Common Pathologies in RC Bridge Structures - A Statistical Analysis

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Electronic Journal of Structural Engineering, 7(2007)

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Common pathologies in RC bridge structures: a statistical analysis

J. Santos, C. Nunes, C. Fernandes & H. Varum

Department of Civil Engineering, University of Aveiro, Campus Universitrio de Santiago, 3810-193 Aveiro,

Portugal

1 INTRODUCTIONBridges are an important part of the country's patri-mony and considerable financial effort is presently

being made to maintain their safety and functionality(Brito et al. 1997). Nowadays, there are two maintasks in bridge engineering. One is the developmentof new projects, considering new construction tech-nologies and new materials. The other, which is

probably the most important, is the maintenance ofexisting bridges in order to prevent their fast deterio-

ration and to keep their serviceability to the increas-ing traffic loads. Preventing deterioration should be-gin in the structures project and execution stages,assuring the quality of the materials, of the projectand of the execution, what implies the knowledge ofthe possible deteriorations and its causes (Johnson1973). In the last decades, the fast deterioration ofexisting bridges has become a strong economicaland technical issue, registered all over the world. Inmost cases, the rehabilitation of a bridge is far moreexpensive then its maintenance, a procedure that

should be carried out correctly during all of thestructures life time. Many factors can lead to the de-terioration of these structures. The most importantones, which have being affecting the bridges for the

last 20~30 years, are (Radomski 2002, Patjawit &Kanok-Nukulchai 2005, Yang et al. 2006): i) Theincreasing traffic and loads of the vehicles, usuallylarger than the values considered at the original de-sign; ii) The bad influence of environmental pollu-tion over the construction materials; iii) The lowquality of the used equipments, like in expansion

joints, bearing equipment, drainage systems, amongothers; iv) Lack of maintenance; and, v) The use ofde-icing salts, which are used only in some particu-lar locations in Portugal. Bridges are also affected

by other multiple hazards, such as floods and earth-quakes (Adey et al. 2003), which are an importantcause of damage and collapse of these type of struc-tures. Earthquakes, such as the 1989 Loma Prietaand 1994 Northridge earthquakes in California, andthe 1995 Kobe earthquake in Japan, have causedcollapse or severe damage to a considerable numberof major bridges that were at least nominally de-signed for seismic forces (Priestley et al. 1996).

ABSTRACT: One of the main tasks in bridge engineering is to maintain the existing bridge stock accordingto current and predicted traffic and safety requirements. Bridges deterioration commonly occurs due to a widevariety of pathological factors, with origin in, for example: unexpected traffic loads, vehicle impacts, envi-ronmental factors, earth movements, chloride attack, carbonation effect, lack of maintenance, de-icing salts,

degradation of the drainage systems, pavement quality. Considering this, a statistical analysis of the mostcommon pathologies in bridge structures, their origin and consequences, was carried out. This analysis was

performed considering the pathologies for the overall structure, and for each bridge component. A total of 85reinforced concrete bridges, representative of the bridge stock in Portugal, were analyzed. Additionally, acomparison of the obtained results with a similar study for Germany was developed. The main differences be-tween the results obtained for each country within this study are pointed out.


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2 INSPECTIONS, MAINTENANCE ANDREHABILITATION

2.1 InspectionsBridge inspection is immanently related with bridge

maintenance and evaluation of the technical condi-tion of bridge structures. The methodology andscope of bridge inspection are usually determinedwith regard to the relevant instructions, guidelines,standards or other official regulations. Bridge in-spection can be classified into the following groups,depending on its scope and frequency (Radomski2002): i) Cursory inspection, carried out by roadmaintenance staff during routine road inspections,normally every day; ii) Basic inspections, carried outusually at least once a year by local bridge inspec-

tors; iii) Detailed inspection, carried out at leastevery five years on selected bridges by regionalbridge inspectors; and, iv) Special inspections, car-ried out by highly qualified experts and researchersaccording to technical needs, normally as a conse-quence of questionable results from basic or detailedinspections. It is necessary to determine the capac-ity, and assess the safety, of a bridge after unex-

pected or accidental loads, in order to establish itsability to resist acting loads, or to indicate the reha-

bilitation and strengthening needs.

