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    Numerical Simulation of GFRP-reinforced Rectangular Concrete Beams and Proposed Design Expressions
    (Budapest Univ Technology Economics, 2025) Sakcali, Gokhan Baris; Yuksel, Isa
    Rebar corrosion, which has emerged as a primary detrimental factor, significantly impacts the structural performance, durability, and overall serviceability of reinforced concrete (RC) structures. In response to this issue, the growing use of GFRP, which offers superior corrosion resistance compared to steel, highlights the need to compare its performance with traditional steel-reinforced beams. To address this need, this study aims to evaluate the flexural behavior of beams reinforced solely with GFRP rebar and assess their structural performance relative to steel-reinforced beams. To achieve this, finite element models of both steel-reinforced and GFRP-reinforced beams were developed using ANSYS software. The analysis focused on load-bearing capacities, displacement characteristics, and crack patterns, and included the calculation of strain energies corresponding to collapse prevention performance limits. Overall, the study concludes that these modifications enhance design guidelines for GFRP-reinforced beams, offering improved practical applications in structural design. Significant findings include the proposed modification to the minimum reinforcement ratio equation in ACI 440.1R-15 for GFRP-reinforced concrete, the introduction of a suggested strain reduction factor for GFRP rebar, and the revision of the effective moment of inertia equation with coefficients of 0.05 and 0.95. These revisions improved the general performance indicator to 1.17, yielding better results compared to other equations in the literature. The study concludes that these modifications enhance design guidelines for GFRP-reinforced beams, offering improved practical applications in structural design.
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    Reconnaissance report on damage caused by the February 6, 2023, Kahramanmaras, Earthquakes in reinforced-concrete structures
    (Elsevier, 2024) Sezgin, Sedef Kocakaplan; Sakcali, Gokhan Baris; Ozen, Sueleyman; Yildirim, Eray; Avci, Eyuebhan; Bayhan, Beyhan; Caglar, Naci
    Two destructive earthquakes occurred in Kahramanmaras, on February 6th, 2023, with magnitudes of Mw = 7.7 and Mw = 7.6, respectively, causing loss of lives and economic loses. A field investigation was carried out in the affected area between February 12th and 26th, 2023, and the findings are detailed in this paper focusing on the damages and causes of failures in reinforced concrete (RC) structures, both in terms of structural and non-structural elements. The seismic history, characteristics of earthquakes, and an assessment of strong ground motion results are also summarized. Recommendations are provided to mitigate future earthquake-induced damages and save lives.
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    Shear Strength Evaluation of Concrete Beams with FRP Transverse Rebar
    (Budapest Univ Technology Economics, 2024) Sakcali, Gokhan Baris; Yuksel, Isa
    Rebar corrosion in traditional reinforced concrete (RC) components may lead to a decrease in service life and carrying capacity. This condition is one of the reasons of the growing popularity of Fiber Reinforced Polymer (FRP) rebars as a corrosion-resistant alternative, particularly in RC infrastructure projects. Because the material properties and behavior of FRP rebar are very different from conventional steel rebar, the calculations used for reinforced concrete with conventional steel reinforcement should be updated for this material. The aim of this study is to propose a new shear strength prediction model for RC beams with transverse steel rebar in order to calculate the shear strength of RC beams with FRP transverse rebar according to TS-500, which is the Turkish Building Code. To achieve this goal, Finite Element Method (FEM) models were created for 27 RC beams with FRP transverse rebars and 9 RC beams without transverse rebars. Furthermore, for RC beams with FRP transverse rebars, a prediction model has been developed. Additionally, 13 prediction models obtained from regulations or scientific studies were compared to the proposed prediction model using a database of 105 tests obtained from previous experimental studies. It was observed that the proposed prediction model provides more consistent results with the test database from the literature compared to the models suggested by other regulations or studies. Therefore, by modifying the shear strength relations recommended in TS-500 for RC beams with transverse steel rebar, they can also be applied to RC beams with transverse FRP rebars.
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    Tensile behavior of C/GFRP-steel hybrid rebars: Effect of volume fraction and helical angle with a proposed analytical model
    (Elsevier, 2026) Senaysoy, Safa; Yilmaz, Ayten Nur Yuksel; Bedeloglu, Ayse; Altin, Yasin; Sakcali, Gokhan Baris
    This study examines the tensile properties of hybrid rebars consisting of a steel core wrapped with layers of Carbon Fiber-Reinforced Polymer (CFRP) or Glass Fiber-Reinforced Polymer (GFRP). The mechanical performance of the Steel-FRP composite bars (SFCBs) was evaluated through axial tensile tests considering two primary parameters: (i) the longitudinal FRP volume fractions (33 %, 40 %, and 47 %) and (ii) the helical wrapping angles (0 degrees, 30 degrees, and 60 degrees). Although SFCBs have gained increasing attention as an alternative to fully FRP or conventional steel reinforcement, the combined influence of fiber volume fraction and helical orientation on their tensile response has not been clearly established. Experimental findings demonstrated the influence of fiber volume fraction and helical angle on the tensile properties of SFCBs. Specimens coated with carbon exhibited greater strength than those coated with glass, especially at larger wrapping angles, while the glass-coated SFCB specimens demonstrated a wider range of deformation capability. The specimen with a 47 % volumetric fraction and a 60 degrees helical wrap exhibited a 21.8 % increase in yield stress compared with that of the steel bar, whereas its glass-fiber counterpart exhibited a 15.9 % increase. Maximum strength was significantly higher in carbon-SFCB rebars than in glass-SFCB ones. In contrast, glass-SFCB rebars showed 59 % higher ultimate strain. As the volume fraction increased, the influence of the helical angle on ultimate strength decreased. Increasing the helical angle from 0 degrees to 60 degrees enhanced the ultimate strength by up to 32 % in carbon-SFCBs and approximately 12 % in glass-SFCBs at a 33 % volume fraction. An analytical model was proposed to predict a five-zone stress-strain behavior, taking into account the effects of volumetric fraction and helical angle. The proposed model effectively replicated the stress-strain patterns of hybrid rebars in every zone with a satisfactory level of accuracy. Generally, the calculated mean absolute percentage errors for key mechanical parameters such as initial stiffness, yield stress, and fiber-contributed stiffness were below 15 %. This study offers a practical framework for designing SFCBs with customised mechanical properties for sophisticated RC applications.