Condition Assessment of Bridges: Past, Present and Future. A Complementary Approach

5/28/2018 Condition Assessment of Bridges: Past, Present and Future. A Complementary Approach

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Condition Assessment of Bridges:Past, Present and Future

A Complementary Approach

ELI FIGUEIREDO

IONUT MOLDOVAN

MANUEL BARATA MARQUES

Universidade Catlica Editora


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Edio: Universidade Catlica Editora, Unipessoal, Lda.Composio: Magda Macieira CoelhoData: dezembro de 2013ISBN: 978-972-54-0402-7

Universidade Catlica EditoraPalma de Cima 1649-023 Lisboatel. (351) 217 214 020 fax (351) 217 214 029

[email protected] www.uceditora.ucp.pt


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Condition Assessment of Bridges:Past, Present and Future

A Complementary Approach

ELI FIGUEIREDO

IONUT MOLDOVAN

MANUEL BARATA MARQUES

Universidade Catlica Editora


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SEMINAR SUMMARYCondition Assessment of Bridges:Past, Present and FutureA Complementary Approach

Eli FigueiredoAssistant Professor Faculty of Engineering, Catholic University of Portugal

Ionut MoldovanAssistant Professor Faculty of Engineering, Catholic University of Portugal

Manuel Barata MarquesFull Professor and Director Faculty of Engineering, Catholic University of Portugal

I SAntnio Perry da Cmara, Armando Rito, Carlos Santinho Horta, Charles R. Farrar,Joaquim A. Figueiras, Jos Carlos Clemente, Keith Worden, Lus Oliveira Santos,Paulo Lima Barros, Robert Veit-Egerer, and Tiago Mendona


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Contents

Preface vii

Notation x

Acknowledgments xi

1. Overview of Bridge Management 1

1.1 Introduction 1

1.2 Bridge management and structural condition assessment of bridges 5

1.3 The motivation for structural condition assessment of bridges 6

1.4 The history of the Portuguese road and rail networksand bridge management 7

1.5 Status of the Portuguese bridges 22

1.5.1 The perspective of the three main bridge owners 23

1.5.2 Other bridge owners 24

2. Bridge Management System (BMS) 272.1 Introduction 27

2.1.1 Definition 27

2.1.2 BMS evolution around the world 28

2.1.3 Current BMS organization 32

2.2 The role of bridge inspections 33

2.2.1 Overview 33

2.2.2 Shortcomings and needs 35

2.3 The role of the Non-Destructive Evaluation (NDE) 36

2.3.1 Overview 36

2.3.2 Visual inspections 37

2.3.3 Other current NDE techniques 37

2.3.4 Shortcomings and needs 38

2.4 The role of the Structural Health Monitoring (SHM) 39

2.4.1 Overview 39

2.4.2 Historical perspective of SHM: from rotating machinery to bridges 42

2.4.3 Economic and safety reasons of the SHM for bridge management 44

2.4.4 The applicability of SHM for structural condition assessment 45


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2.4.5 Model updating 46

2.4.6 Statistical pattern recognition (SPR) paradigm 48

2.4.7 Main challenges of the SHM-SPR process 52

2.4.8 SHM of bridges in Portugal and in China 56

2.4.9 Main lessons from the past of SHM 61

2.4.10 Shortcomings and needs of SHM 63

2.5 Main lessons from the past of BMS 63

2.6 Shortcomings and needs of BMS 65

3. Guidelines for the Future of Condition Assessment of Bridges 67

3.1 Bridge designers recommendations 67

3.2 Bridge owners recommendations 68

3.3 Future trends and recommendations for NDE 69

3.4 Future trends and recommendations for SHM and BMS 71

3.5 How to improve the bridge inspections:the US and the Portuguese experiences 74

3.6 Bridges capable to be upgraded with SHM technology 76

3.7 How to integrate SHM into BMS 78

3.8 Conclusions 804. Summary of the Oral Presentations 85

4.1 Bridge inspections as a tool for rehabilitation, design and maintenance 87

4.2 From structural assessment for retrofitting to integration of SHMon new design of bridges 104

4.3 Visual inspections as a tool to detect damage:current practices and new trends 110

4.4 Bridge management and current state condition

of Brisas highway network bridges 1214.5 An overview on SHM and outstanding research issues 135

4.6 A decade of bridge monitoring in Portugal: the LABEST experience 144

4.7 Machine learning and the Structural Health Monitoring of bridges 153

4.8 Integrated performance assessment addressing long term assetmanagement of engineering structures 156

Sponsor Institutions 173

References 181


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Preface

Improved and more continuous condition assessment of bridges has been de-manded by our society to better face the challenges presented by aging civilinfrastructure. Indeed, the recent collapses of the Hintze Ribeiro Bridge thatkilled 59 people, in Portugal, and the I-35W Bridge in the United States (US),that killed 13 people, pointed out the need for new and more reliable tools to

prevent such catastrophic events. Besides those events, the financial implica-tions and potential impact through optimal bridge management are vast. Forinstance, facing an ageing infrastructure, the United Kingdom Governments2010 Infrastructure Plan signaled the need for enormous investments in in-frastructures, equivalent to 200 billion over the next five years. On the otherhand, the American Society of Civil Engineers reports the cost of eliminating allexisting US bridge deficiencies at $850 billion. These values clearly show that

planned bridge maintenance can lead to considerable savings.

In the last two decades, bridge condition assessment techniques have been de-veloped independently based on two complementary approaches: StructuralHealth Monitoring (SHM) and Bridge Management Systems (BMSs). The SHMrefers to the process of implementing monitoring systems to measure in realtime the structural responses, in order to detect anomalies and/or damage atearly stages. On the other hand, BMS is a visual inspection-based decision-sup-

port tool developed to analyze engineering and economic factors and to assistthe authorities in determining how and when to make decisions regardingmaintenance, repair, and rehabilitation of structures.

While the BMS has already been accepted by the bridge owners around theworld, even though with inherent limitations posed by the visual inspections,the SHM is becoming increasingly appealing due to its potential ability to detect

damage at early stages, with the consequent life-safety and economical benefits.

Recent research suggests that, in an effort to create more robust bridge man-agement, the SHM should be integrated into the BMS in a systematic way.


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Nowadays, there is a generalized consensus about this integration, but few realapplications have been accomplished, mainly because of the lack of interactionbetween all the participants involved in the bridge management field.

Therefore, in an attempt to lay the foundations of a more robust bridge manage-ment, especially in Portugal, an international seminar was organized in Lisbon,in December 2012, with the objective of bringing together bridge designers,bridge owners, researchers, and students to discuss the actual condition of thePortuguese bridges, the current practice in terms of condition assessment andmaintenance needs of the bridges, and to set up new targets and new (or alter-

native) strategies for the next decades.

In terms of the Portuguese bridge condition and current practice, this seminarintended to answer the following questions:

What is the current structural condition of the Portuguese bridges?

How much does it cost to return our aged infrastructure to world-class

levels of performance? Which are the most common damage scenarios encountered in our bridg-

es?

Are the current bridge inspections and maintenance strategies enough tomaintain our bridges?

Is the bridge SHM technology ready for real applications?

Which are the cutting edge technologies currently under development?

In terms of new strategies for the next decades, our vision was to link practiceand research, and also to find new research pathways for condition assessment.Basically, we expected to go through the following points:

Find mechanisms to reduce the bridge maintenance costs by integratingSHM into BMS;

Identify technologies that are ready to transit from research to practice;

Prioritizing research topics that endorse real-world applications;


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Identify the direct benefits for the bridge owners derived from the SHMsystems;

Raise the awareness of the authorities to support new research projects;and

Attract more and better students into the field of condition assessment ofbridges.

Therefore, in order to summarize the conclusions of this seminar, this book ispublished as an extended seminar summary. It is divided in four chapters. InChapter 1, we briefly review the evolution of the bridge management in Portugal

and the current structural condition of the Portuguese bridges. In Chapter 2,we give an overview of the bridge management field, and the BMSs in particu-lar, by focusing the roles of bridge inspections, Non-destructive Evaluation, andStructural Health Monitoring for the structural condition assessment of bridges.In Chapter 3, we present some guidelines for the future of condition assessmentof bridges, which were adjusted according to the input given by the invitedspeakers during the seminar. In particular, we focus on the potential of the SHM

for improving and complementing the information gathered by the visual in-spections of bridges. Finally, each oral presentation is summarized in Chapter 4.

