Modeling of tension stiffening deterioration in RC tensile ties due to rebar corrosion

In this paper a discrete analytical approach is presented to simulate the tension stiffening in a series of corroded RC tensile ties. Rigid Body Spring Network (RBSN) method is employed. Models for corroded reinforcement and a discrete bond model for corroded steel/concrete interface, which is modified based on fib formulation by introducing a bond degrading coefficient relative to the steel mass loss, are implemented in the analysis. The program is used to simulate the loading tests on a series of healthy and corroded RC tensile ties, which were reported in the authors’ previous study. The analysis reproduces well the different crack distributing characteristics of RC tensile ties with different corrosion rates. However, it is revealed through analysis that corrosion-induced local bond loss and the global tension stiffening deterioration may not be equivalent. A loss of 50% of original bond, which usually corresponds to a steel mass loss of about 10%, may not lead to a noticeable tension stiffening deterioration although it leads to a greater local crack-opening due to the change of crack spacing. A further steel mass loss greater than 25% can bring noticeable tension stiffening deterioration. It is suggested that the tension stiffening factor  can be degraded from 0.4 for a conventional case to 0.9 for a severely corroded case, the latter of which corresponds to a steel mass loss of about 35% and the resulting-in bond loss is about 90% of the original. Analysis also reproduces that the appeared first-crack tensile strength of concrete in the tensile tests for a severely corroded RC tie may be much lower than concrete’s actual one because of the corrosion-induced anchorage failure. For lightly corroded RC ties, however, the observed tension stiffening loss in the experiments can not be attributed mainly to bond loss but the possible damage or non-uniformity in concrete cover due to the corrosion cracks. An alternative solution for considering this kind of material deterioration before loading is to introduce a reduction factor to the section or the first-crack tensile strength of cover concrete. However, the quantitative evaluation of cover concrete damage related to the steel corrosion remains for further study.