# Review of the Main Cable Shape Control of the Suspension Bridge
## 3 Construction Control Technology of the Main Cable
### Sag Control of Cable Strands
To reduce the mutual interference between the strands in the erection process, and to alter the fuzzy requirements of the above idea, some scholars have quantified the inter-strand distance. The reference strand will be pressed by general strands, due to internal and external temperature differences. During the erection of the Minami Bisan-Seto Bridge's reference strand in Japan [57], the height of the reference strand was raised compared with the theoretical position according to experience, but no specific basis or numerical value was given. When a suspension bridge was being built in Southwest China, the ideal state was not achieved when the strands were erected according to the principle of \"half approaching, half separation\". To avoid the accumulation of errors, the second reference strand was exploited in time [85]. In the erection of the strands of the Miaozui Yangtze River Bridge [86], all the general strands were raised by 3 cm compared with the reference strand, to prevent the compression of the reference strand. The inter-strand distance was quantified while Jin Dong Bridge's main cable was erected [65]. The inter-strand distance, denoted by d in Figure 12, represents the difference between a circle's diameter having an area equal to a hexagon, and the vertical separation between the top and bottom borders of the hexagon. During the erection of the strands of the Wu Fengshan Yangtze River Bridge [84], the temperature difference of 0.5 \({}^{\circ}\)C determined how far the strands were spaced in the main span's center; that is, to ensure that the strands would not collide with each other over a temperature range of 0.5 \({}^{\circ}\)C.  
According to the literature analysis, currently, there are four methods for controlling the inter-strand distance in the main cable erection process, as shown in Figure 13. The first method is that the inter-strand distance is controlled according to the principle of \"half approaching, half separation\". Nevertheless, it is difficult to achieve due to the existence of errors, and new reference strands must be added [85]. The second approach is to raise all the strands to a particular height [57]. The third method is to lift all the general strands as a whole to a specific height [86], and the fourth approach is to lift all the general strands to a specific height over the adjacent layer [65; 84]. From the above, there is no unified \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Subjects**} & \multicolumn{2}{c}{**Allowable Deviation**} \\  & & **(mm)** \\ \hline \multirow{4}{*}{strands elevation} & mid-span of the main span & \(\pm\)/20,000 \\ \cline{2-3}  & \multirow{2}{*}{reference strand} & mid-span of side span & \(\pm\)/10,000 \\ \cline{3-3}  & & upstream and downstream & 10 \\ \cline{3-3}  & & elevation difference & \(-\)5\(\leftrightarrow\)10 \\ \hline \hline \end{tabular} Note: \(l\) = represents the distance between two adjacent saddle IP points; IP = stands for the theoretical intersection points of the main cable at the saddle.  
\end{table} 
Table 2: Precision requirements of strands erection. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{1}{c}{**Bridge**} &
\begin{tabular}{c} **Allowable Height Difference between** \\ **General Strands and Reference Strand** \\ \end{tabular} \\ \hline Runyang Bridge [72], Ma Anshan Bridge [81] & 0\(\rightarrow\)5 mm \\ \hline a self-anchored suspension bridge in China [82] & 0\(\rightarrow\)15 mm \\ \hline Aizhai Bridge [83] & \(-\)5 mm\(\rightarrow\)+5 mm \\ \hline Wu Fengshan Yangtze River Bridge [84] & \(-\)5 mm\(\rightarrow\)+10 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Control standards for erection accuracy of various bridges. control or evaluation standard for cable erection. The main reason is that the cable erection alignment is sensitive to error factors. Complex influencing factors and an irreversible erection process make it difficult to form a unified and accurate control method.