Structural Health Monitoring of Railroad Bridges ...

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Structures Congress 2012 © ASCE 2012

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Structural Health Monitoring of Railroad Bridges – Research Needs and Preliminary Results F. Moreu1, J. LaFave2, and B. Spencer3 Newmark Civil Engineering Laboratory, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801 1 2 3

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ABSTRACT The initial content of this paper presents results of a survey-based study that identified simplified displacement monitoring of railroad bridges under trains as the main research interest of railroad bridge structural engineers. The second part of this publication describes a railroad bridge classification towards structural health monitoring (SHM) applications, based on current structural engineering problems and challenges identified by the railroad industry for each railroad bridge type. Finally, this paper briefly describes ongoing research related to attempting to monitor railroad bridge deflections by means of using simplified wireless sensors, and preliminary field experimentation and proof of concept validations. PAST AND PRESENT PRIORITIZATION OF RAILROAD BRIDGE STRUCTURAL ENGINEERING RESEARCH TOPICS In the past, workshops have assisted railroad institutions toward directing research efforts based on the current needs of the railroad bridge structural engineering community (e.g., Foutch, 1989). As pointed out by Byers and Otter (2006), between 1970 and 1990 there was only limited railroad bridge structural engineering research activity, but it increased considerably between 1990 and 2005 as a result of a workshop conducted in 1987 to prioritize research in railroad bridges and structural engineering. Further details about the organization of this 1987 workshop, including the participants and a list of the topics discussed and selected, as well as their findings, can be found in a summary report published by the American Association of Railroads (AAR) and other related literature (Foutch, 1989; Groskopf, 1990). Today, more than twenty years now after that workshop, the need for some sort of a new “meeting” to identify current research needs is overdue, especially to help prevent another period of little bridge-related research. Therefore, a new survey of national experts on railroad bridges and structural engineering has been conducted to best identify and prioritize the current research topics in this area, as described in more detail by Moreu and LaFave (2011). The findings of the 2010 survey-based study are briefly summarized in the next section.

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2010 SURVEY POPULATION, METHODOLOGY, AND RESULTS Sixteen engineering and construction experts were interviewed, representing a spectrum of the current population of professionals dedicated to railroad bridge structural engineering in North America. The survey methodology involved first identifying a list of relevant potential research topics from a preliminary literature review and discussions with AAR experts. This list of pre-selected topics was then sent to each of the participants in the survey for their feedback and favorable / unfavorable rankings. Table 1 lists the twenty-two main research topics identified in this surveybased study, and Table 2 shows the ranking of the top six topics. Specifically, this survey-based study ranked measuring deflections under live loads as the current top research interest. Other specific research topics identified were investing in whatever maintenance tools could assist them in measuring and/or improving bridge capacities; developing new methods of measuring bridge foundation robustness during and after scouring events; and research on new materials and construction methods. RAILROAD BRIDGE MANAGEMENT PROGRAM AND RAILROAD BRIDGE MONITORING Effective September 13th, 2010, the FRA’s new rule on Bridge Safety Standards defines new regulations pertaining inspections; load capacity determinations; repairs; and modifications for railroad bridges (FRA, 2010). The new rule determines the contents and obligations related to bridge management programs. This new rule states, “(…) every track owner shall adopt a bridge safety management program to prevent the deterioration of railroad bridges (…)”. This rule requires the adoption of these programs by March 14th, 2011, for all Class I railroads, and subsequently before that date for other different railroads carriers, but not later in any case than September 13th, 2012. For the entire definition of the bridge management program requirements, please go to the FRA 49 CFR Part 237, Subpart B – Railroad Bridge Safety Assurance, 237.33, content of bridge management programs. In light of this new regulation, this research has compiled current and past efforts toward the monitoring of railroad bridges.




