Yusuf Sümer

Fiber-reinforced polymer (FRP) reinforcement has emerged as an important alternative to conventional steel due to its high corrosion resistance and long-term durability. However, studies on the behavior of FRP-reinforced concrete deep beams under shear-dominated conditions remain limited. In this study, the structural behavior of reinforced concrete deep beams strengthened with GFRP and CFRP bars was numerically investigated using the ABAQUS finite element software. A parametric analysis was conducted to evaluate the effects of shear span-to-depth ratio (a/d), concrete compressive strength, tensile reinforcement ratio, and reinforcement type. The results indicate that reducing the a/d ratio from 1.4 to 1.12 increased the maximum load capacity by 37.6% for GFRP beams and 10.0% for CFRP beams, reflecting enhanced arch action. Increasing concrete strength from 25 MPa to 40 MPa led to capacity increases of 64.5% (GFRP) and 41.7% (CFRP), confirming its dominant role. Increasing the reinforcement ratio improved capacity by 6–9% in GFRP systems and over 15% in CFRP systems. CFRP-reinforced beams exhibited 20–55% higher load capacity, while GFRP beams showed greater ultimate displacement (13–18 mm vs. 8–12 mm). Overall, CFRP provides superior strength, whereas GFRP offers enhanced ductility, supporting performance-based design.

Strengthening reinforced concrete (RC) beams using fiber-reinforced polymer (FRP) materials has become a widely accepted technique in structural engineering due to its efficiency, light weight, and resistance to corrosion. Among these materials, glass fiber-reinforced polymers (GFRP) are commonly used for flexural strengthening by bonding fabric sheets to the tension side of beams using epoxy adhesives. In this study, an experimental program was carried out to investigate the flexural behavior of an RC beam strengthened with a GFRP fabric sheet bonded to its bottom surface using epoxy. The beam was tested under three-point bending conditions, with simple supports and a single central point load, to simulate a standard flexural loading scenario. During loading, premature debonding between the GFRP sheet and the concrete surface was observed at advanced stages, leading to slip and reduction in strengthening efficiency. To mitigate this issue, GFRP anchors, made from the same material as the strengthening sheet were introduced to improve the bond. These anchors had varying dimensions in width and height to assess their influence on the overall performance of the beam. The results revealed that both the load-carrying capacity and displacement capacity of the beam increased significantly with the addition of the anchors. The most effective improvement occurred when the anchor width was maximized and the height remained lower than the width, suggesting that wider and flatter anchors enhance bond performance more effectively. A clear proportional relationship was found between anchor width and the beam’s structural performance, while increased anchor height showed a diminishing effect. These findings highlight the critical role of anchor geometry in optimizing the performance of GFRP-strengthened RC beams.

The use of environmentally friendly materials is becoming increasingly important in order to increase sustainability and reduce carbon emissions in reinforced concrete structures. In this context, glass fiber-reinforced polymer (GFRP) bars, which are proposed as an alternative to traditional steel reinforcements, are attracting attention in engineering applications thanks to their advantages, such as high corrosion resistance, low weight, and electromagnetic permeability. However, the lower elasticity modulus of GFRP reinforcement compared to steel causes greater displacement and crack width under bending and shear effects, leading to certain limitations in structural performance. Due to the limited number of comprehensive analyses in the literature that simultaneously consider parameters such as reinforcement diameter, concrete strength, and stirrup spacing, this study aims to reveal the interactive effects of these parameters through numerical analyses and contribute to existing research. In this context, beam models using GFRP reinforcements with diameters of 10 mm and 12 mm, concrete strengths of 25 MPa and 40 MPa, and different stirrup spacings were analyzed using the ABAQUS (2022) software with a three-dimensional nonlinear finite element method.

This study aims to investigate the mechanical behavior of cement mortar and concrete through a hybrid approach that integrates artificial intelligence (AI) techniques with finite element modeling (FEM). Support Vector Machine (SVM) models with Radial Basis Function (RBF) and polynomial kernels, along with Multilayer Perceptron (MLP) neural networks, were employed to predict the compressive strength (Fc) and flexural strength (Fs) of cement mortar incorporating nano-silica (NS) and micro-silica (MS). The dataset comprises 89 samples characterized by six input parameters: water-to-cement ratio (W/C), sand-to-cement ratio (S/C), nano-silica-to-cement ratio (NS/C), micro-silica-to-cement ratio (MS/C), and curing age. Simultaneously, the axial compressive behavior of C20-grade concrete was numerically simulated using the Concrete Damage Plasticity (CDP) model in ABAQUS, with stress–strain responses benchmarked against the analytical models proposed by Mander, Hognestad, and Kent–Park. Due to the inherent limitations of the finite element software, it was not possible to define material models incorporating NS and MS; therefore, the simulations were conducted using the mechanical properties of conventional concrete. The SVM-RBF model demonstrated the highest predictive accuracy with RMSE values of 0.163 (R² = 0.993) for Fs and 0.422 (R² = 0.999) for Fc, while the Mander model showed the best agreement with experimental results among the FEM approaches. The study demonstrates that both the SVM-RBF and CDP-based modeling approaches serve as robust and complementary tools for accurately predicting the mechanical performance of cementitious composites. Furthermore, this research addresses the limitations of conventional FEM in capturing the effects of NS and MS, as well as the existing gap in integrated AI-FEM frameworks for blended cement mortars.

