## 4 Analysis of Structural Uncertainty
### Analysis of Structural Uncertainty
Meanwhile, the influence of the ultimate strain of confined concrete is 43.5%, and that of the ultimate strain of unconfined concrete is 12.8%. In summary, pier-bottom curvature is less sensitive to other parameters, the influences of which are less than 10%. For the curvature of the pylon bottom, the damping ratio has the greatest impact, reaching 55.6%, followed by the peak strain of confined concrete, with an influence of 45.1%. The influence of pylon-section size  
Figure 13: Sensitivity of SFDP under the longitudinal ground motion. (**a**) Curvature sensitivity of pier bottom (**b**) Displacement sensitivity of pier top (**c**) Cable force sensitivity (**d**) Main girder angle sensitivity (**e**) Curvature sensitivity of pylon bottom (**f**) Bearing displacement sensitivity. and height are 43.5%, and that of concrete bulk density is 40.4%. Meanwhile, the impact of the peak compressive strength of confined concrete is 25.1%, and other parameters have little influence on the pylon-bottom curvature. Compared with the other SFDP, there are more parameters that affect the bearing displacement. According to their impact, they are damping ratio, peak compressive strength of confined concrete, concrete bulk density, peak strain of confined concrete, friction coefficient of bearing, component size, ultimate strain of confined concrete and peak strain of unconfined concrete with influences of 53.2%, 45.2%, 41.0%, 35.9%, 30.2%, 29.8%, 26.0% and 12.9%, respectively. Other parameters have little influence on the bearing displacements. The corresponding figures also show that for this type of extradosed cable-stayed bridge, the influence of random parameters on the bearing displacement of each pier and the proportion of variation present different characteristics. In addition, the influences of both the absolute value and sensitivity of random parameters on the cable force are relatively small. The cable force is less sensitive to each parameter, and its variation is relatively small. It further indicates that for this type of bridge, the variation ratio of cable force is less sensitive than other SFDP, and it is difficult to quantify the seismic function damage. The sensitivity Tornado diagram of SFDP affected by random parameters under longitudinal earthquake is shown in Figure 14.  
Sensitivity results of SFDP under the transverse ground motion are shown in Figure 15a-f.  
Figure 14: SFDP sensitivity of Tornado Diagram under longitudinal earthquake. According to Figure 15a-f, for pier-top displacement under transverse ground motions, the maximum influence of the bearing friction coefficient is 84.5%, and the influence of concrete bulk density is 81.1%. Meanwhile, the influence of the peak strain of confined concrete, peak compressive strength of confined concrete and component size are 75.2%, 43.2% and 33.8%, respectively. Compared with other random variables, these five parameters, which are more sensitive, have a greater impact on the dynamic response of the pier-top displacement of an extradosed cable-stayed bridge. For the main girder angle, the maximum influence of the bearing friction coefficient is 69.8%, while peak strain of confined concrete and concrete bulk density are very close with the influence of 66.5% and 65.3%, respectively. The influence of the peak compressive strength of confined concrete is 48.6%, and that of component size is 33.8%. The influence of these five parameters is greater than that of other parameters. For the influence of the pier-bottom curvature, the friction coefficient of bearing can reach 135.5%. The second largest influence on the curvature is concrete bulk density, which can reach 104.7%. The influence of the peak strain of confined concrete is 97.8%, and that of peak compressive strength of confined concrete is 80.4%. Meanwhile, the influence of component size is 48.1%. In summary, pier-bottom curvature is less sensitive to other parameters, for which the influences are less than 10%, except for the damping ratio which has an influence of 19.3%.