Fatigue Behavior of Constructional Steels Subjected to Pitting Corrosion and Elevated Temperature

Abstract

The structural integrity of reinforced cement concrete (RCC) and steel structures is highly dependent on the fatigue performance of their constructional steel, especially in demanding environments like those subject to chloride contamination or fire exposure. These structures are exposed to repeated cyclic loading, including HCF induced by wind and traffic, and LCF arising from seismic activity or thermal cycling. Importantly, the combined effect of both cyclic loading and corrosion significantly accelerates material degradation, necessitating a comprehensive understanding of constructional steel fatigue behavior under such combined stressors. Surface topography, characterized by features like roughness and pits, significantly influences fatigue behavior. In this study, an accelerated corrosion technique was employed to induce localized pitting in the specimens. Moreover, experimental investigations, including microstructural examinations, str performed to quantify the surface roughness changes in reinforcing bars exposed to pitting corrosion and elevated temperatures of upto 700 °C. Predictive models are developed to relate these surface topographic parameters to the severity of corrosion and temperature exposure. Leveraging these models, a framework is proposed for estimating the high–cycle fatigue life of corroded reinforcing bars, providing valuable insights for structural health assessments and design optimization. Further, study experimentally investigated the LCF behavior of reinforcing steel bar subjected to pitting corrosion and elevated temperatures. LCF tests were conducted under stress controlled conditions with a maximum stress level of 0.7 fy and stress ratio of -1. Analysis of resulting hysteresis loop revealed significant detrimental effects of both pitting corrosion and elevated temperature on the LCF performance of the steel specimens. An analytical expression for the stress concentration factor (SCF) based on the inverted Gaussian distribution of pitting corrosion penetration depth along the reinforcing bar's perimeter has been proposed. In addition, LCF behavior of medium strength structural steel exposed to pitting corrosion and elevated temperatures was experimentally investigated using a symmetrical triangular waveform. LCF tests have been conducted with strain amplitudes of 0.6%  ,  0.8% and 1%  , with a strain ratio of -1. LCF tests at varied strain amplitudes revealed an expanding rhombus hysteresis with increasing temperature, accompanied by an 82% drop in fatigue life at 700°C. Analysis of corroded and uncorroded specimens under these conditions showed the influence of strain amplitude and temperature on cyclic life and energy dissipation. A Coffin-Manson model successfully quantified strain amplitude effects, with temperature–dependent coefficients predicted through an established power–law equation. Furthermore, the HCF tests on constructional steels with single and multiple pit sites confirmed a decrease in fatigue life with increased corrosion and stress levels. The developed fatigue S-Nf curve incorporating corrosion severity, offering valuable insights into the development of pitting corrosion in constructional steel.