GCRIS

The seismic performance of reinforced concrete (RC) buildings, particularly those constructed without adequate seismic detailing, remains a critical concern in earthquake-prone regions worldwide. Many of these buildings, often referred to as substandard RC structures, were built before modern seismic codes were established and are characterized by poor material quality and inadequate construction practices. The Southern T & uuml;rkiye earthquakes on 6 February 2023 underscored the urgent need to better understand the seismic behavior of these substandard structures, which frequently fail to meet modern design standards and are prone to damage or collapse. Substandard RC columns, characterized by low concrete strength and inadequate transverse reinforcement, are susceptible to severe seismic damage, increasing the risk of collapse and life loss. While numerous studies have experimentally examined the seismic behavior of RC columns under low to moderate axial load to capacity ratios (typically below 0.30), these conditions do not accurately reflect the reality of many existing substandard columns that are frequently subjected to higher axial compression stresses. This study addresses this critical gap by presenting the first experimental data on the seismic behavior of full-scale, substandard RC columns under high axial load ratios (0.30-0.80). The analysis focused on lateral load-displacement relationships, ductility, plastic hinge length, stiffness, energy dissipation capacity, and residual displacements. Increases in axial load led to more brittle failure modes, reduced displacement ductility and an extended plastic hinging zone. High axial loads also caused accelerated stiffness degradation, reduced cumulative energy dissipation, and progressive residual deformations. Analytical models overestimated deformation capacity, making them unreliable for substandard RC columns under high axial stress. Additionally, predictions using plastic hinge length formulas underestimated the values at high axial loads. The study also evaluated the performance of widely used concrete confinement models in predicting the moment-curvature responses and corresponding ductility for substandard RC columns with low compressive strength and subjected to high axial stress. These findings underscore the critical need for refined modelling approaches and assessment methodologies to improve the seismic evaluation of substandard existing buildings.

Intracellular pH is a key factor in cell homeostasis, regulated within specific compartments, and changes in pH can result from or affect biochemical pathways. This study explores a yellow fluorescent protein EYFP-G65T as a core for a time-resolved pH-indicator. Among the tested designs-a circular permutant, a chimeric SypHer3s-like construct, and an unmodified protein-the unmodified EYFP-G65T performed best for live-cell imaging. Upon two-photon excitation, purified EYFP-G65T exhibited a 4.5-fold increase in mean fluorescence lifetime across pH 5.5-7 and a 7-fold change in its major component's lifetime from pH 6.5-8. Using this indicator, we measured pH values ranging from 6 to 8 in various organelles, and mapped pH shifts in mitochondria and the Golgi apparatus in response to stimuli.

Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

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