# Review on the Service Safety Assessment of Main Cable of Long Span Multi-Tower Suspension Bridge
## 2 The Tribo-Corrosion-Fatigue
[30]). It was revealed that the corrosion rate of steel wire was affected by the temperature, relative humidity, electrolyte solution concentration, type and pH value of corrosive medium, corrosion potential difference, crack depth, external load and other impurities. He proposed that the tensile strength of steel wire of main cable decreased with the increasing loss rate of steel wire cross-section and the larger tensile strength loss rate of steel wire as compared to its yielding strength loss rate. [PERSON] et al. [31] studied the effects of temperature, salt content and pH value on corrosion rates of high strength steel wires of long-span suspension bridge through electrochemical tests (Figures 3-5 in Ref. [31]). They indicated that environmental conditions affecting the corrosion rate of steel wire descended with the order of NaCl concentration, temperature, interaction between temperature and pH, and pH value and temperature. [PERSON] [32] analyzed corrosion conditions of steel wires and distribution laws of corrosion degree in the main cable (Figures 3-14 in Ref. [32]). Statistics of corrosion dimensions of galvanized steel wires indicated that the actual and average corrosion depths satisfied generalized extreme value distributions, and corrosion width and length satisfied lognormal distributions. He also proposed comparisons of tensile curves of steel wires with distinct corrosion degrees (Figure 4-3 in Ref. [32]). Referring to fatigue and fracture behaviors of main cable, [PERSON] [33] indicated the main cable near the tower of long-span suspension bridge presented a larger stress amplitude and was more prone to fatigue failure. He estimated fatigue crack initiation and propagation lives of main cable employing the local stress-strain method and Paris equation, respectively. Meanwhile, he proposed recommended material parameters for the estimation equation of crack propagation of steel wire in the main cable, i.e., \(m=3\) and \(C=1.592\times 10^{-13}\). [PERSON] et al. [34] proposed the fitting formula of stress intensity factor (Equation (3)) based on propagation laws of \"first round and then flat\" crack profiles of steel wire, and calculated the residual strength of steel wire based on fracture toughness. [PERSON] et al. [35] studied the effects of crack shape and dimension on the fracture strength and crack propagation life of steel wire. [PERSON] et al. [36] analyzed the crack propagation laws of steel wires employing the multi-scale modeling and micro fracture mechanics. [PERSON] et al. [37] dynamically monitored fractured steel wires of main cable employing the acoustic emission technology. [PERSON] [38] analyzed fracture mechanisms of steel wires of main cable and found that possible mechanisms of crack initiation and propagation were considered to be pitting corrosion, hydrogen assisted cracking, branched cracking, and corrosion-fatigue (Figures 1, 6, and 7 in Ref. [38]). \[K_{I}=Y(\alpha)\sigma(\pi\alpha)^{1/2} \tag{3}\]  
where \(\sigma\) is the stress of specimen, \(\alpha\) is the surface crack depth, and \(y(\alpha)\) is the geometric correction factor. In conclusion, the researchers analyzed wet corrosion environment and distribution characteristics of temperature and humidity, studied tribological characteristics between steel wires in the main cable and between main cable and saddle in the atmospheric environment, discussed the effects of temperature, salt content, and pH value on corrosion behaviors of main cable, and investigated the fatigue life of main cable, crack propagation, and fracture characteristics of steel wire.