## 4 Improvement Measures  
According to the above analysis, the riding comfort of a straddle-type monorail could not meet the travel requirements under several operating conditions and thus required further improvements. This study proposed some improvement measures from the perspectives of the bridge parameters. A larger vertical response, results in violent bridge vibrations, which affect the riding comfort of a straddle-type monorail. According to the above analysis, the vertical response of a bridge is mainly affected by the vertical stiffness and the load on the bridge; hence, this study attempted to reduce the coupling vibration and improve the riding comfort by increasing the stiffness of the bridge. To increase the vertical stiffness, the beam height could be increased, as shown in Figure 13a. To increase the lateral stiffness of a bridge, two methods were proposed in this study, as shown in Figure 13b,c. The first of these methods involved increasing the thickness of the cross-beams, wherein the thickness of the end cross-beams were changed from 0.78 m to 1.5 m, and the thickness of the middle beam was changed from 0.25 m to 0.5 m. The other method involved setting the external beams between the two track beams, wherein the thickness of the end external beams was 1.5 m, and the thickness of the middle external beams was 0.5 m; note that the height was set to 0.15 m, as it was limited by the height of the track beam, and the construction of the vehicle bogie. The improvement measures are summarized in Table 9.  
In the dynamic analysis, the running speed of the straddle-type monorail was 65 km/h, the height of the bridge pier was 7 m, and the American six-level track irregularity and rated load were adopted. The responses of the bridge and the train under different improvement measures are shown in Figure 14.  
Figure 13: Improvement measures for the bridge—(**a**) increasing the thickness of the inner cross-beams (mm), (**b**) increasing the beam height (mm), and (**c**) setting external cross-beams (mm). \begin{table}
\begin{tabular}{c c} \hline \hline
**Case No.** & **Description of the Improvement Measures** \\ \hline
1 & None \\
2 & Increase the thickness of the inner cross-beams \\
3 & Set two end external cross-beams \\
4 & Set two end external cross-beams and three middle external cross-beams \\
5 & Increase the beam height to 1.7 m \\
6 & Increase the beam height to 1.7 m, and increase the thickness of the inner cross-beams \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Improvement measures. Figure 14a-c show that increasing the width of the inner cross-beams could reduce the deformation and midspan acceleration of the bridge to a certain extent and could substantially reduce the lateral responses of the bridge. The essence of this measure was to increase the local transverse and vertical stiffness of the bridge to weaken the bridge deformation. When only the track beam height was increased (to 1.7 m), the responses of the bridge decreased substantially, and the improvement effect was superior to that of the first method. The reason was that the increase in beam height created a larger cross-section of the track beam; hence, the vertical stiffness was improved. In addition, the section hollowing area remained the same, the section hollowing rate decreased, and the transverse stiffness was improved. When the width of the inner beam was increased on the basis that the height of the track beam was 1.7 m, the bridge response results were similar to that when only the beam height was increased. The reason was that the track beam had a large stiffness, and the increase in stiffness provided by the widened inner beams was not obvious, as compared to the stiffness of the track beam. The vertical deflection, vertical acceleration, midspan torsion angle, and beam end bending angle of the bridge all decreased, whereas the transverse deformation and acceleration of the bridge increased when only two external end cross-beams were placed between the two track beams.