Computation methods of axial forces for main cables and short hangers of suspension bridges

To solve the problem that the axial forces of short hangers can not be measured by vibration method, nodal equilibrium method and analogy method were provided to estimate the axial forces of main cables and short hangers of suspension bridges. Nodal equilibrium method took the suspension points as analytical object to set up the over determined equilibrium equations in which the axial forces of main cables were unknown, the least squares solution of axial forces of main cables was obtained, and the axial forces of short hangers were determined. Analogy method analyzed the relationship between the axial forces of long hangers and the bending moment of equivalent beam, set up the relationship equations between the linetypes of main cables and the axial forces of long hangers to ultimately determine the horizontal tensions of main cables and the axial forces of short hangers. Guizhou Nanpan River Suspension Bridge was taken as an example, and the axial forces of main cables and hangers were estimated by using the two methods respectively. Computation result shows that calculation values by the two methods are close to the values measured by vibration method. The errors of axial forces of main cables by nodal equilibrium method are -4.3% (upstream) and 3.1% (downstream), and the errors by analogy method are -8.6% (upstream) and -0.1% (downstream). The maximum error of axial forces of long hangers by both methods is about 10%. The average errors of axial forces of upstream hangers are less than 2%, and the errors of downstream hangers are about 9%. So nodal equilibrium method and analogy method are effective to determine the axial forces of main cables and short hangers.