All reinforced concrete (RC) design theories are based on the assumption that concrete exhibits a perfect bond with the steel reinforcement. The bond between steel and concrete is essential to the transfer of the load applied from the concrete to the steel reinforcement. When steel bars are corroded, the concrete cracks, and the strength of the bond between the steel bars and the concrete is decreased. Structures such as bridges and marine structures are prone to corrosion. These structures are usually also subjected to repeated loading. Repeated loading can initiate cracks in the concrete surrounding the steel bars that propagate as the number of load cycles increases leading to the destruction of the concrete-steel interface and slip of the steel bars inside the concrete. The combined effect of corrosion and repeated loading reduces the service life of RC structures. This study investigated the effect of anchorage length and confinement from supports, stirrups and carbon fibre reinforced polymer (CFRP) on the bond behaviour of corroded and uncorroded reinforced concrete beams subjected to monotonic and repeated loading.
Adequate rebar-concrete bonding is crucial to ensure the reliable performance of reinforced concrete (RC) structures. Many factors (such as the concrete properties, concrete cover depth, transverse reinforcement, and the presence of corrosion) affect the bond behavior, and consequently the structural performance. This bond behavior is typically described by a bond stress-slip relationship, where there are two critical quantities: bond strength ̶ the maximum shear stress that bond can withstand, and peak slip ̶ the slippage at the interface when the bond strength is reached. It is understood that the bond deteriorates when corrosion is present and behaves differently under two distinct bond failure modes (i.e., splitting and pull-out). While many prior studies have focused on the influence of the aforementioned factors on the bond strength, the impact of the failure mode coupled with corrosion on the bond stress-slip relationship and structural performance have not been thoroughly investigated. This study is aimed to address this issue. In this study, first a probabilistic bond failure mode prediction model that considers various influencing factors including loading type and corrosion is developed in this study. This study uses the bond testing results of 132 beam-end specimens subjected to monotonic and cyclic loading and adopts classification methods to develop the prediction model, which is then used to evaluate the impact of bond behavior on the reliability of a RC beam with a lap splice. Then, multivariate nonlinear regression with all-possible subset model selection and symbolic multi-gene regression are adopted for probabilistic model development for bond strength and peak slip under the two bond failure modes considering corrosion. In particular, a comprehensive bond dataset collected from bond tests on the beam and beam-end specimens in the literature and from the experimental testing conducted in this study, and a criterion to specify the bond failure mode is also proposed. Next, incorporating bond in the structural analysis is investigated. Since in reality, perfect bonding does not exist, especially in beam and column or column and footing connections, reinforcement slip occurs as a result of imperfect bonding. Reinforcement slip in the footing of a RC column can significantly influence the lateral displacement of the column, a critical structural response under lateral loads such as seismic loading. Many past researchers studied and developed models to capture the anchorage slip of rebar; however, a model that can reflect the actual bond-slip relationship (especially in the presence of corrosion) and yet be simple-to-use for structural analysis is not well developed. In this study, a new simple bar stress-slip macromodel is developed to predict reinforcement anchorage slip given a rebar stress. The proposed rebar anchorage slip model is derived by implementing a macromodel solution based on a simple bond stress distribution function that captures the bond stress distribution numerically obtained from a real bond-slip relationship. Available experimental bond stress-slip data collected from literature are used to optimize the model parameter in the proposed bond stress distribution function, which reflects the impact of the structural parameters on the rebar slippage such as concrete strength and corrosion level. The proposed rebar slip model is then incorporated into a fiber beam-column model for numerical analysis, and is further validated by comparing flexural behavior of several RC columns (with and without corrosion) based on the numerical model with the experimental data. The results demonstrate the importance of incorporating rebar slippage and corrosion effect on bond. Using this fiber beam-column model, seismic performance of an example RC bridge column is evaluated, and one can conclude the rebar slip plays a critical role in the seismic evaluation. As the proposed rebar slip macromodel provides simple formulation and it is explicitly expressed with a model parameter that can be updated easily to incorporate new information, it is practical for application in the structural analysis.
This book is intended to provide the reader with a clear and thorough presentation of the effect of localized corrosion on the structural behaviour of the concrete elements from both experimental and theoretical prospectives. Medium scale reinforced concrete beams were tested under different bond lengths, different steel corrosion severities, and different repair techniques. However, a mathematical model was provided to predict the behaviour of the tested specimens. The finding of this study provide useful information for design engineers and contractors because they offer a basis for decision making in terms of the selecting of the appropriate repair strategy and materials for such a deterioration case.
