Effect of Stirrup on Bond Strength Degradation in Concrete Cracked by Expansion Agent Filled Pipes

The corrosion of rebars in reinforced concrete structures cracks the concrete, which leads to the degradation of the bond strength between the rebar and concrete. Since bond deterioration can menace structural safety, bond strength evaluation is essential for proper maintenance. In this study, the authors investigated bond strength degradation by conducting pull-out tests on concrete specimens, with induced crack width and stirrups ratio being the principal parameters. An expansion agent-filled pipe (EAFP) simulates cracks due to the volumetric expansion of the corroded rebar. One advantage of this method is that it allows one to focus on the single effect of an induced crack. The pull-out tests on 36 specimens show that stirrups’ confinement significantly influences the bond degradation due to induced cracks. The authors proposed an empirical model for the degradation of bond strength, considering the impact of induced crack width. The result shows that the induced crack by EAFP can quantify the exclusive consequence of corrosion on bonds. Furthermore, the coefficient of variation is 12% for specimens without stirrup from Law et al. For specimen without and with stirrup from Lin et al., the coefficients of variation are 14% and 17%. The proposed model can predict the corroded specimen from the literature with reasonable accuracy.

Bond Degradation and Residual Flexural Capacity of Corroded RC Beams

An analytical model is developed to predict the residual flexural capacity of corroded RC members. This was established by first developing an analytical model to calculate the residual bond strength at steel-concrete interface. The bond model is then implemented within the framework of the moment resistance method, and a new strain compatibility analysis was developed: to account the analysis of a corroded reinforced concrete beam, to incorporate dependence of the bond response on the stress strain and damage state of the concrete and steel. Method for calculating flexural capacity of corroded RC beams is then proposed, which is based on flexural analysis of RC beams that considers the effect of bond degradation. The predicted results of these models correlated very well with results observed in various experimental studies. This indicates that those developed analytical models tend to estimate conservatively the residual bond strength and flexural capacity of corroded RC beams. .

Bond Degradation and Residual Flexural Capacity of Corroded RC Beams

An analytical model is developed to predict the residual flexural capacity of corroded RC members. This was established by first developing an analytical model to calculate the residual bond strength at steel-concrete interface. The bond model is then implemented within the framework of the moment resistance method, and a new strain compatibility analysis was developed: to account the analysis of a corroded reinforced concrete beam, to incorporate dependence of the bond response on the stress strain and damage state of the concrete and steel. Method for calculating flexural capacity of corroded RC beams is then proposed, which is based on flexural analysis of RC beams that considers the effect of bond degradation. The predicted results of these models correlated very well with results observed in various experimental studies. This indicates that those developed analytical models tend to estimate conservatively the residual bond strength and flexural capacity of corroded RC beams. .

Bonded CFRP/Steel Systems, Remedies of Bond Degradation and Behaviour of CFRP Repaired Steel: An Overview

This literature review has examined the use of FRP composite materials as a potential retrofitting technique for civil structures. Importantly, the various material properties, bond mechanisms, durability issues and fatigue resistance have been discussed. Studies exploring the performance of CFRP repaired steel have strongly indicated its potential as a rehabilitation material. These systems offer many improvements over the current bulky and less chemically resistant methods of bolting or welding steel plate patches. This review has established and highlighted the factors that affect CFRP/steel bond durability, namely surface preparation, curing, corrosion, fatigue loading, temperature and moisture ingress through studies that focus on their effect. These studies, however, often focus on a single influencing factor or design criteria. Only limited studies have investigated multiple parameters applied simultaneously, even though they commonly occur together in industrial practice. This review aimed to summarise the numerous influencing parameters to give a clearer understanding of the relevance of CFRP repaired steel structures.

Numerical Modeling of RC Columns and a Modified Steel Model Proposal for Elements With Plain Bars

The cyclic earthquake loads may accelerate the bond degradation and consequently lead to important bar slippage. The bond-slip mechanism is assumed as a common cause of damage or collapse of existing RC structures loaded by seismic leads. The RC structures designed and built before the implementation of the modern seismic codes and with plain reinforcing bars are particularly affected by the bond degradation. However, perfect bond is assumed in most of the numerical models. The numerical modeling results of two RC columns tested under cyclic lateral load are presented in this paper. One column is built with plain reinforcing bars and the other with deformed reinforcing bars and both have structural detailing typically adopted in pre-1970's structures. For each column, different software and modeling strategies to simulate the cyclic response were adopted. The frameworks OpenSees and SeismoStruct were used to develop the numerical models which were calibrated based on the experimental results. A simple modeling strategy was adopted in the OpenSees models to consider the bond-slip effects. A modified tri-linear steel material model is proposed and adopted to contemplate the slippage of plain reinforcing bars by reducing the steel Young modulus. The tri-linear steel model parameters were obtained empirically based on the experimental results.