# Review on the Service Safety Assessment of Main Cable of Long Span Multi-Tower Suspension Bridge
## 2 The Tribo-Corrosion-Fatigue  
In the aspect of environmental conditions of main cable, [PERSON] et al. [22] presented the corrosion status of main cable in the humid corrosive marine environment (Figure 1 in Ref. [22]) and analyzed anti-corrosion measures. [PERSON] et al. [22] and [PERSON] et al. [23] measured the in-situ temperature and humidity at the saddle and anchor chamber locations (Figures 2 and 3 in Ref. [23]), and indicated the good heat insulation effect of anchor chamber and sharp variations of temperature and humidity at the saddle location greatly affected by solar radiation and air convection. Meanwhile, they proposed that the change and distribution of humidity in the main cable was mainly influenced by the temperature field, and in turn affected the temperature distribution [22]. Considering friction behaviors of main cable, [PERSON] et al. [24] found the friction between parallel steel wires, redistributions of stresses of steel wires adjacent to the fractured wire, and the fractured wire far away from the fracture location restoring part of load-bearing capacity. [PERSON] et al. [25] established the balance equation of friction force between main cable strand and saddle at any longitudinal contact locations (Equation (1)) and basic theoretical equation of frictional characteristics between main cable strand and saddle in the parallel model of sub saddle (Equation (2)). They also proposed the total friction force between the main cable strand and saddle mainly composed of friction forces between the main cable strand and bottom surface/side wall of cable groove. However, the friction force between main cable strand and bottom surface accounted for 70% of total friction force. [PERSON] et al. [26] established the friction resistance model between main cable and saddle of multi-tower suspension bridge, and found the friction resistance between main cable and saddle composed of friction resistances between main cable and saddle groove/diaphrag (Figures 1, 2, and 7 in Ref. [26]). It was revealed that using one horizontal friction plate was more effective in enhancing friction resistance than using one vertical friction plate. However, the total number of vertical friction plate could be much greater than that of horizontal friction plates in engineering practice. Using one horizontal friction plate in the saddle could increased frictional resistance by up to 107% and the nominal coefficient of friction by up to 78%. Using 12 vertical friction plates in the saddle could increase the frictional resistance by up to 187% and the nominal coefficient of friction by up to 128%. \[2\cdot\mu_{0}\cdot f_{H}+\mu_{0}\cdot\sum_{i=1}^{n_{\text{cougar}}}f_{sr}^{i}- \mu_{n}\cdot\sum_{i=1}^{n_{\text{cougar}}}f_{sr}^{i}=0 \tag{1}\]  
\[f(\mu_{0})=\left(2\cdot f_{H}^{c}+4\cdot f_{H}^{b}+f_{sr}^{c}+2f_{sr}^{b} \right)\cdot\mu_{0}-\left(f_{sr}^{c}+2f_{sr}^{b}\right)\cdot\mu_{n} \tag{2}\]  
where \(f_{H}^{c}\) and \(f_{H}^{b}\) are total lateral forces in height ranges of central strands and side strands, respectively, while \(f_{sr}^{c}\) and \(f_{sr}^{b}\) are radial pressure of central and side strands, respectively. According to corrosion behaviors of main cable, [PERSON] and [PERSON] [27] studied the effect of corrosion level on the tensile strength of galvanized steel wire of main cable. [PERSON] [28] and [PERSON] [29] discussed corrosion mechanisms and corrosion protection strategies of main cables of long-span suspension bridge. They proposed that water, harmful gas, and fatigue stress were main reasons of chemical corrosion and stress corrosion of steel wires and thus greatly affected the endurance of main cable. Meanwhile, they suggested the applications of galvanized steel wires to increase the corrosion resistance of steel wires and sealing measures to cut off the contacts between steel wires and external corrosive media. [PERSON] [30] discussed corrosion mechanisms of steel wires and their galvanized layers, and presented reaction mechanisms of galvanized steel wires in the acid solution (Figure 3-1 in Ref.