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Yayın Seismic performance assessment of a post tensioned box girder viaduct(Işık Üniversitesi, 2022-01-31) Arslanboğan, Emir; Umut, Önder; Işık Üniversitesi, Lisansüstü Eğitim Enstitüsü, İnşaat Mühendisliği Yüksek Lisans ProgramıIn the 1999 Marmara earthquakes (Kocaeli and Düzce earthquakes), some of the existing bridges and viaducts were completely or partially destroyed and the earthquake performance of the existing bridges and viaducts began to be questioned. Evaluating the seismic performance of existing structures is one of the most important preliminary steps before seismic retrofitting of structures, as well as a way to validate the analysis and design specifications. The subject of this study is the seismic performance evaluation of the Molla Gürani Viaduct, located in front of the Elmalı Dam on the TEM (O-2 highway) in Istanbul, according to the Turkey Bridge Earthquake Code published in 2020 and its annexes. First of all, all kinds of information, documents, projects, reports and test results related to the viaduct were examined, analyzed and tried to be verified. It has been tried to obtain healthy information about the current situation of the viaduct by making visual inspections in the region where the viaduct is located. The seismic performance assesment of the existing viaduct were made with the Nonlinear Time History Analysis method described in TBEC 2020. The three dimensional model of the viaduct was prepared using the SAP2000 software. The moment-curvature relationship of the sections were determined with the XTRACT section analysis program, using the axial loads obtained from the non-linear static analysis results performed under non-seismic loads. The cracked section stiffnesses and other section properties were modified before dynamic analyses. Due to the large stirrup spacing in the columns, unconfined concrete properties were used in the moment-curvature analyses. The bending cracked section stiffnesses of each column were calculated separately and included in the model. The nonlinear behavior has been tried to be characterized by the acceptance of lumped plastic hinges. For each of the pier columns, 2 plastic hinges in both directions are defined in the foundation-column junction area and just below the 1.4 m solid part at the top end of the columns. The Nonlinear Time History analyses was carried out using 7 earthquake records selected by considering earthquake magnitudes, fault distances, source mechanisms and local ground conditions compatible with DD1 and DD2a earthquake ground motion levels defined in TBEC-2020 Chapter 2. Selected ground motion records are scaled according to TBEC-2020 Section 2.5. As a result of the existing situation analysis of the viaduct, it has been observed that the deformations occurring in the elastomeric bearings in the longitudinal and transverse directions for the DD-1 Earthquake Ground Motion Level are higher than the values allowed in the TBEC-2020 section 5.4.5.1. The fact that the superstructure is continuous and that it is anchored to the abutment by tie bars eliminates the possibility of falling off the support in the longitudinal direction. As a result of possible ruptures that may occur because of high deformations in elastomeric bearings, elastomeric bearings may not fulfill their function. In this case, the viaduct superstructure beams are likely to be free in the transverse direction and may pound each others under the effects of earthquakes, despite the 1.50 m gap between them. In the seismic performance evaluation analyses of the viaduct, it has been determined that the shear keys on the abutments do not have the capacity to meet the earthquake loads. In the observations made in the field, it is seen that macro cracks are formed in the shear keys on the abutments. Limiting elastomeric bearings deformation and strengthening shear keys before a possible Istanbul earthquake in the Molla Gürani viaduct are among the some of the most important precautions to be taken immediately before an earthquake.
