Çağrı Mollamahmutoğlu

This study examines the nonlinear buckling response of functionally graded shallow circular nano-arches within the framework of the stress-driven nonlocal elasticity theory and Euler–Bernoulli beam kinematics. Geometric nonlinearity is incorporated through von Kármán strain-displacement relations, and the governing equations are discretized using the Generalized Differential Quadrature Method (GDQM). A possible equilibrium path, including the post-buckling regime, is traced via the arc-length method to capture potential instability phenomena. A parametric investigation is conducted to explore the influence of boundary conditions, geometric characteristics, nonlocal material length scale, gradation profile, and the extent of a partially applied transverse load on the buckling behavior. The results reveal that shallow nano-arches may exhibit multiple instability patterns, snap-back, and looping — depending on the combined effects of small-scale parameters, material gradation, loading characteristics and Boundary Conditions (BCs). To the authors’ knowledge, this is the first study to analyze the post-buckling behavior of functionally graded shallow nano-arches subjected to non-uniform partial loading using the stress-driven nonlocal elasticity model in conjunction with an arc-length solution strategy.

This study investigates the in-plane shear behavior of solid brick masonry walls, both unreinforced and retrofitted using Reinforced Khorasan Jacketing (RHJ), a traditional pozzolanic mortar technique rooted in Iranian and Ottoman architecture. Six one-block-thick English bond masonry walls were tested in three configurations: unreinforced with Horasan plaster (Group I), reinforced with steel mesh aligned to wall edges (Group II), and reinforced with mesh aligned diagonally (Group III). All the walls were plastered with 3.5 cm of Horasan mortar and tested after 18 months using diagonal compression, with load-displacement data recorded. A detailed 3D micro-modeling approach was employed in finite element simulations, with bricks and mortar modeled separately. The Horasan mortar was represented using an elastoplastic Mohr-Coulomb model with a custom softening law (parabolic-to-exponential), calibrated via inverse parameter fitting using the Nelder-Mead algorithm. The numerical predictions closely matched the experimental data. Reinforcement improved the shear strength significantly: Group II showed a 1.8 times increase, and Group III up to 2.7 times. Ductility, measured as post-peak deformation capacity, increased by factors of two (parallel) and three (diagonal). These enhancements transformed the brittle failure mode into a more ductile, energy-absorbing behavior. RHJ is shown to be a compatible, effective retrofit solution for historic masonry structures.

Historical mosques are some of the most valuable structures in Islamic societies. It is of primary importance to protect these structures and ensure their safe transmission to future generations. This study investigates the adequacy of the buttress system of the Süleymaniye Mosque in Istanbul, regarded as the ‘symbol structure of Ottoman Architecture’, against gravity and horizontal earthquake loads. Although several structural studies have been conducted on this unique building, the absence of any research on the buttress system, which clearly plays a significant role in its survival through many earthquakes, served as the main motivation for this study. After presenting the material properties, a finite element model of the structure was created. Finite element models were also developed for two hypothetical scenarios in which the outer depths of the buttresses were reduced by fifty percent or eliminated. The models and all analyses were performed using ABAQUS software. Gravity load analyses indicated that the mosque does not face any issues related to stresses or displacements. Nonlinear static analyses revealed that, with the current buttress dimensions, the structure can resist horizontal loads up to about 70% of self-weight along the Qibla axis and about 90% along the axis perpendicular to the Qibla. These findings are some of the most significant results obtained thus far in studies investigating the horizontal earthquake resistance of the mosque. Through performance analyses, it was determined that the structure can meet the limited damage performance criterion only with the current buttress depths; however, it cannot satisfy this performance level with reduced buttress dimensions. In conclusion, the study demonstrated that the buttress system of the Süleymaniye Mosque is highly effective against gravity loads and transverse seismic forces and that it was designed not only with practical experience but also with a solid understanding of structural behavior.

Background: The gradation of thermal expansion coefficient was analyzed in the earlier study. The analytical formulation derived here, which is quite different, should be validated to understand the thermal stress distribution in a laminated composite and functionally graded material. Besides this solution, a validated numerical model can also be used to optimize the material gradation of plates in terms of sustainability. Objective: To validate the analytical formulation derived here, an experimental model is presented to understand the thermal stress concentration for functionally graded and laminated composite plates. A numerical model is also validated to extend to understand the effects of the number of layers, the thickness of a layer, the gradation function, the ratio of elastic moduli, and the coating. Methods: The experimental problems in the production of the experimental models with layers of different elastic moduli are discussed here. In the experimental analysis, a three-dimensional photoelastic stress analysis of two- and four-layer composite plate was used to mechanically model the thermal expansion. The analytical solution for the thermal stress in a free plate was derived by the strain suppression method based on the principle of superposition. The numerical models were analyzed using finite element software. The step variation in the experiment was used as a reference point for a continuous or multi-layer (> 2) step variation of material coefficients in the models. Results: The variation of stress concentration is shown for various cases of laminated and continuous gradations of elastic modulus. The four-layer experimental model provides the difference in thermal stress distribution as a result of a layered coating. The validated analytical and numerical models provide reasonable results. An empirical formula to optimize the material gradation in terms of elastic modulus is derived. Conclusions: The experimental model can be used to analyze thermal stress in functionally graded materials. The gradations of the material in the plate or the coating of the plates can be optimized by the validated analytical and numerical models. The empirical formula can be used to determine the elastic modulus of the coating to minimize the stress concentration.

Many historical buildings are covered with vaults or domes. This study investigates the effectiveness of the buttress form on the lateral (out-of-plane) resistance of masonry walls subjected to the inclined vault thrust. For this purpose, a basic cal...