## 6 Conclusions  
In this study, a parameter sensitivity analysis is conducted on the buffeting control of a long-span triple-tower suspension bridge with MTMD. The following conclusions can be drawn accordingly:  
* The buffeting responses of Taizhou Bridge are the most prominent in the central region of each main span. The lateral buffeting displacement is dominated by the AS-L-1 mode and the S-L-1 mode while the vertical displacement is dominated by the AS-V-1 mode.
* The control efficiency of MTMD firstly increases with the augment of the number of TMDs, but the rising trend gradually levels off and finally becomes stable. The effect of MTMD can be fully exerted when the amount of TMDs is big enough with effective frequencies densely distributed in the given frequency bandwidth.
* The augment of the mass ratio has a positive contribution to the control efficiency of the MTMD. However, the structural modal frequency will have a big shift from the design value when the mass ratio is too large, which even leads to the decreasing of the attenuation factor of the MTMD.
* The damping ratio has less influence on the control efficiency of the MTMD. Increasing the damping is beneficial for the energy dissipation of the structure, but when the damping ratio goes up to a certain level, the movement of the mass block will be suppressed to cause the decline of the MTMD control effect.
* When the frequency bandwidth ratio is small, the effective frequencies that can be controlled are rather limited. Hence, the control efficiency of the MTMD firstly increases to a peak with the augment of the frequency bandwidth ratio. However, when the frequency bandwidth ratio increases, the frequency difference between two adjacent TMDs increases. Then, only some discrete frequencies can be controlled, which accounts for the decreasing of the control efficiency.  
Figure 20: PSD comparison of the buffeting displacements with and without MTMD: (**a**) Lateral; (**b**) Vertical.  
* The performance of the MTMD with small frequency bandwidth ratios is sensitive to the frequency variation, but it can be obviously alleviated when utilizing high frequency bandwidth ratios. That means increasing the frequency bandwidth ratio can improve the robustness of the MTMD.
* The preferred mechanical parameters of the MTMD can be easily determined by the presented step-updating framework. With the MTMD application, the buffeting responses of the long-span triple-tower suspension bridge under strong winds can be effectively mitigated.  
The authors would like to gratefully acknowledge the supports from the National Basic Research Program of China (973 Program) (Grant No. 2015 CB060000), the National Science Foundation of China (Grant No. 51378111), the Fundamental Research Funds for the Central Universities (Grant No. 2242015K42028), the Funding of Jiangsu Innovation Program for Graduate Education (Grant No. KYLX16_0258), the Scientific Research Foundation of Graduate School of Southeast University (Grant No. YBJJ1659), the National Project Funded by the China Scholarship Council (Grant No. 201606090054), and the Project of Innovation-Driven Planning in Central South University (2015 CX006). All authors discussed and agreed upon the idea and made scientific contributions. [PERSON] did the numerical simulation and parametric analyses. [PERSON] and [PERSON] wrote the paper and completed the revisions. [PERSON] and [PERSON] gave some reasonable suggestions in simulation and participated in the revisions of the manuscript.  
The authors declare no conflict of interest.