Pei Yan Huang

Fatigue Life Prediction of RC Beams Strengthened with Prestressed CFRP under Cyclic Bending Loads

The application of prestressed carbon reinforced polymer (prestressed CFRP) in reinforced concrete (RC) members can improve the mechanical properties of strengthened structures and strengthening efficiency. This paper proposed a semi-empirical prediction formula of fatigue lives of the RC beams strengthened with prestressed CFRP under bending loads. The formula is established based on the fatigue life prediction method of RC beams and fatigue experimental data of non-prestressed CFRP reinforced beams done before. Fatigue effect coefficient of the formula was confirmed by the fatigue experiments of the RC beams strengthened with prestressed carbon fiber laminate (prestressed CFL) under cyclic bending loads. Fatigue lives of the strengthened beams predicted using the formula agreed well with the experimental data.

Numerical Analysis of KI of Semi-Elliptical Surface Crack in Steel Structure Strengthened with FRP under Tensile Load

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.

Mesoscopic Numerical Computation of Compressive Strength and Damage Mechanism of Rubber Concrete

Evaluations of both macroscopic and mesoscopic strengths of materials have been the topic of a great deal of recent research. This paper presents the results of a study, based on the Walraven equation of the production of a mesoscopic random aggregate structure containing various rubber contents and aggregate sizes. On a mesoscopic scale, the damage mechanism in the rubber concrete and the effects of the rubber content and aggregate-mortar interface on the rubber concrete’s compressive resistance property were studied. The results indicate that the random aggregate structural model very closely approximates the experimental results in terms of the fracture distribution and damage characteristics under uniaxial compression. The aggregate-mortar interface mechanical properties have a substantial impact on the test sample’s strength and fracture distribution. As the rubber content increases, the compressive strength and elastic modulus of the test sample decrease proportionally. This paper presents graphics of the entire process from fracture propagation to structural failure of the test piece by means of the mesoscopic finite-element method, which provides a theoretical reference for studying the damage mechanism in rubber concrete and performing parametric calculations.

Debonding Prediction of RC Beam Flexurally Strengthened with Prestressed FPR

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.

Experimental Studies on Axially Loaded Concrete Columns Confined by Different Materials

The improvement of the load carrying capacity of concrete columns under a triaxial compressive stress results from the strain restriction. Under a triaxial stress state, the capacity of the deformation of concrete is greatly decreased with the increase of the side compression. Therefore, confining the deformation in the lateral orientation is an effective way to improve the strength and ductility of concrete columns. This paper carried out an experimental investigation on axially loaded normal strength concrete columns confined by 10 different types of materials, including steel tube, glass fiber confined steel tube (GFRP), PVC tube, carbon fiber confined PVC tube (CFRP), glass fiber confined PVC tube (GFRP), CFRP, GFRP, polyethylene (PE), PE hybrid CFRP and PE hybrid GFRP. The deformation, macroscopical deformation characters, failure mechanism and failure modes are studied in this paper. The ultimate bearing capacity of these 10 types of confined concrete columns and the influences of the confining materials on the ultimate bearing capacity are obtained. The advantages and disadvantages of these 10 types of confining methods are compared.

Fatigue Crack Propagation Behavior of RC Beams Strengthened with CFRP under High Temperature and High Humidity Environment

Numerical and experimental methods were applied to investigate fatigue crack propagation behavior of reinforced concrete (RC) beams strengthened with a new type carbon fiber reinforced polymer (CFRP) named as carbon fiber laminate (CFL) subjected to hot-wet environment. -integral of a central crack in the strengthened beam under three-point bending load was calculated by ABAQUS. In finite element model, simulation of CFL-concrete interface was based on the bilinear cohesive zone model under hot-wet environment and indoor atmosphere. And, then, fatigue crack propagation tests were carried out under high temperature and high humidity (50°C, 95% R · H) environment pretreatment and indoor atmosphere (23°C, 78% R · H) to obtain curves and crack propagation rate, , of the strengthened beams. Paris-Erdogan formula was developed based on the numerical analysis and environmental fatigue tests.

Prestress Loss of CFL in a Prestressing Process for Strengthening RC Beams

A prestressing system was designed to strengthen reinforced concrete (RC) beams with prestressed carbon fiber laminate (CFL). During different prestressing processes, prestress loss was measured using strain gauges attached on the surface of CFL along the length direction. The prestress loss was 50–68% of the whole prestress loss, which is typically associated with CFL slipping between the grip anchors. Approximately 20–27% of the prestress loss was caused by the elastic shortening of the RC beam. An analytical model using linear-elastic theory was constructed to calculate the prestress loss caused by CFL slipping between the anchors and the elastic shortening of the strengthened beams. The compared results showed that the analytical model of prestress loss can describe the experimental data well. Methods of reducing the prestress loss were also suggested. Compared to other experiments, the prestressing system proposed by this research group was effective because the maximum percentage of prestress loss was 14.9% and the average prestress loss was 12.5%.

Experimental Study on Bond Behavior of FRP-Concrete Interface in Hygrothermal Environment

As the technique of fiber-reinforced polymer (FRP) composite material strengthened reinforced concrete structures is widely used in the field of civil engineering, durability of the strengthened structures has attracted more attention in recent years. Hygrothermal environment has an adverse effect on the bond behavior of the interface between FRP and concrete. This paper focuses on the bond durability of carbon fiber laminate- (CFL-) concrete interface in hygrothermal condition which simulates the climate characteristic in South China. Twenty 100 mm × 100 mm × 720 mm specimens were divided into 6 groups based on different temperature and humidity. After pretreatment in hygrothermal environment, the specimens were tested using double shear method. Strain gauges bonded along the CFL surface and linear variation displacement transducers (LVDTs) were used to measure longitudinal strains and slip of the interface. Failure mode, ultimate capacity, load-deflection relationship, and relative slip were analyzed. The bond behavior of FRP-concrete interface under hygrothermal environment was studied. Results show that the ultimate bearing capacity of the interface reduced after exposure to hygrothermal environments. The decreasing ranges were up to 27.9% after exposure at high temperature and humidity (60°C, 95% RH). The maximum strains () of the specimens pretreated decreased obviously which indicated decay of the bond behavior after exposure to the hygrothermal environment.

Main Crack Propagation Behaviour of RC Beams Strengthened with CFRP under Fatigue Load

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.

Prediction of Bond Strength of FRP-Concrete Based on Multiple Linear Regression Method

External bonding of fiber reinforced polymer (FRP) plates or sheets composites has become a popular technique for strengthening concrete structures all over the world. The bond strength between FRP and concrete is a key factor controlling debonding failure of various forms in FRP-strengthened concrete structures. Based on the test data, the bond strength model of FRP-concrete was proposed using multiple linear regression and dimensional analysis, in which the effect of multiple factors on dependent was considered. Finally, the proposed model was verified through the test data, and then compared with 12 bond strength models have been found in the existing literature. The result shows that the proposed model has a better accuracy. It can be used to predict the bond strength of FRP-concrete.