Papers by Alexandru Țigănescu
Earthquakes and Structures, Oct 1, 2019
International Multidisciplinary Scientific GeoConference SGEM .., Jun 20, 2019
1st Croatian Conference on Earthquake Engineering, Mar 22, 2021
The management of emergency situations generated by natural or man-made disasters is a worldwide ... more The management of emergency situations generated by natural or man-made disasters is a worldwide critical task for both public and private entities. In Romania, seismic hazard represents one of the most dangerous threats, in terms of potential physical and socioeconomic losses. In recent years, taking advantage of the new technology developments and increase of the computational power, significant improvements have been done for seismic risk mitigation, using automatic systems and real-time data. There are two main institutions that perform real-time seismic monitoring of structures in Romania: INFP and URBAN-INCERC. A system for rapid damage and loss assessment (Seisdaro) is currently running at INFP, using post-earthquake generated ShakeMaps, while URBAN-INCERC is in the process of implementing a structural health monitoring system for instrumented buildings in its network, based on the ARTeMIS software. A brief history on the evolution of seismic monitoring of building structures and rapid seismic loss assessment in Romania will be presented. The paper also covers general lessons learned from previous earthquakes that affected the country, data regarding past and present exposure datasets, country-specific fragility functions and various methods and algorithms used for structural health monitoring over the time. Through international and national projects, constant improvements have been done regarding the seismic monitoring of structures and loss estimation. The roadmap for future developments involving the main institutions in charge of the seismic risk reduction, including research, academia and authorities, will be also outlined. Finally, given the complex situations revealed by the pandemic and its potential conjunction with other hazards, some reflections are presented about new multidisciplinary methods and concepts that should be developed, implemented and tested, taking into account more variables such as: social vulnerability, influence of transportation networks and hospital capacities. The validation of these methods should help both private and public entities to increase life safety, to reduce economic losses and downtime.
Civil Engineering Journal, Mar 1, 2020
The paper presents results from an experimental program implemented for three representative buil... more The paper presents results from an experimental program implemented for three representative buildings in Bucharest metropolitan area and aimed to explore the potential of various dynamic identification methods in providing information about building state changes. The objective is to establish reference values of potential use in rapid earthquake damage detection systems. Each of the selected buildings was designed according to a different seismic code, in force at the time of its construction. The methods employed for this study were: the analysis of Fourier spectra, the analysis of the transfer function and the random decrement technique. To validate the results, the fundamental periods of vibration determined experimentally were compared with the corresponding values predicted by the empirical formulas specified in the corresponding editions of the Romanian seismic code. The results revealed consistent values for both the fundamental period and the damping ratio of the buildings. However, small variations of the two parameters were identified, depending on the time the recordings were performed, noise sources and levels and building occupancy. The results, in terms of validated data on the dynamic characteristics of Romanian building stock and of assessment of methods performance, add up to the information pool needed for the development of countrywide pre-and post-earthquake assisted decision tools.
Natural Hazards and Earth System Sciences, May 23, 2020
Due to their widespread and continuous expansion, transportation networks are considerably expose... more Due to their widespread and continuous expansion, transportation networks are considerably exposed to natural hazards such as earthquakes, floods, landslides or hurricanes. The vulnerability of specific segments and structures among bridges, tunnels, pumps or storage tanks can translate not only into direct losses but also into significant indirect losses at the systemic level. Cascading effects such as post-event traffic congestion, building debris or tsunamis can contribute to an even greater level of risk. To support the effort of modeling the natural hazards' implications at the full transportation network scale, we developed a new applicable framework, relying on (i) GIS to define, analyze and represent transportation networks; (ii) methods for determining the probability of network segments to fail due to natural-hazard effects; (iii) Monte Carlo simulation for multiple scenario generation; (iv) methods to analyze the implications of connectivity loss on emergency intervention times and transit disruption; and (v) correlations with other vulnerability and risk indicators. Currently, the framework is integrated into ArcGIS Desktop as a toolbox entitled "Networkrisk", which makes use of the ModelBuilder functions and is free to download and modify. Network-risk is an attempt to bring together interdisciplinary research with the goal of creating an automated solution to deliver insights on how a transportation network can be affected by natural hazards, directly and indirectly, assisting in risk evaluation and mitigation planning. In this article we present and test Network-risk at the full urban scale for the road network of Bucharest. This city is one of Europe's most exposed capitals to earthquakes, with high seismic-hazard values and a vulnerable building stock but also significant traffic congestion problems not yet accounted for in risk analyses and risk reduction strategies.
