Suspender Replacement for a Signature Bridge

Abstract

The suspender is one of the most critical members for suspension bridges. Corrosion is the greatest degradation mechanism for suspenders during their service lives. Practices in North America have shown that the average time for the replacement of suspenders is between approximately 6 and 75 years. In this case study, three pairs of representative suspender ropes were removed and replaced on the Bronx–Whitestone Bridge, which was opened to traffic in 1939. The detailed suspender replacement procedure is presented. A refined three-dimensional (3D) finite-element (FE) model of the suspension bridge was developed to determine the jacking forces during replacement. To ensure that the new suspender tension reached a desirable value, an advanced vision-based sensor was adopted for noncontact force measurement, which eliminated the need for direct access to the suspender ropes to install conventional sensors. Subsequently, the existing suspenders that were removed were inspected visually. Three typical locations along suspenders, where dirt and water easily accumulate, were found to be especially vulnerable to corrosion: directly above the sockets, the section over the cable band, and at the suspender clamps. Finally, testing procedures are described to explain the estimation of the remaining ultimate strength of the removed existing ropes. The overall practices presented in this case study can help guide future suspender-rope replacements and investigations.