“Don’t Replace Your Bridge Too Soon”

Written by Jim Blaze, Contributing Editor
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Bridge inspection using the visual method. A BNSF bridge inspector is working some 300 feet above the Crooked River, near Terrebonne, Ore. AAR photo.

There is a great deal of technology and data science that can help extend track and bridge structure life. But the railroads are not always out in front in exploiting the opportunities. Engineers can see the practical uses of bridge “micro movement” sensor technology. But at the big executive table that allocates the budget resources inside railroads, identified economic opportunities point to the need for the chief financial officer and his or her risk management staff to get directly involved in examining the identified options not seen before sensor data analytics entered the tool box. Perhaps as many of one-half of all visual inspection-based bridge capex decisions are wrong. Why? Because the visual data entered into the sophisticated engineering spreadsheet formulas isn’t accurate enough.

“Don’t Replace Your Bridge Too Soon,” one of the University of Delaware 2019 Big Data in Railroad Maintenance Planning Conference presentations, covered railway bridges. If thought to be defective, they are big-dollar items if the only solution is thought to be complete replacement. There are more than 61,000 railroad bridges in the U.S. freight network—more if we include culverts and those used by the passenger lines and commuter services.

In a presentation by John Schmid, P.E., Parsons Transportation Group and Peter Vanderzee, President and CEO of LifeSpan Technologies, the authors demonstrated how modern sensor-based monitoring technology can be used to create a huge gain for bridge condition assessment.

Bridge conditions are usually cited as one of nine condition assessments following standard federally approved procedures. The problem is that, for more than two decades, it has been known that the combination of visual inspection and standard analysis techniques for highway bridges—the typical condition judgments—can often result in a possible error band of up to +/- two of ten condition levels. That is far less precision than is obtained when engineers measure track geometry or track movement under actual train movement.

The solution for both highway and rail bridges is to use sensors that detect strain/stress values on critical structural members. That process used to be much more expensive, as the older sensors and associated equipment were often destroyed during the monitoring process. Enter better technology. 

LifeSpan Technologies sensors on a railroad bridge.

Sensors that can withstand the demands of both heavy loading and environmental factors have been successfully deployed for nearly 20 years. Connecting the sensors with remote communication capability only added to the benefits. Not only could they communicate, but after a bridge was tested, the sensors and related hardware were most often reusable on other bridges. Now, sensor data can be captured in real time and securely stored until critical forces are detected and transmitted to the cloud, and an alert is sent to the owner’s engineer. These advancements are a major improvement over visual inspection, especially for bridges that are suspected problematic.  

“The challenge for any bridge owner is to continue using visual inspection as the first line of defense, e.g. a ‘blood pressure cuff’, for bridges, but when bridge condition concerns mount, they should know when it’s time utilize structural monitoring solutions as a more definitive condition assessment process, given a good opportunity to safely extend operating life and thereby gain a substantial ROI,” according to Peter Vanderzee.  

This technology has been tested time and again by State DOTs for nearly two decades, but not routinely by the railroads.  However, railroads should be deploying this technology on bridges that are already deemed to be problematic, so there seems little reason to avoid technology use if the technology leads to safe extension of operating life.    

Vanderzee and Schmid documented the case of a Canadian Pacific 110-year-old swing bridge near La Crosse, Wisc. The only information available from visual inspection suggested both substructure concerns and extensive section loss involving critical bridge members.  The recommendation from the visual inspection information was total replacement costing $75 million.  

Image courtesy of Parsons and LifeSpan Technologies.

The actual bridge condition and risk level was pinpointed by using 20 strain sensors, seven accelerometers, four inclinometers and three temperature sensors. They isolated the actual bridge parts that were, in effect, seeing undue stress. This was not possible to determine with visual inspection.  For the 20 strain sensors, more than 860,000 data points were analyzed.   All of this precise data was collected during live loads, without rail traffic interruptions.

Using a calibrated Finite Element Model (FEM) with objective data, the Parsons bridge engineers concluded that:

  • Previous visual movements were mostly from “expected” deflection rates.
  • The swing span trusses were behaving as designed.
  • Future inspections should focus on cross-bracing and the floor system.

The outcome: The 110-year-old bridge needed selective repairs, not replacement. The financial conclusion: The planned $75 million project can be safely deferred as the railroad continues to monitor bridge members for movement at key locations.  

According to Vanderzee, “[A]ssuming a cost of capital at 8%, the decision to use a structural monitoring solution provided the owner with a first-year return of more than 10 times what the project actually cost.  And the yearly replacement cost deferral value continues to build year after year as the bridge stays in service.”

I know what I’d do if I were running a railroad.  I’d get my CFO and risk management executives directly involved so as to enable this superior capex savings tool.

What would you do?

Independent railway economist, Railway Age Contributing Editor and FreightWaves author Jim Blaze has been in the railroad industry for more than 40 years. Trained in logistics, he served seven years with the Illinois DOT as a Chicago long-range freight planner and almost two years with the USRA technical staff in Washington, D.C. Jim then spent 21 years with Conrail in cross-functional strategic roles from branch line economics to mergers, IT, logistics, and corporate change. He followed this with 20 years of international consulting at rail engineering firm Zeta-Tech Associated. Jim is a Magna cum Laude Graduate of St Anselm’s College with a master’s degree from the University of Chicago. Married with six children, he lives outside of Philadelphia. “This column reflects my continued passion for the future of railroading as a competitive industry,” says Jim. “Only by occasionally challenging our institutions can we probe for better quality and performance. My opinions are my own, independent of Railway Age and FreightWaves. As always, contrary business opinions are welcome.”

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