It is important to emphasize that each inspection isunique. The inspection process varies, depending onmany technical, economic and regulatory factors(Branco & Brito 1996, Radomski 2002). Bridge in-spection can be considered as the most importantelement of a bridge evaluation and assessment, andis directly related with bridge rehabilitation, becauseinspections are instituted to determine the existingcondition of the structure from which recommenda-tions for repairs, if necessary, can be formulated

(Brinckerhoff 1993).

2.2 MaintenanceThe term maintenance is usually limited to the cur-rent works performed systematically by maintenanceservices to ensure normal and safe utilization of

bridge structures. These works consist mainly of in-spection, maintenance, repair and replacement, ifnecessary, of expansion joints, bridge deck, drainagesystem, railings, balustrades and barriers, pavement,

bridge bearings, etc, as well, as anti-corrosive pro-tection of some elements, mostly by painting. Inmany cases, the maintenance of existing bridges, ac-cording to the determined technical and economicalrequirements, demands other essential actions, prior

to the current maintenance itself. Therefore, the termmaintenance may also be considered, more widely,as a multi-component process leading to the fulfill-ment of all conditions related to the safe utilizationof existing bridges in the anticipated period of theirfuture service (Frangopol 1999, Radomski 2002).

The actions of maintenance can be divided in twokinds, corrective or preventive actions. Actions ofpreventive maintenance should assure the normaloperation of the bridge and respective equipment,

being able to develop repair works or actions of littledamages. Preventive actions applied to non deterio-rated components are designated as proactive andtheir objective is to delay the time of damage initia-tion. Preventive maintenance actions applied to dete-riorated components are denoted as reactive, andthey aim at eliminating or reducing the effects of the

deterioration process (Yang et al. 2006). Correctivemaintenance consists in important repair actions, in-cluding reinforcement of some of the bridge compo-nents, with the objective of, at least, replace the ini-tial conditions of service, or to ensure better ones(Nunes & Santos 2005).

2.3 RehabilitationRehabilitation means to restore, to make suitable, to

put back in good conditions, to re-establish on a firmbasis, to bring back to full use, to reinstate, to renewand revive. Rehabilitation concerns mostly of thewhole structure, including its primary structuralmembers. However, it can also include works ofmodernization, which are a form of upgrading byadding new features, e.g. new traffic flow arrange-ment, new signs, new lighting, new barriers. Thisterm is commonly applied to structures designed andconstructed prior to availability of these modern fea-

tures. However, modernization can also be consid-ered in a wider meaning. For instance, the upgradingof a bridge requires in many cases its strengthening,new traffic flow arrangement requires the wideningof the bridge deck, and so on (Radomski 2002).

3 PORTUGUESE STATISTICAL ANALYSISA statistical analysis of anomalies and pathologiesdetected in 20 to 30 years old existing reinforced

concrete (RC) highway bridges (viaducts and overhighways), in different locations of Portugal, wasperformed based in inspection reports of bridges,with the objectives of identifying: i) the most com-mon pathologies in RC bridges; ii) the most affected


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components; and, iii) the probable causes of thesepathologies. A total of 85 bridge structures wereanalyzed. The results of this statistical analysis werecompared with a similar study made over 100

bridges in Germany.

3.1 Results analysisFrom the inspection reports of the studied bridgestructures, the most important results were analyzed.These global results obtained from the rapid screen-ing inspection methodology can be a useful tool inalerting the responsible entities about the priority fora more detailed bridge inspection campaign, mainte-nance and rehabilitation.Table 1 summarizes the basis for the global analysisof 85 RC bridge structures in Portugal, concerning

the main pathologies that affect each of their com-ponents. Since each bridge structure is unique be-cause of its function, technical restrictions in theconstruction, age, etc., some components do not ex-ist in every bridge structures, as shown in left col-umn of Table 1 (EP 2003, LUSOSCUT 2003). The

pathologies identified at each bridge component(right column in Table 1) are presented in percent-age relatively to the studied structures in which thiscomponent exists.

From the analysis of Table 1, the following conclu-sions can be drawn:There are components of the bridge structures thatstand out with high percentages of pathologies, suchas the abutments, drainage systems, expansion jointsand bearing equipment.The high percentage of pathologies registered in ex-

pansion joints, bearing equipment and drainage sys-tem is probably due to the lack of maintenance or toa misuse of the structure.The location of the bearing equipment in middlesupports certainly justifies the small incidence of pa-thologies verified at these components, because theyare usually better protected from the water action,

particularly the ones located under continuous gird-ers beams.All the deficiencies in the drainage systems, or the

lack of some of its elements, normally lead toseveral pathologies in other bridge components,such as quick degradation of abutments and bear-ing equipment, as well as to deterioration of the

concrete surface of the structural components andsteel reinforcement corrosion.Superficial pathologies are also generally verified

in the structure. Usually they have no majorstructural stability consequences. The less af-

fected components with the superficial patholo-gies are the pavement and the bearing equipmentin middle supports.