Note that only the Editors are responsible for the opinions and points of viewsexpressed in Chapters 1, 2, and 3. On the other hand, in Chapter 4, the invitedspeakers are responsible for the entire content of their presentations.

Eli Figueiredo

Ionut Moldovan

Manuel Barata Marques

Lisbon, 2013


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Notation

All symbols used in this book are defined when they first appear in the text. Forthe readers convenience, this section contains only the principal meanings ofthe commonly used acronyms and symbols. Some symbols have more than onemeaning, but their meaning should be clear when read in context.

Abbreviations

AASHTO American Association of State Highway and Transportation Officials

BMS Bridge Management System

Brisa Brisa Auto-estradas de Portugal, S.A.

CP Comboios de Portugal

DAQ Data Acquisition System

EP Estradas de Portugal, S.A.

EU European Union

FHWA Federal Highway Administration

GOA Gesto de Obras de Arte (Software)

JAE Junta Autnoma das Estradas

NDE Non-destructive Evaluation

PNR National Roadway Plan (Plano Nacional Rodovirio)

REFER Rede Ferroviria Nacional, EPE

SHM Structural Health Monitoring

SPR Statistical Pattern Recognition

UAV Unmanned Aerial Vehicle

UK United Kingdom

US United States (of America)

UUV Unmanned Underwater Vehicle


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Acknowledgments

First of all, we would like to acknowledge all the sponsors of the internationalseminar Structural Condition Assessment of Bridges: Past, Present, and Fu-ture. Without their support, this effort to push forward the knowledge aboutbridge management could not have taken place.

We would like to thank all the invited speakers, for their will and availability tocome over and give a talk on their specific topics of expertise: Antnio Perry daCmara, Armando Rito, Carlos Flix, Carlos Santinho Horta, Charles R. Farrar,Jos Carlos Clemente, Keith Worden, Lus Oliveira Santos, Paulo Lima Barros,Robert Veit-Egerer, and Tiago Mendona. We would also like to thank HelmutWenzel and Joaquim Figueiras for their initial availability to give a talk at theseminar. Due to unforeseen events, they could not participate, but nominated

Robert Veit-Egerer and Carlos Flix to replace them, respectively.

We would also like to thank the Bastonrioof the Ordem dos Engenheiros (thePortuguese Order of Engineers) Carlos Alberto Matias Ramos, for giving theinstitutional support to the seminar as well as for having chaired one of the ses-sions.

We also would like to thank Assuno Alves and Ivo Boaventura for the testimo-

nies given about the current bridge management procedures carried out at theMunicipal Chambers of Lisbon and Barcelos, respectively.

Lastly but most importantly, we would like to thank all the students involvedin the organization of the seminar, especially Joo Tiago Pereira and Joo PiresMesquita.


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Interpret the past,understand the present, and

design the future of condition assessment of bridges.


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1. Overview of Bridge Management

1.1 Introduction

Around the world, the investment in road and rail networks is huge and bridges,along with tunnels, are by far the most vulnerable and expensive parts per ki-lometer. Bridges play a key role in the backbone of the economies, even thoughtheir importance in our society is often overlooked. The bridge structures aregenerally used to cross rivers, estuaries, valleys, and to improve traffic flow atintersections. Certain bridges can also be high-profile structures rising up aslandmarks in the landscape.

The value of bridges in the national networks has been estimated at 12 billionEuros in France, 23 billion Euros in the United Kingdom (UK), 4.1 billion Eurosin Spain, and 30 billion Euros in Germany [1].

In the United States (US), it is speculated that the first bridge construction boomstarted along with the road construction program mandated by the FederalHighway Act of 1956 [2]. In 2009, the Federal Highway Administration (FHWA)

declared to have in its inventory 603,259 bridges [3]. In the European Union(EU), most bridges in the national road networks have been built after the WorldWar II. Typically they comprise about 2% of the length and about 30% of the val-ue [1], which shows the relatively high cost of bridges in the road network. Nev-ertheless, in Portugal most road bridges have been built during the last 30 years,mainly pushed by the EU funding and the highway construction boom. On theother hand, the rail network had its construction boom in the late 19thcentury.In the recent Global Competitiveness Report, the World Economic Forum classi-

fied Portugal in 4thin terms of quality of roads, which indicates an extensive andefficient road network, and in 26thin quality of railroad infrastructure, whichindicates the underinvestment observed in this sector [4]. Currently, the main


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road and rail networks comprise about 6,200 bridges. The railway bridge lengthcomprises about 1.65% of the total rail network length.

Over the last 60 years, both in the US and in the EU, the emphasis was cen-tered on the construction of new bridges rather than on routine inspections orpreventive maintenance of the existing ones. However, modern societies havereached the point of development where the maintenance of the existing infra-structure is mandatory. For instance, according to the American Association ofState Highway and Transportation Officials (AASHTO), more than 26% of thenations bridges are either structurally deficient or functionally obsolete. The

cost of eliminating all existing bridge deficiencies, as they arise over the next50 years, was estimated at $850 billion in 2006, equating to an average annualinvestment of $17 billion [5]. As a response, in 2010, the US Federal Governmenthas announced plans for a $50 billion, six-year infrastructure investment plan,which includes rebuilding 150,000 miles of roads and bridges, and constructionand maintenance of 4,000 miles of railways [6]. Facing an aging infrastructure,the UK Governments 2010 Infrastructure Plansignaled the need for enormousinvestments of 200 billion over the next five years [7]. Therefore, learning thelessons from the current infrastructure scenario, in some of the most developedcountries in the world, and assuming the Portuguese delay in the economy de-velopment, one can conclude that we do need to act today in order to avoid suchhuge investments, at once, in 20 to 30 years from now, i.e. we need to maintainthe present to preserve the future.

Maintaining bridge structures in a serviceable condition has been challenged

by the wide variety of structural systems. Even though the majority of modernbridges are of reinforced or prestressed concrete construction, there are alsoa large number of composite bridges, steel bridges, cable-stayed bridges, sus-pended bridges, and masonry-arch bridges. Each type of structure behaves dif-ferently, suffers from different types of deterioration, and has different main-tenance needs. Additionally, the increasing volume of traffic, and maximumweights of individual vehicles, means that, for many structures, the loads towhich bridges are being subjected are far higher than those predicted during thedesigning process, which also increase their deterioration. The deterioration isfurther amplified as many modern structures, especially concrete bridges, aresubject to a more aggressive environment than the ancient ones. The effects of


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chlorides, either in a marine environment or from de-icing salts, alkali-silicareaction, carbonation, and inadequate corrosion protection are causing pro-gressive deterioration of the bridges, which leads to a higher frequency of bridgerepairs and possibly reduced bridge load carrying capacity. Bridge maintenanceis also costly, so ensuring that bridges are properly maintained is challenged byreduced governmental or private owners budgets for maintenance activities.

Meanwhile, the collapses of certain bridges around the world have put pres-sure on the authorities to develop solutions to periodically inspect their bridgesand to support maintenance activities. Thus, in the last two decades, numer-

ous Bridge Management Systems (BMSs) have been developed, in the US andinside the EU, to assist engineers on the condition assessment and prioritiza-tion of maintenance activities. A BMS is defined as a visual inspection-baseddecision-support tool developed to analyze engineering and economic factorsand to assist the authorities in determining how and when to make decisionsregarding maintenance, repair, and rehabilitation of bridge structures. Eventhough the BMS technology has already been accepted by the bridge ownersaround the world, its efficiency has been challenged by the limitation of the vi-sual inspections to unveil all the structural anomalies. This limitation may leadto inappropriate or costly maintenance activities in order to cover the uncer-tainty derived from the visual inspections.

As stated by the FHWA [8], the public is demanding to act faster, cheaper, andgreener than ever before. One solution to accomplish that is through the inclu-sion of innovation, research, and new technologies for bridge condition assess-

ment. Therefore, in the last decade, the Structural Health Monitoring (SHM)technology has evolved and become increasingly appealing due to its potentialto detect damage at early stages, with the consequent life-safety and economicalbenefits. The SHM refers to the process of implementing monitoring systems tomeasure in real time the structural responses, in order to detect anomalies and/or damage at early stages. Recent developments [9] have suggested that, in aneffort to create a more robust bridge management, the SHM should be integrat-ed into the BMS in a systematic way. Although there is a generalized consensusabout the need of this integration, few real applications have been accomplisheddue to technological challenges and also due to the lack of interaction betweenall the participants involved in this field.


