Papers by Keyword: Bond-Slip

Abstract: This paper presents a study from an ongoing research project on the bond performance of flexural prisms strengthened using carbon-fiber-reinforced polymer (CFRP) laminates. The primary objective is to evaluate the effect of normal-strength concrete (NSC – 30MPa) and high-strength concrete (HSC - 50MPa) on the bond performance of plain concrete prisms notched at the mid-span and strengthened using CFRP laminates. Six of the twelve plain concrete prisms were strengthened using CFRP laminates, while the remaining prisms were unstrengthened to serve as control specimens. After achieving 28 days of curing in standard lab conditions, all prisms were tested under a four-point bending test. The ultimate mid-span deflection, maximum and ultimate strains at the mid-span, strain distribution at different positions along the length of the laminate, and bond/shear stress versus slip were analyzed to evaluate the bond performance of flexural prisms. The average ultimate load-carrying capacities and mid-span deflection of the NSC and HSC groups were 31.33 and 35.02 kN and 0.55 and 1.54 mm, respectively. The average CFRP strain values at the mid-span corresponding to the ultimate load were 5005 and 3544 με for the NSC and HSC groups, respectively. The maximum attained bond-stress values for NSC and HSC groups were 1.71 and 1.42 MPa, respectively. The corresponding values for slip at maximum bond stress are 0.27 and 0.24 mm for the two groups, respectively. It was concluded from the study that the concrete compressive strength has minimal effect on the flexural bond performance of concrete prisms externally bonded with CFRP laminates.

Abstract: Epoxy coated reinforcements have been used extensively in bridge decks and substructures to protect against corrosion brought on by de-icing salts or marine environments. They need longer development lengths because of poor bond to concrete and special treatments on sites due to vulnerability of damage during transportation, storage and bending process. A new method of pre-heating of reinforcement before coating process using an IGBT(Insulated Gate Bipolar Transistor) control was applied to improve the bond of epoxy coating to reinforcements. In this paper, the bond-slip properties of newly developed epoxy coated bars are investigated and compared to those of black bars. The direct pull out test according to EN Standard was used with varying the diameters of reinforcements. The experimental results show that the new process is very efficient in increasing bond capacity of epoxy coated bars to concrete comparing those of traditional ones.

Abstract: An Ultra High Performance Concrete (UHPC) exhibits very high compressive and tensile strength and excellent durability comparing to those of the conventional concrete. The applications of UHPC to precast and/or prestressed concrete result the optimum utilization of high strength characteristics. This paper experimentally investigates the bond-slip behaviors between prestressing strands and UHPC in pretnesioned members. The diameters of strands, 12.7mm and 15.2mm, the cover depths and tensioning forces are chosen as variables, which are known to affect the bond behaviors. The bond-slip curves for various specimens are obtained and the equations for bond strengths of UHPC are derived based on experiments.

Abstract: A new simple, efficient and accurate finite element model denoted as FEM-B is developed for the analysis of structural behavior of FRP strengthened RC beams with bond-slip effect. Geometric nonlinearity and material nonlinear properties of concrete and steel rebar are accounted for this model. Concrete, steel, FRP and adhesive are modelled as Solid 65, Link 180, Shell181 and Solid 45 respectively. Concrete is modelled using Nitereka and Neal’s model for compression, isotropic and linear elastic model before cracking for tension and strength gradually reduces to zero after cracking, whereas steel is assumed to be elastic perfectly plastic material. The material of FRP is considered to be linearly elastic until rupture, and adhesive is assumed to be linearly elastic. The bond slip between concrete, adhesive and FRP is based on the bilinear law, which is modelled using spring element Combin 39.The developed new finite element model FEM-B is validated against experimental results, and demonstrates to be effective for the structural analysis of FRP strengthened RC beams.

Abstract: The bond between prestressing (PS) steel and concrete plays an important role in pretensioned concrete members because the pretension force is directly transferred from PS steel to concrete by cutting or releasing the PS steels at the end of the members. While in capacity design approaches, designing for bond is considered to be a question of adequate strength along the bar length, in performance-based design approaches, the level of deformation as well as bond strength must be known and the bond-slip curves may give enough information. The purpose of this paper is to derive bond-slip curves for various tensioning forces within Korean design Code experimentally. For this purpose several series of tests have been conducted with different cover depths and tensioning forces. A realistic bond-slip curve is proposed which may be the base for more rational design of pretensioned concrete members.

Abstract: According to the previous experimental research on bond-slip, select push-out test as experimental method research on bond-slip between cold-formed thin-walled steel and foam concrete. Through the observation of the specimens in the push-out test, combining with the natural bonding mechanism and influencing factors summarized the failure mode and its law of composite member. The reference and basis for the experimental research and theoretical analysis of it in the future are provided.

Abstract: The RC beams strengthened by externally bonded steel plates are regarded as composite beams which consist of steel plates and reinforced concrete with bond-slip. Based on the deformation compatibility relationship between steel plates and reinforced concrete, the constitutive relationship which can reflect the mechanical properties of steel plates and reinforced concrete and the bond-slip constitutive law, a nonlinear differential equation for the beam, expressed in the form of the tensile force of steel plates, is derived. A nonlinear analytical solution under the double concentrated load of the RC beams strengthened by externally bonded steel plates is obtained. By which a coordination coefficient in the form of the characteristic value of the beam is deduced. By using the coordination coefficient, a practical nonlinear analysis method, which can exactly reflect the bearing capacity and deformation of the beam is established.

Abstract: In this paper, several FRP-reinforced concrete beams are modelled using a recently developed one-dimensional two-node layered composite beam element which accounts for the bond-slip between reinforcing bars and the surrounding concrete. Effect of different surfaces of FRP reinforcing bars on the structural response of FRP-reinforced concrete beams with bond-slip effect is also investigated. It is found that the type of rebar surface has a significant influence on bond strength and structural behaviour, and that the grain-covered surface provides the best bond between the FRP rebars and concrete, the smooth surface the worst, and FRP rebars with ribbed and braided surfaces perform similarly. Keywords: Bond-slip; Composite beam element; FRP-reinforced concrete beam; Nonlinear finite element analysis

Abstract: This paper presents the experimental results of CFRP plated steel blocks in wet and dry conditions using saltwater. A total of 9 pull test specimens were tested that was divided into two groups; normal and heated saltwater at room temperature and 50°C, respectively. The purpose of this test is to investigate the changes in the debonding capacity of the CFRP plated steel blocks. It was found that both systems showed insignificant increase in bond strength. However, the stiffness of the bonding system increased as the temperature of the saltwater was increased, suggesting the effect of post curing of the adhesive.

Abstract: In consideration of the light weight, high strength, corrosion resistance and construction is convenient of carbon fiber reinforced polymer (CFRP), using CFRP to strengthen structure is becoming more and more widely. However, there is no commonly accepted understanding of the constitutive relationship of the bonding shear stress and slip between concrete and CFRP bonded interface, especially the decline of the constitutive relation is more difficult to measure accurately. An aim of this paper is to improve the experiment to explore bond stress and slip (τδ) constitutive relation of the bonding interface, strive for the experiment to measure the τδ constitutive relation curve of CFRP-concrete interface. Double pull test was proposed with the improved specimen, using the horizontal load, eliminate additional bending moment influence and improve the experimental accuracy. 17 specimens were tested to measure the τδ curves, according to the features of the constitutive relation curves, the mechanical characteristics of the bonding interface was further analysised.