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Table 1. Main research topics sorted by area Railroad Bridge Design Longitudinal force distribution effects, on both super- and sub-structure High speed traffic effects on existing and new railroad bridges Long-span bridge design – new analytical tools and opportunities Upgrading of live load from the current Cooper E80 design load Bridge approach improvements, and new designs for durable bridge approaches Impact force in railroad bridges – estimates and new experiments Transitioning from 286 kips/car to 315 kips/car, and effects on railroad bridges

Railroad Bridge Construction and Maintenance Member replacement prioritization in the field Rapid bridge replacement practice and new techniques Robustness estimation of existing railroad bridges Current practices to extend the life of railroad bridges Economic approach to railroad bridge replacements

Railroad Bridge Management Field inspections for railroad bridges – current problems and solutions Bridge instrumentation and data collection – past, present and future opportunities Railroad bridge rating – current challenges and possible solutions Maintenance of timber railroad bridges in North America

Other Possible Research Topics Study of new materials for railroad bridges – present and future Load and resistance factor design adaption for the design of new railroad bridges Development of new steel bridge standard design sections for given span lengths Finding and estimating railroad bridge damage (local damage detection) Fatigue in railroad bridges – current topics and research opportunities Seismic studies and topics related to railroad bridges in the U.S.

Table 2. 2010 railroad bridges research topics 2010 2010 TOPICS RANKING Deflection measurements 1 High speed trains 2 Long-span bridges 3 Approaches 4 Longitudinal forces 5 New design loads 6




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In 1980, the FRA conducted a study to design research plans towards both track and bridge maintenance. Based on the industry opinion, the topic entitled “technique for evaluating remaining (bridge) life”, was ranked only second to the research named “improve rail metallurgy” (Parsons Brinckerhoff Quade & Douglas, Inc., 1980). Fourteen years later, the FRA also sponsored a more specific study towards monitoring technologies and methods for the SHM of railroad bridges in US, from which conclusions proved that the installation of monitoring integrity into the entire population of railroad bridges in the US would cost more than the money lost by railroad bridge related accidents for a 25 year period of study, even when the false alarm costs to the railroads were included in the monitoring methods and estimates (ENSCO, 1994). These studies showed that the US railroads support studies toward monitoring the performance of railroad bridges, and are interested in exploring the applicability and profitability of using available technology to monitor existing bridges integrity. Furthermore, these two studies about the monitoring of railroad bridge performance were preceded by a classification of the railroad bridge types in the US. Therefore, it is concluded that prior to study SHM applications towards railroad bridges in the US, a comprehensive railroad bridge categorization needs to be established to best assess the current monitoring needs from the railroad community by bridge type. For example, Figure 1 shows one of many 100+ years old steel trusses railroad bridges operating in North American today. This railroad bridge classification identified steel trusses as one railroad bridge types. The next section describes more details about this bridge classification towards SHM applications.

Figure 1 100+ year old RR steel truss bridge over the Mississippi river currently being replaced




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RAILROAD BRIDGE CLASSIFICATION TOWARD SHM APPLICATIONS The proposed classification groups the existing structural challenges and concerns for each particular railroad bridge category. Following the listing of bridge performance challenges, the most pressing concerns are identified for one or several railroad bridge types, and specific monitoring techniques and solutions are proposed. This railroad bridge classification has two goals: 1. To group the main railroad bridge types based in their performance challenges and the current concerns from railroad bridge management departments. 2. To identify SHM applications that can better measure and assist the management of these specific bridge categories, or the entire railroad bridge inventory. A preliminary classification followed current railroad bridge organization found in literature reviews and bridge manuals, such as the American Railway Engineering and Maintenance-of-Way Association (AREMA) (2010). Secondly, this research additionally consulted past FRA bridge classification studies from both 1993 and 2008. In those years, the FRA conducted surveys to the railroads classifying the different types of railroad bridges based in the materials of their superstructure (FRA, 2008a). The results of these surveys and the bridge classification that they used are shown in both Figure 2 and Figure 3.

Figure 2 FRA survey, 1993 results (FRA, 2008b)




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Figure 3 FRA survey, 2008 results (FRA, 2008b) This study proposes a classification of current railroad bridges in the US in accordance with past railroad bridge classification efforts and also assigning a list of railroad bridge structural engineering concerns for each specific railroad bridge type. By using the same bridge classification philosophy lead by railroad agencies in the past, the SHM applications for US railroad bridges will best capture the potential use of these merging techniques for specific bridge performance cases and bridge types. To identify current concerns for each bridge type category, diverse sources were consulted, including the AREMA Inspection manual (AREMA, 2008), the referred FRA studies from the 80’s and 90’s listed before, and other past publications on railroad bridge classification such as work published by Sorgenfrei and Marianos (2000) and the International Heavy Haul Association (IHHA) (2009). The resulting bridge classification towards SHM applications is shown in Figure 4, and it has been made under the following considerations: 1) The material of the main superstructure elements is used as the parameter for the bridge classification. 2) Substructure elements and types are selected for the specific bridge type, and it also includes SHM applications for substructure elements. 3) In addition to the material of the superstructure, the particularity of the bridge and its function is also acknowledged in the case of the movable bridges, which are considered to become a different entity for its own particularity.




