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.
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.
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.
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 pullout. 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.
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 similar to 10% and tensile strength by similar to 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.
