Dynamic Assessment of Timber Railroad Bridges Using Displacements

Abstract

Infrastructure spending is such a large component of a railroad budget that it must be prioritized to meet the concurrent safety and line capacity requirements. Current bridge inspection and rating practices recommend observing bridge movements under a live load to help assess bridge conditions. However, measuring bridge movements under trains in the field is a challenging task. Even when they are measured, the relationships between bridge displacements and different loads/speeds are generally unknown. The research reported herein shows the effects of known train loadings, speeds, and traffic directions on the magnitude and frequency of displacements as measured on timber pile bents of a Class I railroad bridge. Researchers collected both vertical and transverse (lateral) displacements under revenue service traffic and work trains using LVDTs with a sampling frequency of 100 Hz. To investigate the effect of traffic on timber railroad bridges, displacements were measured under crossing events at different speeds and directions of a test train of known speed and weight provided by the railroad for the field experiment. The results indicate that bridge transverse displacements could help to capture critical changes in timber railroad bridge serviceability (i.e., ability to safely carry out railroad operations) as a function of railroad loading, speed, and direction. (C) 2014 American Society of Civil Engineers