Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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Author: search.filters.author.Demir, UgurSubject: search.filters.subject.Column

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  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    Seismic Testing and Modeling of Full-Scale Substandard Rc Columns Retrofitted With Sprayed Gfrm With and Without Basalt Mesh Under High Axial Compression and Shear Demand
    (Asce-Amer Soc Civil Engineers, 2025) Kian, Nima; Demir, Ugur; Ates, Ali Osman; Celik, Oguz C.; Ilki, Alper
    This study presents the experimental and analytical hysteretic behaviors of eight full-scale RC square and rectangular columns. The columns were designed to have different shear spans that represent: (1) a column that complies with the Turkish Government Ministry of Reconstruction and Resettlement's ( 1975) seismic design code, Turkish Seismic Design Code (TSDC); (2) a substandard column; and (3) two sprayed glass fiber-reinforced mortar (GFRM)-retrofitted counterparts of the substandard column with and without basalt mesh. The substandard columns were designed to be subjected to relatively high shear ratios (i.e., the ratio of the shear force that corresponds to the moment capacity to shear strength of the cross section) up to 0.85 and with a high axial load-to-capacity ratio of 0.75. All columns were tested under constant axial load and reversed cyclic lateral displacement excursions. The results revealed that the columns that complied with the TSDC showed satisfactory behavior for seismic performance, and the performance of the substandard columns was extremely poor. However, the hysteretic performance of the substandard columns that were subjected to high axial stress and shear significantly improved after the proposed retrofitting. Finally, a numerical model was developed in OpenSees to reproduce the hysteresis curves of the specimens. The slip of the longitudinal bars at the column-foundation interface, strain penetration into the foundation, and buckling of the longitudinal bars in compression were accounted for in the modeling. The results are in good agreement with the experimental hysteresis curves. The performance levels of the columns are further specified, and the predictions of the current seismic codes were analyzed: (1) the European Committee for Standardization's 2005 code, Eurocode 8: Design of structures for earthquake resistance; Parts 1-3: Strengthening and repair of buildings (EC8-3); and (2) the Turkish Government Ministry of Interior Disaster and Emergency Management Authority's 2018 code, Turkish Building Earthquake Code (TBEC). The TBEC provided more accurate estimates of plastic rotation capacities for substandard specimens. In contrast, EC8-3 overestimated the plastic rotation capacity when shear stresses were relatively high due to lower shear span-to-depth ratios (a/d).
  • Article
    Impact of High Axial Stress on Seismic Behavior of Substandard Reinforced Concrete Columns
    (Elsevier Science inc, 2025) Gundogan, Safiye; Demir, Ugur; Turan, O. Tugrul; Ilki, Alper
    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.