Investigation of the seismic performance of the historical Tokat clock tower and its strengthening with steel elements

In this thesis study, the seismic behavior of the Tokat Clock Tower, an artifact of the Abdulhamid II era and one of the landmark structures located in the city center of Tokat, was investigated, and retrofitting proposals were developed to increase its structural safety. Built with masonry stone and lime-based mortar, the structure is in a high-risk group against earthquake effects due to its slender geometry, mass irregularities, and low tensile strength. The main objective of the study is to determine the current seismic performance of the structure using numerical methods and to retrofit it with steel elements, observing the principle of minimum intervention to the historical fabric. Within the scope of the study, the structure was modeled in three dimensions using SAP2000 software based on the finite element method. In order to obtain a realistic soil-structure interaction simulation, the tower was not fixed directly at the foundation level; instead, a 3D soil block consisting of two different layers (Solid 1 and Solid 2) was modeled based on geotechnical soil investigation report data, and fully fixed boundary conditions were applied to the base of this soil mass. Earthquake effects were analyzed using the Response Spectrum Method for the ZD local soil class and DD-2 earthquake ground motion level, based on the Turkish Building Earthquake Code (TBEC-2018). According to the analysis results; it was determined that the maximum tensile stresses occurring especially in the transition regions of the body in the existing structure reached 1.090 MPa, challenging the tensile capacity of the masonry wall (at a rate of 87%). It was concluded that this situation would create a risk of damage and loss of stability in the body walls in a potential earthquake. Accordingly, a retrofitting model was created by applying external steel belting to the tower body and a steel cross-bracing system to the ground floor openings. As a result of comparative analyses, it was observed that the tensile stresses in critical regions were reduced to 0.819 MPa with the retrofitting, top displacements were limited, and the seismic safety level of the structure was increased. It has been revealed that the proposed method is an applicable, effective, and reversible solution without disrupting the architectural integrity of the historical structure.