Bond Stress-slip Curves Research Articles

Dynamic bond behavior of deformed BFRP bars embedded in concrete subjected to high-temperatures

FRP (fiber reinforced polymer) bars have the potential to become an alternative due to their excellent performance. A 3D numerical model considering the effects of strain rates and high-temperatures on material properties was established to investigate the bond behavior between deformed BFRP bars and concrete under the coupled action of dynamic loadings and elevated temperatures. In the model, the surface feature of BFRP bars was explicitly simulated. The model's validity was verified by comparing the simulation results with the experimental records. It was found that the numerical model can characterize the bond behavior of specimens reinforced with BFRP bars, including the cracking propagation, the failure patterns, and the bond stress-slip curves. The failure mechanism for specimens experiencing the dynamic loading and high-temperatures was revealed by analyzing the strain distributions of the concrete and BFRP bars, which indicate that the difference in the mechanical properties of the concrete and BFRP bars subjected to high-temperatures and dynamic loadings ultimately lead to the discrepancies in failure modes. The bond strength increases nonlinearly with the increases in strain rate at various temperatures while decreasing linearly at a higher temperature, regardless of strain rate. The peak slip increases linearly with the increases in strain rate or temperature. The overall bond performance of specimens is worse under high temperatures than after natural cooling. The strengthening influence of strain rate on the bond performance of specimens attenuates at high temperatures, and the weakening influence of temperature is enhanced. Based on the numerical results and mBPE model at ambient temperature, a semi-empirical model was developed by comprehensively considering the enhancement of strain rate and temperature degradation on bond performance. The validity of the semi-empirical model was verified by comparing the prediction results with the simulation and test results.

Refined simulation of bond-slip behavior between ribbed steel and concrete: Effects of initial stress and temperature

The bond performance between steel and concrete exposed to fire is influenced by many factors, including the presence of an initial load before the temperature increase. To investigate such effect, a 3-D refined simulation model is presented accounting for the heterogeneity of concrete at the mesoscopic level and the external geometry of ribbed steel bars. The rationality and validity of the refined simulation model and of the multi-step analysis were verified by comparison with existing experimental data. Subsequently, the effects of aggregate gradation and distribution, initial loading level and temperature on the bond behavior were analyzed. The load transfer mechanism at the steel–concrete interface as a function of temperature under different loading levels is captured and discussed. It is found that the influence of aggregate grading and distribution on the bond-slip curve can be ignored under the aggregate volume fraction set in this work. Additionally, results show that the damage initially concentrates at the rib tip of the deformed steel bars, with an increase across the concrete section as the slip increases, as it could be expected. However, the bond stress and both stress and strain of steel at the same position decrease as the temperature increases. Finally and most importantly, it is found that the heating and loading sequence induce a different damage evolution inside the specimen, with a significant effect on the bond stiffness, the plateau portion of the bond stress-slip curve and the bond strength associated to a given critical temperature.

Bond performance between deformed bars and concrete containing iron tailing sand exposed to high temperature

Preparing green concrete with industrial waste and construction waste can save natural resources and protect the environment. Therefore, it is necessary to study the bonding performance of green reinforced concrete and its post-fire bonding performance. A total of 45 specimens were prepared, including ordinary reinforced concrete (RC0-S), reinforced concrete with iron tailing sand (RC0-IT), and recycled reinforced concrete with iron tailing sand (RC50-IT). A central pull-out test was conducted on specimens with a rebar diameter of 16 mm and a bond length of 80 mm exposed to 20 °C, 100 °C, 300 °C, 500 °C, and 700 °C, and the failure phenomena, bond stress-slip curve, and ultimate bond strength of three reinforced concrete specimens were compared. The test results show that: (1) The ultimate bonding stress and residual bonding stress of the three reinforced concretes all increase first and then decrease with elevated temperature. (2) When exposed to 100 °C, the bonding properties of the three kinds of reinforced concrete all reached the best. (3) When exposed to the same temperature, the reinforced concrete with iron tailing sand (RC0-IT) has the best high-temperature resistance among the three reinforced concretes. Furthermore, the formulas for calculating the bond strength are proposed, the bond stress-relative slip (τ-s) constitutive model is established, and the predicted results of the model are in good agreement with the experimental results. This study helps to accurately obtain the bond stress of reinforced concrete exposed to high temperatures.

