Canterbury cathedral: structural analysis of the South Aisle

Dissertação de mestrado em Advanced Masters in Structural Analysis of Monuments and Historical ConstructionsThe Canterbury Cathedral at Canterbury Kent, in the UK, seat of the Archbishop of Canterbury, head of the Anglican Church, stands as a monument of English Gothic architecture of immense importance, and is part of the UNESCO World Heritage site. Its central nave and lateral aisles, secluded by the twin bell towers of the west front and the west transept, with a 72 m tower at the crossing, is a fine example of the English Gothic style of the early 14th century. The inspection and damage survey, conducted in the Cathedral’s nave, revealed the generally good condition of the skeleton, with the exception of a repetitive crack pattern on the vault’s intrados, which intensified in a part of the south aisle, including some outward rotating movement and cracking in the south flying buttresses. Ambient vibration tests were carried out at the nave and south aisle roof level, in order to identify the modal response of the structure. A Graphic Statics analysis was conducted ,with the aim to compliment the results of the structural analysis, by investigating the load paths in the structural elements and how the geometrical configuration of the Cathedral’s nave section advocated its structural performance. Through the geometrical survey, a 3D CAD model of a typical transversal section of the nave was elaborated and, accordingly, a FE model was built in Midas FX+ for DIANA software, in order to investigate various hypothesis of structural damage, by reproducing the existing crack pattern and obtaining certain levels of structural safety. The results from the ambient vibrations tests were used for the calibration of the FE model. Different nonlinear static analyses under dead loading were performed, by considering model variables, such as the infill volume, the presence of lateral thrust from the nave’s roof and differential settlements. A validated FE model, having a sufficient correlation with the existing damage was used to determine to safety factor of the structure in both lateral and vertical loading.A Catedral de Canterbury localizada no condado de Canterbury, Reino Unido, sede do arcebispo de Canterbury, chefe da Igreja Anglicana, é um monumento de enorme importância para a arquitetura gótica inglesa, sendo parte do Património Mundial da UNESCO. A sua nave central e corredores laterais, abrigados pelas torres da fachada oeste e do transepto oeste, é um belo exemplo do estilo gótico Inglês do início do século 14. A inspeção e pesquisa de danos, realizadas na nave da Catedral, revelaram um bom estado geral do esqueleto, exceto um padrão de fendilhação que se repete no intradós da abóbada, intensificando-se no corredor sul, incluindo movimento de rotação no sentido exterior e fendas nos arcos dos contrafortes localizados a sul. Foram realizados ensaios de vibração ambiental na nave e no corredor sul ao nível da cobertura, a fim de identificar a resposta modal da estrutura. Uma análise gráfica estática, complementa os resultados da análise estrutural, investigando a distribuição de carga nos elementos estruturais e em que forma a configuração geométrica da seção da