Technical Note
Static andDynamic Testing of High-Speed Rail Bridges in SpainMiguel A. Vicente1; Dorys C. González2; and Gongkang Fu, M.ASCE3
Abstract: There has been a rapid development of high-speed rail in Spain. Many bridges have been constructed to carry these lines. The rel-evant Spanish design codes require static and dynamic testing of these structures for acceptance of the design and construction before openingfor service; such testing is considered too costly in some other countries. This paper presents the concept, practice, and results of such testing for119 precast and posttensioned concrete girder bridges. Their static and dynamic properties and responses to loads have implications for theirstructural safety, serviceability, and possibly durability. Inaccurate models used in design for static and dynamic parameters (such as stiffness,first natural frequency, and damping ratio) may result in incorrect responses and possibly unsafe structures; therefore, in situ testing is required.The test results of these structures also lead to an empirical relation between the first natural frequency and span length and a range of damp-ing ratios for these types of structures, which can be useful for bridge engineers, particularly at a preliminary design stage of similar structures.DOI: 10.1061/(ASCE)BE.1943-5592.0000654. © 2014 American Society of Civil Engineers.
Author keywords: High-speed rails; Bridges; Load testing; Natural frequency; Damping ratio.
Introduction
During the last 20 years, there has been a significant developmentof high-speed rail in Spain. As a result, Spain currently has about3,100 km (1,926 mi) of high-speed rail in service, making it the first inEurope and the second in the world, after China, in terms of total lengthin service. Given the topography and design requirements in Spain, ithas been necessary to construct approximately 1,200 bridges for theselines. According to the governing specifications (Spanish Ministry ofPublic Works and Transport 2005, 2007), these structures are requiredto be load tested, statically and dynamically, before they are accepted forrail traffic. This paper presents the concept, practice, and results of suchtesting for 119 precast and posttensioned concrete girder bridges.
Specification Requirements for Testing
The Spanish high-speed rail is subject to the European design speci-fications (European Commission 1996, 2001, 2007) and, more spe-cifically for interoperability of the trans-European high-speed railsystem, adaptation of the European directives into Spanish instruc-tions (Spanish Ministry of Public Works and Transport 2005).
In particular, the bridges and viaducts are subject to static anddynamic load testing before opening for service. Although suchtesting is required at both stages of the supporting structure only andthe entire completed system, this study focused on the former,namely, the testing of the structure without the track system ofballast, sleepers, and rails, as shown in Fig. 1.
According to the Spanish specifications (Spanish Ministry ofPublic Works and Transport 2007), any structure with a span lengthlonger than 10 m (32.8 ft) is subject to static and dynamic loadtesting. Testing load is designed to verify that the calculationmodelsfor design are appropriate, with respect to load-response relationsand dynamic characteristics. Such testing also conceptually addressesconstruction quality up to the point when testing is performed.
The ITPF-05 (Spanish Ministry of Public Works and Transport2005) specifically requires that the measured responses be fordeflection and tilt for static load testing and for the first naturalfrequency, damping ratio, dynamic deflection, and accelerationfor dynamic load testing. This paper addresses the practice inSpain for bridges in high-speed rail according to the relevantspecifications.
Dynamic Effects Considered in Design
For the design of high-speed rail bridges in Spain, the IAPF-07(Spanish Ministry of Public Works and Transport 2007) repre-sents the governing code for loading. It is a transposition of Part 2 ofEurocode 1 [European Committee for Standardization (CEN) 2002]for practice in Spain. This code explains how the dynamic behaviorof railway loads must be taken into account in bridge design, similarto theUICLeaflet 776-1 (International Union of Railways 2006) andthe China high-speed railway design code (People’s Republic ofChina Ministry of Railway 2009).
Both the natural frequency and damping ratio have a significantinfluence on the dynamic response of the bridge, as well on thecritical speed of the bridge. During the early stages of high-speed railbridge design, it is very useful to have an approximate relationshipbetween the first natural frequency and the span length. This in-formation can help estimate the critical speed of the train. The de-signer can then check whether the critical speed is close to theoperating and limit speeds of the rail service. If that is true, separationof the two is advised strongly by redesigning the span arrangement.The damping ratio also directly influences the magnitude of dynamicresponse of the structure, such as deflections and internal forces. Inturn, it influences the impact factor to be used in design. Therefore,dynamic load testing of these bridges focuses on these two importantparameters.
