Electrical and Computer Engineering ETDs

Publication Date

Fall 12-18-2017


The railroad network in the united states is one of the best in the world, handling around 40 percent of all US freight movement. To maintain the serviceability and cost-effective operation of the railway infrastructure, regular monitoring is essential. Bridges are a critical part of the railway infrastructure and their timely maintenance and repair are important. Measuring transverse bridge displacement under train loading can assist to determine the bridge condition. The traditional methods available for transverse displacement measurement include Linear Variable Differential Transducers (LVDT). However, irregular terrain, remote and inaccessible locations, and the height of railroad bridges make implementation of these sensors for transverse displacement measurement either inadequate, or risky and time-consuming, and sometimes not possible altogether. Alternatively, railroads can monitor transverse bridge displacement using non-contact sensing with instruments such as robotic total station (RTS) and high-speed cameras. In recent years, the use of Laser Doppler Vibrometers (LDV) has started to draw some attention in the field of non-contact transverse bridge displacement measurement. However, in these applications, the instruments are generally placed on a fixed reference close to the bridge. It is not always possible to find this fixed reference point, especially when a bridge is spanning over a large opening, like a water body. In addition, a fixed reference point would require calibration of the measurement for every different bridge individually. Researchers use Unmanned Aerial Systems (UAS) to acquire aerial images for Structural Health Monitoring (SHM). However, this approach requires extensive image post-processing, and in general, complex algorithms development. More importantly, current systems are not capable of measuring dynamic transverse displacements. This MS Thesis presents a novel approach to measure transverse bridge dynamic displacements using non-contact vibrometers mounted on unmanned aerial system. This research proposes algorithms for compensating the measurement errors due to the angular and linear movement vibrometer to obtain accurate transverse bridge displacement measurements. These algorithms are verified in the laboratory using a shake table simulating bridge vibration, and vibrometer movement simulating the motions of a UAS. The results of these tests show that the signal difference between the measured displacements of a moving LDV system and a LVDT are less than 10%. The Root mean squared (RMS) differences are less than 5%. This research also implements and tests the UAV-LDV system in the field. The results of these experiments show that the signal difference between LVDT and the UAS-LDV system is 10%. The RMS difference between the two systems is 8%. The results of this research show that the UAS and LDV can be used together to measure the dynamic transverse bridge displacements and could become an effective tool for campaign monitoring of railroad bridges with application for railroad bridge maintenance and repair prioritization.


Laser Doppler Vibrometer, Dynamic Transverse Displacement, Unmanned Aerial System, Correction Algorithms, Non-Contact, Structural Monitoring


The National Academics of Science, Engineering, and Medicine, Transportation Research Board

Document Type




Degree Name

Electrical Engineering

Level of Degree


Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Dr. Rafael Fierro

Second Committee Member

Dr. Fernando Moreu

Third Committee Member

Dr. Su Zhang

Fourth Committee Member

Dr. David Mascarenas