nave da Catedral afeta o desempenho estrutural da mesma. Através do levantamento geométrico, um modelo 3D CAD de uma seção transversal típica da nave foi elaborado um modelo de elementos finitos, construído em Midas FX + para o software DIANA, a fim de investigar várias hipóteses de danos estruturais, reproduzindo o padrão de fendilhação existente e obtendo os níveis de segurança estrutural. Os resultados dos ensaios de vibração ambiental foram utilizadas para a calibração do modelo de elementos finitos. Foram realizadas analises estáticas nãolineares com cargas permanentes, considerando-se as variáveis do modelo, tais como o volume de enchimento, a presença do impulso lateral da cobertura da nave e assentamentos diferenciais. Um modelo de elementos finitos validado, tendo uma correlação suficiente com os danos existentes, foi utilizado para determinar o fator de segurança da estrutura para carregamentos laterais e verticais.Ο Καθεδρικός ναός του Canterbury, στην πόλη του Canterbury της επαρχίας Kent, της Μεγάλης Βρετανίας, αποτελεί την έδρα του Αρχιεπισκόπου του Canterbury, κεφαλή της Αγγλικανικής Εκκλησίας. Δεσπόζει ως μνημείο Αγγλικής Γοτθικής αρχιτεκτονικής εξαιρετικής σπουδαιότητας και ανήκει στον κατάλογο των Μνημείων Παγκόσμιας Κληρονομιάς της UNESCO. Το κεντρικό και τα δύο πλευρικά του κλίτη περιέχονται μεταξύ των δύο δίδυμων πύργων της δυτικής πρόσοψης και του δυτικού εγκάρσιου κλίτους, με τον κεντρικό πύργο ύψους 72 μέτρων, και αποτελούν ένα χαρακτηριστικό παράδειγμα του Αγγλικού Γοτθικού στυλ των αρχών του 14ου αιώνα. Η επί τόπου έρευνα και μελέτη της παθολογίας, που επικεντρώθηκε στο κεντρικό και πλευρικά κλίτη του ναού, αποφάνθηκε την γενικά καλή κατάσταση του στατικού συστήματος, πέραν μιας αλληλουχίας ρωγμών στο εσωράχιο των θόλων, που εντείνεται σε τμήμα του νότιου πλευρικού κλίτους, περιλαμβανομένης και μιας έξω περιστροφικής κίνησης, με συνεπάγοντες ρωγμές στις νότιες τοξωτές αντηρίδες. Η επιτόπια εκτέλεση ambient vibration tests, στο επίπεδο της στέγης του κεντρικού και του νότιου κλίτους, προσδιόρισαν την ιδιομορφική απόκριση της κατασκευής. Η γραφική στατική ανάλυση της κατασκευής πραγματοποιήθηκε ώστε να απότελέσει ένα ακόμη κριτήριο σύγκρισης με τα αποτελέσματα της στατικής ανάλυσης, μέσω της διερεύνησης των διαδρομών των φορτίων στα στατικά μέλη και του βαθμού επιρροής της γεωμετρικής διάρθρωσης του ναού στη στατική συμπεριφορά του. Μέσω της αρχιτεκτονικής αποτύπωσης, παράχθηκε μια τρισδιάστατη γεωμετρική απεικόνιση μιας τυπικής κάθετης τομής του κεντρικού και πλευρικών κλιτών και μέσω αυτής ένα αριθμητικό προσομοίωμα, μέσω του προγράμματος πεπερασμένων στοιχείων Midas FX+ for DIANA, προκειμένου να διερευνηθούν πιθανές αιτίες δομικής βλάβης. Βασικό κριτήριο αποτέλεσε η αναπαραγωγή του υπάρχοντος μοτίβου ρωγμών και ο καθορισμός επιπέδων δομικής ασφάλειας. Μη γραμμικές στατικές αναλύσεις πραγματοποιήθηκαν, υπό την επιρροή μόνιμων φορτίων και μεταβλητών συσχέτισης, όπως ο όγκος πλήρωσης των θόλων, η παρουσία πλευρικής ώσης μέσω της στέγης και η ύπαρξη διαφορικών καθιζήσεων. Το τελικό παραγόμενο αριθμητικό προσομοίωμα της τυπικής τομής του ναού, έχοντας επαρκή συσχέτιση με την υφιστάμενη βλάβη, χρησιμοποιήθηκε για να προσδιοριστεί ο συντελεστής δομικής ασφαλείας τόσο σε πλευρική και κατακόρυφη ώθηση