<p>The impact of natural hazards on structures and infrastructures is a critical issue that... more <p>The impact of natural hazards on structures and infrastructures is a critical issue that needs to be properly addressed by both public and private entities. To better cope with seismic hazard and to mitigate the risk, long-term multi-sensor infrastructure monitoring represents a useful tool for acquiring information on their condition and vulnerability. However, the current increasing data volume collected using sensors is not suitable to be processed with classical standalone methods. Thus, automatic algorithms and decision-making frameworks should be developed to use this data, with minimum intervention from human operators. A case-study for the application of advanced methods is focused on the headquarters of the Institute for Atomic Physics, a 11-story reinforced concrete building, located near Bucharest, Romania. The instrumentation scheme consists of accelerometers installed at the basement, at an intermediate floor and at the top of the structure. The data were continuously recorded, starting with December 2013. More than 80 seismic events with moment magnitude, M<sub>W</sub>, larger than 3.8 were recorded during the monitoring period. The current study covers the long-term evolution and variation of dynamic parameters (one value per hour), based on both ambient noise sources and small and medium magnitude seismic events. The seasonal variation of these parameters will be determined, as well as their daily variation and the differences between values obtained from ambient noise and from earthquake-induced vibrations. Other atmospheric parameters (e.g. temperature, precipitation, wind speed) will be considered in future studies. The goal of the PREVENT project, in the framework of which the research is performed, is to collect multi-disciplinary data and to integrate them into a complex monitoring system. The current study achieved the first step, focusing on data from the seismic sensors and setting up the premises for a multi-sensor, multi-parameter, more reliable infrastructure monitoring system.&#160;&#160;</p>
International Multidisciplinary Scientific GeoConference SGEM .., Nov 15, 2022
The global development of society requires constant updating of the objectives that education pur... more The global development of society requires constant updating of the objectives that education pursues and how they are achieved. Science education is an area undergoing advanced transformation, both at the level of objectives and methodologies, with a strong social, economic, and knowledge impact. Research-based education is a well-established term, especially in the higher education system. More studies and key policy documents argue that education must be based on cutting-edge research. Essential in this equation is the existence of dedicated frameworks (tools, events, courses, and strategies) and knowledgeable mentors and developers. Through reliable tools, we refer to real learning contexts created by the parties involved in studies and research together with those who analyze how students receive information at their level of knowledge and understanding. Such a context is also the integration platforms facilitating access to data, products, and research services. There are many such platforms, but not so many of them develop components dedicated to an important user category: pupils, students and their teachers. Considering this category of beneficiaries also means collecting feedback on what is relevant to them, what the platform exposes as information, and what actions they can take to be immersed in the research process. Future �Environmental Data Scientists� will need to draw on multiple data and information sources, using data analysis, statistics, and models to create knowledge that is communicated effectively to decision-makers in government, industry, and civil society. Platforms that �expose� monitoring data, offer access to research products, and allow both the interoperability and reproducibility of science and the transparency of the process leading to a shared outcome are essential for the much-claimed paradigm shift towards open science.
Zenodo (CERN European Organization for Nuclear Research), Oct 11, 2022
The paper presents the seismic monitoring network of the TURNKey Project (Towards more Earthquake... more The paper presents the seismic monitoring network of the TURNKey Project (Towards more Earthquake-resilient Urban Societies through a Multi-sensor-based Information System enabling Earthquake Forecasting, Early Warning and Rapid Response Actions) in Bucharest. TURNkey aims to contribute to the mitigation of earthquake risks through European and global scientific collaborations. To reach its objectives the project brings together a strong multidisciplinary team of experts (geophysicists/seismologists, geologists, engineers, disaster risk managers and sociologists) from 21 partner institutions covering 10 European countries. "Testbed 1" (Bucharest) is described in the paper, with its five monitored locations and the deployed seismic sensors and GNSS. The choice of monitored buildings is based upon the characteristics of the design code used in their construction. The paper considers the possible influence of local conditions at the sites of the monitored buildings.