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4) Only one bridge type is identified for each category. Bridges made of different bridge types (notably often the case) are not contemplated in this general classification. 5) In each bridge category section, the typical bridge type is ideally modeled. The fact that more complicated layouts may require different SHM approaches is relegated for a case by case study, which is not the scope of this study. As a consequence, the main bridge categories proposed in this study are: 1. Timber trestles 2. Concrete bridges a. Reinforced concrete bridges b. Arch bridges (including masonry bridges) c. Prestressed concrete bridges 3. Steel bridges a. Steel beams b. Deck plate girders c. Through plate girders d. Truss bridges 4. Movable bridges a. Swing span bridge b. Bascule span bridge c. Vertical lift span bridge In this railroad bridge classification different structural issues are associated to different railroad bridge types. As pointed out during the course of the survey-based study, this bridge classification toward SHM applications also identifies deflection of railroad bridges under live loads as of paramount concern for railroad bridge structural engineers. Particularly, for bridges with high levels of flexibility, such as timber bridges and steel bridges (although measuring deflections of concrete and masonry bridges were also of interest, specifically, movements of substructure under ordinary loadings or after unusual events such as impact, adjacent construction or scouring events). Consequently, studies toward the measurement of bridge deflections with simplified and autonomous wireless sensors have been started at the Newmark Structural Engineering Laboratory (NSEL), in conjunction with the Smart Structures Laboratory Technology (SSTL), and the description and preliminary results of those efforts are described in the following section.




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Figure 4 Railroad bridge classification toward SHM applications RAILROAD BRIDGE DEFLECTION MEASUREMENTS UNDER TRAINS USING WIRELESS SENSORS The final step in this study consisted of the experimentation for railroad bridge deflection measurements by using wireless sensors. Prior to the field experiment collecting data under railroad trains, some preliminary studies combined an understanding of current sensing technologies with an appreciation for railroad bridge structural behavior to identify appropriate sensor locations for performance evaluations, and to develop methods for interpreting acceleration and other dynamic




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response data that could assist to capture the entire movement of the train under load (e.g., from displacements) to characterize bridge performance. In order to lay out an adequate validation campaign for a wireless monitoring method, a systematic strategy was identified in conjunction with the results collected in the survey-based study and the bridge classification towards SHM applications. More particularly, a three step approach was followed, as shown in Figure 5, including sensor development, sensor and algorithm implementation, and actual data collection. Figure 6 describes the field experiment carried out as a pilot method to investigate the applicability of this approach for railroad bridge monitoring under railroad traffic. In October 2011, wireless sensors were installed on a timber trestle to collect data of railroad vibrations under trains. Additionally, potentiometers were used to collect displacement measurements relative to a fixed point mounted on adjacent scaffolding built next to the pier bent to be monitored, arranged by the railroad exclusively for the monitoring of this bridge. Accelerations were also collected from the scaffolding intended to serve as fixed point, and were subtracted from the bridge measured acceleration, in order to compare relative displacements to estimations from relative accelerations.

Figure 5 SHM system for wireless measurements of deflections under trains




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The relative acceleration data collected was analyzed in the laboratory and used to estimate the displacements using an FIR filter proposed by Lee, Hong and Park in 2009 (Lee et al. 2009). This method can be used for zero-mean vibration and displacement cases, but cannot capture non-zero events such as pseudo-static deflection caused by the load of the train. For this preliminary pilot monitoring study, the pseudo-static deflection was identified to a linear trend estimated from the collected deflection at the potentiometers. This same trend was applied to the estimated displacement from the zero-mean vibrations. Figure 7 shows the results of this estimation and the error associated with this experiment, under the aforementioned assumptions. SUMMARY, CONCLUSIONS, AND FUTURE WORK According to the input collected during the 2009-10 survey-based study, railroads need to have the ability to assess the performance of railroad bridges in the field under real railroad traffic, and to then allow objective decision making for bridge network assessment.

