Determination of the earthquake performance of Nur-u Osmaniye Mosque and conservation proposals

Nur-u Osmaniye Mosque, which is the most important building of the same named complex located in the Cemberlitas district of Istanbul Historic Peninsula, next to the Grand Bazaar, is an important Ottoman monument with original architectural and technical features, in terms of Ottoman architectural history as a symbol of the transformation in the 18th century. The construction of the mosque was initiated in 1748 by Sultan Mahmud I and was completed in 1755 by his successor Sultan Osman III. Nur-u Osmaniye, which was first encountered by the religious architect of Baroque art that started to spread in Istanbul with the western influences of the 18th century, is a unique masonry monument, which is described as Ottoman Baroque because of being an interpretation between new western originated Baroque art trend and existing Ottoman traditions and experiences. The oval courtyard of the monument, the polygonal niche (mihrab) and the intensive profiles and decorations on the facades are characteristic of the Baroque style. Nur-u Osmaniye is a particular monument not only its art and architecture, but also Ottoman construction technology. The mosque represents the ultimate levels of Ottoman construction technology in 18th century because of its wooden piled foundation system, interesting substructure with massive walls and the construction techniques such as iron ties used in the construction of superstructure of the building. The other important case to accept the significance of the building is treatise (Risale) of Ahmed Efendi, who was the clerk of construction, named Tarih-i Cami-i Sherif-i Nur-u Osmani, the history of the mosque. The stages of construction of the building are well known because of the Ahmed Efendi's treatise which gives detailed chronological and technical information as a rare historic document. The mosque had experienced several destructive earthquakes, which damaged a lot of historic great mosques and buildings in Historic Peninsula of Istanbul, on the contrary, the mosque is completely intact. Furthermore, there is no damage record in the known historic documents. The researches and observations on the building confirmed the remarkable intact conditions. The studies carried out within the scope of this thesis are evaluated in twelve chapters. In the first part, the purpose, scope and method of the thesis are discussed and the current studies about the structure are examined. In this section, it is also explained that the thesis aims to contribute to the architecture and civil engineering intersection related to the field and the building, taking into consideration the previous studies. In the second part of the work, Baroque style and Ottoman Baroque are examined in general with an overview of Ottoman architecture in the 18th century when the mosque was built. After that, the architectural space organization of the mosque, facade arrangement and decorative elements were examined. The design and construction process of the mosque was investigated in the third section, by means of the excavation, construction of substructure and superstructure and opening ceremony, taking advantage of other historical sources thorough the axis of Risale written by Ahmed Efendi. Natural stone, brick, mortar, wood and iron as the materials used in the construction were discussed in the fourth chapter, and the locations of the mentioned materials were investigated by making definitions of the materials in detail. The fifth section covers the parts in which the structural system elements and masonry system properties were addressed. In this section, the structural system of the building, the structural elements of the structural system and the construction techniques were examined. In the section, each structural system element was discussed in detail; the origins and development of the construction techniques used in the mosque have been examined. In addition, the effects of Baroque style on the elements of structural system were evaluated in general in this section. In the sixth part of the study, the earthquakes and the repairs that were experienced by the mosque were discussed. In this section, the behaviour of structure in the case of important earthquakes that have been experienced since the construction period were evaluated on historical sources. Furthermore, past period repairs of the mosque were examined through historical documents and observation on the structure. The laboratory experiments carried out on the material samples taken from the mosque within the scope of the thesis were discussed in the seventh chapter. The physical, chemical, petrographic and mechanical properties of the materials have been determined in the laboratory investigations carried out in this context. In addition, the operational modal analysis experiments as in-situ dynamic tests carried out on the structure are subjects of the eighth chapter. In this section, two different experiments carried out on the structure and the results were discussed. Based on the measurements of the ambient vibration, the dynamic parameters of the structure were obtained. The numerical analysis on the data obtained in the first experiment was used to determine the main vibration frequencies using Fourier and power spectra. In the second experiment, a software capable of simulating the recorded model was used. The mode shapes were determined on the simple model created by the software, by defining the related points where the devices are located and then by analyzing the acceleration records. In the ninth section of the study, the behavior of the structure under vertical and horizontal loads was investigated via 3 dimensional static and dynamic analysis on the finite element model of the mosque which prepared in this thesis context. The finite element model used in the analysis was calibrated according to the results obtained from the in-situ dynamic operational modal analysis tests. As a result of using calibrated finite element model, the reliability of the numerical analysis was increased. In the tenth chapter, the results obtained from the researches, experiments and analyzes carried out in the previous sections were evaluated together and the earthquake performance of the structure was investigated. The eleventh chapter includes proposals to conserve the building and transferring to the future generations, preserving its unique and authentic characteristic features. The conservation proposals have been developed within the framework of international approaches and conservation principles, in order to preserve the outstanding mosque with its original architectural and as well as technical features. In the twelfth and last section, the results obtained within the thesis were given together. Nur-u Osmaniye Mosque, which is a unique monument in terms of Ottoman architecture and construction technology, has been investigated in architecture and structural engineering intersection through observations, researches, laboratory and in-situ experiments and finite element analysis in terms of architecture, materials, construction technique, structural system and its behavior under vertical and horizontal loads. As a guiding resource, the study aims to contribute to the development of appropriate approaches for the conservation of similar historical masonry structures in terms of the approaches and methods followed.