Turgut Kocatürk

Large displacement static analysis of a cantilever Timoshenko beam composed of functionally graded material

Abstract In this study, non-linear static analysis of a cantilever Timoshenko beam composed of functionally graded material (FGM) under a non-follower transversal uniformly distributed load is studied with large displacements and large rotations. Material properties of the beam change in the thickness direction according to a power-law function. In this study, the finite element of the beam is constructed by using the total Lagrangian Timoshenko beam element approximation. The non-linear problem is solved by using the incremental displacement-based finite element method in conjunction with the Newton-Raphson iteration method. To use the solution procedures of the Newton-Raphson method, there is a need to linearize equilibrium equations, which can be achieved through the linearization of the principle of virtual work. In this study, the effects of large deflections, large rotations and various material distributions on displacements and normal stress and shear stress distributions through the thickness of the beam are investigated in detail. The convergence study is performed for various numbers of finite elements. In addition, some of the particular results of the present study which are obtained for the homogeneous material case are compared with the results of the SAP2000 packet program. Numerical results show that geometrical non-linearity and material distribution play very important roles in the static responses of FGM beams.

Determination of the steady state response of viscoelastically point-supported rectangular specially orthotropic plates by an energy-based finite difference method

Abstract A method based on a variational procedure in conjunction with a finite difference method is used to examine the free vibration characteristics and steady state response to a sinusoidally varying force applied at the center of a viscoelastically point-supported orthotropic elastic plate of rectangular shape. Using the energy-based finite difference method, the problem is reduced to the solution of a system of algebraic equations. The influence of the mechanical properties, and of the damping of the supports to the mode shapes and to the steady state response of viscoelastically point-supported rectangular plates is investigated numerically for a concentrated load at the center for various values of the mechanical properties characterizing the anisotropy of the plate material and for various damping ratios. The results are given for the frequencies and mode shapes of the first three symmetrical modes. Convergence studies are made. The validity of the present approach is demonstrated by comparing the results with other solutions based on the Kirchhoff–Love plate theory.

Post-Buckling Analysis of Functionally Graded Three-Dimensional Beams Under the Influence of Temperature

In this study, post-buckling behavior of functionally graded beams under the influence of temperature loading is investigated by using total Lagrangian finite element model of three-dimensional continuum approximations. Material properties of the beam are both temperature-dependent and position-dependent. In this study, there is no restriction on the magnitudes of deflections and rotations in the beam. The considered highly non-linear problem is solved by using incremental displacement-based finite element method in connection with Newton-Raphson iteration method. With the effects of material gradient property and thermal load, thermal post-buckling configurations are illustrated in detail in post-buckling cases.

Investigation of the Seismic Behavior of a Historical Masonry Minaret Considering the Interaction with Surrounding Structures

ABSTRACT This study examines the seismic behavior of the minaret of the well-known historical structure “Sultan Ahmed Mosque” under strong earthquake motion. Despite their slenderness and height, minarets are towers with well-established earthquake resistance. In general, these structures were constructed adjacent to the main structure and/or its components. Hence, it is expected that the dynamic behavior of the minarets is influenced by the dynamic characteristics of the adjacent structures as well as the contact conditions. In the presented study, the dynamic behavior of the M6 minaret of the Sultan Ahmed Mosque, which is in contact with the portico that surrounds the courtyard of the mosque, is considered. Ambient vibration tests were conducted on site in order to identify the individual and coupled vibration modes of the minaret and the portico. A finite/discrete model was developed and seismic analysis was carried out. The comparative study reveals considerable differences in responses of different models under strong and very strong earthquake motion.

Seismic analysis and investigation of damage mechanism of 57th infantry regiment memorial using finite-discrete element method

The paper deals with the seismic behavior of a masonry memorial which experienced two earthquakes in one year and suffered serious structural damage. The memorial was first built in 1992 to commemorate the soldiers died in great Gallipoli war, which was held between Ottoman Empire and Allied countries in Çanakkale peninsula a hundred years ago. In 2013, it was replaced with the existing one using cut stone masonry units with mortar as bindings. The site investigation has revealed permanent residual damages and failure of material in some specific locations at the uppermost segment of the memorial occurred during the successive earthquake events. In this study, some flaws in the engineering design of the memorial are addressed, which are related to the lateral stiffness distribution along the structure’s height. In addition, the material tests conducted on the specimens taken from the memorial revealed that the material strength is too poor. Ambient vibration tests were also conducted on site in order to identify the modal parameters of the memorial and compare with the results of initial finite element model. Finally, a finite-discrete element model of the memorial was created and analyzed under Çanakkale earthquakes as well as a more intense earthquake occurred in Düzce/Turkey in 1999. The seismic behavior of the original and the existing structure are investigated and compared. Additionally, a retrofitted model of the memorial by using lead bars which tie the masonry units vertically and/or horizontally was created and analyzed. The results show that the performance of the memorial retrofitted by the lead bars is much better than the initial model. In addition, the earthquake resistance of the original structure which has a more appropriate lateral stiffness distribution is higher.