Diagonal compression testing of masonry under fatigue loading and high static loads

Underground railway operations pose a significant impact on overlying, highly sensitive historic masonry structures. Here, the process of structural assessment involves fatigue actions, through induced ground-borne vibrations, from operating underground railways. Considering long-term exposure periods, fatigue can introduce local cracking and losses, which endanger the integrity of both structural and non-structural elements. The lack of experimental fatigue data on tensile actions in masonry and the apparent computational restraints from constitutive cementitious material models that do not account for damage due to repeated loading, increase the complexity of structural assessment, under combined fatigue actions and other hazards. The current paper aims at providing new experimental data on fatigue in historic brick and lime mortar masonry wallets, replicating realistic combinations of static and fatigue loading under diagonal compression. Material deterioration and stiffness degradation are monitored throughout the process. Hence, under moderate amplitudes of fatigue loading and high static loads, cracking occurred, at a relatively low number of cycles, demonstrating the need for more strict vibration thresholds to ensure the integrity of historic masonry buildings.The current work was partly supported by FCT (Portuguese Foundation for Science and Technology), within the INFRARISK PhD program and ISISE, project UID/ECI/04029/2013

Appraising the seismic response of a retrofitted adobe historic structure, the role of modal updating and advanced computations

The concepts of structural assessment and retrofit of historical constructions are of particular complexity and require advanced knowledge in material science, conservation techniques and structural analysis. In particular, adobe constructions, given their low mechanical properties and brittle failure modes, are in immense need of comprehensive assessment and retrofitting plans. The current work focuses on the adobe Church of Kuñotambo in Peru, having experienced long periods of deterioration and earthquake-related damage. Under the ongoing Seismic Retrofitting Project (SRP) of the Getty Conservation Institute (GCI), the structural assessment of the church initiated in 2015 confirmed the low lateral capacity of the building and the poor connectivity between the structural parts. Based on the existing cracks and damage, a strengthening scheme was optimized and validated. After the implementation of the retrofitting plan, the quality of its execution and efficiency were assessed in 2019 with a new in situ campaign, which included ambient vibration testing (AVT) and sonic testing. From the acquired field data, the FE model of the retrofitted church was optimized, by updating the stiffness properties of masonry and discontinuities. Moreover, nonlinear static analyses were performed on the updated model in all in-plan directions. Finally, a displacement-based performance assessment was undertaken, under different earthquake limit states, demonstrating the adequacy of the retrofitting.Partial funding by Getty Conservation Institute – Seismic Retrofitting Project

Finite element modeling and operational modal analysis of a historical masonry mosque

All rights reserved. Finite Element Modeling (FEM) and Operational Modal Analysis (OMA) is herein presented for the historical masonry Kütahya Kurşunlu Mosque within the framework of its seismic performance assessment. The historical structure is located in Turkey which has a high-level seismic activity. A FEM strategy was adopted to construct a numerical model of the structure considering a simplified three-dimensional geometry and a macro-modeling approach for the masonry. A representative numerical model of the existing structure was calibrated and improved according to the OMA results obtained from ambient vibration measurements, performed in-situ. The ambient vibration measurements were operated by using two triaxial accelerometers, that one of the accelerometers was regulated as a reference station whereas the other accelerometer was relocated to seven different points on the top of the walls. Identification of the experimental modal parameters was achieved by performing two different signal processing methodologies, namely the Enhanced Frequency Domain Decomposition (EFDD) and the Stochastic Subspace Identification - Unweighted Principal Components (SSI-UPC). Results obtained from both methods were compared in terms of the Modal Assurance Criterion (MAC) which considers the mode shapes derived in a specific range of frequency. The SSI-UPC method was employed in achieving the experimental modal response of the structure and the results were compared with the eigenvalue analysis results of the preliminary numerical model. A calibration process was carried out in terms of minimizing the difference between the experimental and numerical modal response by a trial and error approach and an average error of 4.9% was calculated for the modal frequencies of the first four global modes of vibration.- (undefined

Structural assessment and seismic vulnerability of earthen historic structures. Application of sophisticated numerical and simple analytical models

Adobe constructions account for a significant portion of the built heritage, associated with early building techniques, material accessibility and low-cost. Nonetheless, adobe buildings, due to their low mechanical properties and overturning resistance, are subject to early structural damage, such as cracking, separation of structural elements and, possibly, collapse in areas of high seismic hazard. The lack of maintenance and absence of adequate retrofitting techniques usually intensifies the loss of historic fabric. The current paper, aims at the structural assessment and seismic safety, in current conditions, of the Church of Kuno Tambo, a religious adobe structure of the 17th century, in Cusco region, in Peru. The inspection and diagnosis involved sonic testing and damage mapping, while ambient vibration tests revealed the modal response of the structure. The assessment of seismic vulnerability, together with the necessity of retrofitting measures were verified through nonlinear static and pushover parametric analyses, complemented with a macro-block limit analysis and a performance based assessment, under local seismic criteria. A more realistic response from dynamically induced ground motions was performed, by a nonlinear time history analysis, according to the Eurocode 8 framework. Through an integrated approach, in situ inspection, testing, numerical and analytical modelling are associated under the scope of reproducing the existing structural damage, the sequence of inelastic behavior and verification of the necessity of retrofitting measures.The current work is part of the Seismic Retrofitting Project, of the Getty Conservation Institute and was partly supported by FCT (Portuguese Foundation for Science and Technology), within the INFRARISK PhD program and ISISE, project UID/ECl/04029/2013.info:eu-repo/semantics/publishedVersio

