Browsing by Author "Zengin, Esra."
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Item A proposed ground motion selection and scaling procedure for nonlinear response history analysis(Thesis (Ph.D.)-Bogazici University.Kandilli Observatory and Earthquake Research Institute, 2016., 2016.) Zengin, Esra.; Akkar, Sinan.With the advancement in performance-based earthquake engineering, nonlinear response history analysis of structures has become more common in recent years. The selection and scaling of ground motions for use in nonlinear response history analysis is one of the most critical steps in performance-based seismic assessment procedures. This study presents ground motion selection and scaling procedure that addresses the uncertainty in the spectral demand with the preserved dispersion within the ground motion set. The candidate ground motion sets are constructed based on dispersion statistics about the target spectral demand. The optimum ground-motion set is linearly scaled by using an optimization algorithm that minimizes the error between scaled median and target spectra. The scaling stage ensures that the median record spectrum provides a reasonable match to target median in a previously defined period interval. This procedure allows performing further modification on each scaled ground motion in order to match the target variance of the scenario-based spectrum. In this study, a novel probabilistic framework is presented to propagate the uncertainties in both ground motion intensity and the structural response on fragility curve estimations. To investigate the effects of uncertainties on seismic damage estimations, the results of this study are compared with those obtained by the conventional fragility curve approach.Item Structural analysis and design of a long span combined cable-stayed suspension bridge crossing the Izmit Bay(Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2010., 2010.) Zengin, Esra.; Orakçal, Kutay.; Tezcan, Semih S.,In designing long span cable supported bridges, geometrical nonlinearity of the structure, including the cable sags, large deflections, and P-Delta effects, is a primary consideration. Also, reaching the initial equilibrium configuration of a cable supported bridge, via a set of geometrically-nonlinear analyses under dead loads, is essential in obtaining the stiffness properties of the cable elements for further analyses. In order to determine the static and dynamic behaviour of the cable supported bridges accurately, static and dynamic analyses should be conducted by considering all sources of geometric nonlinearity. In this thesis, a particular analytical model has been developed for a proposed longspan combined cable-stayed suspension bridge crossing the Izmit Bay. To evaluate the behavior and response of the cable supported bridge, a series of static and dynamic analyses have been conducted under code-compliant service loads as well as using extreme load effects. Bridge displacements and internal forces in the structural members as a result of the applied forces and earthquake effects were calculated in accordance with the load combinations specified by AASHTO-LRFD (2007). Member capacities and deformations were checked per the ASSHTO-LRFD specifications and the structural performance of the proposed bridge was evaluated. The Bosphorus suspension Bridge in Istanbul was also modeled and analyzed within the scope of this work, as a preliminary case study to assess the validity of the modeling and analysis methodologies used.