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In 2008, the AASHTO pointed top five problems for bridges in general: age anddeterioration, congestion, soaring construction costs, maintaining bridge safe-ty, and new bridge needs; and five solutions for bridges: investment, researchand innovation, systematic maintenance, public awareness, and financial op-tions [5]. Therefore, in order to maintain bridge safety at the minimum overallcost, the bridge owners need to act now, by investing in research and innova-tion, in order to be able to perform appropriate systematic maintenance.

In order to interpret the past, understand the present, and design new perspec-tives for the future of bridge management, with focus on the condition assess-

ment of bridges, the Catholic University of Portugal organized the internationalseminar Structural Condition Assessment of Bridges: Past, Present, and Fu-ture, held in Lisbon, in December 2012. Well-known specialists, with differentbackgrounds, were invited to participate, such as bridge owners, bridge de-signers, researchers, and students. As the main outcome of the seminar, thisbook is intended to summarize some of the discussions held on this occasion. Inparticular, Chapter 1 presents a brief history of the Portuguese road and rail net-works and of the development of bridge management in Portugal. Additionally,it summarizes the current state condition of the Portuguese bridges from theperspective of the main bridge owners. Chapter 2 gives an overview of bridgemanagement and its several parts, summarizes some of the main lessons fromthe past, and provides some limitations and needs in terms of bridge conditionassessment. It also highlights the capabilities of the SHM systems for bridge con-dition assessment, including the Non-Destructive Evaluation (NDE) technolo-gy, which can potentially be integrated into the existing BMSs in a systematic

way. Chapter 3 provides some guidelines for the future of bridge management inorder to support the bridge owners, especially the Portuguese ones, to maintaintheir bridges at minimum overall cost, taking all factors into account such as thecondition of the structure, load carrying capacity, rate of deterioration, effecton traffic, duration of the repairs, and the residual life of the structure. Finally,Chapter 4 summarizes the presentations given by the invited speakers.

The reader should note that, the bridge management is a vast multidisciplinaryfield, which makes it difficult for the authors to go through all its main topicsin just one document. Thus, this book is mostly focused on the structural en-gineering point of view, especially on the structural condition assessment of


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bridges. Nevertheless, the authors acknowledge the existence of other topicsof outmost importance to the success of the BMSs, as for instance, informationtechnology and economics.

1.2 Bridge management and structural condition assessmentof bridges

The bridge management (Figure 1.1) has been defined as a multidisciplinary fieldincorporating knowledge from structural engineering, information technology,and economics [10]. The BMSs are computerized tools, which incorporate thatknowledge aiming to optimize maintenance budgets within a stock of existingbridges. The structural condition assessment of bridges is a subset of the struc-tural engineering, concerning exclusively with the assessment of the structureintegrity, defined as the capacity of the structure to fulfill the technical require-ments for use in serviceability limit states and to fulfill the structural capacity

to resist to the ultimate limit states. In general, the outcome of the structuralcondition assessment is a score that quantifies the operational performance ofbridges, which can be subsequently used to support the maintenance programsand to prevent bridge collapses.

Figure 1.1 Bridge management as a multidisciplinary field.


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1.3 The motivation for structural condition assessment ofbridges

The ultimate goal of structural condition assessment will always be the preven-tion of bridge collapses. Actually, the motivation for permanent or temporarystructural condition assessment of bridges has been driven, politically, by cat-astrophic bridge collapses around the world. Indeed, in the US, the safety and/or deterioration of the existing bridges came up, in the late 1960s, when the USHighway 35 Silver Bridge suddenly collapsed on December 17, 1967, and killed46 people. However, despite the tremendous developments observed in the US

since then, the I-35W Bridge over the Mississippi River collapsed in 2007, killing13 people and pointing out the need for new and more reliable tools to preventsuch catastrophic events. In Portugal, the collapse of the Hintze Ribeiro Bridge,in 2001, over the Douro river in Entre-os-Rios, that killed 59 people (Figure 1.2),has been seen as the awakening moment in terms of bridge management, asmentioned by the brigde owners.

Figure 1.2 Front page of a Portuguese newspaper focusing the Hintze Ribeiro Bridge collapse.


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On the other hand, the bridge owners are also interested in the condition as-sessment as a tool to guide and support the bridge maintenance throughout itslife cycle. As mentioned in Section 1.1, the financial implications and poten-tial impact through optimal bridge management are vast, which suggests thatplanned bridge maintenance can lead to considerable savings.

1.4 The history of the Portuguese road and rail networks andbridge management

Based on the political, social, and economic environment as well as the strat-egies implemented throughout the centuries, the evolution of the Portugueseroad and rail networks can be split into five periods (adapted from [11]):

Before 1852;

1852-1910;

1910-1933;

1933-1985;

1985-present.

Until the second part of the 19thcentury, the Portuguese people used to moveby animal-powered transportation and boat. There was not yet any type of rail

network. The first road classification is dated from the 18th

century, more pre-cisely in 1790 [12]. The road network diagram of 1808 (Figure 1.3) indicates theexistence of a massive road network (even though without quality) that coveredmost of the Portuguese territory and connected the main cities. At that time,a trip between Lisbon and Porto used to last three days, approximately. Eventhough most of the roads were unpaved, some roads were paved using the mac-adam. The first macadam road built in Portugal was in 1824, in Lisbon1[13].

1. The asphalt made of bitumen was used only in the early 20thcentury.


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The year of 1844 stands as a historical year as a group of capitalists formed acompany under the name of Portuguese Public Works Company2, which set outto accomplish all the great public works legally authorized for the improve-ment of the countrys communications, and was approved, along with itsstatutes, by a decree of the same year. On the 1 stof March 1845, the companyentered into a contract with the Government, whereby it was entrusted withcarrying out the necessary works to improve the countrys communications,namely the opening and the improvement of several roads and the constructionof the first railway line. The approval of the plans and the supervision of theworks were reserved to the Government. The company was granted with a con-

cession agreement for 40 years on the roads and 99 years on the railways. De-spite such privileges, the company was unable to follow its ambitious plan. Atthe end of 1855, when it was shut down with a negative balance, it had onlyundertaken the construction and improvement of some roads and performedstudies for the Lisbon ring road and east railway lines [14].

The period from 1852 to 1910 is remembered due to the outstanding work car-ried out by Antnio Maria de Fontes Pereira de Melo and the construction ofmost of the national rail network.

In 1852, the Ministry of Public Works3 is created, headed by Fontes Pereira deMelo, whose one of the main goals was to elaborate studies in order to build thefirst railway lines. In 1853, the Portuguese government signed up a concessionagreement with the Central Peninsular Railway Company of Portugal4[15], repre-sented by Hardy Hislop, to build up a rail connection between Lisbon and Spain,

through the city of Santarm. Later on, the Portuguese state resigned the conces-sion agreement and assumed itself the construction of the railway. In October of1856, the first railway was opened between Lisbon and Carregado with a lengthof 36km [16]. The Royal Portuguese Railroad5, nowadays called Comboios de Por-tugal (CP), the main railway operator, was founded on the 11thof May, 1860, bythe Spanish entrepreneur Jos de Salamanca e Mayol. In 1877, in the middle of therailway construction boom, the Maria Pia Bridge is inaugurated (Figure 1.4).

2. In Portuguese: Companhia das Obras Pblicas Portuguesa

3. In Portuguese: Ministrio das Obras Pblicas

4. In Portuguese: Companhia Central Peninsular dos Caminhos de Ferro de Portugal

5. In Portuguese: Companhia Real dos Caminhos de Ferro Portugueses


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Figure 1.3 Military map of the Portuguese national roads in 1808 [13]

(picture with low resolution).

Figure 1.4 Construction of the Maria Pia Bridge over the Douro River, in Porto [17].


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On the other hand, at that time, in spite of huge developments of the rail net-work, the national road network does not observe significant investments bythe Government. Nevertheless, in 1889, the classified road network (estradasreaisand estradas distritais) was estimated at 18,427km. Note that, during thistime, the first level of conservation works used to be done by road menders6(Figure 1.5), who were road conservation workers responsible to overview theircanton and to report to the head of conservation [18]. The road menders werespread around the country and were responsible to maintain the roads (e.g.clean the gutters) as well as to patrol the roads [19].

