Experimental and Numerical Investigation of Bond-Slip Behavior of High-Strength Reinforced Concrete at Service Load

A bond mechanism at the reinforcement-concrete interface is one of the key sources of the comprehensive functioning of reinforced concrete (RC) structures. In order to apprehend the bond mechanism, the study on bond stress and slip relation (henceforth referred as bond-slip) is necessary. On this subject, experimental and numerical investigations were performed on short RC tensile specimens. A double pull-out test with pre-installed electrical strain gauge sensors inside the modified embedded rebar was performed in the experimental part. Numerically, a three dimensional rib scale model was designed and finite element analysis was performed. The compatibility and reliability of the numerical model was verified by comparing its strain result with an experimentally obtained one. Afterwards, based on stress transfer approach, the bond-slip relations were calculated from the extracted strain results. The maximum disparity between experimental and numerical investigation was found as 19.5% in case of strain data and 7% for the bond-slip relation at the highest load level (110 kN). Moreover, the bond-slip curves at different load levels were compared with the bond-slip model established in CEB-fib Model Code 2010 (MC2010). Overall, in the present study, strain monitoring through the experimental tool and finite element modelling have accomplished a broader picture of the bond mechanism at the reinforcement-concrete interface through their bond-slip relationship.

Study of the Interfacial Bond Behavior between CFRP Grid–PCM Reinforcing Layer and Concrete via a Simplified Mechanical Model

This paper presents the results of pull-out tests conducted to investigate the interfacial bond behavior between a carbon-fiber-reinforced polymer (CFRP) grid–polymer cement mortar (PCM) reinforcing layer and existing concrete, and proposes a simplified mechanical model to further study the interface bond mechanism. Four specimens composed of a CFRP grid, PCM, and concrete were tested. The influence of the type of CFRP grid and the grid interval on the interface bond behavior was discussed. The failure patterns, maximum tensile loads, and CFRP grid strains were obtained. The change process of interface bond stress was investigated based on the grid strain analysis. In addition, the simplified mechanical model and finite element model (FEM) were emphatically established, and the adaptability of the simplified mechanical model was validated through the comparative analysis between the FEM results and the test results. The research results indicate that a CFRP grid with a larger cross-sectional area and smaller grid interval could effectively improve the interface bond behavior. The tensile stress was gradually transferred from the loaded edge to the free edge in the CFRP grid. The interface bond behavior was mainly dependent on the anchorage action of the CFRP grid in the PCM, and the bond action between the PCM and the concrete. The FEM results were consistent with the test results, and the simplified mechanical model with nonlinear springs could well describe the interface bond mechanism between the CFRP grid–PCM reinforcing layer and concrete.

Verification of the chemical subsystem of the regional climate model RegCM-CHEM4

New simulation results, obtained from the chemical version of the regional climate model RegCMCHEM4, are presented for Siberian region. The verification of the chemical subsystem of the model with non-hydrostatic dynamical core is carried out using the atmospheric chemical transfer scheme CBMZ (Carbon Bond Mechanism-Z). To define chemical emissions the global RCP (Representative Concentration Pathways) emission dataset prepared by the International Institute for Applied Systems Analysis (IIASA), is used. For gas phase species, we have prepared the 6 hourly chemical boundary conditions from our modified version of the Model for Ozone and Related chemical Tracers, version 4 (MOZART-4). Quantitative estimates of methane emission in the atmosphere of the Siberian region have been obtained.

Finite Element Analysis of Corrosion and Bond-Slip

Although reinforced concrete (RC) has an important advantage that it has virtue durability against an environmental attack, especially the resistance of corrosion of embedded reinforcements, due to the high alkalinity nature of concrete property, unfortunately, the problems of reinforcement corrosion still exist in many reinforced concrete structures. It has brought out many questions on the safety and serviceability of these corroded RC structures. Thus, it needs more effective approach for structural performance evaluation of the corroded structures. The residual capacity of the corroded reinforcement was determined through the evaluation of the volume increase of reinforcing steel and concrete crack propagation. The final determination of the service life of concrete structures was made based on the above evaluation results. Also, the effects of reinforcement corrosion on structural behaviours of RC members are investigated so that the reliable evaluation of structural performances of corroded RC members can be achieved by finite element method (FEM). The corrosion attack penetration has been given as a function of the time as input in the analyses. The load of corrosion applied inside the structural members can be modelled by the displacement around the circumferential surface between the reinforcing bars and concrete. The reduction of capability of the structures is determined from the corrosion level in the service years. Another complex phenomenon that governs concrete behaviour is the transfer of shear force across the interface by bond mechanism between concrete and steel reinforcement. It is a fundamental to most aspects of concrete behaviour. The bond mechanism is influenced by multiple parameters, such as the strength of the surrounding structures, the occurrence of splitting cracks in the concrete and the yielding of the reinforcement. However, when RC structures are analysed using the FEM, it is quite common to assume that the bond stress depends solely on the slip between the bars and concrete. In this the research the relationship of bond slip is also studied using FEM. An analytical study based on fracture mechanics was earned out to investigate the behaviour of three different types of specimens. In recent RC research, finite element modelling techniques have been developed to quickly evaluate the physical phenomena associated with cracking and bond. The non-linear finite element program ATENA with the non-linear material models for concrete, reinforcement bar and bond-slip is used to analyse cracking propagation and bond failure process. The influence between corrosion and bond slip in RC structure is also studied. Therefore, the understanding of serviceability of RC structure is improved. It was concluded that with the increase of load and the propagation of the crack, stress redistributed in the steel- continues until the specimen is damaged. The non-linear finite element fracture analysis shows that non-linear fracture mechanics can be effectively applied to investigate concrete fracture. Also, comparisons between the analyses of crack propagation and stress redistribution obtained using the finite element analysis was in good agreement with tests found in the literature.

