Fatigue reliability evaluation of aging prestressed concrete bridge accounting for stochastic traffic loading and resistance degradation

Fatigue damage accumulation is a critical factor resulting in the failure of prestressed concrete (PC) bridges. The fatigue damage is usually caused by the coupled effect of cyclic vehicle loading and environmental corrosion. This study investigated probabilistic fatigue damage on aging PC bridges considering both stochastic traffic loading and corrosion. A stochastic traffic model was derived based on long-term monitoring data aiming to simulate fatigue stress spectra of critical rebar. The effect of cracks on the fatigue stress spectra was investigated in order to model the fatigue stress state more realistically. A three-stage traffic growth model was established based on traffic volume histories of three highways in China. A fatigue limit state function considering traffic growth and corrosion effect was deduced for fatigue reliability assessment of PC bridges. Numerical results show that the stress amplitude of rebar considering cracks is 1.53 times greater than the rebar with no-cracks, resulting in a decrease of fatigue life by 68 years. In addition, the three-stage traffic growth models lead to 25 years shorter fatigue life than the one considering a linear traffic growth model. Finally, the corrosion effect results in a fatigue life of 44 years. The numerical results provide a theoretical basis for fatigue life estimation and maintenance of aging PC bridges.

Corrosion effects on high-cycle fatigue lifetime and fracture behavior for heat-treated aluminum-matrix nano-clay-composite compared to piston aluminum alloy

In this research, the corrosion effect has been investigated on the high-cycle fatigue lifetime and the fracture behavior for the heat-treated aluminum-matrix nano-clay-composite and piston aluminum alloys. For this objective, after fabricating stir-casted nano-clay-composite, standard samples were machined and rotary bending fatigue tests were performed. To study the corrosion effect, some specimens were corroded in in the 0.00235% H2SO4 solution after 200 hours and then, they were tested under cyclic bending loading. Due to increase in the hardness by adding nano-clay particles and the heat treatment, higher fatigue strength occurred, compared to the base material. Nano-clay particles shortened the fatigue lifetime; however, this effect was less in the corrosion-fatigue lifetime. Moreover, the failure mechanism was the brittle fracture behavior due to the observation of quasi-cleavage and cleavage marks.