Measuring Total Transverse Reference-Free Displacements for Condition Assessment of Timber Railroad Bridges: Experimental Validation

Abstract

Today, the railroad industry carries 4% of the United States’ total freight ton-miles over 1, bridges spanning over 225, km (14, mi) of rail tracks and the demand for railroads will increase by 88% by 235. Railroads maintain their infrastructure to meet this demand and ensure the ability of the bridges to safely carry trains. However, railroad funds are limited and the allocation of resources for operations of maintenance, repair, and replacement (MRR) must be conducted cost effectively. Railroad managers are interested in new and innovative methods to efficiently quantify the structural performance of their bridges. Total transverse bridge displacements provide objective data about structural integrity, informing the prioritization of MRR operations. Measuring bridge displacement with traditional sensors such as a linear variable differential transformer (LVDT) is often difficult because of the need for a fixed reference frame. Likewise, modern reference-free and noncontact response measurement approaches require methods that are expensive, technologically complex, or computationally prohibitive for bridge managers. This paper investigates the feasibility of a novel approach for measuring total reference-free transverse displacements of railroad bridges by aggregating data obtained from multiple sensors, where train derailment because of excessive transverse movement is the main concern. The method implements a finite impulse response (FIR) filter to compute drift-free dynamic displacement by using acceleration measurements. Similarly, a moving average (MA) filter extracts the low-frequency content from inclination captured with two accelerometers. The low-frequency inclination is then converted to pseudostatic displacement using Euler–Bernoulli beam equations. These pseudostatic responses are combined with dynamic displacements derived from accelerometer data, allowing estimatation of the total reference-free transverse displacement in the field. To verify the performance of the proposed method, a cantilever column representing a timber bridge pile was tested in the laboratory using a shake table and excited with a number of displacement measurements taken in the field from a timber railroad bridge. The results were compared to reference displacements captured with an LVDT, demonstrating that total reference-free transverse displacements can be accurately measured. As a conclusion, the proposed approach can be used as a viable tool supporting data-based informed decisions and has the potential to maximize the efficiency of railroad bridge network management systems.