Modal and damage identification based on ambient excitation can greatly improve the efficiency of high-speed railway bridge vibration detection. This paper first describes the basic principles of stochastic subspace identification, peak-picking, and frequency domain decomposition method in modal analysis based on ambient excitation, and the effectiveness of these three methods is verified through finite element calculation and numerical simulation. Then the damage element is added to the finite element model to simulate the crack, and the curvature mode difference and the curvature mode area difference square ratio are calculated by using the stochastic subspace identification results to verify their ability of damage identification and location. Finally, the above modal and damage identification techniques are integrated to develop a bridge modal and damage identification software platform. The final results show that all three modal identification methods can accurately identify the vibration frequency and mode shape, both damage identification methods can accurately identify and locate the damage, and the developed software platform is simple and efficient.

This paper reports a method for strand tension in anchor spans considering rotation. A kind of co-moved coordinate system, a saddle local coordinate system, was set up. This system implemented the rotation of the splay saddle through the rotation of the coordinate system, and all calculations proceeded in this coordinate system. Considering the rotation of the anchoring surface by the rotation of the local coordinate system of the anchoring surface, the anchorage point coordinates of strands were transformed to the local saddle coordinate system. There was a two-layer iteration adopted in the calculation. In the inner iteration, the cable force at the end of the vertical bend was taken as the variable, and the ordinate of the anchorage point was taken as the target value. In the outer iteration, the vertical tangential angle at the end of the vertical bend was taken as the variable, and the ordinate of the anchorage point was taken as the target value. The method carried out the rotation of the splay saddle and anchor surface and was simple, convenient and without approximation. The effect of rotation was considered precisely; it showed stability during the process of two-layer iteration, powerful adaptation and higher efficiency and had been successfully applied in the construction control of the Wufengshan Yangtze River Bridge, the world's first kilometer-level combined highway and railway suspension bridge.