Experimental Study on Bonding Properties between Finishing Rolled Rebar and Grouting Material

In bearing capacity testing of prestressed concrete pipe piles, grouting material is filled up to the bottom of the pipe pile, which is equipped with a finishing rolled rebar. The reaction force of the reaction beam is transferred to the anchor pile through the bonding force between the finishing rolled rebar and grouting material. Therefore, investigating the bonding properties between the finishing rolled rebar and grouting material is essential to remove barriers to the application of the anchor pile method in bearing capacity testing of the prestressed concrete pipe pile. In this study, the bonding properties of 11 groups of specimens were studied through pull-out tests, and the effects of the cover thickness, diameter, and anchorage length of reinforcement on the bond strength between finishing rolled rebar and grouting material as well as on the bond stress-slip curve were explored. The test results showed that the bond stress-slip curve between finishing rolled rebar and grouting material can be divided into two stages, i.e., slip stage and splitting failure stage. In the slip stage, a linear relationship exists between bond stress and slip amount, and microcracks appear in the grouting material around the finishing rolled rebar. In the splitting failure stage, the slip amount increases rapidly under uplift load. Finally, the grouting material around the finishing rolled rebar forms a failure zone, and splitting failure occurs. The bonding capacity and bond strength between finishing rolled rebar and grouting material increase with the increasing cover thickness of the rebar. The bond strength is the maximum for a relative cover thickness of 3.0, and the difference between the maximum and minimum values is more than 9%. The bonding capacity between rebar and grouting material increases slightly with the increasing rebar diameter, but the bond strength decreases with the diameter, and the difference between the maximum and minimum bond strengths is more than 21%. As the contact area between finishing rolled rebar and grouting material increases, the bonding capacity between them increases with the increasing anchorage length of the rebar. However, the bond strength first increases, then decreases, and finally stabilizes with the increasing anchorage length, and the difference between the maximum and minimum bond strengths exceeds 14.64%.

Bond Behavior of Plain Bars in Concrete under Reversed Cyclic Loading.

Plain bars with a diameter of 10 mm are widely used in reinforced concrete buildings, and the bond behavior between the bars and concrete has an essential effect on the seismic performance of concrete structures. Thus, to assess the safety of old buildings and repaired buildings with normal concrete, it was necessary to further investigate the bond performance of the plain bars in the concrete. The bonding tests under monotonic and reversed cyclic loading were carried out on the specimens reinforced with plain bars, and the influences of concrete grade and embedment length on the bond behavior were taken into consideration. The results indicate the maximum bond stress under reversed cyclic loading is less than that under monotonic loading, and this is the same for corresponding slip for the same test parameters. The concrete compressive strength positively affects the maximum bond stress, whereas the embedment length has a negative effect. Based on the elasticity analysis and test data fitting, the expressions of bond stress at characteristic points on the bond stress-slip curves were carried out. Consequently, the bond stress-slip model was established, which could be applied to calculate the bond stress-slip relationships under monotonic and reversed cyclic loading. By comparison between the test curves and proposed model, a good agreement is observed, which indicates that the proposed model can be used to predict the bond stress-slip curve of plain bars in concrete.

