Fatih Sultan Mehmet Asma köprüsü serbest titreşim analizi ve tam ölçekli çevrel titreşim deneyi.

Devastating earthquakes takes place in Turkey and other parts of the world. Suspension bridges represent critical nodes of major transportation systems. Especially in important metropolis, bridges have a strategic importance. Bridge failure poses not only the greatest threat of fatalities from a single devastating earthquake but causes a substantive interruption of emergency efforts. Istanbul has two suspension bridges in service, namely the Bosporus Bridge and Fatih Sultan Mehmet Bridge which provide a major transportation link between the two parts of Turkey, and also join together the European and Asian parts of Metropolitan city. In this paper, sophisticated three-dimensional finite element model of Fatih Sultan Mehmet suspension bridge is developed and the results of the free vibration analysis are presented. In addition, Dynamic parameters of the Fatih Sultan Mehmet Bridge are determined by means of full-scale Ambient Vibration Test at no-traffic condition. Fatih Sultan Mehmet Bridge is a modern suspension bridge, and ranks as the 11th among the longest suspension bridges in the world. The bridge, which was commissioned in 1988, has a main span of 1090.00m. It is a gravity-anchored suspension bridge with no side spans and with steel pylons and double vertical hangers. The daily traffic of the bridge is approximately 220, 000 vehicles. This traffic consists of a combination of local commuters and trans-European commercial transportation. While three dimensional model of the bridge was prepared, great care was given to boundary conditions and links to coincide with actual values. The three-dimensional finite element model of the bridge is developed including geometric non-linearity effects that consist of cable sagging and stress stiffening, the cumber of the deck, and the set-back of the towers. In addition, structural components such as rocker bearings of the bridge are also modeled. The rocker bearings directly affect the deck modes. Defining the hinge supports of the rocker bearings is essential for modeling accuracy. In this study, rocker bearing is modeled as in real structure. Due to the fact that this bearing has great impact on the mode shapes and orders of deck, in these kinds of finite element modeling work, it should be taken into consideration. Non-linear behavior of the flexible long-span three-dimensional bridges is caused by geometric type of deformations. The nonlinear geometric effect due to the cable tension is taken into account by using geometric stiffness matrices. In order to establish the deformed configuration for the dead load, an initial geometric nonlinear analysis is needed. The earth-quake response of the bridge in the analysis starts after the application of the dead load. Therefore, it is necessary to perform a non-linear static analysis to compute the stiffness matrices of the bridge in its dead-load deformed configuration before a dynamic analysis can be performed. For this purpose an iterative scheme for the static analysis is performed by means of a tangent stiffness matrix approach. Hence, natural frequencies and the corresponding mode shapes are calculated using an accurate 3-D finite element model. Physical and analytical understanding of the dynamic response of a suspension bridge is very dependent on the knowledge of its natural frequencies, damping and normal mode shapes of vibration. Performing actual tests on a full-scale structure is the only sure way of assessing its dynamic parameters. Dynamic parameters of a suspension bridge can be determined by means of Ambient Vibration Survey (AVS). Measurements of ambient vibrations were made on Fatih Sultan Mehmet Bridge in order to determine the natural vibration frequencies for the vertical, lateral, torsional, and coupled modes with a 2 Hz resolution, with no traffic load. The ambient vibration survey data are analyzed using basic identification techniques based on the Fast Fourier Transform (FFT) method. The reliability of the model is examined by comparing the natural frequencies of the finite element model with those identified from the ambient vibration tests. Comparisons are also provided with the previous experimental and analytical studies conducted on the bridge. The finite element results of the current study for the modal frequencies as well as the classification of the modes by their dominant actions are compared with the finite element study conducted by Prof. Brownjohn (Brownjohn et. al., 1992). Even though the assumptions of both studies differ, there is close agreement between the results. Reasonable agreement exists between the finite element study and the ambient vibration test for the modal frequencies investigated in this study. [ABSTRACT FROM AUTHOR]