The bond in a reinforcement concrete (RC) structure is represented by the force transfer between the reinforcing bar and the surrounding concrete. All the RC structures are designed to have a perfect bond between the reinforcing bar and the surrounding concrete. However, corrosion of the reinforcing bar in the RC members is one of the main reasons that affect the bond efficiency in RC member. The deterioration of bond in RC element leads to decrease the service life of the RC structure and may result in sudden failure. Most of the previous research focuses on repairing the corroded RC member with FRP wrapping without cleaning the corroded reinforcing bar. The present research investigated the bond behaviour of cleaned corroded reinforcing bar repaired with partial depth repair concrete, transverse reinforcement or fiber reinforced polymer (FRP) sheets. Thirty-six beam-end specimens and twenty-four lap splice beams were cast and tested under static loading. The beam-end dimensions were 600 mm in length, 500 mm in height and 250 mm in width and reinforced with 20M bar. The test variables considered for the beam-end specimens were: four corrosion levels (5%, 7.5%, 10% and 15% mass loss level) and compared with non-corroded bar. Also, four bonded lengths were studied (200 mm, 250 mm, 300 mm, and 350 mm). Moreover, four partial depth repair concrete were used (commercial prepackaged self-consolidating concrete (SCC1), another different commercial prepackaged self-consolidating concrete (SCC2), self-consolidating concrete that was mixed in place and had similar proportions to the monolithic mixes (SCC3) and normal concrete (NC) mix design was also cast in place and had exactly the same proportions as the monolithic mixes but was used as a partial depth repair). All of the partial depth repair concretes were compared with monolithic beam-end specimen. The lap splice beams dimensions were 2200 mm in length, 350 mm in height and 250 mm in width and reinforced with two 20M lap spliced bars in the tension zone of the constant moment region with 300 mm splice length. Also, the lap splice beams were reinforced with two 10M continuous bars in the compression zone. The test variables considered for the lap splice beams were: commercial prepackaged self-consolidating concrete extended with 50% of 13 mm coarse aggregate (SCC50) was used as the main partial depth repair. It should be mentioned that SCC50 was the same partial depth repair concrete (SCC2) used for the beam-end specimens. Also, Three lap splice beams repaired with commercial prepackaged self-consolidating concrete without coarse aggregate (SCC0) were also included to study the effect of coarse aggregate on bond behavior. The lap splice beams repaired with partial depth repair concrete were compared with monolithic lap splice beam. Moreover, two types of confinements were considered in the lap splice beams: transverse reinforcement and carbon fiber reinforced polymer (CFRP) sheets. Six lap spliced beams were confined with transverse reinforcement and six were wrapped with CFRP sheets. This research found that the average bond strength increased as the bar mass loss increased for all bonded lengths. As the bonded length increased, the average bond strength decreased and the corresponding bar slip increased. In the beam-end specimens, the average bond strength of monolithic beam-end specimens was higher than the average bond strength of all types of the partial depth repair regardless the compressive strength of concrete. That was mainly because of internal shear cracks at the interface between the partial depth repair and the substrate concrete. However, since there was not shear at the constant moment region in the lap splice beams, the lap splice beams repaired with partial depth repair concrete with similar properties of monolithic concrete and had higher concrete strength showed higher average bond strength than the monolithic lap splice beams. Although the partial depth repair concrete SCC0 had higher compressive strength than SCC50 and the monolithic concrete; it had the lowest average bond strength. That because the absence of the coarse aggregate in SCC0 led to a decreased splitting strength and reduced fracture energy; and so the average bond strength was decreased. All self-consolidating concrete (SCC) partial depth repairs showed better bonding than the normal concrete (NC) partial depth repair. The bond strength of beams repaired with FRP sheets was higher than that of the beams confined with transverse reinforcement. The transverse reinforcement increased the average bond strength and the corresponding slip by (15% - 29%) and (32% - 62%) compared to the unwrapped beams, respectively. However, the beams confined with FRP sheets showed an increase in the bond strength and the corresponding slip by (34 - 49%) and (56 - 260%) compared to the unconfined beams, respectively. A multiple linear regression analysis was conducted to predict the effect of mass loss level, bonded length and presence repair concrete on the average bond strength of beam-end specimens. Also, a model was calibrated to predict the average bond strength with increasing the mass loss level of the reinforcing bar of lap splice beams. Moreover, another model was used to allow the design engineers to estimate the bond stress distribution along the spliced reinforcing bars as the splitting crack propagated.
The focus of the dissertation was to provide an in depth investigation towards the fatigue performance of Carbon Fiber Reinforced Polymers (CFRP) which were externally bonded onto concrete beams as a repair and strengthening technique for internally corrosion damaged RC beams. It was identified that more research concerning the fatigue performance of externally bonded CFRP laminates used as a composite material for originally damaged concrete structures was required. Therefore, there was a need to study the failure mechanisms between the externally bonded CFRP, corrosion damaged internal steel, and patch repaired section and the original substrate concrete with respect to the long term performance, whilst treating the system (CFRP, substrate concrete, patch repair and bonding agents) as a composite material. The methodology of the dissertation included the introduction of accelerated corrosion techniques to degrade the internal steel reinforcement. The damaged RC beams were repaired by removing the damaged concrete, treating the corroded internal steel reinforcement, replacing the damaged concre te section removed with a rapid-hardening high strength patch repair mortar, and finally externally bonding CFRP laminates along the patch repaired section and entire tensile face to restore the bending capacity lost due to the reduction of internal steel and subsequent patch repair. Two of the six RC beams which were patch repaired and CFRP strengthened, were subjected to a monotonic load in order to establish the ultimate static load at failure for the RC beams. The ultimate static load at failure was then used to derive the maximum imposed cyclic fatigue loading that was applied. The remaining four RC beams were then subjected to constant sinusoidal cyclic loads at varying amplitudes, the range of amplitude dependent on the corresponding static load at failure for the identical RC beam.