Effect of Bonding Area on Bond Stress Behavior of GFRP Bars in Concrete

The application of Glass Fiber Reinforced Polymer (GFRP) bars is suitable for concrete structures that are susceptible to corrosion, owing to their corrosion-resistant characteristics. Therefore, it is feasible to reduce the concrete cover on reinforced concrete beams by utilizing GFRP bars. However, this can reduce the bonding strength between GFRP bars and concrete. Therefore, this study aims to investigate the bonding behavior between GFRP bars and concrete as a preliminary test for structural applications. The bond stress behavior between GFRP bars and concrete was analyzed by 18 pull-out tests. The test specimens comprised GFRP bars with three different variations, namely GFRP bars with concrete cover (GFRP-C), GFRP bars without concrete cover (GFRP-E), and GFRP bars with a complete wrapping of GFRP sheet (GFRP-C-Sheet). The bond stress-slip curve, bond strength, and failure pattern were utilized to analyze the effect of each variation. The research results indicate that the bonding stress between GFRP bars and concrete was strongly influenced by the concrete cover, where the bonding strength decreased by 65%. Nevertheless, the utilization of a complete wrapping GFR) sheet resulted in a 26.4% increase in bonding stress. The present study has identified three distinct modes of failure, including pull-out (GFRP-C), concrete crushing (GFRP-E), and GFRP sheet debonding (GFRP-C-Sheet). Doi: 10.28991/CEJ-SP2023-09-010 Full Text: PDF

Study on local bond behaviors between steel bars and high-strength concrete exposed to early disturbances

This paper investigates the effects of early vibration exposure on the local bond behaviors between deformed steel bars and high-strength concrete (HSC). The effects of steel fiber and vibration intensity (ranging from static to peak particle velocity (PPV) of 10 cm/s) on the deterioration laws of bond performances and mechanisms were revealed. Finally, an empirical prediction model was developed to uniformly describe the bond stress-slip relations of specimens subjected to different vibration levels. Results indicated that early vibration could produce separation gaps and the surrounding viscous layers around steel bars, leading to the reduction/elimination of initial debonding resistances. Besides, the failure mode of pull-out specimens may alter due to the degradation of concrete. The bond stiffness of HSC is more vulnerable to environmental vibration (up to 62.6%), followed by bond strength (39.4%) and compressive strength (33.7%). The bond toughness of specimens, especially with the addition of steel fibers, is less sensitive to vibration (29.8%/6.8% for HSC/HSFRC). The increases in concrete strength grades and additions of fibers significantly enhance the threshold resistance to early vibration, making it a recommended solution for vibration scenarios. Using a consistent expression, the proposed empirical model reasonably reproduces bond stress-slip curves of specimens with/without vibration exposure.

Experimental study and numerical simulation on the bonding properties of rubber concrete and deformed steel bar

In this study, the pull-out test was carried out by placing strain gauge in the groove of steel bar. The effects of rubber volume incorporation rate (0%, 10%, 20%, and 30%), steel bar diameter (14 mm,16 mm,18 mm, and 20 mm) and anchorage length (4d, 5d, and 6d) on the bonding performance of deformed steel bar and rubber concrete were studied. The failure modes of the specimens are observed and the ultimate bond stress and slip of the specimens are calculated. On this basis, the distribution laws of relative bond stress under different influencing factors and the bond stress-slip curves at different anchoring positions are obtained. In addition, the bond stress-slip constitutive model of deformed steel bar and rubber concrete considering rubber incorporation rate is established. Through non-dimensional treatment of the bond stress at different positions x (distance from the free end) under the same slip value, the bond position functions of deformed steel bar and concrete with different rubber incorporation rates are obtained. Finally, the nonlinear spring element Spring2 is used to simulate and analyze the bonding property and slip. The experimental results are in good agreement with the simulation results.