Figure 6 Railroad bridge data collection layout


Displacements, d (cm)

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0.26 0.13 0

----0.13

Error, e (cm)



-0.26

0.13

Measured - Estimated Displacement

0 -0.13

Figure 7 Measured vs. estimated displacement Along these lines, this study identifies real-time displacement measurements under live loads as a priority for research and development today by the railroad industry. In order to better develop instrumentation and data collection for simplified railroad bridge monitoring and implementation, this research proposes a classification of North American railroad bridges toward SHM applications, identifying their main structural engineering issues and concerns by bridge type, to best narrow which locations and other practical considerations should be addressed for their specific monitoring case. Finally, this research proposes the implementation of post-data analysis algorithms for wireless sensors to eventually lead to a method that could provide railroad managers with wireless real-time deflection measurements under trains. A field experiment shows good correlation between the estimated and collected displacements. Additional data collection, both in laboratory settings and on other railroad bridge types, is in progress, including displacements of superstructure structural members. ACKNOWLEDGMENTS Assistance in developing and executing this article was supplied in part by the Rail Transportation and Engineering Center (RailTEC) at the University of Illinois at Urbana-Champaign, and partially funded by the AAR Technology Scanning Program. Additional financial support for this research was provided in part by the Max Zar Scholarship 2009-10, granted by the Structural Engineers Foundation (SEF) of the U.S., and the 2010 SEI ASCE O. H. Amman Research Fellowship. The first author also acknowledges support from the Junta de Andalucía Talentia (Spain) Fellowship (2010-11).




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REFERENCES AREMA (2008), “AREMA Bridge Inspection Handbook”; AREMA Committee 10, Structures, Maintenance, & Construction. AREMA (2010), “Manual for Railway Engineering”; Volume 2, Structures; AREMA Association. Byers, W. G. and Otter, D. (2006), “Reducing the stress state of railway bridges with research: researchers at TTCI stay on top of railway bridge research to ensure safety, cost effectiveness and maximum life cycle of materials”; Railway Track & Structures, February. ENSCO Inc., Applied Technology & Engineering Division (1994), “Overview of Railroad Bridges and Assessment of Methods to Monitor Railroad Bridge Integrity”; U.S. Department of Transportation, Federal Railroad Administration; Report number DOT/FRA/ORD-94/20; June. Foutch, D. A. (1989), “National Workshop on Railway Bridge Research Needs: Summary Report”; AAR Technical Center, Chicago, IL. UIUC, Report No. R-710. July. FRA (2008a), “Railroad Bridge Integrity Working Group Upgrade”; Railroad Safety Advisory Committee (RSAC), Railroad Bridge Working Group; Handouts (Railroad Bridge Working Group Report: Final Report and Recommendations); September 10th. FRA (2008b), “Railroad Bridge Integrity Working Group Upgrade”; Railroad Safety Advisory Committee (RSAC), Railroad Bridge Working Group; Presentations (Railroad Bridge Working Group Report: Final Report and Recommendations); September 10th. FRA (2010), DOT. 49 CFR Parts 213 and 237. RIN 2130-AC04. Bridge Safety Standards. Federal Register / Vol. 75, No. 135 / Thursday, July 15, 2010/ Rules and Regulations. Pp. 41281-41309. Groskopf, Ralph (1990), “AAR Bridge Research Program Progress Report”; Railway Age; Sep 1990; 191, Iss. 9; pg. 103-104. IHHA (2009), “Guidelines to Best Practices for Heavy Haul Railway Operations. Infrastructure Construction and Maintenance Issues”; D&F; Scott Publishing, Inc., International Heavy Haul Association, 656 pp. Lee, Hong and Woo Park (2009); “Design of an FIR filter for the displacement reconstruction using measured acceleration in low-frequency dominant structures”; Int. J. Numer. Meth. Engng 2010; 82:pg. 403–434. Moreu, F. and LaFave, J. (2011); “Survey of current research topics – Railroad Bridges and Structural Engineering”; Railway Track & Structures, September, pg. 65-70. Parsons Brinckerhoff Quade & Douglas, Inc. (1980); “Track and Bridge Maintenance Research Requirements”; U. S. Department of Transportation, Federal Railroad Administration; Report Number FRA/ORD-80/11; March. Sorgenfrei, D.F. and Marianos, Jr., W.N. (2000); “Railroad Bridges”; Bridge Engineering Handbook; Ed. Wai-Fah Chen and Lian Duan; Boca Raton: CRC Press.