Métodos experimentais para investigar os efeitos de subsidência do solo e vibrações em edifícios de patrimônio arquitetónico, induzidos por estruturas subterrâneas

Tese de doutoramento em Engenharia CivilStructural assessment for cultural heritage structures, in the proximity of operating underground railways is twofold, by induced soil movements, from tunneling construction, and by fatigue, through induced ground-borne vibrations, from railway operations. Both hazards are found interacting, with effects on durability. Yet, a multi-hazard response assessment remains an open challenge, since many constitutive material models do not account for cyclic deterioration. This thesis is focused on field monitoring, experimental testing and analytical applications, with the aim of obtaining a clear knowledge on the in-plane capacity and damage, in simulated, historic, brick masonry and lime mortar specimens. First, fatigue tests in diagonal compression in wallets, replicated different levels of cyclic and static loading. Second, in-plane tests on a differential displacement uplift were conducted in piers and spandrel masonry specimens and the effectiveness of repair and strengthening, namely of grouting injections and a Fiber Reinforced Cementitious Matrix system (FRCM), were assessed. Considering the fatigue tests in diagonal compression, under medium to high amplitudes of induced ground-borne vibrations and high static loads, they have resulted in cracking, at relatively low number of cycles. As for the experimental works on the in-plane behavior in piers and spandrel specimens, under a vertical uplift, a sequential in-plane failure is identified through flexural and shear cracking in the spandrel, together with a final, sliding, shear crack in one of the piers, while the repair and strengthening schemes, both were tested effective, providing sufficient shear capacity and displacement ductility.O avaliação estrutural do património arquitetónico, nas proximidades das ferrovias subterrâneas em operação, é duplo, seja por subsidência do solo devido à construção de túneis, seja pela fadiga, provocada por vibrações induzidas no solo, por operações ferroviárias. Ambos os perigos estão interagindo, com efeitos na durabilidade. No entanto, uma avaliação da resposta a múltiplos perigos é um desafio em aberto, dado muitos modelos constitutivos de materiais não considerarem a deterioração cíclica. Esta tese foca-se nas campanhas de monitoramento e experimental, e em aplicações analíticas, com o objetivo de obter um conhecimento claro sobre a resistência no plano e dano, em provetes de alvenaria de tijolo e argamassa de cal históricos. A primeira relativa a ensaios de compressão diagonal com fadiga em muretes, com diferentes níveis de carga cíclica e estática. Na segunda campanha, foram realizados ensaios no plano com assentamento diferencial de elevação em provetes representativos de nós coluna-viga de paredes de alvenaria, e foi avaliada a eficácia de reparação e reforço, nomeadamente de injeções de calda e de sistemas de matriz cimentícia reforçada com fibras (FRCM). Considerando os ensaios de compressão diagonal com fadiga, sob amplitudes médias a altas de vibrações induzidas no solo e elevadas cargas estáticas, ocorreu fissuração a um número de ciclos relativamente baixo. Relativamente à campanha experimental sobre o comportamento no plano dos provetes pilar-coluna, sob deslocamento de elevação, observou-se uma sequência de falhas, através de fissuras por flexão e corte nas vigas, em conjunto com uma fissura final, deslizante, devido a corte, num dos pilares, enquanto as soluções de reparação e reforço, ambos provaram ser eficazes, proporcionando resistência ao corte e ductilidade suficientes.Fundação para a Ciência e a Tecnologia (FCT) - PD/BD/128052/201

Seismic behavior and assessment of masonry heritage structures. Needs in engineering judgement and education

Built cultural heritage is at risk due to manmade and natural hazards. The seismic vulnerability of ancient masonry buildings is particularly difficult to assess and requires specialized technical skills. Key aspects are the materials properties and nonlinear effects, the morphology of the structural elements, the connections between structural elements, the stiffness of horizontal diaphragms and the building condition. This paper addresses the holistic approach recommended for the structural assessment of historic masonry buildings and the developments in the areas of inspection, diagnosis, monitoring and non-destructive testing, with applications to emblematic monuments. The methodology covers a step-by-step approach, based on historical research, an inductive study on similar structures, and a range of surveying, experimental, analytical and numerical tools, all aimed at evaluating the structural response and defining safety levels. Attention is given to the need of conservation engineering background of professionals and ways to attain this goal