Bond performance and physically explicable mathematical model of helically wound GFRP bar embedded in UHPC

Due to the superior corrosion resistance, glass fiber reinforced polymer (GFRP) reinforced ultra-high performance concrete (UHPC) structure has been regarded as an attractive alternative to traditional RC structure exposed to harsh environments. In this work, upon the pull-out tests of 54 specimens, the bond behaviors between helically wound GFRP bar and UHPC were investigated, with an emphasis on the evaluation of the effects of GFRP bar diameter, embedment length, concrete cover thickness, and fiber characteristic parameters (i.e., volume fraction and aspect ratio) of steel-polypropylene hybrid fiber. The bond failure mode, ultimate bond strength, and bond stress-slip curve were analyzed. The results showed that the bond damage at GFRP-UHPC interface mostly occurred on the GFRP bar surface due to the relatively lower strength of GFRP ribs. The bond strength presents an upward trend with an increase in the thickness of concrete cover and volume fraction of steel fiber, whereas it decreases with the increase of GFRP bar diameter and embedment length. Moreover, the fibers in the UHPC matrix exerted a significant impact on the bond behaviors that could alter the bond failure mode from the concrete splitting failure to the pull-out failure. Finally, based on the experimental observations, a new physically explicable mathematical bond stress-slip model was proposed to reproduce the main features of the whole debonding process. The satisfactory predictions against the test results from independent research demonstrated that the proposed three-phase analytical model represents a compromise between accuracy and generality, providing a beneficial reference to the design of the GFRP reinforced UHPC structure.

Bond of Seawater Scoria Aggregate Concrete to Stainless Reinforcement

This study investigates the bond between seawater scoria aggregate concrete (SSAC) and stainless reinforcement (SR) through a series of pull-out tests. A total of 39 specimens, considering five experimental parameters—concrete type (SSAC, ordinary concrete (OC) and seawater coral aggregate concrete (SCAC)), reinforcement type (SR, ordinary reinforcement (OR)), bond length (3, 5 and 8 times bar diameter), concrete strength (C25 and C30) and concrete cover thickness (42 and 67 mm)—were prepared. The typical bond properties (failure pattern, bond strength, bond-slip curves and bond stress distribution, etc.) of seawater scoria aggregate concrete-stainless reinforcement (SSAC-SR) specimen were systematically studied. Generally, the failure pattern changed with the concrete type used, and the failure surface of SSAC specimen was different from that of OC specimen. SSAC enhanced the bond strength of specimen, while its effect on the deformation of SSAC-SR was negative. On average, the peak slip of SSAC specimens was 20% lower while the bond strength was 6.7% higher compared to OC specimens under the similar conditions. The effects of variables on the bond strength of SSAC–SR in increasing order are concrete type, bond length, concrete strength and cover thickness. The bond-slip curve of SSAC-SR specimen consisted of micro-slipping, slipping and declining stages. It can be obtained that SSAC reduced the curve curvature of bond-slip, and the decline of curve became steep after adopting SR. The typical distribution of bond stress along bond length changed with the types of concrete and reinforcement used. Finally, a specific expression of the bond stress-slip curve considering the effects of various variables was established, which could provide a basis for the practical application of reinforced SSAC.

Bond Degradation Mechanism and Constitutive Relationship of Ribbed Steel Bars Embedded in Engineered Cementitious Composites under Cyclic Loading

In order to investigate the bond degradation mechanism and constitutive relationship of ribbed steel bars in engineered cementitious composites (ECCs) under cyclic loading, 12 groups of specimens were tested in this paper. The design parameters included ECC compressive strength, ECC flexural toughness, cover thickness, and anchorage length. The results indicated that the degradation of the bond behavior of the ribbed steel bars in the ECCs under cyclic loading was mainly caused by the degradation of the properties of the ECC material itself, concentrating on the development of cracks in the ECC, the extrusion and shear failure of the ECC between the steel bar ribs, and the continuous grinding of the ECC particles on the shear failure surface. The degradation of the bond stress-slip curves under cyclic loading was mainly reflected by the degradation in the ultimate bond strength and unloading stiffness. According to the monotonic loading test results, a monotonic bond stress-slip relationship model was proposed. On this basis, through building the hysteretic rules of the bond stress-slip curves under cyclic loading, a calculation model was proposed to predict the bond stress-slip constitutive relationship between the ribbed steel bars embedded in the ECCs under cyclic loading. Finally, the validity of the proposed model was verified by a comparison between the model curves and the tested curves.

