedral isoparametric finite elements for discretizing the concrete domain and truss elements for the steel reinforcement. The proposed approach has been tested on two RC specimens focusing on structural members with insufficient shear reinforcement and high shear stresses. The numerical behavior has been validated by the comparison of the numerical with experimental data found in the international literature. The effect of choosing different approaches of the smeared crack method (fixed and rotated) is also investigated.
COMPDYN Proceedings, Dec 31, 2022
Proceedings of the 8th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015)
The assessment methods for estimating the behavior of the complex mechanics of reinforced concret... more The assessment methods for estimating the behavior of the complex mechanics of reinforced concrete structural elements were primarily based on experimental investigation, followed by collective evaluation of experimental databases from the available experimental literature. There is still a lot of uncertainty today about the strength and deformability criteria that have been derived from tests due to the differences in the experimental test setups of the individual research studies that fed into the databases. Following these investigations, the regulatory methods of seismic assessment were developed. The topic covered in this research is the effect of test setup on the derived criteria, and the second-order effects that the test setups have introduced into the behavior of structural elements. The research focuses on elements that exhibit pronounced strength degradation with plastic deformation and brittle failure characteristics. The shear strength reduction that has been attributed to the magnitude of the imposed ductility is investigated, and it is determined how much of this degradation is recognizable, i.e., how much is a consequence of the experimental setup nonlinearity. While the available methods of assessing shear strength differ because they are all empirical, they all acknowledge the contribution of individual resistance mechanisms, such as concrete, transverse reinforcement, and axial load. The experimental setup nonlinearity has an impact on the last of these three contributions. In this work, the experimental results are correlated with a revised formulation of column shear strength after the values have been corrected, with a special focus on elements with inadequate structural detailing configuration. Finally, through the use of machine learning algorithms the development of an improved formula for predicting the shear capacity of reinfroced concrete columns is performed.
Proceedings of the 8th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015)
The fundamental period of structures is an important parameter to consider when designing structu... more The fundamental period of structures is an important parameter to consider when designing structures in seismic-prone areas. Currently, the formulae available in the international literature and design codes fail to capture the true dynamic behaviour of structures, especially when they are founded on soft soils. It is necessary to develop more accurate models for predicting the fundamental period while taking into account the soil-structure interaction (SSI) effect. For the needs of this research, a dataset of 49,154 models (98,308 numerical results) was created for developing a predictive model for calculating the fundamental period of steel structures. The SSI phenomenon was also considered with structures modelled with a soil domain with varying depths. The model used herein is an Artificial Neural Network (ANN). The ANN model was able to predict the fundamental period with a correlation of 99.99% and a mean absolute percentage error (MAPE) of 0.7%.
Advances in civil and industrial engineering book series, Mar 17, 2023
COMPDYN Proceedings, 2021
This paper focusses on the ongoing discussion of developing a single relationship that can accura... more This paper focusses on the ongoing discussion of developing a single relationship that can accurately predict the shear capacity of slender, reinforced concrete (RC) beams without stirrups. To date, the main approach used to predict the shear capacity of RC beams, has been based on the derivation of a formula from experimental data. In this study, the approach uses the development of RC FEM models without stirrups, where the beam width is larger or equal to the section height and tested under three-point bending. The models were created and analysed by using Reconan FEA software, where the obtained results from the nonlinear analyses were used to construct a large database of 10,000 beams with varying material and geometric properties. Artificial Intelligence (AI) training was performed by using machine learning algorithms on the numerically generated database to develop predictive models and to develop an improved formula for predicting the shear capacity of RC beams without stirrups. The proposed predictive formula was validated against an available ACI database of RC beams that were assembled by using experimentally tested, physical beams without stirrups. The predictive formula was also compared with the design code formulae proposed by ACI 318-19 and Eurocode 2. According to the numerical findings of this research work, the proposed formula outperformed both design formulae demonstrating significant potential in replacing the current design approach.
Journal of the South African Institution of Civil Engineering
Capturing and understanding the ultimate limit state behaviour of reinforced concrete piles embed... more Capturing and understanding the ultimate limit state behaviour of reinforced concrete piles embedded in soil requires the use of advanced tools or the performance of expensive tests. An experiment was performed where reinforced concrete piles embedded in a stiff unsaturated clay profile were load-tested on-site. However, even though in-situ experiments can provide engineers with valuable insight, their cost and time limitations come with restrictions, especially when dealing with a parametric investigation on the soil's material properties, the size of the piles, or the piles' material properties. The objective of this research work was to numerically model the nonlinear mechanical behaviour of laterally loaded full-scale piles through detailed 3D modelling, and perform an in-depth parametric investigation to provide answers to unknown factors that the actual physical experiment could not answer. Furthermore, this work serves as a pilot project that will be used to pave the ...