In 1892 a law was passed to create the Board of Directors of the State Railways,but most railways remained in private ownership albeit with greater regulation.Actually, and due to the rapid increase of railway lines and bridges, the bridgemanagement was first handled by the CP. The CPs Regional Bridge Brigade and

Bridge Review Brigade7were responsible tomanage the railway bridges. The Region-al Bridge Brigade was divided into differentregions throughout the country and wasresponsible for routine inspection and cur-rent maintenance such as small repairs andcleaning. The Bridge Review Brigade wasonly responsible for the principal inspec-tions [20]. By 1895, Portugal had a rail net-work of 2,344km [17] as shown in Figure 1.6.

Figure 1.5 Road menders dressing fromJunta Autnoma das Estradas.

Figure 1.6 Map of the Portuguese rail network in 1895,including the former Portuguese colonies.

6. In Portuguese: Cantoneiros; In French: Cantonniers

7. In Portuguese: Brigada de Reviso


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The period between 1910 and 1933 is remembered as an era of political instabil-ity and by the rise of the automobile industry.

After the 1910 revolution, which deposed the monarchy, the democratic but un-stable Portuguese first republic was established. Recognizing the importance ofthe bridge safety, in 1912 the state declares that some university specialists mustbe part of a commission to verify the safety of bridges [11]. In 1913, the road net-work is officially classified into national and municipal roads (estradas naciona-is, estradas municipais, and caminhos vicinais). In 1926, after the 28thof MayRevolution, Portugal implemented an authoritarian regime of social-catholic

views, which, in 1933, was recast and renamed as the New State8. In 1927, theJunta Autnoma das Estradas9 (JAE) was founded after the extinction of theGeneral Administration of Roads and Tourism10, in order to organize and devel-op the Portuguese road network. Signs of the growing power of motorists weregiven by the creation of the Portuguese Automobile Association11, which becameone of the strongest players in the national road action.

The period between 1933 and 1985 is marked by the vision of Duarte Pacheco,engineer and politician, in the middle of the 20thcentury, and by the develop-ment of the road network.

In 1933, the whole classified road network (national and municipal) was esti-mated at 16,900km. In the same year, Duarte Pacheco, Minister of Public Works,created a commission to analyze the proposal to build a road and railway bridgein Lisbon. However, the proposal was subsequently put aside in favor of the

Marechal Carmona Bridge, in Vila Franca de Xira (1951) the closest bridge toLisbon to cross the Tagus River.

In recognition of the importance of the road network, in 1945 the Portuguesestate elaborated the first real National Roadway Plan PNR 4512. According withthe PNR 45, the classified national road network was estimated in 20,597km

8. In Portuguese: Estado Novo

9. Which is today EP Estradas de Portugal S.A.

10. In Portuguese: Administrao Geral das Estradas e Turismo

11. In Portuguese: ACP Automvel Club de Portugal

12. In Portuguese: Plano Rodovirio Nacional 1945


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[12]. In 1948, in later reorganization, marked by the end of the World War II andthe construction of new roads and bridges, it was created the Bridge DirectorateServices13, from the Construction Services Directorate14, with greater autono-my, being also responsible for the current conservation works. Its primary re-sponsibility was to build and maintain the road network in Portugal.

In 1953, the Minister of the Public Works created a new commission to analyzethe construction of a bridge over the Tagus River, in Lisbon. In 1959, a publictender was launched to build up a road and railway bridge. Due to economicreasons, later on, the Portuguese authorities decided to give up the idea of a rail

line, even though it was decided to leave the structure prepared for a later up-grade. In 1962, the United States Steel International Inc. was put in charge of itsconstruction. On the 6thof August 1966, the four-lane Salazar Bridge (nowadaysthe 25 de Abril Bridge) was inaugurated after 45 months of construction works(Figure 1.7).

Around this time, the JAE had four Bridge Brigade teams, for bridge mainte-nance activities, with specialized people, located in Almada, Vila Franca de Xira,and Porto. The fourth one was a team with a mobile vehicle 15(Figure 1.8), es-pecially designed to perform small bridge repairs throughout the country [20].

Due to the increasing importance of the road network, and to the need of short-ening the journeys between the main cities, in 1972, Brisa Auto-estradas dePortugal, S.A. (Brisa) was created for construction, operation, and maintenanceof tolled highways.

In 1975, and following the Carnation Revolution16, the CP was nationalized.

In the early and mid 1980s, the JAE undertook several internal changes, such asthe ending of the Bridge Brigades and the road menders. In consequence, mostof the maintenance activities were outsourced from the private sector and were

13. In Portuguese: Direco dos Servios de Pontes

14. In Portuguese: Direco dos Servios de Construo

15. In Portuguese: Carro oficina

16. In Portuguese: Revoluo dos Cravos, aps o golpe de estado ocorrido a 25 de Abril de 1974


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essentially reactive rather than planned. Note that the road menders were pres-ent as conservation workers since the 19thcentury.

The period between 1985 and present day is marked by the integration of Portu-gal into the EU and the arrival of European funding for the construction of newroads. This period stands as a Portuguese golden age for highway construction.In 1985, one year before the integration of Portugal into the EU, the PNR 45 wasreplaced by the PNR 8517. In 1991, three years before the established deadline,Brisa completed the highway A1 between Lisbon and Porto, which marked thebeginning of a new era in the national road paradigm the construction of a

massive highway network. As a way to show the excitement around this in-auguration, Figure 1.9 shows the 27m-high sculpture, by Charters de Almeida,raised in Condeixa for the inauguration of the highway A1. With the completionof the A1, the length of national highways was set in 409km.

At this time, the bridge inventories and inspections were summarized in hand-filled forms. For instance, Figure 1.10 shows several registration records18fromCP related with a bridge inventory, describing structural details about the

bridge. Additionally, Figure 1.11 shows a bi-annual inspection datasheet from JAE sum-marizing one inspection performed, in 1992,to the Pinho Bridge over the Douro River.Note that the bridge inspector pointed outthe need for cleaning of the draining systemand the sidewalks, rail maintenance, and

also a special bridge inspection for reassess-ment of bearings and cracking observed insteel components. However, these hand-filled forms were vulnerable, i.e. they wereeasily lost, stolen, damaged or destroyed.

Figure 1.7 Inauguration of the Salazar Bridge(currently 25 de Abril Bridge) in 1966.

17. In Portuguese: Plano Rodovirio Nacional 1985

18. In Portuguese: Ficha de Cadastro


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Figure 1.8 Mobile vehicle from JAE for small repairs and maintenance activities [20].

Figure 1.9 Charters de Almeida sculpture to commemoratethe accomplishment of the highway A1 in 1991.


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Figure 1.10 CPs registration records dated from 1989 [20].

Figure 1.11 JAE inspection records dated from 1992 [20].


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In the 1990s, the CP also underwent a change in the bridge management strate-gy, namely the reorganization of the internal maintenance teams, the reductionof the number of people involved in maintenance activities, and the extinctionof the workshop19 in the city of Ovar, which was responsible to support, lo-gistically, the maintenance activities performed on the bridges throughout thecountry (Figure 1.12). Part of the capabilities, for small repairs, were moved tothe city of Entroncamento. The reorganization of the maintenance teams ledto the extinction of the Regional Bridge Brigades and the creation of four bri-gades for bridge maintenance located in Porto, Guarda, Lisbon, and Faro. Thoseteams were responsible for annual routine inspections and were in charge of

basic maintenance activities, without special technology and means. Significantrepairs needed to be outsourced. One also observed the extinction of the BridgeReview Brigade and the creation of a bridge inspection team, with more trainedpeople and special equipment, responsible for main inspections uncovered bythe four regional brigades [20]. Finally, at this time, a plan for periodic observa-tion and instrumentation of bridges was put into place.

Figure 1.12 Workshop of Ovar.

19. In Portuguese: Oficina


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In 1997, REFER Rede Ferroviria Nacional, EPE (REFER) was created as a publiccompany responsible for providing the public service of managing the nation-al rail network infrastructure in Portugal. REFER is subject to the supervisionof the finance and transport ministers. At this point, CPbecame exclusively atrain service operator.