Monitoring of induced groundborne vibrations in cultural heritage buildings: miscellaneous errors and aliasing through integration and filtering

Cultural Heritage Buildings are considered highly complex, having evolved over time, and contain various heritage components. These assets are becoming increasingly at risk due to unprecedented transformation processes in cities, from underground railways. Experimental and monitoring strategies can serve as diagnostic tools on the effects of long-term exposure to induced vibrations, from this new source. The current work presents the Structural Health Monitoring (SHM) outcomes in the Church of the Angels (Igreja dos Anjos), a monument of the early 20th century, in Lisbon, Portugal, directly over a subway station, in a shallow railway line, subjected to groundborne vibration.Criteria from international standards provide threshold values, mostly in terms of velocity, which are linearly related to stress and strain fields. Specific criteria for non-structural components are usually set, accounting among others, frequency bandwidths and levels of intermittency. Even if recommendations specify the velocity as a primary measurement, it is often needed to obtain velocity-time histories from acceleration data, as accelerometers are widely used in practice. Weak signal processing, low sampling frequencies, the type of integration in time or frequency domain and digital filtering, with incorrect cut-off frequency bandwidths, may lead to processed signals, distorted in terms of shape, phase and amplitude.The current work is supported by FCT (Portuguese Foundation for Science and Technology), within the INFRARISK PhD program and ISISE, project UID/ECI/04029/2013

Lessons from structural analysis of a great gothic cathedral: Canterbury cathedral as a case study

Damage in Gothic cathedrals can occur due to single extreme events or long-term processes, often associated with large deformations and cracking. This paper presents the damage survey and structural assessment of a UNESCO world heritage site and one of the oldest, most visited and most known Christian temples in the UK: Canterbury Cathedral, in Kent. Inspection and damage survey showed repetitive crack patterns on the vault's intrados, with more severity in the south aisle, including outward rotating movement and cracking in the south flying buttresses. Ambient vibration tests were carried out to identify the structure modal properties. An FE model of a typical transversal section of the nave and lateral aisles was prepared, and calibrated based on the tests. Nonlinear static analyses were performed, considering the main parameters of influence to the structure, as the construction process, the infill volume, the presence of lateral thrusts from the nave's roof and differential settlements. A validated FE model, presenting sufficient correlation with the existing damage was used to determine the safety factors for lateral and vertical loading, which according to the local hazard are considered adequate. A comparison with limit analysis, based on the static approach, was also carried out.The current study has been partly financed by the Dean and Chapter of Canterbury Cathedral and supported by the Morton Partnership Ltd consulting structural engineering company and, in particular, Claudio Corallo

Traditional techniques for the rehabilitation and protection of historic earthen structures: The seismic retrofitting project

Historic earthen structures are a significant portion of the built heritage worldwide and are associated with intangible building techniques, wide material availability and low-cost construction. Nonetheless, dueto their low mechanical properties and, often poor connections, historic earthen structures are susceptible to early structural damage, and even collapse in areas of high seismic hazard. Inaddition, the lack of maintenance can further reduce structural performance and durability. The Getty Conservation Institute (GCI)'s Seismic Retrofitting Project (SRP) aims to research, designand test low-tech retrofitting techniques, as well as to implement maintenance programs, enhancing the performance of historicearthen buildings in seismic areas where the most advanced equipment, structural skills and materials are not easily available. Results: Accounting for recommendations from national building codes, conservation principles and local practices, the complete design, assessment and implementation of strengthening for twoprototype buildings in Peru, involved in the SRP, are discussed; the Church of Kuno Tambo and Ica Cathedral. Conclusions: Theretrofitted structures, complied with performance criteria and seismic local demands, with sufficient safety and acceptable levels of repairable damage.This work was carried out with funding from the Getty Conservation Institute (GCI) as part of its Seismic Retrofitting Project. This work is also partially financed by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds, through FCT - Foundation for Science and Technology, within the scope of the projects POCI-01-0145-FEDER-007633 and UID/ECI/04029/2013