Finite Element Analysis of Corrosion and Bond-Slip

Although reinforced concrete (RC) has an important advantage that it has virtue durability against an environmental attack, especially the resistance of corrosion of embedded reinforcements, due to the high alkalinity nature of concrete property, unfortunately, the problems of reinforcement corrosion still exist in many reinforced concrete structures. It has brought out many questions on the safety and serviceability of these corroded RC structures. Thus, it needs more effective approach for structural performance evaluation of the corroded structures. The residual capacity of the corroded reinforcement was determined through the evaluation of the volume increase of reinforcing steel and concrete crack propagation. The final determination of the service life of concrete structures was made based on the above evaluation results. Also, the effects of reinforcement corrosion on structural behaviours of RC members are investigated so that the reliable evaluation of structural performances of corroded RC members can be achieved by finite element method (FEM). The corrosion attack penetration has been given as a function of the time as input in the analyses. The load of corrosion applied inside the structural members can be modelled by the displacement around the circumferential surface between the reinforcing bars and concrete. The reduction of capability of the structures is determined from the corrosion level in the service years. Another complex phenomenon that governs concrete behaviour is the transfer of shear force across the interface by bond mechanism between concrete and steel reinforcement. It is a fundamental to most aspects of concrete behaviour. The bond mechanism is influenced by multiple parameters, such as the strength of the surrounding structures, the occurrence of splitting cracks in the concrete and the yielding of the reinforcement. However, when RC structures are analysed using the FEM, it is quite common to assume that the bond stress depends solely on the slip between the bars and concrete. In this the research the relationship of bond slip is also studied using FEM. An analytical study based on fracture mechanics was earned out to investigate the behaviour of three different types of specimens. In recent RC research, finite element modelling techniques have been developed to quickly evaluate the physical phenomena associated with cracking and bond. The non-linear finite element program ATENA with the non-linear material models for concrete, reinforcement bar and bond-slip is used to analyse cracking propagation and bond failure process. The influence between corrosion and bond slip in RC structure is also studied. Therefore, the understanding of serviceability of RC structure is improved. It was concluded that with the increase of load and the propagation of the crack, stress redistributed in the steel- continues until the specimen is damaged. The non-linear finite element fracture analysis shows that non-linear fracture mechanics can be effectively applied to investigate concrete fracture. Also, comparisons between the analyses of crack propagation and stress redistribution obtained using the finite element analysis was in good agreement with tests found in the literature.

Bearing Resistance and Failure Mode of Bolted-layered Cemboard Panels

The fabrication of precast slab can be made from wide range of material either neat concrete, foamed concrete or even composite. Until recently, a new interest has been discovered. Instead of wet concrete mixing process in plant, the precast slab can be substituted with fibre cement board or commonly referred as cemboard that meets the specific load requirements with minimum thickness. However, cemboard panel is preferable for lightweight floor system due to its physical strength limitation. Its thickness that relatively small around 15 mm to 25 mm contribute to the drawback and subsequently prohibited the application of cemboard panel as heavyweight floor system. Small specimens are prepared to determine the optimum orientation of bolts and type of bond by analysing the bearing resistance and bond-slip behaviour. It was found that the bearing capacity is governed by polyurethane glue. Meanwhile, the bond-slip behaviour is effectively controlled by the steel bolt. If the steel bolt is solely used as bond mechanism, the bearing capacity will rely on its quantity and capacity and increasing the quantity of steel bolt will eventually lead to the higher value of bearing resistance.

Corrosion Effect on Bond Loss between Steel and Concrete

This chapter is devoted to the effects of steel corrosion on bond relationship between steel and concrete. One of the basic assumptions in design of reinforced concrete members is the perfect steel - concrete bond mechanism, so that strain of reinforcing bar is the same as that of the surrounding concrete and these two different materials act as one. However, corrosion of steel reinforcement consists one of the main durability problems in reinforced concrete members, downgrade the bond behavior and therefore their structural integrity. Corrosion degrades the reinforcement itself, reducing the initial cross-section of the steel bar and its mechanical properties. Furthermore, tensile stresses in surrounding concrete caused due to oxides on the corroded reinforcement, lead to the gradual development of tensile field to the surrounding concrete, with spalling of the cover concrete and loss of bond mechanism as a consequence. In this chapter, an overview of damage of reinforced concrete due to steel corrosion is given, focused on the bond mechanism; factors that play key role in the degree of bonding and, also, proposed models of bond strength loss in correlation with the surface concrete cracking due to corrosion are indicated. To conclude, the ongoing research in this area of interest is presented, based on recent scientific studies.