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    Effect of longitudinal reinforcement ratio on residual flexural capacity of high-strength reinforced concrete beams exposed to impact loading
    (Elsevier Science Inc, 2024) Dok, Gokhan; Caglar, Naci; Ilki, Alper; Yilmaz, Cemal
    In this study, it was aimed to investigate the dynamic impact and post-impact performances of high-strength reinforced concrete (RC) beams, which have different ductility and load-bearing capacities. The dynamic behavior and impact damages of RC beams were compared after exposure to a constant magnitude of impact energy. The applied impact energy was obtained by dropping a mass of 360 kg from a certain height of 3 m. The cross-section dimensions and length of the specimens were selected to carry out the experiments in full-scale. The tested specimens were designed with five different longitudinal reinforcement ratios for demonstrating distinct structural behavior mechanisms that vary from pure flexure to pure shear, representing different ductilities, loadbearing capacities and potential failure characteristics. The post-impact behavior of the impacted RC beams was also assessed by performing quasi-static bending tests on the impact-damaged specimens and the obtained results were compared with the identical undamaged reference RC beams. The results demonstrated that the longitudinal reinforcement ratio (which was intentionally designed for different specimens to exhibit different structural responses from pure shear to pure flexural and different shear-flexure mechanisms) significantly influences the dynamic response and damage intensity of the beams, which, in turn, affect their post-impact static performance. Key structural characteristics, including residual displacement, ductility, energy dissipation, load-carrying capacity, and stiffness, were analyzed. It was found that the mechanical properties of the beams deteriorated markedly after impact exposure. A crucial finding of this research is the notable shift in failure modes from flexural to shear after impact, depending on the damage severity. In RC beams, shear damage remains insignificant under both impact loading and subsequent static loading when the ratio of shear strength to flexural strength (Vr/Mr) exceeds 1.5. Conversely, when this ratio is less than 1.5, the behavior transitions to being shearcritical or shear-dominant. This study presents, for the first time, comprehensive experimental results on the impact-induced damage progression, failure mechanisms, and residual behavior of high-strength RC beams. These insights are vital for understanding the performance of RC structures under impact loads and contribute significantly to the field of structural engineering, particularly in designing impact-resilient structures.
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    Experimental and numerical investigation on residual behavior of high strength reinforced concrete beams subjected to different impact velocities
    (Pergamon-Elsevier Science Ltd, 2026) Dok, Gokhan; Caglar, Naci; Ilki, Alper; Yilmaz, Cemal; Serdar, Ahmet Hamdi
    This study investigates the dynamic and residual behavior of full-scale high-strength reinforced concrete (RC) beams subjected to low-velocity impact. The aim is to assess both the immediate response under impact and the residual load-carrying capacity after impact, providing a basis for evaluating the post-impact reliability of RC members. Experimental tests were performed by dropping a constant 360 kg mass from heights of 1.5 m, 2.0 m, and 3.0 m, generating distinct impact energies. Beams with different longitudinal reinforcement ratios were designed to represent varying ductility and load-carrying capacities. Dynamic parameters such as impact force, acceleration, displacement, and crack development were measured during impact, while subsequent three-point bending tests evaluated the residual stiffness, strength, and ductility of the impacted beams in comparison with undamaged reference specimens. The results revealed significant reductions in mechanical properties, including stiffness and energy absorption, with a clear tendency for failure modes to shift from flexure to shear under higher impact energies. Residual displacement ductility was substantially diminished, indicating limited serviceability after severe impacts. To complement the experiments, validated finite element models were developed in ABAQUS using a two-step procedure, transferring the damaged state from impact simulations to quasi-static loading. Numerical predictions closely matched experimental findings, with less than 3 % deviation. The combined results highlight the necessity of reassessing the post-impact performance of RC beams and offer practical guidance for improving design provisions against extreme loading conditions.
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    Nonlinear finite element analysis of steel fiber reinforced concrete beams subjected to impact loads
    (Pontificia Univ Catolica Chile, Escuela Construccion Civil, 2024) Serdar, Ahmet Hamdi; Caglar, Naci; Demirtas, Gamze; Saribiyik, Mehmet
    Steel fiber reinforced concrete, compared to the conventional concrete; is a composite building material that performs much better in terms of parameters such as ductility, energy absorption capacity, fracture toughness, fatigue resistance, and the use of steel fiber reinforced concrete (SFRC) in structures has become widespread. In this study, a nonlinear finite element model (FEM) has been developed that can represent the behavior of beams produced by using steel fiber concrete subjected to impact load. For this purpose, a finite element model of beam series produced with fiberreinforced concrete obtained from the literature was created. The ABAQUS package program was used to create models simulating the behavior. Numerical results showed that the model could successfully capture the experimental results of beams selected from the literature. In addition to simulation, a parametric study was also performed to investigate the effect of stirrups, reinforcement ratio, and drop height on the behavior of SFRC beams under impact loads. The results of the parametric study showed that increasing the fiber ratio and reinforcement ratio positively affected the behavior of SFRC beams in terms of displacement recovery.
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    Nonlinear finite element study on the improvement of torsional strengthening of RC beams with diagonal shear reinforcement
    (Pontificia Univ Catolica Chile, Escuela Construccion Civil, 2024) Subasi, Rojda Orman; Caglar, Naci; Demirtas, Gamze; Ozturk, Hakan
    Experimental and numerical studies are carried out by many researchers in order to examine the nonlinear behavior of reinforced concrete (RC) beams under the torsion moment and to improve the torsional moment capacity. In this study, a numerical study is performed to investigate efficiency of diagonal shear reinforcement (DSR) on the response of RC beams subjected to pure torsion. A nonlinear numerical model was constituted to simulate the response of the RC beams by using ABAQUS software program and verified with the selected experimental results from literature. The numerical analysis results proved that the nonlinear numerical model is quite successful in simulating the nonlinear behavior of RC beams and DSR makes a very significant contribution to the torsional moment capacity of the RC beam subjected to pure torsion.
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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.