152 research outputs found
Effect of damage on the dynamic characteristics of St. Nicholas cathedral in Cyprus
No full textThe protection of monuments from aging and natural hazards, such as earthquakes, is very important since such structures are part of the cultural heritage of many countries around the world. In order to protect them from earthquakes, their structural system has to be identified and their capacity to withstand dynamic loads has to be clearly understood. Due to the large size of such structures and the limitations imposed by antiquities departments on the methods that can be used to obtain the properties of the materials of these structures and their dynamic characteristics, the ambient vibration survey method seems to be the most appropriate one to be used. Once the dynamic characteristics are identified, they will form a bench mark and any deviation in these parameters will be used for the identification and localization of damage caused to the structure, either due to environmental factors and aging, or due to an earthquake. In this work the dynamic characteristics of St. Nicholas Cathedral obtained through ambient vibration survey and the subsequent calibrated FE model are presented. Then a numerical sensitivity analysis is performed, in which damage is inflicted at vulnerable sections of the structure and the effects of this damage on the dynamic characteristics of the structure are recorded. Finally, conclusions are drawn on the type of sensors and locations they should be placed, as well as on the effectiveness of a monitoring system in identifying and localizing damage on the structure
Seismic vulnerability assessment of masonry buildings
No full textThe clear majority of masonry buildings in the Eastern Mediterranean region were designed and constructed with no seismic design considerations based on the standard design practice during the 50’s-70’s. These specific buildings pose significant seismic risk mainly due to the above, and requires complicated upgrading measures to increase its seismic capacity. Therefore, it is vital for communities to adopt the appropriate assessment tools in order to quantify their vulnerability and decide on the remedy measure to ensure their sustainability from future earthquake events. The scope of this work is to compare and illustrate the results from existing assessment methods for such buildings and emphasize their advantages in order to aid the selection of the most appropriate one.Complete
Time-History Analysis
No full textThe purpose of this paper was the study of different types of nonlinear analysis and how they can be effectively used for the seismic assessment of structures. The differences between them and the differences between linear types of analysis. Moreover, from using software to analyze different structures to understand their effectiveness and compare them to linear analyzes.
For the analysis, two buildings were used. The first one is a building with four floors, and each floor has normal column and beam layout. The other building has seven floors 4which are has an irregular column and beam layout. The columns dimensions are reduced from floor to floor. There are beams supported on beams and there is inadequate wall system in the one direction, as most of the walls have their main axis in the other direction. All the above made the analysis and how the hinges are formed more interesting to examine.Complete
Αποτίμηση Σεισμικής Επάρκειας Επταώροφης Πολυκατοικίας με την Μέθοδο Ανάλυσης Push Over και Ενίσχυση της Κατασκευής
No full textIn the present master thesis, the assessment of the seismic adequacy of an existing building made of reinforced concrete will be studied. The building under study is a seven-storey residential building, which was built in 1987 and is located in Limassol. The analysis of the building is performed with the software program SAP2000 v23.1.0 of the company Computers and Structures, Inc.
Initially, a general theoretical approach is being presented for the assessment of seismic adequacy in existing structures and then follows a detailed description of the simulation of the building in consideration, at the analysis software. In order to obtain a first behavior image of the building, certain elastic analyzes are being performed, under the action of the stress of vertical and seismic loads.
Additionally, for the calculation of the load-bearing capacity assessment of the building, it is analysed with the method of non-linear static analysis (push over), where the adequacy of its load-bearing capacity is concluded. Finally, the available coefficient of behavior (q) of the building is estimated and its adequacy is confirmed by the method of modal response spectrum analysis.
