Browsing by Author "Ergun, S"

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    Mechanical properties of Acropora cervicornis aragonite skeleton by using multiscale models based on micro-CT data
    Altintas, G; Cankal, D; Kilic, G; Ergun, S
    Corals, crucial for ocean ecosystems, face threats such as ocean acidification from global warming and pollution, which weaken their skeletons. This study focuses on Acropora cervicornis, known for its hard but fragile structure, requiring strength and flexibility to withstand the forces from climate-driven atmospheric events. An experiment using uniaxial mechanical loading from the initial stage to complete failure at a very low strain rate (1.2821 x 10-5 s-1) was conducted to ascertain the mechanical properties of corals. The geometric properties and Young's modulus were analysed based on various levels of micro-architectural details from micro-CT data, with resolution values influencing the measurements. The highest resolution model showed a Young's modulus approaching 22.265 GPa and porosity at 40.448%. Calibration of finite element models incorporating micro-architectural details enabled a precise comparison of parameter effects and more accurate results, highlighting the significance of resolution in modelling coral mechanical properties.
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    Effect of Hysteretic Models on Seismic Behavior of Existing RC Structures
    Ergun, S; Demir, A
    The aim of this study is to investigate the effect of hysteretic models on displacement demands of reinforced concrete (RC) structures having various irregularities and determine more proper hysteretic models for different types of RC structures. The RC structures having irregularities such as soft story and overhang were analyzed with nonlinear pushover and nonlinear time-history methods. Concrete compressive strength, stirrup amount, and the number of stories for the structures were variable parameters. Totally, 25,664 analyses were carried out. Displacement capacities and performance levels of structures were determined using nonlinear pushover analysis. Exceedance ratios of performance levels and displacements demanded from the structures of 100 severe ground motions that occurred worldwide were obtained using nonlinear time-history analysis (NTHA). In NTHA, various hysteretic models were used to define inelastic behavior of RC structures. The analyses show that the hysteretic models have a significant effect on displacement demands of RC structures. Finally, proper hysteretic models are suggested according to the type of structure and purpose of occupancy. (C) 2014 American Society of Civil Engineers.
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    Experimental and numerical investigation of walls strengthened with fiber plaster
    Basaran, H; Demir, A; Bagci, M; Ergun, S
    The topic of this study is to investigate behaviors of masonry walls strengthened with reinforced fiber plaster under diagonal tensile loads. Full blend brick 100x50x30 mm in dimensions were used to make masonry walls with dimensions of 400x400x100 mm. Three different samples were manufactured by plastering masonry walls with traditional style, with 3% polypropylene or with 5% steel fiber. All the samples were tested using ASTM 1391- 81 standards. The propagation of damage on samples caused by diagonal tensile load was observed and load-displacement graphs were plotted for each sample. A finite element software (ABAQUS) was used to obtain numerical values for all samples and crack patterns and load-displacement responses were obtained. Experimental and numerical results were compared.