1Professor, School ofCivil Engineering,Univ. of Burgos, 09001Burgos,Spain (corresponding author). E-mail: [email protected]
2Professor, School of Civil Engineering, Univ. of Burgos, 09001Burgos, Spain. E-mail: [email protected]
3Professor and Chair, Dept. of Civil, Architectural, and EnvironmentalEngineering, Illinois Institute of Technology, Chicago, IL 60616; formerly,Changjiang Scholar Chair Professor, Chinese Education Ministry, TongjiUniv., Shanghai 200092, China. E-mail: [email protected]
Note. This manuscript was submitted on July 8, 2013; approved onMay 19, 2014; published online on June 13, 2014. Discussion periodopen until November 13, 2014; separate discussions must be submitted forindividual papers. This technical note is part of the Journal of BridgeEngineering, © ASCE, ISSN 1084-0702/06014006(3)/$25.00.
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Experimental Program
The experimental campaign reported here consisted of static anddynamic load testing of 119 bridges over waterways, roads, andland, on several high-speed rails in Spain. These tests were con-ducted over the last 10 years or so. Static load–induced deflectionand dynamic load–demonstrated natural frequency and dampingratiowere acquired during testing.Awide range of span lengths from20 to 90m (65.6 to 295.2 ft) was included, for various superstructuresystems of precast prestressed I-beams and U-beams, cast in situposttensioned concrete slabs, and concrete box girders. The mainobjectives of testing are summarized as follows:1. To obtain correlation between the theoretical and measured
deflections and between the theoretical and measured firstnatural frequencies, to establish an understanding regardingthe quality of the design calculation models.
2. To obtain an empirical relation between the measured firstnatural frequency and also the damping ratio to the bridge spanlength, depending on the structure type. Such relationships areuseful at an early stage of structural design to avoid resonance.
Four superstructure types were included in the testing program:(1) isostatic spans with precast, prestressed concrete superstructure(IPP); (2) hyperstatic spans with precast, prestressed concrete su-perstructure (HPP); (3) isostatic spanswith posttensioned cast in situconcrete superstructure (IP); and (4) hyperstatic spans with precast,posttensioned cast in situ concrete superstructure (HP).
Experimental Program Results
Measured Vertical Deflection
Fig. 2 shows the ratio of span length multiplied by the number oftruck lanes to measured maximum deflection versus span length for119 bridges tested in this program. Each dot in the figure representsone bridge. The deflection was measured at the midspan section. Itappears that this ratio decreased with an increase in span length. Thesame alsowas evident when the dots were plotted separately for eachof the four superstructure types.
Measured First Natural Frequency and Damping Ratio
Fig. 3 displays the measured first natural frequency versus spanlength for all 119 bridges tested. Each dot represents one bridge. Inthe case of multispan bridges, the natural frequency was for thelongest span, because it was expected to be the minimum naturalfrequency or very first natural frequency of all spans. One sees inFig. 3 that there was a trend of decreasing natural frequency withspan length, which does not appear to significantly depend on thestructure type.
An effort was made to extract this relation, which can be usefulfor bridge designers. The following is given to describe this relation:
f ¼ a1 × L2a2 (1)
where f 5 first natural frequency (Hz) as defined previously; L5 span length (m); and a1 and a2 5 model coefficients. For higherfidelity, themodel coefficients were identified, respectively, for eachof the four superstructure types included in the test program, using
Fig. 1. Test loading for a multispan bridge (image by Miguel A. Vicente)
Fig. 2. Span length to measured deflection versus span length multi-plied by number of truck lanes for 119 bridges (1 m5 3:3 ft)
Fig. 3. Measured first natural frequency versus span length for 119bridges (1 m5 3:3 ft)
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statistical regression. The results are shown in Table 1, with re-spective R2 values. Note that this statistical relation is similar to thatproposed by Paultre et al. (1992) for highway bridges. Some low R2
values in Table 1 are attributable to these variables: (1) constructionmethod (precast or cast in place), (2) material properties, (3) to-pology other than span length, (4) span type (simple versus con-tinuous), and (5) bearing supports.
