Numerical and Experimental Study on the Steel Strands under the Coupling Effect of a Salt Spray Environment and Cyclic Loads

Abstract

Composed of multi-strand parallel high-strength wires or steel strands, the stayed cables have been widely used recently in stayed bridges or suspension bridges owing to their light weight and high bearing capacity, especially the steel strands. Meanwhile, chloride-induced corrosion of steel strands is one of the most considerable factors for the durability of the stayed cable exposed to marine environments. The fatigue caused by both cyclic loading and corrosion can affect the life of the steel strands. Besides, the current studies related to the effects of the aforementioned two impact factors on the life of the steel strands either considered the fatigue only, or took the two impact factors into account separately. The coupling effects of fatigue and corrosion on the life of the steel strands are required to be further explored and discussed. Consequently, it is essential to create a model to predict the life of the steel strands with the coupling effects taken into consideration. In this paper, an indoor physical experiment of the steel strand specimens exposed to marine tidal environment was carried out. To avoid accidental errors, the whole specimens were divided into 20 groups, with each group having two steel wires with a 5 days, 10 days, and 15 days cycle for the test. The corrosion of steel strands was observed at various exposure times and it was found that the pits were formed on the surface with the chloride ion erosion to the steel strands. Deeper and sharper pits result in greater pitting-local stress and a shorter fatigue life, which is also the main reason for reducing the carrying capacity of the steel strands. However, a detailed description for this problem is lacking in current domestic and foreign literature, because the pit is hard to predict owing to its complex nature. In order to simulate the evolution of the pits, the stochastic pitting-corrosion model was set up by the neural network method to evaluate the pit evolutions over time. In addition, an empirical formula consisting of length–width ratios, length–depth ratios, and depth-to-width ratios of the pits was obtained to determine the stress concentration factor based on the multi-dimensional linear regression method. The fatigue notch factor of components can be deduced by the stress concentration factor, and the life of the steel strands can be deduced by both of them. The findings are expected to be useful in realistically predicting the durability of wire structures.

Experiment on Corrosion Fatigue Life of Steel Strands under the Coupling Effects of Chloride Environment and Alternating Loads

“…e load amplitudes are Δσ � 100 MPa, Δσ � 200 MPa, and Δσ � 300 MPa. e maximum load is 0.4 f ptk (744 MPa [11], f ptk is the standard value of ultimate strength of steel strand). Single loading cycle is 4 hours, and the upper and lower limits stress is converted every 2 hours.…”

“…To ensure the accuracy of the test, the specific chloride corrosion solution configuration is shown in Table 2 [11].…”

“…When preparing the solution, put the sodium chloride into the pure water at first, the concentration is controlled at about 50g/L. After mixing copper dichloride (CuCl 2 •2H 2 O) with the concentration of 0.26 g/L, add glacial acetic acid to control the pH value of the salt spray solution between 3.1 and 3.3 with temperature kept at 25°C [9][10][11]. After the test, the corrosion products on the surface of steel strands are cleaned by distilled water and dried, and residual corrosion products on surface or gaps that cannot be wiped off mechanically need further operations.…”

“…Chemical composition of salt solution[11].Table 2 is reproduced from Xuanrui et al, Numerical and Experimental Study on the Steel Strands under the Coupling Effect of a Salt Spray Environment and Cyclic Loads. Materials, 2019; 13 (3)).…”

A new design of cable anchor for ultra-high fatigue stress cable net of largest telescope in the world

“…In other words, the smaller the maximum Mises stress on the steel strands is, the more favorable it is for the full utilization of the tensile properties of the steel strands. According to the previous research [29][30][31] and the special requirements of the FAST engineering, when the maximum Mises stress is not greater than 110% of the tensile stress, the stress concentration of the steel strand is acceptable, otherwise, it is not acceptable. It can be seen from table 1 that the single-cone anchor does not meet the requirements.…”