Michalis Fragiadakis

National Technical University of Athens | NTUA · Department of Structural Engineering

Seismic events pose a significant threat to industrial facilities, and the risk assessment of non-structural components (NSCs) within these structures is paramount for ensuring the safety and functionality of critical infrastructure. This paper presents a novel approach utilizing machine learning techniques to enhance the seismic risk assessment of...

The paper proposes a rapid fragility assessment methodology for the assessment of deteriorated reinforced concrete (RC) bridges. The proposed methodology combines calibrated material models and appropriate modelling tools to assess the structural capacity of a bridge. Initially, the extent of deterioration in the bridge members is assessed using no...

A new stochastic methodology for the generation of artificial, fully non-stationary, and spectrum-compatible seismic accelerograms is proposed. The model operates in the time-frequency (TF) domain and combines spectral representation techniques with signal processing operations. More specifically, a zero mean stationary Gaussian stochastic process...

Time-history analysis requires the use of suites of accelerograms that represent the input ground motion. A simple and computationally efficient stochastic methodology for the generation of suites of fully non-stationary artificial accelerograms is presented. The proposed methodology ensures that the record suites have a given target spectral mean...

A novel, practical, and computationally efficient probabilistic methodology for the stochastic generation of suites of fully non-stationary artificial accelerograms is presented. The proposed methodology ensures that the produced ground motion suites match a given target spectral mean and target variability for the whole period range of interest. T...

A large number of existing reinforced concrete (RC) buildings have surpassed their anticipated service life and show signs of degradation due to aging; this degradation is a function of the construction practices adopted in the past as well as environmental conditions. This paper discusses seismic fragility and the risk assessment of RC structures,...

The reliable assessment of bridge capacity is necessary in order to ensure the functionality of the roadway network under normal, or emergency operating conditions. Damage due to the interaction with the environment (e.g., corrosion of coastal reinforcement) has been observed in many cases, even in newly built interurban road networks. Therefore, t...

Bridges are in direct interaction with the environment and thus are exposed to various natural hazards such as earthquakes and floods, that may result in severe damage and substantial direct and indirect losses. The multiple hazard events may be subsequent single events (e.g., a flood event followed by an earthquake) or combined multi‐hazard events...

Recent severe earthquakes highlighted the high vulnerability of artistic assets. Thus, the seismic assessment and formulation of preservation strategies of artifacts are key challenges of modern earthquake engineering, which require theoretical and experimental investigations. The present paper discusses the outcomes from large scale shake table te...

The paper proposes the use of supervised machine learning (ML) methods for quickly predicting the seismic response of rocking systems when subjected to seismic excitations. Different supervised ML algorithms are discussed, while a relatively simple and a more sophisticated algorithm are examined in detail. Specifically, the two algorithms compared...

The recent advances in sensing technology and in the field of artificial intelligence (AI) have boosted the development of techniques based on machine learning (ML) for structural health monitoring (SHM). The chapter provides a discussion on the application of machine learning (ML) methods for vibration-based SHM. The fundamental principles of mach...

In this chapter, the physical analysis and optimisation of the morphing behaviour have been performed by means of numerical High-Fidelity (Hi-Fi) fluid-structure interaction simulations. The most advanced turbulence modelling approaches in the context of CFDSM (Computational Fluid Dynamics Structural Mechanics) have been used. This effort had as ma...

A novel methodology for the fragility and risk assessment of ancient freestanding monolithic columns and colonnades is presented. The proposed approach is based on a modeling that can be implemented in a general purpose seismic design software, thus avoiding time-consuming and/or complicated simulations. Furthermore, a novel performance-based fragi...

A new stochastic methodology for the generation of artificial, fully non-stationary, spectrum-compatible accelerograms is proposed. Time-history analysis requires the use of suites of accelerograms that can be either recorded, or artificially generated. Hazard consistency can be achieved if their mean spectrum is matched to a target design spectrum...

The paper presents a novel methodology for the fragility assessment of ancient freestanding colonnades. The stability of column arrays is compared with freestanding columns. The modelling of the structures is based on proposed simplified approach that can be implemented in a general-purpose seismic design software, thus avoiding time-consuming and/...

