Real-Time Reference-Free Displacement of Railroad Bridges during Train-Crossing Events

Abstract

Today, railroads carry 40% of the United States’ freight tonnage, and the demand for this service is expected to double in 20 years. The railroad infrastructure contains more than 100,000 bridges spanning over 225,000 km of tracks. Half of those bridges are over 100 years old. Accordingly, safe and efficient railroad operations depend on the continuous maintenance of this aging bridge network. Recent research has demonstrated that bridge displacements can be utilized as an indication of structural integrity in the prioritization of maintenance, repair, and replacement (MRR) operations. However, existing response-measurement methods either require expensive technological instrumentation or are based on complex structural modeling assumptions. Furthermore, many of them do not accommodate real-time monitoring. This paper proposes a new methodology fusing multimetric measurement data obtained from reference-free sensors, such as accelerometers and tiltmeters, in real time to provide accurate transverse displacement measurements inexpensively. Twenty-four percent of railroad bridges in the United States are timber. Therefore, to study the performance of the proposed method, a realistic train-crossing event was simulated by using a numerical model of a timber pile bent. Timber piles were simplified as free-standing cantilever beams accounting for the soil–structure interaction based on literature and industry input. The model was excited dynamically with real train input loads collected at the site. The analysis reproduced nonsymmetric bridge responses, including pseudostatic displacements observed in the field, which conventional accelerometers cannot measure. The pseudostatic displacements from tiltmeter data were extracted using simple Euler-Bernoulli beam equations that can be estimated for any railroad timber pile bent, requiring only the length of the pile above ground as the input. These pseudostatic responses were combined with dynamic displacements derived from accelerometer data, allowing the estimation of the transverse displacement in the field without the need of a finite-element model. Researchers compared measured responses to displacements estimated by the proposed data-fusion method. The results indicate that transverse bridge displacements can be determined by combining pseudostatic and dynamic responses in real time more precisely compared to previous methods. Consequently, more effective MRR prioritization can be undertaken with accurate response measurement.