However, a small coefficient of behaviour (q) is observed, which is due to the small available plasticity of the construction and based on the data obtained from the inelastic analyses, we come to the conclusion that it is necessary to fortify the building. At the end, it is strengthened with the method of reinforced concrete jacket in vertical elements of the construction of the supporting body.Στη παρούσα μεταπτυχιακή διατριβή θα μελετηθεί η αποτίμηση της σεισμικής επάρκειας ενός υφιστάμενου κτιρίου από οπλισμένο σκυρόδεμα και η ενίσχυσή του. Το υπό μελέτη κτίριο είναι μια επταώροφή πολυκατοικία, η οποία κατασκευάστηκε το 1987 και βρίσκεται στην Λεμεσό. Η ανάλυση του κτιρίου πραγματοποιείται με το λογισμικό πρόγραμμα SAP2000 v23.1.0 της εταιρείας Computers and Structures, Inc.
Αρχικά γίνεται αναφορά στην γενική θεωρητική προσέγγιση για την αποτίμηση της σεισμικής επάρκειας σε υφιστάμενες κατασκευές και ακολουθεί η αναλυτική περιγραφή της προσομοίωσης του υπό εξεταζόμενου κτιρίου στο λογισμικό ανάλυσης. Για την απόκτηση μιας πρώτης εικόνας συμπεριφοράς του κτιρίου εκτελούνται ορισμένες ελαστικές αναλύσεις, υπό τη δράση των κατακόρυφων και σεισμικών φορτίων.
Στη συνέχεια, για τον υπολογισμό της αποτίμησης φέρουσας ικανότητας του κτιρίου,
αναλύεται ανελαστικά με τη μέθοδό της μη γραμμικής στατικής ανάλυσης (push over), όπου συμπεραίνεται η επάρκεια της φέρουσας ικανότητας του. Ακολουθεί η εκτίμηση του διαθέσιμου συντελεστή συμπεριφοράς (q) του κτιρίου και μέσω της μεθόδου της ιδιομορφικής ανάλυσης φάσματος απόκρισης, εκτιμάται η επάρκεια του.
Ωστόσο παρατηρείται μικρός συντελεστής συμπεριφοράς (q), ο οποίος οφείλεται στην μικρή διαθέσιμη πλαστιμότητα της κατασκευής και βάση των στοιχείων που προκύπτουν από τις ανελαστικές αναλύσεις, καταλήγουμε στο συμπέρασμα ότι είναι απαραίτητη η ενίσχυση του κτιρίου. Στο τέλος, ακολουθεί η ενίσχυση του με την μέθοδο κατασκευής μανδυών σε κατακόρυφα στοιχεία.Complete
Πρωτοβάθμιος αντισεισμικός έλεγχος κτηρίων
No full textThe primary seismic assessment is a crucial tool for the rapid and cost-effective evaluation of the seismic vulnerability of buildings. This thesis examines its application in Cyprus, with emphasis on the adopted methodology, evaluation criteria, and findings from existing research. It presents the current legislative framework, analyzes the condition of the existing building stock, and investigates the key factors that influence structural seismic performance.
Additionally, the thesis compares primary with secondary seismic assessments, highlighting their differences in terms of precision, required data, and technical expertise. A comparative overview of international practices is also included, showcasing policies implemented in other earthquake-prone countries such as Greece, Italy, Japan, and the United States. These countries have adopted mandatory inspection systems, especially for public and high-occupancy buildings, and have established retrofitting programs based on risk prioritization.
Finally, the thesis proposes targeted improvements for optimizing the effectiveness of primary seismic assessment in Cyprus, aiming to ensure public safety, reduce seismic vulnerability, and enhance the resilience of the built environment.Ο πρωτοβάθμιος αντισεισμικός έλεγχος αποτελεί ένα κρίσιμο εργαλείο για την ταχεία και οικονομική εκτίμηση της σεισμικής τρωτότητας των κτηρίων. Στην παρούσα μελέτη εξετάζεται η εφαρμογή του πρωτοβάθμιου ελέγχου στην Κύπρο, με έμφαση στη μεθοδολογία, τα κριτήρια αξιολόγησης και τα πορίσματα των υφιστάμενων ερευνών. Παρουσιάζεται το υφιστάμενο θεσμικό πλαίσιο και αναλύεται η κατάσταση του κτηριακού αποθέματος, καθώς και οι βασικοί παράγοντες που επηρεάζουν τη σεισμική συμπεριφορά των κατασκευών.