For the damping ratio associated with the first natural frequency,Fig. 4 shows the result plotted against span length as well. Nev-ertheless, no correlation between them was observed, whereas thedamping ratio varied between 1 and 4%.The same alsowas observedfor the damping ratio grouped by superstructure type. For the 119bridges tested, Table 2 displays the average and SD for each su-perstructure type. Except for the hyperstatic spans with precast,posttensioned cast in situ concrete superstructure (HP), all structuretypes had an average damping ratio a little more than 2%.
Conclusions
The main conclusions of this work may be summarized as follows:1. Results of static load testing showed that the ratio of span
length multiplied by the number of truck lanes to the measureddeflection appeared to decrease with span length. The isostaticspans with posttensioned cast in situ concrete (IP) superstruc-ture showed smaller values among the four types tested. Thespan type contributed to this behavior.
2. The presented experience identified a regression relation be-tween span length and first natural frequency for high-speedrailway bridges in Spain. Options were offered for such corre-lation to be used or not, depending on bridge superstructure
type, with respective statistical significance as shown inTable 1. The correlation may be used preliminarily to esti-mate the bridge’s behavior with regard to resonance, impactfactor, and performance.
3. Three of the four superstructure types tested were found tohave an average damping ratio above 2%, with the fourth at1.8%. It appears that a 2% average value can be used as areasonable estimate for design purposes.
4. This work also offers the Spanish experience for comparisonwith practices in other jurisdictions, which is needed by bridgetest engineers.
Acknowledgments
The authors express their deepest appreciation to the Spanish Min-istry of Public Works for allowing publication of the data presentedherein. They also extend their gratitude to INDAICO INGENIEROSS.L. for assisting in these tests and providing relevant information.
References
European Commission. (1996).Council directive 96/48/EC of July 23, 1996on the interoperability of the trans-European high speed rail system,Brussels, Belgium.
European Commission. (2001). Directive 2001/16/EC of the EuropeanParliament and of the council of March 19, 2001 on the interoperabilityof the trans-European conventional rail system, Brussels, Belgium.
European Commission. (2007). Commission directive 2007/32/EC of June1, 2007 amending annex VI to council directive 96/48/EC on the in-teroperability of the trans-European high speed rail system andannex VI to directive 2001/16/EC of the European Parliament and ofthe council on the interoperability of the trans-European conven-tional rail system, Brussels, Belgium.
European Committee for Standardization (CEN). (2002). “Actions onstructures—Part 2: Traffic loads on bridges.” Eurocode 1, Brussels,Belgium.
International Union of Railways. (2006). “Loads to be considered in railwaybridge design.” UIC Leaflet 776-1, Paris.
Paultre, P., Chaallal, O., and Proulx, J. (1992). “Bridge dynamics anddynamic amplification factors. A review of analytical and experimentalfindings.” Can. J. Civ. Eng., 19(2), 260–278.
People’sRepublic ofChinaMinistry ofRailway. (2009). “Code for design ofhigh speed railway.” TB 10621-2009/J 971-2009, China Railway Press,Beijing (in Chinese).
Spanish Ministry of Public Works and Transport. (2005). “ORDEN FOM/1951/2005, de 10 de junio, por la que se aprueba la instrucción sobre lasinspecciones técnicas en los puentes de ferrocarril.” ITPF-05, Madrid,Spain (in Spanish).
Spanish Ministry of Public Works and Transport. (2007). “ORDEN FOM/3671/2007, de 24 de septiembre, por la que se aprueba la instrucciónsobre las acciones a considerar en el proyecto de puentes de ferrocarril.”IAPF-07, Madrid, Spain (in Spanish).
Table 1. Coefficients a1 and a2 Found for Eq. (1)
Typology a1 a2 R2
All 37.79 0.54 0.337IPP 266.97 1.09 0.732HPP 65.77 0.70 0.688IP 25.12 0.48 0.290HP 22.00 0.39 0.142
Fig. 4. Measured damping ratio versus span length for 119 bridges(1 m5 3:3 ft)
Table 2. Statistical Parameters of Damping Ratio for 119 Tested Bridges
Typology Number of specimens Mean (%) SD (%)
IPP 27 2.41 0.64HPP 28 2.04 0.55IP 7 2.24 1.19HP 57 1.76 0.58
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