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Corrosion of the steel reinforcing bars in concrete structures is one of the major maintenance problems. Corrosion results in expansive pressure on the surrounding concrete, which causes i...

After the collapse of Myaungmya Bridge in April 2018, the safety of infrastructure became an urgent task and attracted increased public interest in Republic of the Union of Myanmar. After the incident, monitoring systems were installed in several suspension bridges, of the same structure type as Myaungmya Bridge, recording unwanted bridge movements. The observations indicate that a large deformation occurred, rendering the current bridge condition different from its original design, though the safety of the current condition is unclear. Therefore, in this study, numerical models are simulated utilizing the data from detailed observations made by the monitoring system, to confirm the safety of the bridge. Twantay Bridge was chosen as the bridge analysis target. Linear time history analyses were performed on Twantay Bridge, in which the seismic performance was evaluated by comparing the stresses generated in the main members with the allowable stresses. Moreover, by comparing the analysis results obtained from two models – a design drawing model of the Twantay Bridge, and a model that reproduced the present condition of the bridge – the current bridge performance was confirmed. The information obtained from this analysis is useful in the field of maintenance and will allow Myanmar officials to effectively plan and take corrective action for the requisite maintenance of the damaged bridge.

In this study, a 3 dimensional rigid body spring model (RBSM) was used to simulate the combined effects of alkali-silica reaction (ASR) and delayed ettringite formation (DEF) induced concrete damage. To model the mechanical reduction of concrete after deterioration, expansion was considered as the index and the initial strain was introduced as the damage history. Firstly, for each damage type, the simulated cracking patterns and mechanical reduction of concrete were compared with the existing experimental findings, good agreement was reached which verified the reliability of the proposed simulation method. Then the parametric study was conducted to understand the combined effects of ASR and DEF since they may coexist in site. Surface cracking and internal crack numbers were analyzed to correlate the mechanical reduction. More importantly, the quantitative interaction of the two type damages was further discussed to clarify the mechanical properties loss of concrete under the combined effects, which is hard to achieve from experimental studies. The proposed method is efficient in simulating of durability problems of concrete and the simulated results are significant to the concrete structure design and durability evaluation under harsh environmental exposure.

In corroded reinforced concrete (RC) structures, there is a need to understand the degree of internal corrosion of the reinforcing bars in order to evaluate residual performance and ensure a rational maintenance regime. The authors have developed a computational approach for estimating the distribution of corrosion along the length of a reinforcing bar from the observed surface crack widths. The approach is based on mesoscale simulations of reinforced concrete, using rigid-body-spring models (RBSM), guided by Model Predictive Control (MPC). The current study extends that research to account for differing (smaller) crack openings, multiple instances of localized corrosion, and added confinement due to the presence of stirrups. Accuracy of the proposed approach is demonstrated through comparisons with laboratory tests of steel corrosion within concrete. The crack distribution observed on the concrete surface is automatically reproduced by optimized application of internal expansion within the mesoscale model, from which the corrosion distribution is estimated. The estimated corrosion distribution is accurate when compared to the measured corrosion of bars removed from the test specimens. In the case of specimens with stirrups, crack distributions and openings are accurately simulated by the MPC-RBSM system. Estimated corrosion levels are close to the measured values with some variations. The main reasons for these variations are the greater crack widths and higher corrosion levels in the stirrup-confined specimens. The simulated crack patterns are similar to those observed on the experimental specimens, indicating that specimen damage is simulated well. The internal stress and cracking distributions simulated by this method of meso-scale discrete analysis provides useful information for evaluating damage level that cannot be observed at the surface.

Corrosion induced rebar deterioration and concrete cracking alter the local bond interactions in reinforced concrete. An experimental methodology for investigating changes in the local deformation at the interface, caused by rib height reduction and corrosion layer is proposed. The effect of concrete cracking is eliminated by re-casting corroded rebars into new specimens. Local bond interaction is examined using uniaxial tensile tests and recorded through an observation window. The recorded interaction was analysed using Digital Image Correlation (DIC). Prior to visible crack formation, strain distribution maps revealed diagonal cracks indicating that the bond failure is associated with mechanical anchorage until a degree of corrosion of around 12%. Measurements of local opening and sliding behavior at the interface confirm that the slipping interactions become dominant with increase in corrosion. Differences in the shape of individual rib tips and flat lengths in specimens with higher corrosion cause significant variation in local bond interaction.