Pathologies verified in secondary componentssuch as footways, rail-guards or safety-guards do notaffect the global structural safety. However, when

they are very severe, like unstable cracking or bro-ken fastenings of the guards, they should not be dis-regarded, because can even be a threat to pedestri-ans.

Table 1. Pathologies of each component in bridgestructures analyzed.

Bridge component Bridges wherethis compo-nent exists

(out of 85)

Patholo-gies iden-tified

(%)Deck 85 57Abutment 85 73Wing wall 82 22Expansion joints 62 64Bearing equip-ment

65 62

Intermediate bear-ing equipment

67 17

Slopes 83 54Drainage system 59 71Cornice 85 37Guard-rail 85 57

Safety-guard 79 53Pavement 83 10Footways 82 48Other components 85 54

3.2 Most common pathologiesTable 2 summarizes the most common pathologiesobserved at each component of the bridges underanalysis.The main pathologies verified in RC components,

namely in decks, abutments and wing walls are con-crete cracking and delamination with consequentconcrete spalling, and reinforcement exposure andcorrosion. These pathologies may have their originin a poor finishing of the concrete surfaces, or in aninadequate arrangement of the steel reinforcement oreven by an inadequate concreting or demoulding.The pathologies related to the drainage systems, likegarbage and fragments accumulation, are essentiallydue to improper use and to the absence of mainte-

nance (EP 2003, LUSOSCUT 2003).Graphics in Figures 1-4 show the pathology inci-dence that affect decks, abutments, expansion jointsand slopes, respectively.


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32.5

50

17.5

0

10

20

30

40

50

60

Concrete spalling,

with reinforcement

exposure

Concrete

cracking

Water dipping

P

ercentage(%)

Figure 1. Pathologies in decks.

Table 2. Main pathologies at each component of theanalyzed bridges.Affectedcomponents Pathologies

Concrete spalling with reinforcementexposureCrackingDeck

Water drippingConcrete spalling with reinforcementexposureCrackingAbutments

Water drippingCracking and/or spalling with rein-forcement exposureWing wallsReinforcement exposureAccumulation of fragments over ex-

pansion jointsDeformation of the expansion jointExpansion

joints Cracking parallel to the joint, allowingthe infiltration of water to the abut-mentProtective sleeves damagedCorrosion of the metallic elementsBearing

equipment Partial or total degradation of thebolts massive protectionAffixing publicityWater dripping caused by lack of pro-tective sleeves

Bearingequipmentat interme-diate sup-

port Concrete delaminationSlopes covering damaged

Slope covered with vegetation causingthe obstruction of the drainage ele-ments

Slopes

Erosion of the vegetable slopeAccumulation of fragmentsLack of certain elementsDrainagesystems Broken elementsCracking, spalling and delamination ofconcreteConcrete spalling due to impactsCornices

Bending mortars detachmentCorrosionCar impactsGuard-rails

Lack of restrains, or restrains damagedwith corrosionCar impactsLack of restrains, or restrains damagedwith corrosion

Safety-guards

Lack of elements

Pavement Damaged pavement coveringAccumulation of fragmentsLack or cracking of the floor coveringFootways Lack of protection plates on the ex-

pansion zoneGarbageLack of barrierOther com-

ponents Growing vegetation near the bridge

structure

10

32

58

0

10

20

30

40

50

60

Concrete spalling,

with reinforcementexposure

Concrete

cracking

Water dipping

Percentage(%)

Figure 2. Pathologies in abutments.

1310

3

7

20

47

0

10

20

30

40

50

60

Lackof

elements

Parallel

cracking

Percentage(%)

Damaged

restrains

Holesinthe

pavement

paralleltothe

joint

Fragments

accumulation

Deformationof

thejoint

Figure 3. Pathologies in expansion joints.

45

2431

0

10

20

30

40

50

60

Slope's coveringdamaged

Slope covered withvegetation causing the

obstruction of thedrainage elements

Erosion

Percentage(%)

Figure 4. Pathologies in slopes.