Study on Bond Performance between Corroded Deformed Steel Bar and DS-ECC.

In order to study the bond performance between desert sands engineered cementitious composites (DS-ECC) and corrosion steel bars, seven groups of specimens were designed and manufactured. Through the center pull-out test, the effects of different types of desert sands, the rate of corrosion (0, 5, 10 and 15%), and the anchorage length of steel bars (5d and 8d) on the bonding properties of DS-ECC and corrosion steel bars were studied. Moreover, a de-rusting agent was used to remove the corrosion, and three groups of specimens were pulled out from the center of the de-rusted steel bars. The results showed that both Tengger DS-ECC and Mu Us DS-ECC have good bond properties with corrosion steel bars. The bond stress slip curves between DS-ECC and corrosion steel bars can be divided into four stages: the micro-slip, slip stage, failure stage and residual stage. The bond stress slip curves between DS-ECC and de-rusted steel bars can be divided into the micro-slip stage, failure stage and residual stage, and splitting and pulling-out failure occurs in DS-ECC specimens. The ultimate bond strength is the highest when the corrosion rate is 5%. The bond toughness index is positively correlated with the anchorage length of steel bars, and negatively correlated with the corrosion rate of steel bars. According to the test results, the bond-slip mathematical relationship is established.

Bond-slip behaviours between preplaced aggregate concrete (PAC) and steel bars

In this article, 54 specimens with diverse types and strength grades of concrete and various embedded lengths and diameter of steel bars were prepared and the bond-slip behaviours between preplaced aggregate concrete (PAC) and steel bars was evaluated by pull-out tests. Then, a bond stress-slip constitutive relationship was proposed on the basis of the thick-walled cylinder model. Finally, the accuracy of the proposed bond-slip constitutive relationship was verified by finite element analysis (FEA) simulation. The results indicated that the bond stress-slip curves could be roughly divided into four sections. The bond strength for PAC under different concrete strength grades were all superior to those for normal concrete (NC). The proposed theoretical model provided a good prediction of bond strength for PAC with reasonable parameters selection. The simulated bond stress-slip curves for PAC were basically in accordance with the testing results which illustrated that the proposed bond-slip constitutive relationship was reasonable. In the future, the accuracy of the evaluation of the bearing capacity of precast concrete structures composed of PAC will be significantly improved by introducing the proposed bond-slip constitutive model.

Bond properties between concrete and high ductility cementitious composite with totally recycled fine aggregate

In order to explore the potential of high ductility cementitious composite with totally recycled fine aggregate (R-HDCC) as building repair material, the bond properties between concrete and R-HDCC were investigated through the double-face shear test in this study, which could be helpful for promoting the recycling of waste concrete, reducing environmental pollution and attaining better repair efficiency. The effects of concrete compressive strength, R-HDCC compressive strength and fiber volume fraction of R-HDCC on the bond properties between concrete and R-HDCC were analyzed in detail, and compared with those between concrete and high ductility cementitious composites with natural fine aggregate (N-HDCC). The acoustic emission technique was employed to monitor the internal damage of specimens, and the obtained signals were used as basis for analyzing the load bearing process. The experimental results showed that concrete/R-HDCC bonding specimen performed a higher bond strength and ductility than concrete/N-HDCC due to the tighter bond interface. The bond stress and slip at peak points on the bond stress-slip curve of concrete/R-HDCC specimens increased with the increasing of concrete compressive strength, R-HDCC compressive strength and fiber volume fraction of R-HDCC, while the bond stress at ultimate point decreased with the increasing of fiber volume fraction due to the larger slip and energy produced by more fibers pulled-out. Finally, the trilinear bond stress-slip model applicable to concrete/R-HDCC bonding specimen was established based on the statistical analysis of experimental results.

