Civil Engineering ETDs

Publication Date

Spring 5-2017


The railroad network carries 40 % of the freight in the US. Railroad bridges are the most critical part of the network and they need to be properly maintained for safety of operations. Railroad managers need to inspect the bridges in order to assess their structural condition. Railroad managers are interested in measuring displacements under train crossing events to prioritize their bridge management and safety decisions. However, bridge displacements are difficult to collect in the field, because they require a fixed reference from where to measure. Accelerations can be used to estimate dynamic displacements but to this date, the pseudo-static displacements cannot be measured using reference-free sensors. This study proposes a method to estimate the total displacements of a railroad bridge under live train loads using acceleration and tilt data without a need for fixed reference. Researchers used real bridge displacement data representing different bridge serviceability level under train traffic. This study explores the design of a new bridge deck-pier experimental model that simulates the vibrations of railroad bridges under traffic. This experiment configuration includes the use of a shake table to input the recorded signal from the field into a railroad pile bent. Reference-free sensors measured both the inclination angle and accelerations of the pile cap. The different acceleration readings are used to estimate the total displacements of the bridge using data filtering. The estimated displacements are then compared to the true responses of the model measured with displacement sensors. The results show that this method can cost-effectively measure the total displacement of railroad bridges without a fixed reference. In addition, this paper studies the use of a low-cost data acquisition platform to measure reference-free dynamic displacements of railroad bridges by combining low-cost microcontrollers and accelerometers. Researchers used the new system to measure accelerations and reconstruct reference-free displacements from several railroad bridge crossing events. The results obtained from the proposed low-cost sensors were compared with those of commercial sensing equipment. The results show that low-cost sensors and commercial sensing systems can measure reference-free displacements with comparable accuracy. The results of this study show that the proposed platform estimates reference-free displacements with a peak error between 20 % and 30 % and a root mean square (RMS) error between 10 % and 20 %, which is similar to commercial SHM systems. The proposed low-cost system is approximately 300 times less expensive than the commercial sensing equipment. In conclusion, this study evaluates the accuracy of cost-effective systems to measure the reference-free displacement of railroad bridges. The conclusions of this study propose a cost-effective method to measure the reference-free displacement of railroad bridges that all railroad companies can afford. The ultimate goal of this research is to provide stakeholders with means to design, develop, own, and operate their own SHM systems.


Structural Health Monitoring; Displacements; Accelerations; Low-Cost; Tilt

Document Type




Degree Name

Civil Engineering

Level of Degree


Department Name

Civil Engineering

First Committee Member (Chair)

Fernando Moreu Alonso

Second Committee Member

Mahmoud Reda Taha

Third Committee Member

Timothy Jack Ross