Measurement and Comparative Study on Movements of Suspenders in Long-Span Suspension Bridges

Abstract

Unanticipated damage has been observed in short suspenders near the midspan and/or ends of long-span suspension bridges. The observed damage poses a major threat to public safety if it results in fracture of suspenders which, in extreme cases, may lead to the progressive collapse of a structure. This study presents an investigation of the vibrations of suspenders, stresses in the suspender lower ends, and movement of the main cable relative to the girder based on field measurements of the Jiangyin Yangtze River Bridge (JYB) to determine the excitation-induced responses and damage mechanisms of the suspender. The results revealed that longitudinal relative movement between the main cable and girder under repetitive traffic loads could result in cyclic local bending deformation and large stress concentrations in short suspender ends; however, for long suspenders that are more flexible, the bending deformation was distributed over a larger length, preventing high stress concentrations and subsequent fatigue damage. A comparative study was conducted on the Runyang suspension bridge (RSB), which is similar to the JYB except that rigid central clamps were substituted for the shortest suspenders at midspan to inhibit differential movement and damage of the short suspenders. Results demonstrate that the central clamp can significantly mitigate the bending stress in the short suspenders by reducing the relative motion between the main cable and girder in the RSB.