Dimitrios BILIONIS
Dimitrios V. Bilionis graduated from the 2nd Public High School of Argos in 2004. He started his undergraduate studies in the School of Civil Engineering of the National Technical University of Athens (NTUA) in Fall 2004. He graduated from the NTUA in 2011. He attended graduate studies at Iowa State University (USA) starting in Fall 2011. He graduated from the Iowa State University in Spring 2013 with a Master’s of Science Degree with major in Civil Engineering and minor in Statistics. During his graduate studies, he worked as a Graduate Research Assistant for the Institute for Transportation of the Iowa State University. He has been a PhD student at the NTUA since Spring 2014. He has received honors/awards such as: the «Thomaidis Award» from the NTUA and the «Spring 2013 Graduate Research Excellence Award» from the Iowa State University. He was also a recipient of the Gerondelis Foundation Graduate Student Scholarship ($5000) in 2012, as a graduate from a Greek university who pursues graduate studies in the USA. Dimitrios joined the Institute of Steel Structures at NTUA in 2014. His major research interests focus on the performance analysis of steel structures (such as wind turbines and steel lattice towers) under multiple environmental hazards, the application of statistical and probability methods in Civil Engineering problems and the development of data analysis tools. He has a demonstrated research experience with participation in research projects and publications of journal and conference papers. He is also a member of the Technical Chamber of Greece and the Association of Civil Engineers of Greece.
JOURNAL PAPERS
Now - 2014
Bilionis D.V., Vlachakis K., Dasiou M.E., Vayas I., Vamvatsikos D., Lagouvardos K. (2022). Risk assessment of rehabilitation strategies for steel lattice telecommunication towers of Greece under extreme wind hazard. Engineering Structures, 267: 114625.
Abstract | The risk and losses associated with the wind-induced failure of existing steel lattice telecommunication towers are assessed for a number of upgrade/replace/redesign schemes. Specifically, a performance-based wind engineering framework is employed for assessing a typical tower topology used by EU telecommunication network operators over four different cases: a conventional design, its corroded version after 60 years, a strengthened version of the corroded tower by applying fibre-reinforced polymer plates, and a redesign with high-strength steel. Multiple potential sites of installation were considered throughout coastal and mainland Greece, comprising two different groups of design wind speed. Mischaracterization of the site-specific wind distribution is by far the most important risk factor, with corrosion coming right behind. Still, selecting a rehabilitation approach does not depend only on site and tower characteristics, but also on the projected direct and indirect losses. By considering service to different populations, even after 60 years of corrosion, the “Do Nothing” approach may still be competitive when serving few residents and for short projected lifetime, while an upgrade is considered optimal for larger towns, or wherever higher revenue is on the line.
Sakka E.G., Bilionis D.V., Vamvatsikos D., Gantes C.J. (2020). Onshore wind farm siting prioritization based on investment profitability for Greece. Renewable Energy, 146: 2827-2839
Abstract | A feasibility study is presented on mid-size onshore wind farms in Greece, taking into consideration two metrics for the evaluation of the profitability of the pertinent investment, namely the net present value, and the internal rate of return. An operationally complete wind park of ten 3.2 MW turbines is considered, incorporating all required power conversion/transmission, and transportation infrastructure that an owner would have to construct. Actual wind speed data are employed from 285 weather stations installed throughout the country and covering a period of 1 to 12 years. The costs of installation, operation, and financing are explicitly accounted for over a standard lifecycle of twenty years. Given the regulated wholesale price for renewable electrical power, the proximity of many sites to ports, and the relatively uniform cost of investing, it is the wind potential that remains the governing factor affecting the financial viability of the wind park. Accordingly, the most profitable areas are the Aegean islands, the south-central mainland coastline, east Peloponnese, and south Attica. Most other regions of mainland Greece are found to be either marginally profitable or to generate a net loss given the current wholesale prices, wind turbine technology and investment costs.