Numerical modelling of bond mechanism of ETS FRP bar‒concrete joints with long embedment length

In this study, the bond behaviour between the embedded through-section fibre-reinforced polymer (ETS FRP) bars and concrete is investigated using nonlinear finite element (FE) analysis. The pull-out scheme for the investigation of the interfacial interaction of ETS FRP bars adhesively bonded to concrete is presented. The proposed numerical study also considers the ETS FRP bar‒concrete joints with long bond (embedment) length. First, a trapezoidal bond model describing the bond stress‒slip curves of ETS FRP‒concrete interfaces is adopted. Second, nonlinear FE models incorporating the developed bond model analysing the bond behaviour of the ETS FRP bar‒concrete joints are validated against the pull-out test results. The reliable FE models are then used in a parametric study to investigate the effects of key features, such as the properties of adhesives, FRP bars, and concrete, on the bond performance of the ETS FRP bar‒concrete interfaces. The analyses demonstrate the effectiveness and accuracy of the FE models. Expressions for the maximum bond force and the effective bond (embedment) length are rationally formulated based on the parametric study. • FEM coupled with a bond–slip law for ETS FRP bar-to-concrete joints is proposed. • Proposed FEM can predict bond behaviour between ETS bar and concrete well. • Failure in bonded joints is analysed via cohesive zone using trapezoidal bond model. • Properties of FRP, adhesive and concrete affect ETS bonding performance. • Proposed equations for bond strength and effective bond length are highly accurate.

Study on bond behaviour of stainless steel reinforced concrete

The stainless steel rebar (SSR) and concrete are mainly bonded to transfer force and coordinate deformation. Therefore, it is necessary to study the bond behavior of stainless steel reinforced concrete. In this paper, the reinforced concrete specimens of carbon steel rebar (CSR), austenitic stainless steel rebar(ASSR) and duplex stainless steel rebar (DSSR) are made by taking concrete strength, steel rebar diameter, anchorage length, thickness of concrete cover and stirrup ratio as test parameters. Through the pull-out test, the failure phenomenon, bond stress-slip curve, ultimate load and ultimate bond strength of three kinds of reinforced concrete specimens are compared. The influence regularity of different factors on the bond behavior of SSR concrete is studied.. The bond strength formulas of ASSR and DSSR concrete are obtained by data fitting. The test results show that: (1) Both CSR concrete specimens and ASSR concrete specimens are mainly damaged by steel pulling out; (2) The failure mode of DSSR concrete specimens is mainly concrete splitting failure; (3) The change of concrete strength has the greatest influence on bond slip of DSSR concrete, followed by CSR concrete, and finally ASSR concrete; (4) CSR concrete has the best bond slip performance, followed by DSSR concrete, and finally ASSR concrete; (5) The recommended design value and calculation formula of anchorage length of ASSR and DSSR are given.

Bond-slip behaviour of lightweight aggregate concrete based on virtual crack model with exponential softening characteristics

A theoretical analytical model of bond stress-slip between lightweight aggregate concrete and rebar is presented by using the virtual crack model of fracture mechanics to analyze the nonlinear exponential softening characteristics of lightweight aggregate concrete in this paper. Various critical points at different stages are calculated by using simplified expressions. Moreover, a theoretical analytical model for bond-slip mechanism considering the effect of the stirrup is additionally presented. To simulate the relationship of bond stress-slip, a Python program is developed to generate connectors between rebar and concrete corresponding nodes. Furthermore, a three-dimensional finite element model is also developed to consider the impact of radial stress around the rebar. Compared with the bond stress-slip curves of experimental results, the theoretical analytical model of bond-slip behavior effectively reflects the interaction of rebar and lightweight aggregate concrete, and the three-dimensional finite element model demonstrates how cracks within lightweight aggregate concrete expand. At the interface between lightweight aggregate concrete and rebar, the bond stress is not uniformly distributed alongside the bond length. Due to the inhomogeneity of the bond stress, the bond strength calculation equation needs to be modified. Meanwhile, the modified results are well consistent with the bond-slip test.