IOP conference series, May 1, 2021
The post-earthquake evaluation of structural integrity is a critical point to be addressed in cas... more The post-earthquake evaluation of structural integrity is a critical point to be addressed in case of emergency situations triggered by the occurrence of seismic events. A valuable method that can provide important indices to experts performing this operation is the monitoring of structures with seismic sensors that record how the structure responds to earthquake ground motion. In the case of permanent monitoring systems, reliable information can be obtained by comparing the data recorded before, during and after the earthquake, and checking if any abnormal vibrations of the structure or dynamic parameter changes have occurred. The presented study analysed comparatively, for an 11-story reinforced concrete building, vibration data recorded before, during and after the October 28th, 2018 earthquake (MW = 5.5). Continuously recorded data was used to determine the hourly values of the fundamental frequency of the building. The short-term behaviour (72 hours) was assessed, highlighting the modal parameters variation during, before and after the earthquake. In addition, an analysis of the data recorded one and a half hours before the earthquake and one and a half hours after the earthquake provided useful information on the evolution of the building state and on how this “recovered” after the earthquake.
IOP conference series, Dec 16, 2020
The paper intends to evaluate and analyze the accelerometric data recorded on certain buildings l... more The paper intends to evaluate and analyze the accelerometric data recorded on certain buildings located in the Bucharest metropolitan area, one of the most exposed in Europe, with three strong earthquakes with magnitude MW&amp;gt;7 in the last century. Starting from information comprised by databases for soils and buildings existing in Bucharest, certain types of structures were selected, according to their specificity (old buildings, retrofitted, etc.) and being continuously seismic monitored. The selected three buildings are equipped with seismic isolators and viscous dampers. The response of these structures, at the ground level, subjected to medium intensity earthquakes will be discussed in terms of peak accelerations and spectral accelerations. Based on the currently accepted standpoint that the dynamic response of certain structures subjected to earthquakes is strongly dependent of the ratio between the natural period of the structure and the dominant period at the construction site, a comparative analysis against free-field data is presented. There would be presented the improvement of seismic response of isolated buildings in Bucharest and the reason these buildings were protected choosing this method. The aim is to provide warnings regarding the severity of seismic events, by means of characteristics of the ground motion, gathered from the response spectra, which may be given soon after the seismic event took place. All the data recorded on instrumented structures during two seismic events (MW = 5.5 and MW = 4.8), together with the subsequent analysis, can represent a reference study for future earthquakes with similar magnitude. The integration of near-realtime seismology with performance-based earthquake engineering allows for providing the information useful for earthquake engineers and decision makers and can enhance the mitigation of seismic risk.
Shock and Vibration, Aug 29, 2018
e real-time analysis of a structure's integrity associated with a process to estimate damage leve... more e real-time analysis of a structure's integrity associated with a process to estimate damage levels improves the safety of people and assets and reduces the economic losses associated with interrupted production or operation of the structure. e appearance of damage in a building changes its dynamic response (frequency, damping, and/or modal shape), and one of the most effective methods for the continuous assessment of integrity is based on the use of ambient vibrations. However, although resonance frequency can be used as an indicator of change, misinterpretation is possible since frequency is affected not only by the occurrence of damage but also by certain operating conditions and particularly certain atmospheric conditions. In this study, after analyzing the correlation of resonance frequency values with temperature for one building, we use the data mining method called "association rule learning" (ARL) to predict future frequencies according to temperature measurements. We then propose an anomaly interpretation strategy using the "traffic light" method.
Zenodo (CERN European Organization for Nuclear Research), Dec 20, 2022
Frontiers in Earth Science, Apr 7, 2022
The seismic instrumentation of structures in order to assess their condition and to track it over... more The seismic instrumentation of structures in order to assess their condition and to track it over long periods or after representative events has proven to be a topic of large interest, under continuous development at international level. The seismic hazard of Romania poses one of the most dangerous threats for the country, in terms of potential physical and socioeconomic losses. In recent years, taking advantage of the new scientific and technological advances, among which the exponential growth in computational resources, significant improvements have been made in extending the seismic networks for structural monitoring and using the data as input for products and services addressed not only to the research community but also to stakeholders. The paper covers focused aspects of the topic for Romania, referring to past developments of the most important institutions and seismic networks in the country and the current status, including the research and regulatory gaps. Currently, three main research and academic institutions perform structural health monitoring of twenty-two buildings in Romania. As the number of monitored buildings grows and new actors in the private sector start to get involved in the process, the need for data standardization and a regulatory framework increases. Ongoing national and international projects (PREVENT, SETTING, TURNkey) address these issues and outline the roadmap for future actions of the main institutions responsible for seismic risk reduction, including authorities, research and academia.