In this study, the analysis of reinforced concrete (RC) beams strengthened with Fiber Reinforced Polymer (FRP) composites against bending and shear loads was carried out with the finite element technique, using ABAQUS software, which is widely used in simulating experimental circumstances in numerical studies. It has been reported that buildings in areas damaged by earthquakes are generally constructed using low-strength concrete and inadequate reinforcement. Additionally, construction errors also contribute to reducing the load-bearing capacity of structural elements. For this purpose, nine rectangular cross-section RC beams were experimentally constructed using low-strength concrete and inadequate bending and shear reinforcement. These beams were strengthened by wrapping them in different configurations with Carbon and Glass FRP (CFRP and GFRP) composites to resist shear and bending forces in both transverse and longitudinal directions, and their load-displacement curves were obtained. Subsequently, a three-dimensional Finite Element Model (FEM) was created to validate the experimental results. The FEM validation demonstrated high accuracy in replicating experimental outcomes, emphasizing the influence of mesh size, dilation angle, and concrete constitutive models on simulation fidelity. Parametric studies revealed that increasing longitudinal reinforcement diameters had minimal effect on load capacity but highlighted the critical role of transverse reinforcement, as reducing stirrup spacing significantly improved load-bearing capacity. GFRP-reinforced beams exhibited superior ductility and a 15% higher strength compared to CFRP, suggesting their suitability for applications demanding enhanced displacement capacity. Furthermore, the findings underline the need for refined FEM models to better capture inclined fiber orientations and optimize structural reinforcement strategies.

Numerous approaches and inputs for nonlinear finite element analysis used for modeling reinforced concrete systems under cyclic loads have been outlined. Practitioners usually take into account a number of significant factors when modeling, for example deciding upon the constitutive relations, the connection among concrete and steel reinforcement, and the mesh sensitivities, in order to accurately simulate the nonlinear response of reinforced concrete under cyclic loads. Therefore, it is essential to thoroughly assess popular modeling approaches and develop a reliable modeling approach with reliability, stability, and consistency. A modeling technique and practical guidelines for nonlinear finite element analysis of reinforced concrete frames subjected to cyclic loading are described in this study, taking into account the influence of parameters such as dilation angle, stiffness recovery, friction coefficient, and mesh sizes. The hysteretic force–displacement behavior and load-carrying capacity of reinforced concrete frames subjected to cyclic loading have been compared using numerical and experimental curves. Discrete fracture paths are specified in the model’s geometry to achieve an accurate depiction of the stress distribution and an adequate fit of the hysteretic behavior. The proposed modeling approach provides a precise representation of the stress distribution and hysteretic behavior while keeping computational costs reasonable.

Aim: Increasing the resistance of reinforced concrete load-supporting components to external loads or restoring their original strength by utilizing fiber-reinforced composite materials has become an increasingly utilized technique in recent years. Because this process provides a wrapping effect on the concrete, it effectively boosts the element's strength and contributes to shear strength and energy absorption capacity. This paper presents the results of a comprehensive FEM investigation on the behavior of axially loaded square reinforced concrete columns with rounder corners that have been strengthened with carbon fiber-reinforced polymer CFRP wraps. First, a finite element model verified by experimental work, which allows laboratory experiments to be carried out in a computer environment, was obtained using ABAQUS software. 27 square reinforced concrete columns measuring 200*200*1100 mm were modelled and analysis was carried out using a non-linear finite element analysis. Three parameters of concrete strength, type of wrapping (full and partial) and the distance between stirrups were considered. According to the analysis results, significant increases were observed in the compressive strength of square reinforced concrete columns wrapped with CFRP compared to the unwrapped columns. It has been determined that full wrapping of the column increases the strength more than 3 times compared to ½ wrapping. It was found that the increase in ductility was relatively limited. Method: First, a numerical model of an experimental study from the literature was generated in the computer environment utilizing the non-linear finite element approach in this study. A parametric analysis was then performed to test the column strengths under various conditions in order to acquire extensive data. ABAQUS finite element software was used to examine all numerical models developed for the parametric study under axial load. Results: According to the parametric study results, fully wrapped columns performed significantly better than strip wrapped columns. It was determined that as the concrete strength increased, the strength of the confined columns increased more than twice. Conclusion: The numerical model implemented using ABAQUS finite element software confirmed the axial loaded column experiment obtained from the literature with an acceptable approximation. Parametric study conducted with the proposed finite element model showed that the percentage of wrapping with FRP composites plays an important role in increasing the axial load-carrying capacity of the column.

Concrete-encased filled steel tube (CEFST) beams prepared by placing steel tube in RC beam is a beam type that has widespread use. The current study examines the effects of steel tube geometry and support conditions on the behavior of CEFST beams under impact loading. First, CEFST beam specimens with different lengths and different tube section geometries (circular and square) were produced in the laboratory. These four test specimens with two different support conditions were exposed to impact load tests. Finite element models of the test specimens were created using Abaqus\Explicit software. In the next stage, 4 finite element models were verified by the experimentally obtained damage conditions, maximum displacements, and support reaction forces. In the final stage, as parametric study 12 finite element models were prepared in addition to 4 verified models and analyzed under low velocity impact loading. In addition to experimental values, Von Mises stresses, Equivalent plastic strain, Friction energy, and Damage energy values were also obtained by the numerical study and thus the effects of steel tube geometry and support conditions were comparatively examined. The obtained results showed that CEFST beams with a square tube section exhibited better performance under a sudden load such as impact compared to the beams with a circular tube section. Moreover, both numerical and experimental results pointed out that the beam length beyond support has a positive impact on the performance of beam under impact loading.