CONFERENCE PAPERS
Now - 2014
Chatzidaki A., Ntaifoti A., Bilionis D.., Gantes C., Vamvatsikos D. (2023). Fatigue damage assessment of the Egnatia Odos sign-support structures under spatially-correlated time-varying wind fields. Proceedings of the 10th Hellenic National Conference on Steel Structures, Athens, Greece. (in greek)
Abstract | A methodology is proposed for assessing the long-term wind-induced fatigue damage accumulation of steel sign-supporting structures of highways, as it applies to Egnatia Odos. These structures are usually configured as portal, L-shaped or T-shaped frames, consisting of one or two columns and a horizontal beam that supports the sign. During their lifetime, they are exposed to environmental conditions thus being susceptive to corrosion, while the critical load is the wind that subjects them to fatigue due to its dynamic nature. To this scope, the cumulative fatigue damage is computed for the critical connections of the sign-supporting structures on a site-agnostic basis for 10min loading intervals, both for corroded and for non-corroded structures. This data is combined with 10min wind time-series that are compatible with the long-term weather hazard at the location of the structures and are computed based on alternative climate change scenarios. The aim is to assess the damage accumulation due to fatigue for the critical connections of the structures during their lifetime. The proposed methodology allows assessing the long-term risk due to fatigue for an ensemble of spatially distributed sign-support structures and is incorporated into a tool that aims to help road operators rapidly assess the state of the highway assets and help them efficiently manage their inspections.
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Bilionis D., Vlachakis K., Dasiou M-E., Vamvatsikos D., Vayas I., Lagouvardos K. (2023). Performance-based wind assessment of steel lattice telecommunication towers in coastal regions of Greece. Proceedings of the 10th Hellenic National Conference on Steel Structures, Athens, Greece. (in greek)
Abstract | Steel lattice towers are widely used for supporting telecommunication antennas. Herein, a performance-based analysis of a 48 m steel lattice telecommunication tower is presented. The tower has been designed according to the Eurocode requirements for coastal areas of Greece considering a basic wind speed value of 33 m/s. First, the fragility assessment (probability of failure) of the particular tower against various combinations of wind speed
and direction is carried out. Then, after elaborating time series of wind data from selected islands or coastal regions throughout Greece and based on the resulting wind speed and direction distributions, the corresponding risk of the tower is calculated for each location and the results are displayed on the geographical map of Greece. In practice, the above procedure introduces a framework for evaluating the performance of steel lattice towers against extreme wind. The present framework can be elaborated as a useful tool by mobile phone companies in the context of planning and/or upgrading their networks. Furthermore, by assessing and comparing the resulting risk levels of the various locations (coastal regions), inferences about the validity of Eurocode National Annex assumption for a single basic wind speed value of 33 m/s for all coastal regions in Greece can be derived.
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Bilionis D.V., Vlachakis K., Bezas M-Z., Tibolt M., Vamvatsikos D., Vayas I. (2022). Performance-based assessment of a steel lattice power-transmission tower: A case study in Germany. Proceedings of the 3rd International Conference on Natural Hazards & Infrastructure ICONHIC 2022, Athens, Greece.
Abstract | Power transmission towers are tall steel lattice structures used for supporting the conductors of a power transmission line, constituting essential parts of an entire power network. Past experience has shown that even a failure of a single tower can cause cascading effects to its adjacent towers leading to a total collapse of a whole line. Transmission towers are susceptible to severe weather conditions including low temperatures, snow and high winds. Specifically, high winds in combination with ice accumulation increase the lateral and vertical loads to levels causing damages ranging from local failures to global collapse. This effect is even more intense in case of aged towers with members weakened by corrosion effects. Herein, the focus is on a single suspension transmission tower widely used in Central Europe and designed according to the EN 50341-1:2012 and EN 50341-2-4:2016 assuming installation in Germany. The structure’s fragility in both initial and corroded state against wind and icing loads was estimated via nonlinear dynamic analyses. The climatic hazard was estimated by deriving the joint probability of wind speed and ice thickness based on meteorological data obtained for Central-East Germany. Finally, the assessment of the structure’s risk for each of the two states considered was made by combining the tower’s fragility results with the climatic hazard. Assessing the risk of a single tower is a precursor of estimating the reliability of an entire power transmission network, offering a useful decision-support tool on the need to maintain or upgrade a power line network.