Artificial, hazard consistent accelerograms are today necessary in everyday engineering practice. A large number of proposed models can be found in the literature, while seismic codes recommend the use of artificial records but do not propose a specific model. The models for the stochastic generation of records can be classified to: source-based, s...

A novel methodology for the risk assessment of ancient freestanding colonnades is presented. The modelling of the structures is based on proposed simplified approach that can be implemented in a general-purpose seismic design software, thus avoiding time-consuming and/or complicated simulations. For the fragility assessment, pertinent performance c...

The paper investigates the seismic response of museum artifacts that can be modeled as two-block systems. Its main purpose is to provide appropriate equations for accurate predictions of their seismic response. Museum artifacts, often, consist of an exhibit placed on top of a solid pedestal, thus forming a two-block system. The system considered in...

This paper focuses on the line-segment Bembo-Saint Francis of the masonry walls of Chandakas in the city of Heraklion, Greece. The construction of the wall was decided in 1462, but 100 years were needed until the design was finalized and construction began at the beginning of the 16th century. The line-segment was constructed as part of the fortifi...

The paper discusses the fast seismic performance assessment of structures using truncated pulse-like ground motion records. It is shown that it is possible to truncate a pulse-like signal using a novel wavelet-based definition that identifies the duration of the predominant velocity pulse. The truncated time-history is still able to efficiently rep...

The ARCHYTAS platform is based on using (i) reliable mechanical models and damage thresholds for assessing structural performance (ii) a network of sensors for updating the model parameters, (iii) detailed estimates of earthquake and flood hazard at the sites of interest and (iv) a state-of-art approach for multi-hazard risk assessment that can del...

A novel modeling approach for the seismic response assessment of rocking frames is presented. Rocking frames are systems with columns that are allowed to fully, or partially, uplift. Despite the apparent lack of a mechanism to resist lateral forces, they have a remarkable capacity against earthquake loading. Rocking frames are found in old structur...

SCIENCE is a large bilateral project between Greece and China introducing advanced engineering research to the service of monument protection. In particular, SCIENCE develops a new approach to estimate the vulnerability of cultural heritage monuments through the innovative technique of multitemporal Synthetic Aperture Radar Interferometry (MT-InSAR...

A new technique is proposed for determining the response of multi-degree-of-freedom nonlinear complex multi-body systems with singular parameter matrices subject to combined periodic and stochastic loads. The singular parameter matrices are due to adopting redundant coordinates for modeling the system governing equations of motion. Considering that...

The paper presents a thorough investigation on the effect of flexibility on the static and dynamic response of freestanding rocking columns and rocking frames. The systems examined are allowed to fully, or partially, uplift and they have a remarkable capacity against seismic loading. Bending deformations affect the uplift conditions but also alter...

The paper presents a fully performance-based seismic reliability and risk assessment framework for freestanding structural components and contents that can be modelled as rocking rigid blocks. It shown that a drift-driven Incremental Dynamic Analysis approach can be adopted in order to obtain the floor timehistories which are then used as input for...

The ultimate objective of the SpaCeborne SAR Interferometry as a Nonivasive tool to assess the vulnerability over Cultural hEritage sites (SCIENCE) is to predict the vulnerability of the archaeological sites to ground deformation in time and space and protect them against natural/man-made damage. The SCIENCE project aims to develop, demonstrate, an...

The seismic performance assessment of structures using truncated pulse-like ground motion records is discussed. It is shown that it is possible to truncate pulse-like signals using a novel wavelet-based definition that identifies the duration of the predominant velocity pulse. The truncated time history can efficiently reproduce the increased seism...

The paper proposes an efficient methodology that allows to design smart deformable aeronautical configurations that are able to achieve pre-defined target shapes by adjusting the temperature of Shape Memory Alloy (SMA) actuators. SMA-based actuation finds extensive application in morphing concepts which are adopted in aeronautics to enhance the aer...

Τα Ευρωπαϊκά μουσεία φιλοξενούν μεγάλο μέρος της παγκόσμιας πολιτιστικής κληρονομιάς. Παράλληλα, οι σεισμοί αποτελούν σημαντική απειλή για τα μουσεία εκθέματα αλλά και τα κτίρια που τα φιλοξενούν. Είναι, λοιπόν, σαφές ότι η αντισεισμική θωράκιση των μουσείων και των θησαυρών τους, αποτελεί βασική προτεραιότητα. Παρά την ωριμότητα της επιστήμης της...

