Steven Chase 1, Yaw Adu-Gyamfi 2 and Paul Fuchs 3 1&2 Department of Civil Engineering, University of Virginia 3 Fuchs Consulting Inc.

 Explain why this is an important advance in bridge inspection  Introduce thermoelasticity  Provide overview of the project  Answer any questions

 Have you driven over a highway bridge recently? ◦ Yes ◦ No

 Root cause of many collapses and failures

 The current practice is to rely on hands on visual inspection ◦ Tedious ◦ Expensive ◦ Dangerous ◦ Unreliable  Damage already exists

 Were you concerned about the safety of the bridge you drove over? ◦ Did not even think about it. ◦ I was concerned. ◦ I was terrified. ◦ I don’t drive.

 Develop a device that automates detection and monitoring of fatigue cracks on steel bridge by imaging dynamic stress concentrations at fatigue- prone details. ◦ Identify and quantify precursors to fatigue cracks ◦ Improve detection of existing cracks ◦ Assess effectiveness of any repair or retrofit actions

 The relationship between the temperature change and the strain in the object is expressed as:

 Second term: Temperature change due to conduction 0 Neglect if stress change occurs fast enough

Computer Simulations Laboratory Testing Field Deployment Load Characterization Data Capture Signal Processing Results Key Components Data Acquisition Signal Processing Results Set up and Data Acquisition

 Initial project funded by MAUTC

Stress Concentrations

First TSA image obtained with proof of concept project. Demonstrated the use of a low cost camera was feasible MS Thesis by Matt Kantner Follow on project funded by VCTIR to develop field system

 Is this explanation of the thermoelastic effect understandable ◦ Yes ◦ You lost me with the first equation ◦ I think I understand

 Develop ability to use random events  Design and develop a complete field system  Test capabilities and limits in laboratory  Conduct field tests on actual bridge with cracks

 Steel Specimen: with ½ inch diameter Hole in plate.  Loading frame holds specimen. ◦ Used to apply loads to specimen. ◦ Actuator creates the forces. ◦ Computer controller coordinates actuator movement. MTS Hydraulic Grip. Flat Plate with Hole Specimen

 Uncooled micro-bolometer camera  Frame rate: 60 Hz  Resolution: 256 by 324 pixels

 Embedded computer and touch screen interface  DAQ system: acquires data from load cell and IR camera simultaneously  High level signal from MTS or low- level signal from strain gage interface

Total samples per trigger (Strain Gauge and Infrared Camera ) Pre-trigger durationPost-trigger duration Trigger Occurs (Begin Data Logging) Time Threshold

Correlation Denoised output Loading Event Temperature Variation

Raw Data Thermoelastic Response

Crack

 Deploy system for extended period of time  Acquired data triggered by multiple truck events  Extract stress concentration of fatigue prone details due to random truck loading

Camera Viewing a DetailField Computer

Large dynamic stresses due to heavy truck loads at connection plate web weld termination

 Do you think the TSA system is a valuable addition to the methods available to detect and evaluate fatigue cracks? ◦ Yes ◦ No ◦ Don’t know ◦ Depends on cost, ease of use and interpretation of data collected

 A TSA system has been developed based on a low-cost microbolometer thermal imager, a dedicated field computer (for triggering data acquisition) and signal processing algorithms for extracting small changes in stress associated with dynamic loading events.  The TSA system has been validated with computer simulations, laboratory and field tests.

 Laboratory and field testing show that at moderate to high stress levels, the TSA system can be used to image stress concentrations.  The system will be delivered to VCTIR and will be deployed in high stress locations in the future.  Future implementation will focus on introducing this new method to bridge owners in US and globally.

FUCHS CONSULTING INC.