Even though in the first years Brisas activity was mainly focused on the con-struction (project, works coordination, and supervision) and operation of newhighways, the maintenance of those later became a priority. Therefore, since1991, after the conclusion of the highways A1 and A5, as well as the initial

stretches of A3 and A4, an infrastructures management system for the globalnetwork was internally required. Thus, in 1994, Brisa developed the first Portu-guese BMS STONE20.

In 1995, one assisted at the beginning of periodic inspections for importantstructures. In 1997 was initiated the development of a BMS called GOA21, whichwould later become the prominent Portuguese BMS. In 1998, the MunicipalChamber of Lisbon22acquired and implemented the GOA system. In 1999, RE-FER also implemented the GOA system.

In 1998, a new National Roadway Plan PNR 2000 was approved, which wasessentially an optimization of the PNR 85. In the same year, in order to alleviatethe congestion of the 25 de Abril Bridge, the cable-stayed Vasco da Gama Bridgewas opened to traffic. Additionally, the sidewalls of the 25 de Abril Bridge wereextended and retrofitted to accommodate six road lanes. In 1999, the lower plat-

form of the bridge was prepared to carry two rail tracks. In the same year, JAEwas split into three agencies: Instituto das Estradas de Portugal (IEP), responsi-ble for the regulation and supervision of the national road sector, Instituto paraa Construo Rodoviria (ICOR), responsible for the road construction works,and Instituto para a Conservao e Explorao da Rede Rodoviria (ICERR),which was responsible for the maintenance and operation works.

20. In Portuguese Manual para a Manuteno Programada das Obras de Arte Rodovirias

21. Acronym for Gesto de Obras de Arte

22. In Portuguese Cmara Municipal de Lisboa
http://en.wikipedia.org/wiki/Comboios_de_Portugalhttp://en.wikipedia.org/wiki/Comboios_de_Portugal


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As a means of showing the excitement around the highway construction boom,in 2001, ten years after the accomplishment of the highway A1, Portugal almostquadrupled the length of its highways (1,659km)!

However, on the 4thof March 2001, the Entre-os-Rios tragedy showed the defi-ciencies of the bridge management carried out in Portugal and marked the shiftto a new era of bridge management. The tragedy occurred after many days ofintense rain and consequent increase of the river stream, when one of the piersof the Hintze Ribeiro Bridge, owned by IEP, over the Douro River, collapsed re-sulting in the partial fall of the deck. The collapse dragged together a bus and

three cars, killing 59 people (Figure 1.13). In an emergency response, from Aprilto June of the same year, the ICERR launched a program for emergency inspec-tions. After 349 bridge inspections, three bridges were closed down and load/speed restrictions were enforced on 56 more. Retrofit projects were developedfor 60 bridges. Meanwhile, the ICERR and REFER promoted campaigns for un-derwater inspections. On the 4thof May, 2002, the new Hintze Ribeiro Bridgewas inaugurated.

Figure 1.13 Hintze Ribeiro Bridge collapse in 2001.


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In 2002, ICOR and ICERR were merged into a single agency, namely the IEP. Inearly 2004, and after several years of hesitations, the renamed Estradas de Por-tugal, S.A. (EP) finally acquired the GOA system. In 2005, the EP promotes anannual program for underwater inspections. In 2006, roughly 1,700 bridges arereported as being subjected to principal inspections.

In 2007, the government decided to create a new institute Instituto de In-fra-estruturas Rodovirias (InIR), which was mandated to regulate and super-vise the national road sector. In the same year, the Lezria Bridge, the longest

one in Portugal (10km, roughly), included in the Brisas highway network, wasofficially opened to traffic with a monitoring system composed of a dense sensornetwork over 400 sensors.

In 2008, about 1,200 bridges were subjected to principal inspections. In 2012, inanother governmental reorganization, the InIR is integrated into a new institute Instituto da Mobilidade e dos Transportes, IP.

As described in Chapter 4, currently, the three main Portuguese owners (Brisa,EP, and REFER) use the GOA system, as a database with relevant informationof their special structures, and have their own teams and internal resources to

Figure 1.13 Hintze Ribeiro Bridge collapse in 2001.


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perform routine and principal bridge inspections, with the exception of theunderwater and special inspections. However, the structural condition assess-ment still relies heavily on visual inspections. For this reason, and in order toimprove the structural condition assessment, the three owners have already in-stalled monitoring systems in some of their bridge structures, namely the 25 deAbril Bridge in Lisbon, the Lezria Bridge in Carregado, and the So Joo Bridgein Porto.

Finally, in order to summarize the current Portuguese road and rail networks,Figure 1.14 shows the evolution of the national railway length since 1853 and

Figure 1.15 shows the evolution of the highway network along with the total na-tional road network since 1960 and 1990, respectively. Table 1.I summarizes thetotal length of the highway network as well as the total length of the nationalroad and rail networks.

Figure 1.14 Current railway length in kilometers (adapted from [17] and [21]) until 2010.


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Figure 1.15 Evolutions of the highway (1960-2011) and national road network (1990-2011)(adapted from [21]).

Table 1.I Total length of the Portuguese highway network as wellas national road and rail networks in 2011.

Highway Network National Road Network National Rail Network

Length (km) 2,737 13,511 2,843

1.5 Status of the Portuguese bridges

In Portugal, currently there are three main bridge owners, namely Brisa, EP,and REFER, plus the Municipal Chambers. Brisa was created in 1972 and, in fourdecades, it has become one of the largest tolled highway operators in the worldand the largest private transport infrastructure company in Portugal. EP is acompany owned entirely by the Portuguese State. REFER is also a state-ownedcompany and was created to manage the Portuguese rail infrastructure, previ-

ously under control of CP, which is currently exclusively a train service opera-tor. In Portugal, the 308 Municipal Chambers are responsible for bridges incor-porated in the network of secondary roads.
http://en.wikipedia.org/wiki/Comboios_de_Portugalhttp://en.wikipedia.org/wiki/Comboios_de_Portugal


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1.5.1 The perspective of the three main bridge owners

The main owners have the inventory database organized according to the typol-ogy of the special structures, which may include bridges, viaducts, footbridg-es, culverts, cattle creeps, and tunnels. Herein, and for simplification reasons,the term bridge is defined as a structure used to span physical obstacles such asbodies of water, valleys, or roads. Thus, it includes bridges (span bodies of wa-ter), viaducts (span valleys), footbridges, overpasses (cross over another roador railway), and underpasses (constructed for the benefit of secondary roadsand railways). For completeness, culverts, cattle creeps, and tunnels are still

covered here, as those structures also carry out lessons that can help solving thechallenges posed by aging bridge structures.

In Chapter 4, the inventory of special structures is summarized for each owner.Additionally, it contains information about the current condition of thosestructures, the bridge management and maintenance strategies implement-ed (which includes the identification of the type of bridge inspections and the

maintenance activities), the currently observed damage scenarios, and the fu-ture developments and recommendations.

Concerning the past and the present, and based on the description of each own-er, the following conclusions can be drawn regarding the structural conditionof the bridges:

Even though REFER has a longer tradition in bridge inspection, interven-

tion, and maintenance activities, the Hintze Ribeiro Bridge disaster, in2001, has been seen as a changing moment, or turning point, in terms ofbridge management for all owners;

Nowadays, the three bridge owners use the Portuguese BMS GOA, asan organized and systematic methodology to provide information abouttheir patrimony and to assist them on the prioritization of the interven-tions according with the budgetary constraints;

According with the bridge definition given above, the three main ownersaccount for 6,200 bridges, approximately; additionally, they also possess,in their inventory, approximately 2,600 culvert and cattle creeps;


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Taking into account the last two levels of structural condition rating ad-opted by each owner, one may conclude that only 3.2% of the specialstructures are considered structurally deficient; on the other hand,taking into account the first three levels, one may conclude that 84.8%of the special structures are considered in a good to excellent condition;

The most common damage scenarios identified are: generalized concretedegradation (cracking, delamination, and corrosion of the reinforcingbars), corrosion of metal components, degradation of the expansion jointsand bearings, and degradation of corrugated metal culverts; note that thealkali-silica reaction is identified as one of the main degradation mecha-

nism of the concrete; the rapid degradation of corrugated metal culvertshas pushed the owners to perform considerable investments in order tomaintain them; and

The three main owners have already installed monitoring systems in someof their special structures; the reduced number of monitoring systems hasbeen justified by their relatively low benefit-cost ratio; some examples ofbridges incorporated with those systems are: the 25 de Abril Bridge in Lis-bon, the Lezria Bridge in Carregado, and the So Joo Bridge in Porto.

