Safety Assessment of the Antisliding between the Main Cable and Middle Saddle of a Three-Pylon Suspension Bridge Considering Traffic Load Modeling

Abstract

The antisliding safety of the middle saddle is a key issue for the design of three-pylon suspension bridges. Vehicle load is the main adverse effect, especially unsymmetrical vehicle load. A general mechanical model on the saddle sliding behavior is reviewed and proposed, and then characteristics of load responses of the main cable are investigated to explore a simplified live load computational method. Based on the deterministic approach from codes and a reliability-based approach, the antisliding safety of the middle saddle is discussed and assessed for the Taizhou Yangtze River Bridge, which has two symmetrical spans of 1,080 m. The study shows that geometric nonlinearity caused by dead load has a big effect on the load responses of the main cable, so it must be included in the design. Further, the maximum difference between the geometrically linear and nonlinear cases due to live load is up to 12.71%, whereas in all conditions, the balanced static friction coefficient is smaller without consideration of the geometric nonlinearity caused by live load. This means that the assessment of the antisliding safety of saddles is more conservative when live load geometric nonlinearity is not included, and the linear superposition principle between traffic load and influence surface can be directly applied. The results based on the deterministic approach from codes indicate that the antisliding safety factor of the middle saddle is larger than 1, which ensures that there is no sliding between the middle saddle and the main cable. However, the results from different codes differ because of the different requirements for the parameters. Therefore, based on a reliability approach, a probabilistic model of the saddle with balanced static friction coefficient is developed, which includes the effect of traffic by using weigh-in-motion (WIM) data and random synthetic vehicle flow simulation. In the paper, the maximum static friction coefficient model is obtained through the experimental data of cables, and the antisliding safety assessment of the saddle is made for different traffic conditions. All antisliding reliability indices are larger than 4.9, indicating that the saddle has good antisliding behavior in reserve.