Combined effect of corrosion and strain rate on the bond behavior: A two-stage simulation

The objective of the study is to investigate the bond performance between corroded steel bar and concrete subjected to dynamic loadings. A 3D refined simulation model is established, in which the geometrical shape of corroded rebar can be explicitly described. In addition, the shape variation of steel bars due to corrosion and the materials strain rate effect are also considered. In the simulations, a two-stage analysis (stage I: corrosion induced expansion, and stage II: dynamic relative slip) approach is utilized to explore the influences of corrosion and strain rate on the dynamic bond performance. Firstly, the corrosion expansion displacement is applied on concrete surface in contact with rebar to simulate the corrosion expansive behavior. After obtaining the damage pattern of concrete caused by corrosion and then taking this state as the initial condition, we apply a dynamic load on the loading end of corroded rebar to evaluate its dynamic bond behavior between the corroded rebar and concrete. A good agreement is obtained between the simulated results and the available experimental results on the failure patterns and corroded bond stress-slip curves. The combined effects and quantitative relationship between corrosion level and strain rate on the bond behavior are discussed. Also, the simulated bonding strength and peak slip present good consistency with the available test data. Furthermore, a modified bond stress-slip model considering the influence of corrosion level and strain rate on the bond strength as well as the peak slip is proposed.

Modelling of bond behavior of deformed bar embedded in concrete after heating to high temperatures: A mesoscale study

A three-dimensional (3D) mesoscale model was established in the present work with considering the heterogeneity of concrete materials and the surface characteristics of deformed steel bars. In the simulation, the interaction between deformed rebar and concrete is taken into account, including mechanical interlocking and frictional resistance. The sequentially coupled thermal-stress analysis procedure was employed to model the process of pull-out of deformed steel bar after cooling from high temperature. Comparison with the results of the pull-out test illustrates the correctness of the mesoscale simulation results. Then, the influence of aggregate types and elevated temperatures on the bond properties were discussed. Considering the simulation results, a calculation formula for the bond stress-slip curve after cooling from high temperature was proposed based on the recommendations in the existing codes for the cases of room temperature. The results show that the reduction of peak bond strength is directly bound up with the heat transfer and mechanical performance of the aggregates. When the deformed rebar is pulled out under the displacement load, the development process of concrete cracks with different aggregates is obviously different. Comparing the results obtained by the calculation formula proposed in the present work with the numerical simulation results, one can notice the good consistency between them, which means the effectiveness of the proposed formula.

3D meso-scale modelling of the bonding failure between corroded ribbed steel bar and concrete

Subjected to a corrosive environment, the macroscopic behavior of reinforced concrete structures is closely related to the bond property between rebar and concrete. For assessing the material performance and evaluating the nonlinear bond behavior of the interface between corroded ribbed rebar and concrete, and finally revealing the meso-mechanical failure mechanism of the reinforced concrete structure, we propose a 3D mesoscopic model in the current paper. The following elements that may influence the macroscopic behavior of the reinforced concrete are considered in the model: (1) the friction resistance and the mechanical interaction between corroded ribbed rebar, rust and concrete (2) the surface characteristic of threaded ribbed bar. The proposed mesoscopic model allows us to assess the influences of corrosion on the bond performance of corroded reinforced concrete through a two-stage analysis: after considering the expansive behavior of the reinforced concrete in the model, we apply a pull-out force on the corroded rebar to evaluate the bond-slip behavior between the corroded rebar and concrete. For validating our model, we compare the failure patterns and corroded bond stress-slip curves calculated by the model and obtained by experimental means and found a good consistency between them. Finally, a modified model was developed to describe the corroded bond stress-slip relationship. It has been found that when relative slip is applied, the concrete continues to crack along pre-existing cracks caused by corrosion products until the concrete splitting failure accorded. With the increase of corrosion level, the shape of the bond stress-slip curve is similar with a significantly degradation of the bond strength and peak slip, especially at small corrosion levels. Through comparing the proposed modified formula with the existing test data, one can find that the proposed modified formula can effectively characterize the corroded bond stress-slip relationship between deformed rebar and concrete.