1.5.2 Other bridge owners

The number of bridges owned by each Municipal Chamber varies with the sizeof the Chamber, in terms of population and area. There is not too much infor-

mation available about neither the state condition of those bridges nor the num-ber of bridges under control of the Chambers.

The authors can claim though, through personal interviews performed after theSeminar, that currently the Municipal Chamber of Lisbon owns, roughly, 160bridges (most are overpasses and underpasses) and tunnels. This value does notinclude pedestrian bridges. On the other hand, the smaller Municipal Cham-ber of Barcelos owns 10 bridges over rivers, approximately. The status of those

bridges is not reported herein due to the lack of coherent information. Never-theless, through those interviews, it was possible to unveil four main challengesthat Chambers face in the bridge maintenance process, namely:


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Continuously shrinking public budgets for active maintenance activities;

Reduced number of people involved in the maintenance process;

Through the last decade, especially due to the shrinking budgets causedby the economic crisis, the division for maintenance activities has beenmarginalized, which gives them less power to take action; and

In the last years, and due to the declassification of some national roads tomunicipal roads, the EP has transferred the responsibility of inspectionand maintenance activities for the bridges incorporated in those roads, tothe Municipal Chambers; however, the shrinking budgets of the Cham-

bers, along with lack of internal organization to conduct regular bridgeinspections, might delay some preventive maintenance activities.


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2. Bridge Management System (BMS)

2.1 Introduction

2.1.1 DefinitionInitially, the BMSs were simply inventories of basic information about the bridg-es such as construction date, location, owner details, etc. Then, and as shownin Figure 1.10 and Figure 1.11, they evolved to incorporate information derivedfrom scheduled inspections and from maintenance activities. Currently, BMSsintend to cover all activities performed during the service life of bridges, fromdesign to demolition, by taking into account public safety, authorities budget-

ary constraints, and transport network functionality. They possess mechanismsto ensure that the bridges are regularly inspected, evaluated, and maintained ina systematic way. Broadly speaking, the main goal of a BMS is to ensure safetywhile minimizing costs. Therefore, even though there is not a unique definition,a BMS can be defined as a visual inspection-based decision-support tool devel-oped to analyze engineering and economic factors and to assist the authoritiesin determining how and when to make decisions regarding maintenance, re-

pair, and rehabilitation of structures.

However, the BMSs still rely heavily on bridge inspections, especially on thequalitative and not necessarily consistent visual inspections, which may com-promise the structural evaluation and, consequently, the maintenance deci-sions as well as the avoidance of bridge collapses. Note that the inspectors maynaturally overlook certain structural problems, especially in parts of the struc-ture where the access is difficult. Therefore, the reducing maintenance budgets

have pushed to the advent of more complex BMSs capable to optimize main-tenance at minimum long-term cost for the transportation network. The ideais to transform the current BMSs from visual inspection-based to continuous


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assessment-based decision-support tools, which takes information from long-term monitoring and bridge inspections.

In that sense, in the last years, the NDE and the SHM fields have emerged to aidthe bridge management with more quantitative information. As explained inCross et al.[22], the NDE concerns the health assessment of a structure, or itscomponents, through offline non-damaging procedures. Although most of thetechniques used for NDE might be used for SHM purposes, one should keep inmind that NDE normally occurs as a local event in time, often applied to a smallarea of a structure where damage is thought to be present. On the other hand,

SHM assumes an online approach, continuous in time and global in nature, withthe aim of autonomous monitoring. One should also note that SHM is more thanmonitoring, as simply collecting data does not constitute SHM. Rather, SHM as-sumes a continuous strategy of damage identification based on monitoring andinterpreting the collected data. Nevertheless, it is fair to observe that NDE maybe incorporated into the SHM systems, but not vice-versa.

At the current stage, it is important to note that SHM and NDE technologies donot intend to replace the visual inspections, rather they intend to provide accu-rate assessment and, at most, reduce the bridge inspection frequency.

2.1.2 BMS evolution around the world

The BMS evolution has been triggered by the challenges posed by aging bridgesaround the world. The reports of several catastrophic bridge failures and theincrease of maintenance costs have pushed the authorities to upgrade, progres-sively, the existing BMSs.

The US has been the leading force of the BMS development, mainly due to thefast deterioration of their bridges and the number of observed catastrophic fail-

ures. In the US, during the first bridge construction boom, which started alongwith the road construction program mandated by the Federal Highway Act of1956 [2], the whole emphasis was centered on the construction of new bridgesrather than on routine inspections or preventive maintenance of the existing


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ones. Actually, the concern regarding the safety and/or deterioration of existingbridges emerged in the late 1960s, when the pin-connected link suspension USHighway 35 Silver Bridge suddenly collapsed on December 17, 1967, and killed46 people (Figure 2.1). This catastrophic event prompted the FHWA to estab-lish the National Bridge Inspection Program in 1970. This program required thebridges to be inspected every two years and the creation of the National BridgeInventory database. Despite the efforts to inspect the bridges, in June 1983 theMianus River Bridge on the I-95 collapsed, killing three people. This disastercaused concerns regarding fatigue and fracture-critical bridges. The NationalTransportation Safety Board determined the disaster was the result of undetect-

ed anomalies in the pin and hanger assembly by the inspection and maintenanceprogram. In 1987 and 1989, the scour-induced failures at the Schoharie CreekBridge in New York and at the Hatchie River Bridge in Tennessee, respectively,pushed the need to design bridge piers to resist scour and also the initiationof the underwater bridge inspection program [2]. Realizing the need to inspectthe bridges for scour, the FHWA issued a technical advisory in 1988 revisingthe National Bridge Inspection Standards to require evaluation of all bridges forsusceptibility to damage resulting from scour.

Figure 2.1 Collapse of the Silver Bridge on December 17, 1967, that killed 46 people in the US.


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In the early 1990s several software packages were developed to assist in manag-ing bridges, such as PONTIS and BRIDGIT in the US, and DANBRO in Denmark[23].

In Portugal, until 1990s and as reviewed in Section 1.4, the bridge managementwas carried out in a simplified manner, but with skilled technicians. Few acci-dents were reported due to lack of maintenance, which can also be explainedby the reduced number of bridges. However, the early management systemshad significant information flaws, derived by the manual filing systems. More-over, they were not prepared to interact with financial programming as well as

the needs of the whole transport network. In mid 90s, Brisa gave the first steptowards the creation of a BMS, namely with the development of STONE. Nev-ertheless, the Hintze Ribeiro Bridge collapse (Figure 1.13) of 2001 stands as thetipping point in terms of bridge maintenance. The bridge disaster boosted thePortuguese authorities for regular bridge inspections. The collapse of the cente-nary bridge, owned by EP, was later related to streambed scouring23caused byillegal sand extraction, which compromised the integrity of the foundations ofthe pillars. This disaster also pushed the authorities to realize the need of peri-odic underwater bridge inspections. Therefore, in the early 2000 the GOA sys-tem was released [24] and adopted by the main owners.

In spite of huge developments of the automated BMSs, in 2007, the MinneapolisI-35W Bridge over the Mississippi River, Minnesota, collapsed during the rushhour killing 13 people. Later, the National Transportation Safety Board deter-mined that the probable cause of the collapse was the inadequate load capaci-

ty of the gusset plates at one node along with additional weight on the bridge[25]. However, in 2005, the bridge was rated as structural deficient accord-ing to the National Bridge Inventory database and, in 2006, subsequent reportfound cracking and fatigue problems [26]. In the same year, in a less advertizedevent, a heavy truck collapsed the 40-year-old Harp Road Bridge in a rural areaof southwest Washington State. The reasons of the non-fatality accident wererelated to live load caused by the truck that was much higher than the designcapacity of the bridge. These incidents clearly showed the insufficiency of the

23. Scour is the result of erosive action of flowing water, excavating and carrying away material from thebed and banks of streams or rivers. Bridge scour is the removal of sediment, such as sand and rocks, fromaround bridge piers and abutments.


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BMSs to avoid bridge collapses and have put pressure on the authorities to im-prove the current BMSs.

Figure 2.2 Collapsed north section of the Minneapolis I-35W Bridge, Minnesota, in the US [25].

