## 5 Conclusions  
Structural uncertainty is an important factor for seismic fragility analysis of high-speed railway extradosed cable-stayed bridges. It is an effective way to study the influence of random parameters on seismic demand response with nonlinear dynamic time-history analysis by using probabilistic reliability method fully considering the random distribution of the parameters. Based on the above analysis, several conclusions can be drawn as follows:  
1. SFDP are greatly affected by structural uncertainty. The sensitive parameters with the greatest influence on dynamic response are the friction coefficient of bearing, concrete bulk density, damping ratio, peak compressive strength of confined concrete, component size and peak strain of confined concrete. The secondary parameters are the strength and strain of unconfined concrete, the impact of which on the bridge cannot be ignored. The other parameters are insensitive to responses of high-speed railway extradosed cable-stayed bridges;
2. The effects of material properties and cross-section should be fully considered for nonlinear dynamic time-history analysis. Therefore, accurate calculation of material parameter characteristics and accurate simulation of structural characteristics are the prerequisites for ensuring accurate and reliable calculation results. In addition, the variation ratio of cable force is less sensitive than other SFDP, and it is difficult to quantify the seismic function damage;
3. Structural uncertainty has a great impact on the dynamic response of high-speed railway extradosed cable-stayed bridges, and it is quite different from traditional static parameter sensitivity analysis. Therefore, it is necessary to clarify the influence of random parameters on the bridge dynamic responses, and to explore the relationship between seismic demand and structural random parameters.  
Based on probability and mathematical statistics, this study examined the sensitivity of structural uncertainty of high-speed railway extradosed cable-stayed bridge to seismic fragility demand parameters, and the influence of structural parameter changes on seismic demand parameters was obtained. On the basis of this, a seismic vulnerability analysis of a high-speed railway extradosed cable-stayed bridge will be carried out in the near future. The seismic damage characteristics of the bridge will be systematically studied, and the seismic damage probability of the structure will be proved; this will provide reference for bridge design and post-earthquake operation management. Furthermore, the research on structural health monitoring (SHM) will be carried out in the near future using the method proposed in this paper.  
Conceptualization, M.X.; Software, J.Y. and S.H.; Validation, H.J. and Y.Y.; Investigation, B.S.; Data curation, B.S.; Writing--original draft, J.Y.; Writing--review & editing, M.X.; Funding acquisition, M.X. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Sichuan Science and Technology Program, grant number 2020 YJ0081; the Fundamental Research Funds for the Central Universities, grant number 2682021 CX011; and the Science and Technology Research and Development Project of China National Railway Group Co., Ltd., grant number P2019T001. The authors would like to express their sincere gratitude to the sponsor for the financial support.  
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The authors declare no conflict of interest.