# Review of the Main Cable Shape Control of the Suspension Bridge
## 3 Construction Control Technology of the Main Cable
### Sag Control of Cable Strands  
An important step in building the main cable is adjusting the strands' sag. Controlling the sag of the cable strand, regardless of the type of erection technique used, is essential for maintaining control over the main cable shape. Particularly, China is experiencing a period of tremendous development for suspension bridges, where many of the recent \begin{table}
\begin{tabular}{c c c} \hline \hline
**Item Compared** & **AS Approach [57; 59; 63]** & **PPWS Approach [57; 58; 62; 64]** \\ \hline production & on-site strand forming; steel wire needs joint length; steel wire crossing is inevitable; quality is difficult to control & factory-production; uniform length; controllable quality. \\ \hline \multirow{2}{*}{erection} & larger affected by weather; slower erection; no need for large equipment; more temporary equipment & fast erection; large capacity requirements for transport and traction equipment \\ \hline \multirow{2}{*}{f forced condition} & the small bending radius of the anchor head leads to larger secondary stress; anchor connection with the large and complex force & uniform cable force; small secondary stress; simple anchor connection structure \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of characteristics of two methods. Figure 9: The main procedures of the PPWS method: (**a**) arrangement and binding of the steel wire, (**b**) the strand forming, (**c**) transportation of the strand, (**d**) the traction of the strand, (**e**) adjustment of the strand, (**f**) main cable forming. works on this subject have been carried out. Through literature surveys [57; 64; 65; 66], the general principles for the current adjustment of the sag of cable strands are summarized in the following. 1. [label=(0)]
2. Sag adjustment method
3. In installing the main cable, the first strand is usually exploited as the reference strand, whose mid-span sag is controlled through absolute elevation. A strand other than the reference strand is called a general strand, whose mid-span sag is controlled by the height difference from the reference strand. The adjustment of each cable strand is carried out in accordance with the principle of the main span first, then the side span, and finally, the anchor span. The core of sag adjustment calculation is aimed at determining the relationship equation between the adjustment of the unstressed cable length and the deviation of the sag, which is called the cable adjustment formula here. Although the cable adjustment formula [67; 68] derived from the parabolic theory is easy to calculate, there are differences between the parabola and the actual shape of the cable. [PERSON] et al. [69] used catenary theory to derive the cable adjustment formula and obtained accurate results. However, the calculation is cumbersome and requires repeated iterations. Unlike the above derivation, [PERSON] [70] utilized the strand adjustment formula obtained via data fitting to adjust the reference strand of the Ying Wuzhou Yangtze River Bridge in China. An improved approach for reference strand adjustment calculation was also proposed by [PERSON] et al. [71]. The main cable shape equation was expanded using the Taylor formula at the targetfree cable state. The relationship between the cable length adjustment and the mid-span vector height variation was then obtained by solving the expanded equation. The method is easy to calculate and is highly accurate. The key to sag adjustment is to ensure the accuracy of the reference strand alignment. In order to prevent the reference strand from being squeezed and become drooping by the general strand in the later stage, some scholars have made special treatment of the reference strand, such as the use of relative reference strands [72; 73], adding strands that are not part of the main cable as a reference [74], and canceling the sag adjustment step [75]. To reduce the error accumulation in the main cable section of the Run Yang Bridge, [PERSON] et al.