Around the world, the increasing number of bridges and the continuous needto maintain the existing ones, along with the information technology revolu-tion, brought about the generalization of the BMSs. Nevertheless, to date, thestructural condition assessment of these systems essentially relies on weightedindices based on visual inspections and/or preliminary NDE technologies. Forinstance, at the 50thanniversary of the Interstate Highway System, Walther andChase [27] stated that despite the advances in BMS, the condition assessment ac-

tivities still rely heavily on visual inspections, which inherently produces wide-ly variable results as described in Section 2.2.2. The same authors argued thatthe challenge would be to develop better assessment methodologies, that cangenerate better prediction models, to support the owners decisions regardingbridge safety assessment and maintenance.

Therefore, the current limitations of the visual inspections, which have been

identified as a shortcoming in BMS, have driven the research to developmentson long-term monitoring, namely to the advent of SHM and various forms ofNDE, whose results may be integrated into the BMS in a systematic way.


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2.1.3 Current BMS organization

Even though there is not a unique standard organization, a typical BMS can besplit into six main modules as follows [1]:

Inventory;

Condition assessment;

Structural assessment;

Comparison of maintenance options;

Optimal maintenance program; and

Prioritized maintenance program.

The results from the bridge inspections are used to provide a measure of thebridge condition through condition ratings. Two approaches have been usedworldwide. The first one is based on a cumulative condition rating obtained froma weighted sum of all the condition assessments of the elements/components.This approach has been adopted by the Portuguese GOA system, as highlightedin Section 4.4 by the bridge owner. The ratings generally range from zero to five.The second approach gives the assessed condition of the bridge as the highestcondition rating of the bridge elements/components. In both approaches, thehigher the condition rating, the worst the structural condition.

The FHWA has developed a software package called PONTIS, which allows a

choice of optimization policies at the network level while being based on mini-mizing life-cycle costs. It recommends maintenance for each structure by car-rying out a cost-benefit analysis where the benefit is calculated from the savingmade from maintaining the bridge immediately compared to postponing themaintenance for one or more years. Currently, PONTIS is probably the mostadvanced BMS. A particular feature of PONTIS is its statistical approach to thecondition of bridge elements, where each element of a bridge is considered aspart of a family of elements isolated from the individual bridges. The softwareuses a simple form of Markov chain to model the progress of deterioration, andtransition probabilities are applied to model the change of the condition ratingof each element [1].


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2.2 The role of bridge inspections

2.2.1 OverviewThe general concept of bridge inspection has always existed, with its effectivepractice varying between simple local visual inspections to more complex formsof online monitoring using sensor networks. Until the middle of 20 thcentury,the reduced number of inspection programs was tied with the reduced numberof bridges and the lack of a regular maintenance strategy. After the World WarII, this scenario changed in several countries, especially in the US and Europe,

with all the emphasis centered on the construction of new bridges at a mini-mal cost but with little effort on bridge inspections and maintenance activities.As mentioned in Section 2.1.2, the inspections started to be the focus of bridgeowners with the collapse of the Silver Bridge, in the US in 1967. Afterwards, na-tional standards and programs, which establish how bridge inspections shouldbe accomplished and at what frequency, were created around the world, bring-ing the concept of planned and organized bridge inspections. Thus, the main

objectives of bridge inspections are:

To ensure the safety of the bridge;

To identify any maintenance, repair, and rehabilitation works that needto be done; and

To provide a basis for planning and funding of the required works.

Currently, around the world, the bridge inspections are generally divided intofive categories:

Inventory inspection;

Routine inspection;

Principal or in-dept inspection;

Special inspection; and

Underwater inspection.


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As mentioned in Section 4.3, the inventory inspection is the first inspection ofa new or existing structure, as it becomes part of the bridge inventory. It servesto verify the information gathered previously and to look for missing informa-tion. The routine and principal inspections are the two most common inspec-tions. The routine inspection aims to look for maintenance needs. Normally, itis performed every two years and it does not need access equipment. The prin-cipal inspection is used to look for structural defects and is normally performedevery five years (or when required). The special inspection should be used toperform a close inspection of a particular area or defect that is causing con-cern. It is undertaken when required and normally needs access equipment. It

may also require supplementary tests, such as load test, structural monitoring,and physical or chemical tests in the laboratory. The underwater inspection isused to detect defects in submerged structural elements (masonry, concrete,or steel) and to identify bridge scour. In Portugal, the underwater inspectionsare performed routinely only after the Hintze Ribeiro Bridge collapse in 2001.The bottom line of underwater inspections, as described by the bridge owners,is to accurately record the present condition of the bridge foundations and thestream, and to identify conditions that are indicative of potential problems withscour and stream stability for further review and evaluation. Actually, scour isstatistically considered the most common cause of highway bridge failures inthe US [28]. From 1961 to 1976, 46 out of 86 major bridge failures were result ofscour near piers. Note that during that period, more bridge failures were causedby scour than by earthquakes, wind, structural, corrosive, accidental, and con-struction-related failures [29]. A glimpse on bridge scour research and evalua-tions can be found in references [30, 31].

Furthermore, as described in Section 4.3, the general procedure of bridge in-spection can be split into three main stages: planning, performing, and report-ing. In Section 4.1, the reader can find some examples of bridge inspectionsand further maintenance interventions. The examples shown are based on thebridge inspections carried out on the Kwanza Bridge in Angola as well as theAguieira Bridges, the Figueira da Foz Bridge, and the Barra Bridge in Portugal.


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2.2.2 Shortcomings and needs

In Portugal, since early 2000, the main bridge owners have made a success-ful effort in order to implement an effective bridge inspection program in theframework of a BMS. Bridge inspections can reveal substantial information re-garding the structure condition and can be supplemented with a wide range ofNDE tests. However, in general, the current bridge inspections, as a mean ofincluding condition information into the BMSs, have several limitations as dis-cussed in Chapter 4:

The condition rating system used, especially based on the visual inspec-tions, depends highly on human-based evaluation and the ratings do notexhibit a high degree of consistency when performed by different inspec-tors;

The rating accuracy is unknown, as the assessment is generally restrictedto the visible spectrum, which cannot identify hidden flaws or anomalies;

The bridge inspections and the supplementary NDE tests are time con-

suming and expensive; and

The accuracy and reliability of routine and principal inspections could beincreased through more training of the inspectors in the types of damagescenarios to be found and the methods to identify them; as highlightedby the bridge designers in Sections 4.1 and 4.2, the experience gatheredfrom the rehabilitation projects and bridge inspections have brought tothe conclusion that in order to have proper rehabilitation projects and

proper budget estimations, it is important to have inspectors that are welltrained, capable to take risks, see beyond what they see in order to get agood diagnosis, and have a thorough mapping of the damages.

In 2001, the FHWA performed a comprehensive study on the reliability of rou-tine and principal inspections [32] as applied to highway bridges. For the rou-tine inspection, bridge inspectors were provided with similar information,instructions, and tools. The condition rating system required that inspectors

assigned a rating from 0 to 9 that reflected the structural capacity of a bridgeand described any structural deficiencies and the degree to which they are dis-tributed. The routine inspections were completed with significant variability,and the condition ratings assigned varied over a range of up to five different rat-


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ings. It is predicted that only 68 percent of the condition ratings will fall withinone rating point of the average, and 95 percent will fall within two points. Ad-ditionally, the study found that, in general, most inspectors visually examinedeach of the primary bridge components, but inspection tools usage was minimaland few detailed examinations were completed. Even though typically used byless than 50 percent of the inspectors, the most common inspection NDE toolsused during the routine inspection tasks included a masonry hammer, flash-light, tape measure, and binoculars. In terms of principal inspections, it washighlighted that they may fail to detect or identify the specific types of defectsfor which the inspection is prescribed, and may not reveal deficiencies beyond

those that could be noted during a routine inspection.

Recently, in order to verify the accuracy of the visual inspections, the EP con-ducted parallel inspections (inspections performed by two different teams) onabout 2.5% of the internal inspections conducted annually by EP techniciansduring the biennium 2010/2011, in order to obtain a Quality Certification of theperformed works and methodologies proposed by these inspections. The classi-fication showed contradictions regarding the condition of the slopes.

Clearly, there is a need to support the bridge inspections with more NDE tech-niques capable to enhance the condition of the bridges and to integrate morequantitative information into condition ratings and, consequently, the BMSs.The idea is not to substitute the current condition rating, rather to adjust andimprove it with more quantitative information as proposed in [9].