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Gerontati A., Bilionis D.V., Vamvatsikos D., Tibolt M. (2022). Modular modeling and risk assessment of power transmission lines under extreme weather hazards. Proceedings of the 3rd International Conference on Natural Hazards & Infrastructure ICONHIC 2022, Athens, Greece.
Abstract | Power transmission lines are the “highways” of electricity, consisting of conductors supported on steel towers. Transmission towers are categorized as support or angle/dead-end based on their capability to resist along-line loads transmitted by the conductors. They are vulnerable to severe weather and in particular the combination of high winds and ice accretion that could lead to catastrophic failures. It is thus of great interest in the system design to arrest the propagation of a single tower failure that may trigger a series of failures of adjacent ones, considerably lengthening the duration of power outage. A modular multi-span model of a power line is proposed for the assessment of the behavior of the tower-line system and the severity evaluation of such failures. Fault tree analysis is employed to examine the failure propagation to adjacent towers under extreme weather hazard, which allows the assessment of consequences at the level of an entire system of interleaved support and angle/dead-end transmission towers. The aggregated economic losses for an operational lifetime of 60 years are investigated using the proposed model versus a simplified approach, where all towers are exclusively characterized as support ones without considering successive failures.
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Bilionis D.V., Vamvatsikos D. (2019). Wind performance assessment of telecommunication towers: A case study in Greece. Proceedings of the COMPDYN2019 Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Crete, Greece
Abstract | Steel lattice towers are widely used by telecommunication companies to install radiowave dish antennas for the expansion of their network. They are tall highly-optimized structures for which severe weather conditions including low temperatures, snow and high winds are the governing loading conditions. Specifically, high winds in combination with accumulated ice on the members of the structure and the dishes are the leading causes of collapse. The focus is on a standardized model of a telecommunication tower used by major telecommunication companies in Greece. The model is designed according to European Standards for areas located at distances lower than 10km from the coastline. The tower is 48 meters tall, having a square cross-section whose dimensions generally reduce with height and it employs channel and angle steel sections. Non-linear dynamic analyses were performed in order to estimate the fragility of the structure to wind and/or icing conditions. Wind loads were simulated via a 3D wind field fully capturing the spatial and temporal variation of wind speed over the entire profile of the tower for different reference values of wind speed. The impact of ice was assessed by considering a range of different uniformly thick layers of ice that increase the weight as well as the cross-section area of all members and dishes. The ultimate goal of this work is to provide the fragility functions for every potential combination of wind and icing conditions that could be observed during the service life of the structure. Thus, by incorporating the corresponding climactic hazard surfaces, the risk of tower collapse is estimated over its entire projected lifetime, offering a useful decision support tool to telecommunication companies regarding the need to replace or upgrade their existing tower network on a caseby-case basis.
Bilionis D.V., Vamvatsikos D. (2015). Probabilistic fatigue analysis of offshore wind turbines. Proceedings of the COMPDYN2015 Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Crete, Greece
Abstract | Wind Turbines constitute a sustainable and effective solution for the production of energy using wind power. Offshore wind turbines especially are becoming of special interest. However, their design poses great challenges, since an offshore structure is subject to combined wind and wave dynamic loading that is characteristic of the site of installation. The purpose of this paper is to provide a case study of fatigue life assessment for the cross-section at mudline (foundation) of a standard offshore wind turbine with a monopile design, under a probabilistic framework and assuming the thickness of the examined cross-section as the design variable. Two potential sites of construction in the Aegean Sea of Greece were examined. A probabilistic approach was employed in order to determine the fatigue life based on anemological data at each of the two sites of interest. At its basis is an extensive Monte Carlo simulation of wind (velocity) and wave (height, period) characteristics. The results show the dependence of fatigue life on the local wind and wave conditions, the cross-section geometry (i.e. the thickness of the foundation’s pile) and the welded connection detail. All in all, the more benign conditions in the Aegean allow simpler connection details and smaller thickness of foundation pile’s cross-section to still have acceptable performance.
