**2. Investigation and analysis of corrosion and fatigue conditions of bridge cable structures under service environment**

The survey of cable-stayed bridges built around the world shows that cable-stayed bridges are facing serious challenges and threats from cable durability issues (**Figure 1**). For example, the South Pan River Bridge in Guizhou, the original main bridge was a 240-meter span steel truss suspension bridge, which was put into operation in November 1998 and has been in operation for less than 17 years, the main cable and sling suffered from severe corrosion was dismantled in 2015 and rebuilt as a continuous rigid structure bridge. Built in 2012, the Ximo River Bridge on the county highway from Zamu Town to Murdo in Bomi County, Tibet was also facing replacement when its main cable and sling were found to be seriously corroded during an inspection in 2017. The cable of cable-stayed bridges and the suspenders of halfthrough and through-arch bridges are more frequently replaced due to corrosion damage and reduced reliability. The St. Nazaire Bridge in France suffered from severe corrosion during its service life, with extensive rusting and spalling of the cable

#### **Figure 1.**

*Corrosion and fatigue damage of cable-stayed bridges in mountainous areas with cable-stayed cable, suspension cable, and main cable.*

#### *Corrosion Fatigue Behavior and Damage Mechanism of the Bridge Cable Structures DOI: http://dx.doi.org/10.5772/intechopen.109105*

surfaces. After two years of operation, the Kohlbrand Estuary Bridge in Germany suffered from severe corrosion at the lower anchorage end of its cable, with 25 broken wires in the cable, and the entire bridge was replaced at the cost of \$60 million or four times as much as original cost. The cost of replacing the corroded cable-stay on the Maracaibo Bridge in Venezuela is also about \$50 million.

Japan and the United States have conducted experimental and theoretical studies on the corrosion of cable for a long time, especially the corrosion of cable in the marine environment. The Honshu-Shikoku Bridge Management Department in Japan has accumulated years of survey data through on-site investigations and detailed knowledge of the damage caused by corrosion of cable in several cable-stayed and suspension bridges during operation and has conducted research on preventive maintenance methods for cable, proposing measures such as anticorrosion coating coverage, ventilation, and dehumidification, as well as static and dynamic behavior monitoring [1]. Kheyroddin [2] used seawater as a corrosive medium and carried out accelerated corrosion tests under static stress to comparatively study the anticorrosion effect of different protection systems. In addition, Barton [3] focused on the corrosion behavior of lasso in NaCl corrosive medium by artificially accelerated corrosion experiment, obtaining the weight loss of steel wire samples, hydrogen concentration, elongation, etc. The results of the study showed that water and temperature are the environmental factors most likely to cause corrosion of lasso, and accelerated corrosion test proves that the most serious corrosion occurs at the anchored end of lasso, the middle and the top end is less affected by corrosion, and the increase of NaCl concentration in the solution and temperature will accelerate the corrosion process of galvanized steel strands. In 1987, Dolley [4] and Mahmoud [5] surveyed nearly 100 cable-stayed bridges around the world and conducted a visual inspection of the bridges, finding that "nearly 200 cable-stayed bridges built worldwide in the last few decades are at risk due to cable corrosion." The new parallel wire system that was introduced in Japan also has a corrosion resistance life of only 25–30 years. Cablestayed bridges are experiencing serious challenges and threats from cable durability issues [6–10].