Proceedings of the 14th International Conference on Agents and Artificial Intelligence, 2022
With the development of technology and building materials, the world is moving towards creating a... more With the development of technology and building materials, the world is moving towards creating a better and safer environment. One of the main challenges for reinforced concrete structures is the capability to withstand the seismic loads produced by earthquake excitations, through using the fundamental period of the structure. However, it is well documented that the current design formulae fail to predict the natural frequency of the considered structures due to their inability to incorporate the soil-structure interaction and other features of the structures. This research work extends a dataset containing 475 modal analysis results developed through a previous research work. The extended dataset was then used to develop three predictive fundamental period formulae using a machine learning algorithm that utilizes a higher-order, nonlinear regression modelling framework. The predictive formulae were validated with 60 out-of-sample modal analysis results. The numerical findings concluded that the fundamental period formulae proposed in this study possess superior prediction ability, compared to all other international proposed formulae, for the under-studied types of buildings.
Proceedings of the 8th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015)
8th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering Methods in Structural Dynamics and Earthquake Engineering, 2021
The modeling of large-scale reinforced concrete (RC) structures through 3D detailed modeling is n... more The modeling of large-scale reinforced concrete (RC) structures through 3D detailed modeling is not feasible due to the excessive computational demand that is required during different phases of the analysis. Especially when the overall objective is to perform nonlinear dynamic analysis of RC structures that also take into account the soil-structure interaction effect by discretizing the soil domain with hexahedral elements. These large-scale models have a significant computational demand when analysed, where the use of high-performance computing and parallel solution algorithms is currently the only solution in achieving reasonable computational times. One of the computationally demanding processes during this type of analysis, is the embedded rebar mesh generation, where millions of elements have to be created. This research work proposes a new load distribution algorithm that optimizes the numerical response of a previous parallel embedded rebar mesh generation algorithm incorporated in Reconan FEA. After the implementation of the proposed parallel algorithm, it was found that the computational time was decreased by an average of 57.48% compared to the performance of the old parallel algorithm.
Proceedings of the 14th International Conference on Agents and Artificial Intelligence, 2022
The fundamental period of buildings is an important parameter when designing seismic resistant st... more The fundamental period of buildings is an important parameter when designing seismic resistant structures. The current formulae proposed in design codes for determining the fundamental period of steel structures cannot accurately predict the fundamental period of real structures. In addition, most of the current formulae only consider the height of the structure in their formulation, while soil structure interaction (SSI) and the orientation of the I-columns that influence the fundamental period are usually neglected. This research focuses on the use of machine learning algorithms to obtain a new formula that accounts for different geometrical features of the superstructure, where the SSI effect is also considered. After training and testing a 40-feature formula, an additional 138 out-of-sample numerical results were used to further test the accuracy of the proposed formula's prediction abilities. The validation resulted in a correlation of 99.71%, which suggests that the proposed formula exhibits high predictive features for the steel structures considered in this study.
Proceedings of the 6th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2017
Considering Soil-Structure-Interaction (SSI) in Finite Element Analysis (FEA) is accounted for th... more Considering Soil-Structure-Interaction (SSI) in Finite Element Analysis (FEA) is accounted for through explicit representation of the soil domain allowing for departures from fixed base conditions and constraints. The performance evaluation of a six-story reinforced concrete (RC) shear wall with and without SSI is presented in this paper. The soil domain and Reinforced Concrete (RC) elements including walls, slabs, and foundations are modeled using 3D 8-noded hexahedral brick elements. Furthermore, longitudinal and transverse reinforcement are modeled as embedded rod elements while the cracking of concrete is modeled via the smeared crack approach. Nonlinear pseudo-static and cyclic pushover analyses are carried out on fixed and flexible base models. The soil in the flexible base model represents a site class E soil type according to ASCE7-10. A parametric study is performed on different pushover loading profiles prior to the comparison between fixed and flexible base systems. The performance evaluation of the two systems is done through direct comparison of pushover curves, displacement, strain locations and cracking patterns. Based on the numerical findings, the RC wall in the SSI model is found to exhibit higher lateral displacements yet lesser levels of strain concentrations for the any given horizontal deformation. Additionally, the superstructure toughness developed in the fixed base model is higher than the SSI model due to the vertical displacement of the soil medium. Finally, cracks in the slabs are found to be more prominent in the SSI model at the upper floors due to the accumulated lateral displacement of the wall and the overall more flexible behavior of the model. In conclusion, soil flexibility (SSI) is found to have a considerable effect on the overall structural system behavior.
Research software manual with detailed examples on how to use Reconan FEA.
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Teaching Documents by George Markou
Papers by George Markou