Frontiers in Earth Science, 2022
Earthquakes can generate a significant number of casualties within seconds, as well as high econo... more Earthquakes can generate a significant number of casualties within seconds, as well as high economic losses. The lack of rapid and coordinated emergency intervention can contribute to much greater losses. In this paper we develop a framework taking advantage of the ArcGis Network Analyst extension, able to account for post-earthquake conditions and reflect travel times. By combining 1) network characteristics with 2) direct seismic damage information, 3) models to determine road obstruction potential, 4) traffic information and time-dependent post-earthquake modeling but also 5) emergency intervention facilities (hospitals or fire stations) and considerations regarding their functional limitations, this framework can provide important support for the management of emergency intervention but also for risk reduction planning. Main results consist of maps showing travel times for various scenarios and moments after an earthquake, inaccessible areas, vital roads for access or an identif...
IOP Conference Series: Earth and Environmental Science, 2021
The paper presents results from a study on monitoring the long-term variation of the dynamic char... more The paper presents results from a study on monitoring the long-term variation of the dynamic characteristics of an 11-story reinforced concrete building located near Bucharest. Since the deployment, in December 2013, of a permanent monitoring system, 89 seismic events with a moment-magnitude (MW) larger than 3.8 were reported. Out of these, 80 were recorded properly by the seismic sensors and the data was used to extract the fundamental frequency and the damping ratio of the building for each event. The main method used to compute the dynamic parameters was the Random Decrement Technique. A dependency of the resulting fundamental frequencies on the maximum accelerations at the base and on top of the building was observed. Due to the structural peculiarities, the fundamental frequency of the building on the transverse direction was lower than the one on the longitudinal direction, this being reflected also by the experimental results. The maximum drop in the fundamental frequency was...
The management of emergency situations generated by natural or man-made disasters is a worldwide ... more The management of emergency situations generated by natural or man-made disasters is a worldwide critical task for both public and private entities. In Romania, seismic hazard represents one of the most dangerous threats, in terms of potential physical and socioeconomic losses. In recent years, taking advantage of the new technology developments and increase of the computational power, significant improvements have been done for seismic risk mitigation, using automatic systems and real-time data. There are two main institutions that perform real-time seismic monitoring of structures in Romania: INFP and URBAN-INCERC. A system for rapid damage and loss assessment (Seisdaro) is currently running at INFP, using post-earthquake generated ShakeMaps, while URBAN-INCERC is in the process of implementing a structural health monitoring system for instrumented buildings in its network, based on the ARTeMIS software. A brief history on the evolution of seismic monitoring of building structures and rapid seismic loss assessment in Romania will be presented. The paper also covers general lessons learned from previous earthquakes that affected the country, data regarding past and present exposure datasets, country-specific fragility functions and various methods and algorithms used for structural health monitoring over the time. Through international and national projects, constant improvements have been done regarding the seismic monitoring of structures and loss estimation. The roadmap for future developments involving the main institutions in charge of the seismic risk reduction, including research, academia and authorities, will be also outlined. Finally, given the complex situations revealed by the pandemic and its potential conjunction with other hazards, some reflections are presented about new multidisciplinary methods and concepts that should be developed, implemented and tested, taking into account more variables such as: social vulnerability, influence of transportation networks and hospital capacities. The validation of these methods should help both private and public entities to increase life safety, to reduce economic losses and downtime.