2.3 The role of the Non-Destructive Evaluation (NDE)

2.3.1 Overview

The NDE is a multi-disciplinary field concerned with the development of mea-

surement techniques to characterize the materials, components, and structureswithout damaging their integrity. NDE is included into bridge inspections as ameans of structural condition assessment. Note that Non-Destructive Testing(also known as NDT) is a term that is often used, interchangeably, with NDE


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[38]. Normally, the measurement techniques are based on visual, ultrasonic, ra-diographic, thermographic, electromagnetic, and optic methods.

2.3.2 Visual inspections

Visual inspection is the most common and basic NDE technique used in bridgeinspections and it serves as the baseline with which many other NDE techniquesmay be compared. The visual inspections have been the main source of condi-

tion information in the BMSs, but their reliability, in terms of bridge conditionassessment, is very often questionable as they are qualitative and not necessar-ily consistent, as confirmed by the study carried out by the FHWA (see Section2.2.2).

2.3.3 Other current NDE techniques

The number of inspection technologies has increased rapidly in the last decades.As summarized in Section 4.3, some of the most used NDE techniques for con-crete structures are given below:

Schmidt/rebound hammer test used to evaluate the surface hardnessof concrete;

Covermeter testing used to measure the distance of steel reinforcingbars beneath the surface of the concrete and also to measure the diameterof the reinforcing bars;

Carbonation depth measurement test used to determine whether mois-ture has reached the depth of the reinforcing bars, essential for corrosion;

Ultrasonic pulse velocity testing mainly used to measure the sound ve-

locity in the concrete and hence the compressive strength of the concrete;


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Penetration resistance or Windsor probe test used to measure the sur-face hardness and hence the strength of the surface and near surface lay-ers of the concrete;

Permeability test used to measure the flow of water through the con-crete;

Radiographic testing used to detect voids in the concrete and the posi-tion of pre-stressing ducts;

Sonic methods using an instrumented hammer providing both sonicecho and transmission methods;

Infrared thermography used to detect voids, delamination, and otheranomalies in concrete as well as to detect water entry points in buildings;

Half-cell electrical potential method used to detect the corrosion po-tential of reinforcing bars in concrete;

Impact echo testing used to detect voids, delamination, and otheranomalies in concrete;

Ground penetrating radar or impulse radar testing is a method that usesradar pulses to image the subsurface, and therefore, to detect the positionof reinforcing bars or pre-stressing ducts; and

Tomographic modeling uses the data from ultrasonic transmission testsin two or more directions to detect voids in concrete.

For more details on specific NDE methods, the reader is advised to consult thedocumentation provided by the American Society for Nondestructive Testing[34].

2.3.4 Shortcomings and needs

Based on the point of view of bridge designers, bridge inspectors, and bridge

owners, the current practices of bridge inspections, using some sort of NDEtechniques, have permitted to conclude that some of the existing NDE tech-niques have the following limitations and needs:


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Early signs of deterioration are often not seen based on the human visualperception;

The accessibility to some components of the bridge is difficult and costly; Most of the NDE methods have limited range and wide area coverage needs

multiple access points;

High level of personal skills is required to distinguish relevant signalsfrom noise; and

Specific training is needed for the inspectors to handle NDE techniques.

2.4 The role of the Structural Health Monitoring (SHM)

2.4.1 Overview

The process of implementing an autonomous damage detection strategy for

aerospace, civil, and mechanical engineering infrastructure is referred to asSHM. The SHM process involves the observation of a system over time usingperiodically sampled response measurements from an array of sensors, the ex-traction of damage-sensitive features from these measurements, and the statis-tical analysis of these features to determine the current state of system health.For long-term SHM, the output of this process is periodically updated, provid-ing information regarding the ability of the structure to perform its intendedfunction in light of the inevitable aging and degradation resulting from opera-tional environments. After extreme events, such as earthquakes or blast load-ings, SHM is used for rapid condition screening and aims to provide, in nearlyreal time, reliable information regarding the integrity of the structure [35, 36].

The basic idea of SHM is to build up a system similar to the human nervous sys-tem [37], where the brain (computer) processes the information and determinesactions (maintenance activities), and the nerves (sensors) feel the pain (dam-

age), as shown in Figure 2.3.


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Heuristic forms of sensing-based damage detection have probably been aroundas long as man has used tools. Developments in sensing-based damage detectionare closely coupled with the evolution, miniaturization, and cost reductions indata acquisition (DAQ) systems and digital computing hardware. The develop-ment of sensing-based damage detection has been driven by the rotating ma-chinery, aerospace, offshore oil platform, and civil infrastructure applications.To date, the most successful applications of sensing-based damage detectionhave been accomplished from condition monitoring of rotating machinery.

In terms of conceptual approach, SHM is a multi-disciplinary field that involves

smart sensors, wire or wireless networks, data acquisition, damage identifica-tion, model updating, safety evaluation, and prognosis. Nevertheless, current-ly, a typical SHM system for bridges is given by the general layout depicted inFigure 2.4, where the data is collected by sensing systems (sensors and DAQ sys-tems) and sent via the Internet to a data storage unit. After the processing phase,periodically, these data are compared with historical information (ideally usingartificial intelligence algorithms). At this stage, some kind of performance eval-uation is normally carried out, in order to detect deviations from the baselinecondition. Finally, the results are sent to the owner for decision approval.

As stated in Section 4.5, the inherent multidisciplinary nature of the researchrequired to realize SHM solutions, coupled with the life-safety and economicadvantages that this technology can provide, and its broad applications, quali-fies it as a Grand Challenge problem for engineering in the 21stcentry.


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Figure 2.3 SHM analogy with the human nervous system [38].

Figure 2.4 General layout of permanent SHM systems [39].

Information Processing - Brain(e.g. central station, computers)

Sensory System- Nerves(e.g. sensors and DAQ systems)


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2.4.2 Historical perspective of SHM: from rotating machineryto bridges

The damage identification in the past was mainly performed based on visual in-spection methods, with occasional application of conventional NDE techniquessuch ultrasonic and acoustic emission (e.g. tap tests on train wheels). However,vibration-based damage detection methods have received considerable atten-tion during the last 40 years. A brief review of the SHM historical evolution us-ing vibration-based structural damage identification is given herein. However,the reader is referred to Doebling et al.[40] and Sohn et al.[41] for a review of

literature on this subject.

The most successful application of damage identification using vibration-basedmethods has been reported for rotating machinery. The shorter lifetime, con-trolled operational and environmental variability along with well-defined dam-age types, permitted one to build up large data sets, from both undamaged anddamaged conditions, and to pave the way for application of pattern recognition

algorithms. In the broad sense, a pattern recognition algorithm simply assignsestimated vibration spectra to types of damage. A relatively recent state of theart review on monitoring rotating machinery was made by Randall [42, 43].

The aerospace industry has pioneered the transition of SHM from research topractice in a variety of civilian and defense applications. In early 1980s, the de-velopment of the space shuttle motivated the aeronautics community to im-plement vibration-based methods. The Shuttle Modal Inspection System was

developed to detect fatigue damage in the fuselage panels, typically coveredwith a thermal protection system making the visual inspection difficult. Thissystem has been used, successfully, to detect and locate damage in hidden com-ponents using analytical and measured modal correlation procedures [35]. An-other successful SHM application, in the aerospace industry, is the RotorcraftHealth and Usage Monitoring System that was developed in early 1990s. Thissystem was initially installed in the rotor drive train and gearbox components

for early failure detection. Well-defined operational conditions (e.g. the varia-tion in rotor speed) provide the basis to correlate vibration spectrum changeswith component degradation. Even though it was initially implemented to in-crease flight safety, it has been commercially developed for economic benefits,


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such as increasing mission reliability, downtime reduction, and customizationof maintenance actions [44].

During the 1970s and 1980s, the oil industry also made attempts to identify dam-age, in particular to detect damage in offshore platforms, using vibration-basedmethods. These methods were mainly based on inverse modeling approaches,where analytical models are adjusted with measured natural frequencies. Themain issues challenging the damage detection procedure were: the operation-al and environmental variability present in those structures (e.g. platform ma-chine noise), difficult access for measurement, changing mass caused by rise

and fall of sea lev

Condition Assessment of Bridges: Past, Present and Future. A Complementary Approach

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