Analytical methods for the assessment of hanger forces of a suspension bridge based on measured main cable configuration

Abstract

The accurate measurement of the hanger tensile forces of suspension bridges is crucial for construction control and bridge maintenance. However, the commonly used vibration frequency method is not applicable to the short-hanger force assessment. The configuration of the main cable of a suspension bridge is closely related to hanger forces so that the main cable configuration can reflect the hanger forces. Based on the multi-segment catenary theory, this study proposed an analytical algorithm for the reverse assessment of hanger forces based on the measured configuration data of the main cable. First, the relationship between the hanger force and two critical parameters, that is, the horizontal force of the main cable and the catenary parameter, is established, in which the influence of the saddle arc on the main cable configuration is considered. Then, the horizontal force of the main cable is used as the breakthrough point, and a geometric condition (measuring the coordinates of a non-hanging point on the main cable) or a mechanical condition (measuring the tension of a long hanger by the vibration frequency method) is added. Using the nonlinear generalized reduced gradient method, the nonlinear equations are solved, and all hanger forces are identified. The proposed method feasibility and effectiveness are proved using a suspension bridge with a main span of 730 m as an example. The results show that the algorithm of adding a mechanical condition is lower in sensitivity, less affected by the accuracy of the additional condition, higher in precision, and easier to control, comparing to that of adding a geometric condition. Meanwhile, the horizontal force of the main cable and each hanger force exhibit a nearly perfect linear correlation.