Nonlinear response history analysis (NRHA) is the most accurate seismic performance assessment method but it can be computationally intensive when it is applied to multi degree of freedom (DOF) structural systems. Machine learning techniques have gained increasing interest in engineering fields and can consist a powerful tool for reliable predictio...

Technical report of the Hellenic Association for Earthquake Engineering on the structural and geotechnical aspects of the 26/11/2019 Albania earthquake

Although large ground motion databases are widely available today, in many occasions, the selection of ground motion records still hampers the use of nonlinear response history analysis in seismic engineering practice. This paper presents a novel optimization-based tool for creating subsets of ground motion records extracted from large databases. E...

The article studies the inelastic seismic response assessment of structures with spatially varying material properties via the stochastic finite element method. This is a problem with a complex response function due to stochastic variability and material nonlinearity. Existing formulations either assume linear-elastic behaviour, or use dense models...

Multistorey buildings often have a valuable inventory consisting of objects that their possible damage during an earthquake will cause unacceptable losses. The paper presents a novel, fully performance‐based seismic reliability and risk assessment framework for freestanding structural components and contents that can be modelled as rocking rigid bl...

The seismic response of freestanding building contents that are hosted in different stories of a structure has not received yet the appropriate attention in the literature, despite the fact that the possible damage of the contents may result to excessive losses. Considering that valuable objects, e.g. artefacts, hospital equipment, computer servers...

Earthquakes are a major threat to monuments and to museums and their valuable contents worldwide. The protection of cultural heritage structures and also of museums and their treasures against earthquakes is hence a top priority. The paper will present large scale shaking table tests on cultural heritage assets and will emphasize on the use computi...

The paper presents a novel modelling approach suitable for the seismic response assessment of a variety of rocking structures. Initially, it is shown that the simplest case of a rigid block freestanding on a rigid base can be solved with the proposed approach which consists of a simple beam element with a negative-stiffness nonlinear rotational spr...

The paper investigates the dynamic response of frame structures. These structures have freestanding columns that can partially uplift and rock under a seismic excitation. Such frame structures are found in either ancient or modern structures. Today rocking frames find application in the seismic design of bridges due to remarkable resistance of thes...

The paper investigates the dynamic response of museum artefacts which are freestanding on a solid pedestal. The artefacts examined, include primarily symmetrical and unsymmetrical statues, busts or sculptures. Pedestals are commonly adopted in order to bring up, on the eye-level, the artefacts. This results to a system of two-bodies that may rock o...

The finite element method is the most widely used approach for simulating problems related to earthquake engineering, while the rocking motion of free-standing blocks, or systems is a state-of-the-art problem that concerns the structural and the geotechnical engineering communities. The paper examines the modelling of various rocking structures usi...

The paper examines the rocking motion of museum contents (i.e. statues, busts, sculptures) free-standing on a pedestal. Pedestals are commonly adopted in order to lift on the eye-level artefacts of low height. This results to a system of two bodies that may rock or slide under a seismic excitation. Older pedestals are usually made of concrete, or m...

European museums host a large portion of the most significant cultural heritage assets in the world, while earthquakes are a major threat to museums and their contents worldwide. Therefore, it is evident that the protection of museums and their treasures against earthquakes is a top priority. The paper presents novel and cost-effective risk mitigat...

Valuable objects that are hosted in multistorey buildings are susceptible to seismic loading. It is, therefore, necessary to assess their seismic vulnerability and mitigate losses after major earthquakes. The seismic response of an object housed in a multistorey building is influenced by the dynamic characteristics of both the building and the obje...

A new modeling for the seismic response assessment of free‐standing, rigid or flexible, pure rocking systems is presented. The proposed modeling is based on equivalent single degree‐of‐freedom (SDOF) oscillators that can be implemented with common engineering software or user‐made structural analysis codes. The SDOF models adopted use beam elements...

Multi-storey buildings may have a valuable inventory consisting of objects that their possible damage during an earthquake may cause unacceptable losses. The seismic response of building contents depends on the geometry of the object, the dynamic characteristics of the building and the storey that the object is located. We discuss the vulnerability...