From the 85 RC bridge structures analyzed in Portu-gal (see Tables 1 and 2, and Figs 1-4), the followingcan be observed:


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57% of the bridges evidenced pathologies in thedeck. 83% of those pathologies are related to con-crete: spalling and consequent reinforcement expo-sure (33%), or cracking (50%). Water dripping wasalso observed in 18% of the structures with patholo-gies in decks.

73% of the 85 analyzed bridge structures show defi-ciencies in the abutments. In these structures themost common pathologies observed were: waterdripping (58%), concrete cracking (32%) andspalling with reinforcement exposure (10%).54% of the structures show problems regarding theexpansion joints. Parallel cracking represents 47%of those pathologies, 20% are excessive deforma-tions, 13% are referred to the joints restrains, 10%are fissures and holes in the pavement parallel to the

joint, and 3% are related to the lack of elements in

the joints.54% of the analyzed structures have pathologies inthe slopes. 45% of those pathologies are related tothe damaged covering. In 31% of the bridges it wasverified erosion in the slopes. Slopes covered withvegetation causing the obstruction of the drainagesystem was verified in 24% of the bridges underanalysis.

4 STATISTICAL ANALYSIS OF THE COMMONPATHOLOGIES IN GERMANY

The main results of a study made over 100 overhighways bridge structures in Germany (less than 50years old) are summarily presented in Table 3 (Favre1989).

Table 3. Main pathologies registered in the Germansurvey.

Main pathologies Percentage of af-fected structures(%)

Reinforcements corrosion 17Concrete cracking 11Concrete degradation 13Expansion joints degrada-tion 31

Bearing equipments degra-dation 14

Drainage systems degrada-tion 27

Rail-guards degradation 58Pavements degradation 32Degradation of the water-

proofing materials 21

Degradation of the substruc-ture 27

The elements affected with higher number of pa-thologies are rail-guards, pavements, expansions

joints and substructures. Concrete spalling is fre-quently detected, probably due to exposure to de-icing salts, commonly used on Germany.

5

COMPARISON BETWEEN THEPORTUGUESE AND THE GERMANRESULTS

The global results obtained from the analysis of pa-thologies in 85 RC bridges in Portugal were com-

pared with a similar study from a German survey.Analyzing the data from the Portuguese inspectionreports it can be concluded that the survey is veryextensive, pointing out even the first sign of the pa-thologies. Even if clear differences in both studies,

related to the degree of detail in the inspection pro-cedures, were recognized, the comparative analysisis assumed valid based on the similarities in terms of

bridge typologies and problems.Figure 5 compares the obtained global results, fromthe Portuguese and German surveys, for the moresignificant and challenging pathologies. The pa-thologies were arranged into two groups, concerningif they affect or not principal structural components.In both studies, it was evident a significant numberof pathologies that may lead to consequences in

some important bridge components with structuralsafety implications at long term, and not only withaesthetical consequences.


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40

58 56 5860

73

58

1317 11 13

31

14

27

58

32

0

10

20

30

40

50

60

70

80

Reinforcement'scorrosion

Concrete cracking Concrete degradation Expansion jointsdegradation

Bearing equipment'sdegradation

Drainage system'sdegradation

Rail-guard'sdegradation

Pavement'sdegradation

Percentage%

Portuguese Survey

German Survey

Structural components Non structural components

Figure 5. Main pathologies detected in bridge structures in Portugal and Germany.

The pathologies represented in Figure 5, assembled

into two groups, depending if they affect or notstructural components, allow the following conclu-sions:In Portugal, the main pathologies are due to the highexposure of the bridge structures, and particularly ofsome of their components. For example, non struc-tural components, such as the elements of the drain-age system are affected in 73% of the cases, and the

bearing equipment in 60%. The concrete surfacesare affected in 58% of the studied bridges withcracking, and in 56% with general degradation.In the German survey the pathology with the highestincidence is the rail-guard degradation, verified in58% of the analyzed cases. Generally, the patholo-gies that affect non structural components have thehighest percentages, having smaller implications interms of safety of the structure at long term. The se-vere climatic conditions, certainly, have direct im-

plications into a strict quality control during theconcrete manufacturing, concreting and demouldingof the structural elements, adoption of larger con-

crete covering thicknesses, a good protection of thefinal concrete surface with waterproofing materialsand a proper resistance to freeze-thaw cycles. The

bridges designed and constructed with this level ofexigencies result into structures with a higher dura-

bility.