Reinforced concrete (RC) structures are widely used, yet prone to damage induced by reinforcement corrosion which causes susceptibility of concrete spalling and eventually a reduced serviceable life. The visual inspection has been performed usually for structural assessment, but this does not account for the local interactions between rebars. Consequently, detailed scrutiny is required to consider the effects of various parameters on the initiation and propagation of corrosion-induced cracking. This experimental study considers the effect of multiple and multidirectional rebars on the development of corrosion cracking. Additionally, the effect of the location of corrosion and the change in order of corrosion occurrence is investigated in this research. For this purpose, reinforced concrete panels with unidirectional and multidirectional rebar arrangements and varying cover depth are tested using an accelerated corrosion technique. The results show a significant role of confinement in controlling the widths of cracks provided by both reinforcement arrangements. Moreover, the effect of boundary conditions along with increased confining pressure alters the generation of cracks in a unidirectional reinforcement arrangement. In the absence of enough surrounding concrete, cracks along non-corroding rebars can also form because of the expansion of adjacent corroding rebars. The inclusion of multidirectional reinforcement alters the crack direction and causes cracking along non-corroding rebars. Further, previously generated cracks may close considerably by the pressure from adjacent rebar corrosion. This study also facilitates the comprehension of the impact of influencing factors affecting corrosion cracking in real structures.

The confining effect of concrete cover and stirrups reduces the rate of bond deterioration due to corrosion. However, the large dispersion in recorded experimental data makes it difficult to clearly separate the influence of cover depth and stirrup confinement on bond degradation. This study utilises the discrete 3D Rigid Body Spring Model (RBSM) to conduct a meso-scale investigation regarding the effect of cover thickness and stirrup confinement on internal crack evolution and pull-out behaviour in corroded reinforced concrete models. The simulation scheme is divided into two stages. In stage 1, different degrees of corrosion are introduced, producing cracking in the cover concrete; in stage 2, the corroded main reinforcement is pulled out from the damaged concrete. 3D RBSM is advantageous because the concrete is randomly meshed to reduce mesh bias on crack propagation and the actual geometry of the deformed bars is modelled. The simulation results clarify that the presence of thicker cover delays crack initiation but increases the rate of crack opening. Stirrups do not have any significant effect on crack initiation but effectively restrict crack growth. An investigation of the internal stress in the simulation models shows that tensile stresses generated in stirrups during corrosion are responsible for reactionary confining pressure that restricts crack propagation. Load-displacement curves show reductions in pull-out capacity, stiffness and ductility with increasing corrosion damage. The relative influence of crack opening and stirrup volume on the rate of bond degradation with respect to average surface crack width are discussed and compared with published experimental results and an empirical equation.

The utilization of post-installed anchors is growing fast to connect both structural and non-structural members. Adhesive anchors are one type of post-installed anchors which are formed as threaded bars. They can be post-placed into concrete with the help of epoxy adhesive. On the one hand, improvement of the performance of post-installed anchors, unlike cast-in-place anchors, has not drawn attention much. On the other hand, due to the complexity of their performance, a numerical study can be a supportive method for the experimental study. This paper addresses the effect of post-installed reinforcement (PR) on the adhesive anchors under tensile loading in both experimental and numerical studies. Reinforcing steel bars as post-installed reinforcement (fully embedded in concrete) were used to ameliorate the performance of the adhesive anchors under tensile force. Rigid Body Spring Model (RBSM) was developed as a simulation that is based on discrete analysis at mesoscale. Pull-out capacity, displacement, failure mode, and concrete cone geometry were measured by the experiments and the RBSM simulation. In addition, internal stress, strain, cracking patterns were investigated by the RBSM simulation. Moreover, some comparisons were conducted through the existing standard. In general, PR assist the anchors to have higher pull-out capacities, lower displacement as well as leading smaller size of concrete cone failure. Due to PR, the internal tensile stress of concrete changed to compressive stress resisting greater pull-out force. The higher strain is obtained at near the top of the anchors and at the mid-span of PR. Furthermore, cracking patterns in concrete were mostly within the area between the anchor and PR. Post-installed reinforcement can be considered as a method to improve the performance of adhesive anchors under tensile loading. This is validated by the RBSM simulation, which agrees with the experimental results.

Steel fiber reinforced concrete (SFRC) at the structural scale exhibits an enhanced fatigue performance compared to conventional reinforced concrete (RC) with lower stress levels and longer fatigue life. The steel fibers contribute to the crack-bridging strength of the concrete, but how this degrades in the tensile stress zone of an SFRC structural beam during flexural cyclic loading remains unknown. This makes the fatigue design and safety verification of SFRC beams an unexplored area. In this work, the degradation in crack-bridging strength of SFRC structural beams with 1.5% by volume of hooked-end steel fibers under different flexural fatigue stress levels is evaluated over the fatigue life using an inverse analysis method. The experimental flexural response is monitored during static and fatigue tests, and compared with the calculated one from the section analysis calculations through the execution of the inverse analysis method. Based on the results, the crack-bridging strength is shown to degrade gradually at different flexural fatigue stress levels over the fatigue life. Further, the residual flexural capacity at the end of fatigue life is shown to be little different from the original capacity obtained in static loading when the flexural fatigue stress level is low.

