Techno Press
Tp_Editing System.E (TES.E)
Login Search
You logged in as...

cac
 
CONTENTS
Volume 38, Number 2, August 2026
 

Abstract
This study examines the detailed flexural behavior of reinforced concrete (RC) beams strengthened using fiber-reinforced polymer bars (FRPs) by the near-surface mounted (NSM) method. In addition, the strengthened beams were studied under the effect of prestressing the FRP rebars to increase the beam's strength and serviceability. Two approaches were utilized in this study, analytical and numerical, to fulfill the objectives of the study to provide design guidelines and mathematical expressions to describe the behavior of the prestressed near-surface-mounted (PNSM) beams. The numerical analysis was done using the nonlinear finite element analysis method using ABAQUS software, where models were validated firstly using experimental data from literature. After that, an extensive parametric study was done considering different prestressing levels (0, 30, and 50%), FRP material (Basalt (BFRP) and Glass (GFRP)), and concrete compressive strength (20, 30, 40, 50, and 60 MPa), with the bar diameter to groove size ratio kept as 1.5, per the ACI440 code provision. It has been found that increasing the utilized compressive strength has a proportional relationship with energy absorption and an inversely proportional one with ductility behavior. Moreover, increasing the prestressing level has a major effect on the ultimate deflection behavior, where the resulting decreasing percentages are high and range between 41% and 60%. In addition, the yielding load has similar behavior to that observed for the cracking one, but with lower values. Finally, natural logarithmic equations have been proposed for estimating the improvement or reduction percentages upon strengthening the RC beams by NSM and PNSM, and compared with the ACI440 predictions, where it behaves well. Based on that, the results of this study could be used as a design guideline for strengthening RC beams with BFRP and GFRP rebars using NSM and PNSM techniques.

Key Words
ACI440; concrete strength; NSM bars; prestressing; XFEM

Address
Department of Civil Engineering, Jordan University of Science and Technology, Irbid, Jordan

Abstract
The crack extension resistance curve is important to evaluate the fracture behavior of dam concrete and is typically determined using an analytical method, where the load and the corresponding effective crack length are substituted into the linear elastic fracture mechanics (LEFM) formula. In this study, the experimental crack extension resistance curve is initially obtained based on the measured crack lengths during the fracture process. Subsequently, the numerical method based on the crack propagation criterion with initial cracking toughness is employed to determine the crack extension resistance curve and shows good agreement with the experimental curve. However, due to the effective crack length being smaller than the measured crack length, a discrepancy exists between the calculated curve from the analytical method and the experimental curve. To address this issue, a modified method is proposed by establishing a relationship between the effective and measured crack lengths to improve the crack-length representation used in the analytical determination of the crack extension resistance curve. According to the modified method, the recalculated crack extension resistance curves exhibit good agreement with experimental curves. This indicates that the improved crack-length representation can enhance the reliability of the analytical determination of the crack extension resistance curve for the dam concrete investigated in this study.

Key Words
crack extension length; crack extension resistance curve; dam concrete; fracture mechanics

Address
Xingyu Zheng, Mengdi Jia: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, 116024, P.R. China
Zhimin Wu: School of Civil Engineering and Architecture, Zhejiang University of Science & Technology, Hangzhou, 310023, P.R. China

Abstract
Incorporating recycled aggregates into concrete and confining within steel tube leads to an efficient structural member called as recycled aggregate concrete-filled steel tube (RA-CFST) column, offering a sustainable solution for reusing construction and demolition waste. This study investigates the axial compressive behavior of RA-CFST columns with square and rectangular cross-sections and develops an artificial neural network (ANN)-based predictive model for ultimate load capacity. The effects of recycled coarse aggregate content, concrete strength, and steel tube properties are considered. The proposed ANN model is trained and validated using experimental data from RA-CFST specimens tested in compression. Results demonstrate that the ANN model significantly outperforms existing design approaches, including EC4 and GJB formulations, in predicting axial load capacity. The findings confirm that recycled aggregates can be effectively utilized in CFST columns without compromising structural performance, while the developed model provides a reliable and accurate prediction tool for design purposes.

