Stuctural behaviour of Zal Mahmut Pasa Mosques and review of past damages

Assessment of existing historical masonry structures is a crucial step on conserving and passing the cultural heritage on next generations. The vital phases of the assessment are to define architectural feautures and structural properties in detail, recording the earthquakes hit the structure, fire or any incident that might have caused to structural changes -such as removal of walls, additions, effects of previous restorations, construction material and techniques of its era. In the first chapter of this thesis, an introduction is made. In the second chapter, general information about Classical Period Ottoman Mosques is given. Construction techniques and structural aspects of these mosques are explained. Location of structure in the field, foundations of the structure, stone foundations on solid ground and improvement applications of foundations on weaker soils are explained. Brief information about dome, archs and pendentives are given to exemplify the structural elements. Importance of cover elements in Classical Period Mosques is explained. Cut stone walls, roughly-hewn stone walls, rubble stone walls and brick stone alternate walls (was used at Zal Mahmutpasa Mosque) are studied. Mortars and joints, timbers, columns, column bases and cover facing which are structural elements are mentioned. Using iron in structural systems and support systems are dwelled on. Informations about using plaster Classical Period Mosques, floors and minaret forms is given. Building materials which are used in Classical Period Mosques, such as mortar, stone, brick, wood, iron bar and lead are investigated in terms of engineering properties. Young's Modulus, tensile strength, compressional strength and shear strength of these materials are given and a literature review are performed. In the third chapter of thesis, micro modeling and macro modeling in masonry constructions are explained. Also brief information about finite element method, linear analysis and non-linear analysis are given. In the fourth chapter, monitoring of structure vibrations, experimental and operational modal analysis, data collection and sensors are explained generally. In the fifth chapter, location of the structure and field conditions are given. The structure is located in Zal Mahmut Paşa Külliyesi (Zal Mahmut Pasha Social Complex) at Zal Paşa Street, Eyüp. The Külliye (the Social Complex) was constructed in an inclined field and due to the inclination and elevation difference, stairs were used between two courtyards of the mosque. Also inclination caused that the facades of the structures were constructed at different levels. In east facade, an extra basement was constructed. It is seen that, this asymmetry in the geometry of structure is the main cause of damages. Moreover, the other parts of the Külliye is investigated and additional information in literature about the architect of the structure and by whom it was built in which date are given. These architectural and geometrical information are presented about Sinan's work of art: Plan layout of the dome is 24,90 mx26,30m and elevation between top point of dome and ground floor is 21,06 m. Pendentives is used as transition element under the dome. Differently from the other works of Sinan, the weight of the dome is carried by four main archs and elephant feet piers under the archs. Face walls of the structure and the dome system are structurally independent. On the contrary, in the other works of Sinan, weight of the dome was transferred by half domes to the face walls or main archs are hidden in the walls. In the fifth chapter, recent condition of the structure is investigated and it is observed that some critical regions of structure have been strengthened using reinforced concrete. A literature review is performed to understand the reason of these applications explained in Sinan's artwork. It is thought that these application were made as a result of an important earthquake and the earthquakes which affected the structure are investigated. There is no information about Zal Mahmut Paşa Mosque on 1766 Istanbul earthquake. On the other hand, in 1894 İstanbul Earthquake outer wall of structure was cracked, minarets were collapsed and according to sources the structure was severely damaged. In order to get further information about structure archives of Republic of Turkey Ministry of Culture and Tourism Directorate General of Cultural Assest and Museums' and 'Republic of Turkey Prime Ministry Directorate General of Foundations' reviewed. As a result of review of archives it is seen that one of the tie rods of the structure's main arch broke, qibla wall was displaced significantly and one of the arches was displaced 25 cm along gravitational direction. A strengthening project was prepared due to these destructive damages. Detailed information about this project is reached and it is understood that this project involves the applied reinforced concrete observed at site. The project also gives information about the strength of connection between tie rod and columns and it is written that tie will be repaired in suitable applications in future. This tie rod was discovered by author during their investigations and was repaired. Moreover, vibration data is collected by utilizing 20 accelerometers from different places to determine natural vibration frequency and modal shape of structure. Artemis software was used to derive frequency and modes of structure. The structure is analyzed in finite element program Abaqus. Modal analysis of structure is performed and calculated frequency values are compared with measured values in site. Linear elastic analysis of structure is performed using equivalent earthquake load method. Compressive, tensional, shear stresses and displacement values for critical regions obtained as results of these analysis were presented. Compressive stress results obtained from finite element analysis show that, stresses occurred by G+EY45° loading case in gathering part of elephant-foot that tied with broken tie rod is 2,46MPa, and also determined as 3,78 MPa for basement of same part. A compressive stress value of 1,91MPa under G-EX load case occurs on main arch which is over the broken tie rod. Tensional stress value of 0,85Mpa is also obtained on same arch under G-EX MPa. A comment on the reason of tie rod rupture was made as: The rod was tied with the longest elephant-foot of structure as the mosque is located on a sloping land. It is confirmed that the stiffness of this foot is 40% less than the others. The larger displacement in this less-rigidity elephenat-foot under lateral loads may cause the rupture by increasing tensional forces for tie rod.