This paper presents an analytical investigation of the role of the reinforcing bars in the perpendicular beams of beam-column knee joints with mechanical anchorages. A computer simulation using 3D Rigid Body Spring Model (3D RBSM) is used for the analysis of RC beam-column joints in consideration of the effect of multidirectional arrangement of reinforcing steels. Simulation results provide beneficial information for understanding the macroscopic behavior because the internal stresses and crack conditions can be investigated. In this study, the beam-column joint simulation models are varied in the number of reinforcements to study the role of the reinforcing bar in perpendicular beam. Simulation results show that the capacity can be increased when reinforcing bars are added in the perpendicular beams. Through the study of the internal stresses and cracks using numerical simulation, the function of the longitudinal reinforcement in the perpendicular beams is to transfer the stresses from the joint to the perpendicular beams by means of the dowel action which is obtained by utilizing the multiple layers meshing of reinforcement and the local strain distribution. Ultimately, this research also shows that 3D RBSM can be a useful tool for the analysis of the RC beam-column joints with multidirectional arrangement of reinforcing steels based on a case-by case basis that cannot be addressed by the design code and conventional numerical methods.

Rebar corrosion can lead to significant deterioration in bond strength between steel and concrete. However, since confinement is lost as the concrete cracks, the changes in frictional bonding and mechanical bonding resulting from corrosion remain unclear and there is a need for an efficient tool that can evaluate the bond performance of corroded concrete structures. In this study, an innovative pull-out test is used to study changes in bonding in reinforced concrete after rebar corrosion, then a discrete meso-scale model based on the Rigid Body Spring Model (RBSM) is developed to simulate the observed bond behavior. To isolate the effects of concrete cracking, after an initial pull-out test, the corroded rebars are obtained and used as the reinforcement in newly cast sound specimens that are subject to a further pull-out test. A corrosion acceleration method is used to obtain corroded rebars. Different types of reinforcement (round rebars and deformed rebars) are studied. The results are used to study changes in frictional bonding and mechanical bonding at different degrees of corrosion. It is found that, without concrete cracking, the frictional bond in specimens with both round and deformed rebars significantly increases with the amount of corrosion, while total bond strength of specimens with deformed bar is almost unchanged because mechanical bonding is weakened. In the presence of concrete cracking, for specimens reinforced with a corroded round rebar, bond capacity increases initially (up to 3% corrosion) and then falls as corrosion increases, while bonding in those with a corroded deformed rebar shows a consistent decrease. In the RBSM-based simulations, the effect of corrosion is modeled by adjusting springs at the corroded interface. Constitutive models of shear and normal springs are developed to simulate corrosion and reflect the changes on frictional and mechanical bonding. Simulated results for load-displacement relationship, pull-out capacity and crack pattern are in good agreement with the experimental results. The numerical simulation is used to visualize internal stress development and strain distribution along the rebar as the degree of corrosion increases, a result that cannot be obtained by experimental methods. The results demonstrate that RBSM is a useful tool for evaluating the mechanical performance of corroded reinforced concrete structures.

Internal stresses induced by the alkali silica reaction (ASR) and delayed ettringite formation (DEF) can cause cracking and degrade the mechanical properties of concrete, but the relationship between these phenomena remains unclear. In this study, crack patterns and the loss of compressive strength and elastic modulus of concrete after ASR and DEF expansion are simulated at the mesoscale using a three-dimensional Rigid Body Spring Model (3D RBSM). Concrete expansions induced by ASR and DEF are introduced in the model by applying initial strain on the springs of interfacial transition zone (ITZ) and mortar elements as damage history respectively. After verifying the model with single aggregate, further analysis of differences in concrete cracking due to ASR and DEF damage is carried out. The effect of the percentage of reactive aggregate is studied in the cases of ASR damage, while different intensified expansion areas are considered in the case of DEF. The simulated losses of mechanical properties of the concrete are compared with the experimental results and good agreement is obtained. It is found that the loss of mechanical properties is dominated by internal cracks rather than the surface crack pattern. Compressive strength is highly dependent on the development of large cracks while elastic modulus is closely related to the total number of cracked faces. More importantly, regardless of the intensified expansion area, the mechanical properties are consistent with expansive cracking damage.