Key Words
artificial neural network; axial load capacity; predictive model; recycled aggregate; ultimate strength

Address
Süleyman İpek: Department of Civil Engineering, Yaşar University, 35100, İzmir, Türkiye
Ayşegül Erdoğan: Department of Architecture, Gaziantep University, 27310, Gaziantep, Türkiye
Esra Mete Güneyisi: Department of Civil Engineering, Gaziantep University, 27310, Gaziantep, Türkiye
Erhan Güneyisi: Department of Civil Engineering, Harran University, 63300, Şanliurfa, Türkiye

Abstract
In this study, the importance of the balanced reinforcement ratio in reinforced concrete beams, which are horizontal load-bearing structural elements, is examined, and a theoretical formulation for trapezoidal reinforced concrete beams is derived and validated through finite element method-based numerical analyses. Based on existing formulations for rectangular reinforced concrete beams available in the literature, a balanced reinforcement ratio expression is developed for trapezoidal sections. The obtained formula indicates that the balanced reinforcement ratio depends on material strengths and the section width ratio b1/b2. Using this formulation, beam models with balanced, under-reinforced, and over-reinforced ratios are created. In addition, the flexural behavior was monitored via the finite element analysis (FEA). Moment-curvature relationships obtained from the analysis indicated that the beams perform brittle behavior in the case of balanced and over-reinforced conditions while they perform ductile behavior when they are in the under-reinforced condition. Ultimately, the derived balanced reinforcement ratio formulation was validated using FEA.

Key Words
balanced reinforcement ratio; ductile and brittle failure; nonlinear analysis; reinforced concrete beam; trapezoidal cross-section

Address
Haci Tektaş, Kasim Mermerdaş: Civil Engineering Department, Harran University, Şanliurfa, Türkiye
Süleyman Ipek: Civil Engineering Department, Yaşar University, İzmir, Türkiye

Abstract
Strength development represents the interaction between steel and concrete; it is an area of active research. Many models simplify the stress distribution along the embedment length of steel reinforcement for ease of approximation. However, in reality, the stress distribution at the steel-concrete interface is complex, non-linear, and is affected by several factors. The current manuscript details the development and validation of a new cyclic shear-lag piece-wise linear material model that can be used to accurately depict the local-interfacial bond condition of the steel reinforcement embedded in concrete with a variety of end hook conditions. The presented model holds superiority over the past published research models for its simplicity and accuracy, with 2.1% average error as compared to the experimental data, which demonstrates the model's advantage, leading to ease of application in numerical analysis. The bond behavior of the steel reinforcement is analytically modeled as a non-linear interface. The deformational response to the cyclic loading is divided into six potions three for the compression push-in and three for tension pull-out. Stiffness cycling, i.e., degradation and recovery owing to crack opening and closure because of lateral pressure, along with Poisson's ratio effects, are included in the current model. The phenomenon of multiple crack extension, crack coalescence, and stress shielding has been taken into consideration in the presented model. The validity of the presented model is ascertained by comparing the predicted cyclic deformational response to the numerical simulation as well as experimental results, and a good agreement is ascertained. The presented piecewise linear cyclic shear-lag model can be used to simulate the multi-crack extension deformational response of a variety of steel reinforcement embedded in concrete.

Key Words
AI numerical validation; analytical model; crack coalescence; crack curing; cyclic loading; experimental validation; multi-crack extension; Poisson's ratio effect; simplified stiffness cycling; stress shielding

Address
Department of Mechanical and Energy Engineering, College of Engineering, Imam Abdulrahman Bin Faisal University, P.O. Box 1982, Dammam 31441, Eastern Province, Kingdom of Saudi Arabia

Abstract
This study proposes new analytical and numerical models for concrete compression members strengthened with FRP. Two large databases were developed from published studies. The first database included 500 FRP-wrapped concrete specimens. The second database contained 282 FRP-reinforced concrete columns with FRP bars, hoops, and spirals. Existing confinement and axial capacity models were critically assessed using statistical indices. A new nonlinear confinement relationship was developed. It achieved an R2 of 0.91 and an RMSE of 0.18, outperforming previous models. A new axial capacity model for FRP-reinforced columns was also proposed. It showed an R2 of 0.741, compared to 0.71 for the best existing model. A detailed finite element model was developed in ABAQUS and validated against experimental results. The mean error between experiments and FE predictions was 3.23% for axial capacity and 11.83% for axial deformation. For FRP-tube-wrapped members, the average difference in axial capacity was 4.67%. A parametric study of 220 models was conducted. Increasing the FRP longitudinal ratio from 1.2% to 2.2% increased axial capacity by up to 179%. Increasing column diameter from 100 mm to 350 mm led to capacity gains exceeding 2000%. Strong agreement was found between FE results and the proposed analytical model, with R2=0.95. The proposed models provide accurate and practical tools for design of FRP-strengthened compression members.