Bulletin of Earthquake Engineering, 2021
As part of the development of a European Seismic Risk Model 2020 (ESRM20), the spatial and tempor... more As part of the development of a European Seismic Risk Model 2020 (ESRM20), the spatial and temporal evolution of seismic design across Europe has been studied in order to better classify reinforced concrete buildings (which represent more than 30% of the approximately 145 million residential, commercial and industrial buildings in Europe) and map them to vulnerability models based on simulated seismic design. This paper summarises the model that has been developed to assign the years when different seismic design levels (low code, moderate code and high code) were introduced in a number of European countries and the associated lateral forces that were specified spatially within each country for the low and moderate codes for typical reinforced concrete mid-rise buildings. This process has led to an improved understanding of how design regulations evolved across Europe and how this has impacted the vulnerability of the European residential building stock. The model estimates that ~60% of the reinforced concrete buildings in Europe have been seismically designed, and of those buildings ~60% have been designed to low code, ~25% to moderate code and 15% to high code. This seismic design model aims at being a dynamic source of information that will be continuously updated with additional feedback from local experts and datasets. To this end, all of the data has been made openly available as shapefiles on a GitLab repository.
<p>The lockdown measures taken to control and stop the spread of the novel coronavirus (COV... more <p>The lockdown measures taken to control and stop the spread of the novel coronavirus (COVID-19) in cities around the globe caused an unprecedented reduction of anthropic activities. The signature of this reduction, different from one place to another, has been captured by the seismic stations installed in the urban areas where lockdown restrictions have been implemented. Bucharest, the capital of Romania, was no exception from this phenomenon.</p><p>In this paper, we investigate the effect of the COVID-19 lockdown measures imposed by the Romanian authorities on the high-frequency ambient seismic noise (ASN) data recorded by the Bucharest Metropolitan Seismic Network (BMSN). BMSN consists of 26 stations of which 19 are equipped with strong motion sensors and 7 have both short-period velocity and accelerometer sensors. All the stations are continuously recording the ground motion and the data is sent in real-time to the data center of the National Institute for Earth Physics.&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;</p><p>The reduction of ASN was first observed at stations installed in educational units (kindergartens, schools) starting with 11th of March 2020, when the Romanian government decided to close the schools in Romania. For these stations, the largest reduction of ASN, up to 82%, was noticed in the 25-40 Hz frequency band. On 16th of March the state of emergency was imposed in Romania and a few days later, on 25th of March, the stay-at-home order was issued. These new restrictions caused substantial reduction in urban traffic and people&#8217;s mobility and reflected in significant reduction of ASN at almost all the other BMSN stations, located either free-field or in buildings. For these stations, we observed a decrease of the noise levels by as much as 66% in the 15-25 Hz frequency band. We also correlated the ambient seismic noise with other types of data that might be affected by human activity, such as the mobility data from Google and Apple, and we found good correlation between ASN in different frequency bands and various mobility data categories. Finally, we showed that the noise reduction due to lockdown measures improved the signal-to-noise ratio of the stations in the Bucharest area, allowing us to record smaller earthquakes which otherwise would not have been recorded.</p>
Solid Earth, 2021
After the World Health Organization declared COVID-19 a pandemic in March 2020, Romania followed ... more After the World Health Organization declared COVID-19 a pandemic in March 2020, Romania followed the example of many other countries and imposed a series of restrictive measures, including restricting people's mobility and closing social, cultural, and industrial activities to prevent the spread of the disease. In this study, we analyze continuous vertical component recordings from the stations of the Romanian Seismic Network-one of the largest networks in Europe, consisting of 148 stations-to explore the seismic noise variation associated with the reduced human mobility and activity due to the Romanian measures against COVID-19 in detail. We focused our investigation on four frequency bands-2-8, 4-14, 15-25 and 25-40 Hz-and found that the largest reductions in seismic noise associated with the lockdown correspond to the high-frequency range of 15-40 Hz. We found that all the stations with large reductions in seismic noise (>∼ 40 %) are located inside and near schools or in buildings, indicating that at these frequencies the drop is related to the drastic reduction of human activity in these edifices. In the lower-frequency range (2-8 and 4-14 Hz) the variability of the noise reduction among the stations is lower than in the high-frequency range, corresponding to about 35 % on average. This drop is due to reduced traffic during the lockdown, as most of the stations showing such changes in seismic noise in these bands are located within cities and near main or side streets. In addition to the noise reduction observed at stations located in populated areas, we also found seismic noise lockdown-related changes at several stations located far from urban areas, with movement of people in the vicinity of the station explaining the noise reductions.
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Papers by Alexandru Țigănescu