Papers by Author: Pei Yan Huang

Abstract: Peeling along the interface between FRP and concrete under fatigue load is the common failure pattern for the RC structures strengthened with FRP. In this paper, five groups specimens were subjected to fatigue load to study the fatigue mechanism for bonding interface between carbon fiber laminate (CFL) and concrete. The Δσ~N curves for the bonding interface were derived from the experiments, the laws of strains and slip on interface were analyzed in this paper.

Abstract: Fatigue behavior of reinforced concrete (RC) beam can be improved by externally bonded fiber reinforced polymer (FRP). However, propagation behavior of a crack on the RC beam will have serious effect on the fatigue life of the beam strengthened with FRP. In this paper, a finite element (FE) procedure was developed to analysis the stress intensity factor (SIF) of the main crack and an experimental study was conducted to investigate the propagation rate of the main crack of the RC beam strengthened with carbon fiber laminate (CFL) under cyclic bending load. The FE analysis results show that the SIF near the main crack tip increases at the beginning and then decreases with the fatigue crack propagation. When relative crack length α is equal to 0.3, the SIF is maximum. When α approaches 0.75, the SIF approaches zero. A total of 3 RC beams strengthened with CFL were tested. The experimental results show that it is possible to divide the process of the crack propagation into three distinct phases, including crack initiation and then quickly propagation, stable propagation and then rest and unstable propagation. A semi-empirical equation based on the Paris Law was developed to predict the crack propagation rate.

Abstract: Fiber reinforced polymer (FRP) is widely applied in the concrete and steel structure reinforcement field because of its high strength and convenient constructability in civil engineering. The adhesive joint is the weakness of the reinforced structure, but with the complicated stress distribution for analytic method. Numerical method provides the best solution to the further analysis. In this paper, a finite element method (FEM) of double lap joint model was established with ANSYS to investigate the shear stress in the adhesive joint of the reinforced structure, the shear stresses were analyzed in detail in both length and thickness direction in civil engineering. The results show that, 1) the FEM calculation results of shear stress of adhesive and the theoretical calculation values are consistent within the main part of the adhesive; 2) FEM is the effective method to further study the shear stress distribution of the adhesive, meshing size has great influence on the results of calculation; 3) to obtain more accurate analysis of shear stress distribution, the non-linear characteristics of the adhesive should be considered

Abstract: Defects like surface crack often appear in steel structures. To ensure the structural integrity and security, the new material such as fiber reinforced polymer (FRP) was adopted for strengthening and repairing. In this paper, three dimensional semi-elliptic surface crack in steel tension specimen strengthened with carbon fiber laminate (CFL) was studied, and numerical analysis was undertaken by Abaqus finite element software to study the stress intensity factor (SIF, KI) of the surface crack for CFL reinforcement effect. The results showed that, strengthening effect of CFL in front side was better than the back side of the steel plate; Crack shape ratio, a/c, had greater influence on strengthening effect in front side compared with little effect in the back side; The changes of crack relative depth, a/B, affected strengthening effect.

Abstract: The fatigue performance and durability of the reinforced concrete (RC) beams strengthened with fibre reinforced polymer (FRP) laminates is an advanced research topic in civil engineering. The crack propagation life is the dominant part of the whole fatigue life of the cracked RC members strengthened with FRP laminates under cyclic loads. In this paper, a theoretical and experimental study was conducted to investigate the rule of the fatigue crack propagation of the RC beams strengthened with carbon FRP (CFRP) under constant cyclic bending load. A total of 5 RC beams with sizes 1850×100×200mm strengthened with CFRP were tested. The results show that it is possible to divide the process of the crack propagation into three distinct phases, including crack initiation and then quickly propagation (Phase I), stable propagation and then rest (Phase II) and unstable propagation (Phase III). In accordance with Paris-Erdogan Law, a semi-empirical equation was developed to predict the crack propagation rate. The empirical coefficients of the equation were obtained from the fatigue test results. To validate this equation, the predicted fatigue life of crack propagation calculated by it is compared with the data obtained from tests. It shows the agreement is good.

Abstract: Debonding failure mode usually occurs in the concrete structure flexural strengthened with fiber reinforced polymer (FRP) under cyclic loading. This paper presents an experimental investigation into the fatigue behavior of the FRP-concrete interface of reinforced concrete (RC) beams strengthened with prestressed FRP. 8 small-scale beams were tested under three-point bending cyclic loading. The propagation behavior of the fatigue interface cracks is addressed, and curves showing the growth law of interface cracks are presented. Results from these tests show that the propagation process of interface cracks had three stages, including rapid, stable and unstable growth. The stable propagation phase experienced the most part of the whole test, and the failure mode of all failed beams was debonding following the fatigue fracture of the tensile steel bars. In addition, the influence of FRP prestressing level on the fatigue lives of strengthened beams is discussed, and an empirical formula is developed to predict the fatigue lives of such members. The results show that the fatigue life increases with the prestressed level of FRP. This study provides an insight on the potential long-term performance of FRP-strengthened beams submitted to fatigue loading conditions.

Abstract: Fiber Reinforced Polymer (FRP) has been effectively used for strengthening concrete beams. In this study, nonlinear finite element (FE) model of the beam strengthened with CFRP is established to analyze the debonding failure caused by the adhesive hollow defects. The constitutive relationship of the adhesive layer in the FE models is similar to Monti’s bi-linear mode. Three different locations of the hollows are considered in the FE models. The principal stresses in the concrete, the debonding stresses in the adhesive and the stress in CFRP are calculated. The results show that the effect of the locations of the hollow is marginal on the principal stresses in the concrete. When the hollow appears close to the interfacial end, the debonding stresses in the adhesive and the shear stress in the CFRP are significant, which easily causes the debonding failure.

Abstract: Intermediate crack debonding is a common failure mode of reinforced concrete (RC) beam flexurally strengthened with externally bonded prestressed fiber reinforced polymer (FRP). This study analyzes the effects of flexural cracks and interface softening behavior on the interface shear stress of RC beam strengthened with prestressed FRP under three-point bending loads, and presents an analytical solution for the FRP axial force at the flexural crack section of the strengthened beam. By regarding the interface fracture energy as the debonding criterion, a new theoretical model to predict the debonding load-carrying capacity of RC beam strengthened with prestressed FRP is proposed.

Abstract: Based on time-dependent reliability theory, intermediate working state is considered, combining with current specifications, concrete filled steel tubular (CFST) arch bridge is discussed as a case, determination principle of three-stage mode is given. The direct correspondence from reliability indices to working states is made clear consequently. Introducing state variables, dynamic Monte-carlo method is presented. Basic formulas of failure probability and damage probability are derived by variable time increment method. The bridge is an CFST arch bridge with 83.6 meter-span, which operated for 10 years. According to test result, dynamic Monte-carlo method is used to estimate the reliability of this bridge. The analysis result shows that, in the tenth year, both damage reliability index and failure reliability index are above target reliability index. The example bridge is in safe working state at present. This conclusion is consistent with the facts.

Abstract: Concrete is assumed as a three-phase composite material composed by aggregate, mortar matrix and the bond layer between them in mesoscopic. The damage constitutive relationships of the composed materials are determined. A local meso-model of reinforced concrete (RC) beams strengthened with hybrid FRP was established to investigate the crack propagation and failure modes. The results show that the deformation, damage and failure of the concrete occurred near the ends of the interface.