Key Words
axial capacity; concrete compression members; confinement model; finite element analysis; FRP confinement; FRP-reinforced columns

Address
Mohd Ahmed: 1) Department of Civil Engineering, College of Engineering, King Khalid University, Abha, 61421, Saudi Arabia; 2) Center for Engineering and Technology Innovations, King Khalid University, Abha 61421, Saudi Arabia
Anwar Ahmed: Department of Civil Engineering, College of Engineering, Northern Border University, Arar 73222, Saudi Arabia
Umara Nasir: Department of Civil Engineering, University of Engineering and Technology Taxila, 47050, Pakistan

Abstract
Substantial quantities of waste bricks are produced in urban renewal projects, and recycled brick coarse aggregate (RBCA) can be combined with natural pebbles to prepare recycled brick-pebble aggregate concrete (RBPC). However, the mechanical properties of RBPC under different strength grades, aggregate gradations, and substitution ratio (SR) remain insufficiently understood. Therefore, the mechanical properties of RBPC were investigated. The findings are as follows: (1) Pebble concrete fails at the pebble-mortar interface; RBPC exhibits more RBCA splitting. (2) RBPC with 25% an SR of SR shows higher compressive and tensile strength than 0% and 50% SR. The 5-31.5 mm aggregate increases its compressive strength by ~10% and tensile strength by ~30% vs 5-16 mm. (3) The elastic modulus decreases as the SR increases; both peak stress and strain are maximized at 25% SR. (4) A stress-strain relationship has been proposed, and can be used in ABAQUS to accurately simulate the tests.

Key Words
particle size of coarse aggregate; RBPC; substitution ratio; the stress-strain relationship

Address
Biao Liu: 1) Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education, Northwest A&F University, Yangling 712100, China; 2) College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling 712100, China
Zhaoyu Zheng, Linshu Wang, Kaiwen Zhang, Ao Zhao: College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling 712100, China

Abstract
To address the limitations of traditional analytical models with excessive simplification and the finite element method (FEM) with severe meshing bottlenecks in predicting the macroscopic mechanical properties of reinforced concrete (RC) slabs, this paper establishes a fast Fourier transform (FFT)-based multi-scale computational homogenization framework. First, a two-phase plain concrete representative volume element (RVE) model is constructed to obtain equivalent matrix parameters, and an RC voxel model that explicitly incorporates reinforcement and the interfacial transition zone (ITZ) is subsequently developed. The accuracy and efficiency of the FFT method are verified by comparing the stress field distribution and effective elastic moduli with those obtained from high-precision FEM solutions. On this basis, the effects of reinforcement ratio, orthotropic characteristics, concrete creep, reinforcement corrosion, and material parameter variability on the effective elastic modulus of RC slabs are quantitatively analyzed. The results show that the FFT method avoids complex mesh generation, has higher computational efficiency and stability than FEM, and controls the relative error of effective modulus prediction within 2%. The reinforcement ratio is positively correlated with the elastic modulus of RC, and the FFT method can accurately capture the Poisson constraint strengthening effect of bidirectional reinforcement, which corrects the prediction deviation of traditional one-dimensional theories on material orthotropy. Under long-term service conditions, concrete creep is the dominant factor leading to the stiffness degradation of RC structures, whereas uniform reinforcement corrosion (within a rate range of 0%-20%) has a relatively minor impact on macroscopic elastic stiffness. The sensitivity analysis indicates that the elastic modulus of the concrete matrix is the core parameter affecting the overall stiffness of the composite, and the variability of steel modulus has little influence. This study provides an efficient and high-precision numerical method for multi-scale performance prediction and durability evaluation of hydraulic RC structures.

Key Words
computational homogenization; creep and corrosion; effective elastic modulus; fast fourier transform (FFT); poisson constraint effect; reinforced concrete slab

Address
Hubei Key Laboratory of Construction and Management in Hydropower Engineering, and College of Hydraulic and Environmental Engineering, China Three Gorges University, Yichang, 443000, China

Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2026 Techno-Press ALL RIGHTS RESERVED.
P.O. Box 33, Yuseong, Daejeon 34186 Korea.
General Inquiries: info@techno-press.com / Journal Administration: admin@techno-press.com