Bilionis D.V., Vamvatsikos D. (2015). A probabilistic approach for fatigue damage analysis of an offshore wind turbine. Proceedings of the 8th GRACM International Congress on Computational Mechanics, Volos, Greece
Abstract | Wind Turbines constitute a sustainable and effective solution for the production of energy using wind power. Offshore wind turbines especially are becoming of special interest. However, their design poses great challenges, since an offshore structure is subject to combined wind and wave dynamic loading that is characteristic of the site of installation. The purpose of this paper is to provide a case study of fatigue life assessment for the cross-section at mudline (foundation) of a standard offshore wind turbine with a monopile design. Two potential sites of construction in the Aegean Sea of Greece were examined. A probabilistic approach was employed in order to determine the fatigue life based on anemological data at each of the two sites of interest. At its basis is an extensive Monte Carlo simulation of wind (velocity) and wave (height, period) characteristics. The results show the dependence of fatigue life on the local wind and wave conditions, the crosssection size (e.g. diameter and thickness of the foundation’s pile) and the welded connection detail. All in all, the more benign conditions in the Aegean allow simpler connection details and smaller in size cross-section of foundation pile’s cross-section to still have acceptable performance.
Bilionis D.V., Vamvatsikos D. (2015). Probabilistic fatigue life assessment of an offshore wind turbine in Greece. Proceedings of the 25th ISOPE International Ocean and Polar Engineering Conference, Kona, USA
Abstract | Wind Turbines constitute a sustainable and effective solution for the production of energy using wind power. Offshore wind turbines especially are becoming of special interest. The purpose of this paper is to provide a case study of fatigue life assessment for specific crosssections of a standard offshore wind turbine with a monopile design, under a probabilistic framework. Two potential sites of construction in the Aegean Sea of Greece were examined. The results show the dependence of fatigue life on the local wind and wave conditions, the cross-section geometry and the welded connection detailing. All in all, the more benign conditions in the Aegean allow simpler connection details to still have acceptable performance.
Bilionis D.V., Vamvatsikos D. (2015). Fatigue analysis of an offshore wind turbine in Mediterranean Sea under a probabilistic framework. Proceedings of the 6th MARINE International Conference on Computational Methods in Marine Engineering, Rome, Italy
Abstract | Wind Turbines constitute a sustainable and effective solution for the production of energy using wind power. Offshore wind turbines especially are becoming of special interest. However, their design poses great challenges, since an offshore structure is subject to combined wind and wave dynamic loading that is characteristic of the site of installation. The purpose of this paper is to provide a case study of fatigue life assessment for the cross-section at mudline (foundation) of a standard offshore wind turbine with a monopile design, under a probabilistic framework and assuming the diameter and thickness of the examined crosssection as the design variables. Two potential sites of construction in the Aegean Sea of Greece (part of Mediterranean Sea) were examined. A probabilistic approach was employed in order to determine the fatigue life based on anemological data at each of the two sites of interest. At its basis is an extensive Monte Carlo simulation of wind (velocity) and wave (height, period) characteristics. The results show the dependence of fatigue life on the local wind and wave conditions, the cross-section size (e.g. diameter and thickness of the foundation’s pile) and the welded connection detail. All in all, the more benign conditions in the Aegean allow simpler connection details and smaller in size cross-section of foundation pile’s cross-section to still have acceptable performance.
Bilionis D.V., Vamvatsikos D. (2014). Assessing the behaviour of an offshore wind turbine under uncertain wind and wave dynamic loading. Proceedings of the 8th Hellenic National Conference on Steel Structures, Tripoli, Greece
Summary | Offshore wind turbines constitute a modern solution for the production of energy using wind power. However, they are subject to uncertain loads due to the combination of dynamic parameters, such as wind and waves. For this reason, the valid assessment and appropriate design against those parameters are real challenges for the engineers. The purpose of this paper is to present a methodology for the analysis of a standard offshore wind turbine sited at a specific area in the Aegean Sea. In specific, the loads due to the combination of wind and waves are calculated by statistically processing anemological and wave data of the area using appropriate software. Finally, the calculated loads are used in order to specify the annual fatigue damage and the predicted fatigue life of the structure.