6 VISUAL INSPECTION: RESULTS IN RECENTBRIDGE STRUCTURES

In parallel to this research work on the pathologiesin existing bridges, visual inspections made overnew bridge structures with just eight months of ser-vice, were performed.

Even if they are new, the inspected bridges already

show various pathologies, due essentially to misuseand lack of thorough in the finishing works of theconcrete surfaces, pavements, drainage systems, etc.Among other pathologies, it were observed accumu-lation of construction waste and other fragmentsover the expansion joints, and reinforcement without

proper concrete cover already with signs of the be-ginning of corrosion process. Figures 6-10 show ex-amples of the pathologies and defects detected in theinspections to these new bridge structures.

Figure 6. Bearing equipment.


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Figure 7. Expansions joints.

Figure 8. Drainage grids.

Figure 9. Cracked abutment wings.

Figure 10. Concrete surfaces improperly finished.

Figure 6 shows the first signs of corrosion in thebearing equipment and also a drainage trench thatconduct the water towards the equipment. In Figure7, the accumulation of construction waste and otherfragments evidences the faster degradation of theexpansion joints, inhibiting its correct structural

function. This indicates the lack of maintenance andmisuse of the structure. In Figure 8 it can be ob-served that the grid spacing is not proper. Thus,waste and fragments will get into the drainage sys-tem causing eventually its malfunctioning. Figure 9shows the cracked wing of an abutment, which al-lows the water infiltration, instead of conducting itto the drainage system, and possibly affects thestructural behavior and soils stability. Figure 10 pre-sents an example of concrete surfaces not accuratelyfinished, leading to potential problems, such as steel

reinforcement corrosion and concretes degrada-tions.

7 FINAL COMMENTSIn both, Portuguese and German surveys, the ana-lyzed bridges are very similar in terms of structuralgeometry and materials. The pathologies observedare also analogous.Although being very important to the global safety

of the superstructure, foundation's pathologies werenot considered in this work, since they were notmentioned in the analyzed surveys.The comparison made over the main global results,suggests that the incidence of pathologies verified inexisting bridge structures is higher in Portugal thanin Germany. This is probably due to the combinationof important aspects, such as: detailing in the design

projects without concern on durability concepts andthe absence of a systematic inspection, maintenance

and repair of the first superficial pathologies de-tected in the bridges, preventing their developmentto a more severe scenario.An integrated management system which guides theregular assessment inspections and alert to the

bridge structures pathologies which can developmore serious damages can certainly help in reducingthe observed high pathologies incidence in bridgesverified in Portugal. The development of an inte-grated bridge management system and the imple-mentation of a maintenance policy can reduce the

costs in future repair operations.A more detailed study should be conducted, consid-ering not only the presence of the pathologies visu-ally detected, but also with its categorization accord-ing to specific intensity classification. This method


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can contribute to the bridge prioritization forstrengthening measures, and even to identify the

bridges in need of an urgent intervention.

8 ACKNOWLEDGEMENTSThe authors would like to acknowledge EngineerRomana Ribeiro from EP Estradas de Portugal,and Engineers Adan Monteiro, Lus Trabulo and H-lio Costa from LUSOSCUT, for their precious helpin the supplied material and guided visual inspec-tions to the bridges.

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Branco, F. A., and Brito, J. 1996.Bridge management from de-sign to maintenance.

Brito, J., Branco, F.A., Thoft-Christensen, P., and Sorensen, J.D., An expert system for concrete bridge management,Engineering Structures, Vol. 19, No. 7, 1997, pp. 519-526.

Brinckerhoff, P. (ed. L. G. Silano) 1993.Bridge inspection andrehabilitation. New York: John Wiley & Sons Inc.

Estradas de Portugal [EP] 2003. Annual report of bridge struc-tures inspections.

Frangopol, D. M. 1999.Application of life cycle reliability-

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Nunes, C., and Santos, J. 2005. Patologias em obras de arte debeto armado e pr-esforado. University of Aveiro (inPortuguese).

Patjawit, A., and Kanok-Nukulchai. W., Health monitoring ofhighway bridges based on a Global Flexibility Index,En-gineering Structures, Vol. 27, 2005, pp. 1385-1391.

Priestley, M. J. N., Seible, F., and Calvi, G. M. 1996. Seismicdesign and retrofit of bridges. New York: John Wiley &Sons Inc.

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Common Pathologies in RC Bridge Structures - A Statistical Analysis

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