The paper examines the seismic response of rocking frames with both rigid and flexible columns using simplified Finite Element modeling. Rocking frames are found in both ancient and modern structures. In ancient structures free-standing columns are capped with a freely supported rigid beam (architrave) forming a rocking frame. Today rocking frames...

A simplified approach is presented for the seismic performance assessment of liquid storage tanks. The proposed methodology relies on a nonlinear static analysis, in conjunction with suitable ‘strength ratio-ductility-period’ relationships, to derive the associated structural demand for the desired range of seismic intensities. In absence of availa...

Multi-storey buildings may have a valuable inventory consisting of objects that can be damaged during an earthquake causing unacceptable losses. Building contents are often modelled as equivalent rocking rigid blocks, while their dynamic response depends on the geometry of the object, the characteristics of the building and the storey that the obje...

Although large ground motion databases are today widely available, the selection of records still hampers the use of nonlinear response history analysis in engineering practice. We propose a method that is based on a novel optimization algorithm in order to create subset of records chosen from a large database. Existing heuristic methods select and...

A performance-based earthquake engineering approach is developed for the seismic risk assessment of fixed-roof atmospheric steel liquid storage tanks. The proposed method is based on a surrogate single-mass model that consists of elastic beam-column elements and nonlinear springs. Appropriate component and system-level damage states are defined, fo...

Rocking motion implies that a structure under seismic loading exhibits rigid body rotation around pre-defined pivot points. Its stability primarily relies on utilizing the rotational inertia through (purposely) activated dynamic motion. This paper focuses on slender bridge frames that exhibit rigid planar rocking behavior. It examines rocking frame...

Valuable objects, or contents, are often hosted in multi-storey buildings. Such a valuable inventory may be damaged during an earthquake causing unacceptable losses (e.g. museum exhibits) or impairing the functionality of the building (e.g. damage on hospital equipment, or cloud servers). Emphasis is placed on acceleration-sensitive building conten...

An earthquake with a moment magnitude reported as 6.0 from INGV (Istituto Nazionale di Geofisica e Vulcanologia); occurred at 03:36 AM (local time) on 24 August 2016 in the central part of Italy. The epicenter was located at the borders of the Lazio, Abruzzi, Marche and Umbria regions, about 2.5 km northeast of the village of Accumoli and about 100...

A three-dimensional surrogate model is presented for the seismic performance assessment of cylindrical atmospheric liquid storage tanks. The proposed model consists of a concentrated fluid mass attached to a single vertical beam-column element that rests on rigid beam-spokes with edge springs. The model is suitable for rapid static and dynamic seis...

The aim of this paper is to investigate the dynamic response of planar circular arches with variable cross-section subjected to seismic ground motions. Arches have a wide range of application (e.g. bridges, roofs) thanks to their capacity to span large areas by resolving vertical actions into compressive stresses and confining tensile stresses. The...

While large databases of strong ground motion records are today widely available, the selection and scaling of ground motion records hampers the use of nonlinear response history analysis for the seismic design and assessment of structures. Past research is primarily focused on the use of heuristic methods for obtaining records whose mean spectrum...

Presented herein is a methodology for the seismic and hydraulic assessment of the reliability of water distribution networks (WDN) based on general seismic assessment standards, as per the American Lifelines Alliance (ALA) guidelines, localized historical records of critical risk-of-failure metrics, and hydraulic simulations using adapted EPANET mo...

Incremental dynamic analysis (IDA) is a powerful method for the seismic performance assessment of structures. IDA is also very efficient for handling uncertainty due to the mechanical properties of the structure. In the latter case, IDA should be performed within a Monte Carlo framework requiring the execution of a vast number of nonlinear response...

1. Abstract In this paper a robust and efficient methodology is presented for treating large-scale reliability-based, structural optimization problems under seismic loads using the pushover analysis method. The optimization problem is solved with the Evolution Strategies method, while the reliability analysis is carried out with the Monte Carlo sim...

Multi-drum columns are articulated structures, made of several discrete bulgy stone blocks (drums) placed one on top of the other without mortar. The multi-drum column is a typical structural element of temples of the Classical, Hellenistic and earlier Roman period. Despite the lack of any lateral load resisting mechanism, these columns have surviv...