Επιπρόσθετα, η εργασία συγκρίνει τον πρωτοβάθμιο με τον δευτεροβάθμιο αντισεισμικό έλεγχο, αναδεικνύοντας τις διαφορές τους ως προς το βάθος αξιολόγησης, την ακρίβεια και τις τεχνικές απαιτήσεις. Στο πλαίσιο της διεθνούς σύγκρισης, παρουσιάζονται πρακτικές και πολιτικές που εφαρμόζονται σε άλλες χώρες με έντονη σεισμικότητα, όπως η Ελλάδα, η Ιταλία, η Ιαπωνία και οι Ηνωμένες Πολιτείες. Οι χώρες αυτές έχουν θεσμοθετήσει συστηματικούς μηχανισμούς ελέγχου, υποχρεωτικές επιθεωρήσεις σε δημόσια και κρίσιμης σημασίας κτήρια, και προγράμματα ενίσχυσης με βάση την εκτίμηση του σεισμικού κινδύνου.
Τέλος, προτείνονται στοχευμένες βελτιώσεις για την ενίσχυση της αποτελεσματικότητας του πρωτοβάθμιου αντισεισμικού ελέγχου στην Κύπρο, με σκοπό τη διασφάλιση της ασφάλειας των πολιτών, τη μείωση της σεισμικής τρωτότητας και την αύξηση της ανθεκτικότητας του δομημένου περιβάλλοντος.Complete
Photovoltaic reactive power compensation scheme: An investigation for the Cyprus distribution grid
No full textVoltage deviation resulting from the power generation of distributed Renewable Energy Sources (RES) can be a serious problem especially as the penetration of RES is increased in the distribution grids. For example, residential photovoltaic (PV) systems can raise the voltage of the low voltage distribution feeder due to reverse power flow. Especially at the peak PV power production, the network voltage might even deviate from the upper voltage limit as defined by the grid regulations, causing cascading problems to neighboring consumers and to the grid. This paper investigates the residential PV reactive power (Q) compensation scheme adopted in Cyprus by the local authorities in order to restrict the voltage from deviating over the maximum allowable 10% limit. This paper performs a simulation-based investigation regarding the effectiveness of the existing regulations of the Electricity Authority of Cyprus (EAC). The investigation is enabled by applying the Q-compensation scheme on several PVs installed in a typical low voltage distribution feeder. The current EAC grid regulations are fixed for all PV systems irrespective of the PV system size and the distance/location from the secondary distribution transformer. Modified compensation schemes consisting of shifting forward or reverse the Q-compensation characteristic line are also investigated in this paper. The results of this case study show an improvement to the grid voltage by providing necessary compensation based on their distance from the substation.© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, in-cluding reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to serv-ers or lists, or reuse of any copyrighted component of this work in other works.
Z. Ali, N. Christofides, L. Hadjidemetriou and E. Kyriakides, "Photovoltaic reactive power compensation scheme: An investigation for the Cyprus distribution grid," 2018 IEEE International Energy Conference (ENERGYCON), Limassol, 2018, pp. 1-6. doi: 10.1109/ENERGYCON.2018.839874
A Computationally Efficient Current Controller for Simultaneous Injection of both Positive and Negative Sequences
No full textReducing the required processing time of current controllers used in grid side converter (GSC) of renewable energy systems (RES) allows to optimize the limited processing resources and at the same time minimize the cost of the processors required. In addition, the transient behavior of these controllers must be fast and with low overshoot for the GSC to support the grid during off-nominal grid conditions and according to the grid code requirements imposed. For a converter to respond accordingly, the injection of both positive and negative sequences of fundamental current under off-nominal grid conditions is necessary. The work presents a GSC current controller that meets all modern grid requirements expected. It has been developed by introducing two modifications to an existing current controller. Experiments and simulations have been performed to validate the operation of the proposed current controller in terms of complexity and performance. Consequently, the new current controller requires 22% less processing time and can achieve a faster and more accurate response in order to meet modern grid code requirements under off-nominal conditions.This work was supported by the Research Promotion Foundation (RPF, Cyprus, Project KOINA/SOLAR-ERA.NET/1215/06), by the Ministry of National Infrastructure Energy and Water (Israel) and the SOLAR-ERA.NET (European Union's Seventh Framework Programme).
© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
Z. Ali, L. Hadjidemetriou, N. Christofides, and E. Kyriakides, "A computationally effi-cient current controller for simultaneous injection of both positive and negative sequenc-es," in Proc. IEEE ECCE-Europe (EPE), Warsaw, Poland, 2017, pp. 1-10.
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An Advanced Current Controller with Reduced Complexity and Improved Performance under Abnormal Grid Conditions
No full textElectricity grid regulations are frequently revised in order to accommodate the ever-increasing penetration of distributed renewable energy systems (RES). Interconnected RES are required to operate conditionally under normal and abnormal grid conditions. Furthermore, RES are required to have fault ride through (FRT) capability so that they can provide voltage and frequency support to the grid. The FRT operation may necessitate the injection of positive, negative or both sequence components of current. Therefore, appropriate control techniques are needed that can perform under all grid conditions (faults and harmonics) without violating the grid codes. A benchmarking comparison between two existing current control techniques motivated the proposal of a new current controller with an improved performance and lower computational complexity. The proposed controller allows accurate injection of pure sinusoidal positive, negative or both sequences currents under normal and abnormal grid scenarios. The proposed control strategy can work with considerably lower computational complexity and with improved response as compared to the two existing controllers.This work was supported by the Research Promotion Foundation of Cyprus (RPF, Cyprus, Project KOINA/SOLAR-ERA.NET/0114/02), by Energinet.dk (ForskEL, Denmark) and the SOLAR-ERA.NET (European Union's Seventh Framework Programme).
© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
Z. Ali, L. Hadjidemetriou, N. Christofides, and E. Kyriakides, "An advanced current controller with improved performance and complexity under abnormal grid conditions," in Proc. IEEE POWERTECH, Manchester, UK, 2017, pp. 1-6. DOI: 10.1109/PTC.2017.7981082.
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Performance Enhancement of MAF based PLL with Phase Error Compensation in the Pre-Filtering Stage
No full textThe large scale integration of Renewable Energy Sources (RES) requires sophisticated control techniques for efficient power transfer under faults and/or off-nominal grid conditions. A RES is efficiently integrated to the grid via proper control of the Grid Side Converter (GSC) by accurately estimating the grid voltage phase angle. Moving Average Filter (MAF) based Phase Lock Loop (PLL) techniques provide reduced complexity, however, they present disadvantages under specific grid fault conditions. The most recent MAF based technique is the EPMAFPLL, which provides improved dynamic response and reduces the phase error under off-nominal grid frequencies. However, the EPMAFPLL presents high phase and frequency overshoot at the time of fault. Furthermore, inaccurate harmonic mitigation under off-nominal grid frequencies was not investigated in EPMAFPLL. A modified EPMAFPLL (EPMAFPLL Type 2) is proposed in this paper. The modified EPMAFPLL accurately compensates the offset errors under off-nominal grid frequencies, offers lower frequency overshoot and faster dynamics under faults. In addition, it provides accurate compensation of grid voltage harmonics under off-nominal grid frequencies.ADDITIONAL NOTES:
This work was supported by the Research Promotion Foundation of Cyprus (RPF, Cyprus, Project KOINA/SOLAR-ERA.NET/0114/02), by Energinet.dk (ForskEL, Denmark) and the SOLAR-ERA.NET (European Union's Seventh Framework Programme).
© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
Z. Ali, L. Hadjidemetriou, N. Christofides, and E. Kyriakides, "Performance enhance-ment of MAF based PLL with phase error compensation in the per-filtering stage," in Proc. IEEE POWERTECH, Manchester, UK, 2017, pp. 1-6.
DOI: 10.1109/PTC.2017.7981086.
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