Performance Evaluation through Field Testing of Century-Old Railroad Truss Bridge

Abstract

Research has been carried out to evaluate the structural behavior and influence of aging on a century-old steel railroad truss bridge. The structure is located in Connecticut and services a large number of trains traveling into and out of New York City. The trusses are made of built-up members, with either multiple eyebars or laced channel sections. All panel point connections are joined with true pins and the interior panels are indeterminate. The bridge had experienced problems relating to the lateral shifting of some of the middepth pins. This study was carried out to evaluate the structural behavior and live load distribution throughout the bridge. A major component of the research involved extensive field monitoring. The results show that the actual live load distribution is significantly different than expected from conventional analytical approaches that were most likely used in the original design. The load distribution in multiple eyebar elements is far from uniform, and the distribution of shear through indeterminate panels is significantly different than expected from a normal truss analysis. Significant out-of-plane bending was found in the truss due to floorbeam end rotations, which is thought to be the major factor that is causing the pins to move. The study shows the necessity of using field monitoring to better understand the behavior of older bridges prior to the design of renovation approaches.