uic 778 4r defects in railway bridges lv en

8/9/2019 UIC 778 4R Defects in Railway Bridges Lv En

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UIC Code 778-4 R

1st Edition, 01.07.1989. Revised Draft 10-09- 2008, 27-11-2008, 14-01-2009, 15-02-

2009, 18-04-2009

Reviewed by the Panel of Structural Experts 04-02-2009

Defects in railway bridges and procedures for

maintenance

Union Internationale des Chemins de fer, UICInternationaler EisenbahnverbandInternational Union of Railways


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Summary

This leaflet gives guidelines and recommendations covering procedures for the maintenanceand strengthening of railway bridges. Arrangements and methods for inspection are presented;defects are described; methods for monitoring and assessment are given; and procedures formaintenance, repair, strengthening and renewal are defined.

The purpose is to update the 1989 edition of UIC Code 778-4R and to implement results from aEuropean Integrated Research Project (2003-2007) on “Sustainable Bridges – Assessment forFuture Traffic Demands and Longer Lives” (TIP3-CT-2003-001653) within the 6th FrameworkProgramme.

Table of ContentsSummary ..........................................................................................................................................2

Table of Contents .............................................................................................................................2

1 - Inspection of railway bridges and detection of defects...............................................................3

1.1 - General.................................................................................................................................3

1.2 - Arrangements for inspection................................................................................................61.2.1 - Detail and frequency.....................................................................................................6

1.2.2 - Routine inspections.......................................................................................................6

1.2.3 - Principal Inspections.....................................................................................................61.2.4 - General Inspections.......................................................................................................7

1.2.5 - Documents ....................................................................................................................8

2 - Defects in existing bridges..........................................................................................................9

2.1 – Definitions...........................................................................................................................9

2.2 – Detection and measurements of defects..............................................................................92.2.1 - Overview of methods and equipment ...........................................................................9

2.2.2 – Methods for metal bridges..........................................................................................11

2.2.3 – Methods for Masonry Bridges....................................................................................13

2.2.4 – Methods for Concrete Bridges ...................................................................................15

2.2.5 – Methods for Bearings and Foundations .....................................................................17

2.3 - Classification of defects.....................................................................................................19

3 - Monitoring ................................................................................................................................20

3.1 Testing methods: ..................................................................................................................203.2 Data processing methods:.....................................................................................................20

3.3 Sensors: ................................................................................................................................204 - Methods for Load and Resistance Assessment.........................................................................21

5 - Maintenance, repair / strengthening and renovation.................................................................22

5.1 - Maintenance......................................................................................................................22

5.2 - Repair................................................................................................................................22

5.3 - Strengthening ....................................................................................................................23

5.4 - Renewals ...........................................................................................................................24

Bibliography...................................................................................................................................25Appendix A – Notation .................................................................................................................27


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Figure 1. Regular operation and maintenance of bridges. If there are questions regardingsafety, serviceability or durability, action can be taken according to Figures 2 and 3.From SB-GUIDE (2007).

Figure 2. Special stage of operation and maintenance of bridges when there is a special concernregarding . safety, serviceability or durability. After decisions are made and actions taken (thelast line in the figure), the bridge is returned to regular operation and maintenance according toFigure 1. The assessment procedure is further illustrated in Figure 3 taken from SB-Guide 2007.

Special stage

Investigation and assessment

BRIDGE

ASSESSMENT(Carried out in

phases)

Special inspections

supported by more/lessadvanced tests

(quantitative information)

Focused

monitoring throughlimited time period

(quantitative information)

Required

performance

confirmed?

Decision making and action taken

Redefine use Intensify

monitoring

ReplacementStrengthening and/or repair

Regular operation and maintenance

BRIDGE

MANAGEMENT(Administration)

Regular inspections

followed by condition

assessment

(qualitative information)

Optional

Structural Health

Monitoring

(qualitative information)

Regular, minor

maintenance

(preventive, corrective)

Bridge

Management System

(more/less advanced)

Political and economical requirements

(higher loads and speeds, increased traffic volume,extended service life, etc. )


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Figure 3. Flow chart for the assessment of existing bridges as part of the process with the

special stage of operation and maintenance in Figure 2. Three phases are identified: Initial,Intermediate and Enhanced, depending on the complexity of the questions involved.’ Taken fromSB-LRA (2007).

Doubts

PHASE 1 - INITIALSite visit

Study of documentsSimple calculation

PHASE 2- INTERMEDIATEMaterial investigations

Detailed calculations/analysisFurther inspections and monitoring

PHASE 3 - ENHANCEDRefined calculations/analysisLaboratory examinations and

field testingStatistical modelling

Reliability-based assessmentEconomical decision anal sis

Simplestrengthening

of bridge

Updatemaintenance,

inspection andmonitoring strategy

Redefine use andupdate maintenance,

inspection andmonitoring strategy

Demolitionof bridge

Strengtheningof bridge

Unchangeduse of bridge

Doubts confirmed?Yes

Yes Yes

Yes

No No

No

No

omp ance wcodes and

regulations?

mp e repa r orstrengthening

solve theproblem?

Sufficient loadcapacity? Acceptable

serviceability?


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1.2 - Arrangements for inspection

1.2.1 - Detail and frequency Inspections should be made with varying degrees of detail and at varying frequencies,depending on the type of inspection and taking account of the nature and previous condition ofthe structure. Apart from ordinary surveillance when train and track staff continuously monitorthe bridge when passing it; a distinction is made between three levels of inspection:

- Routine inspection: Annual inspection from ground level by trained examiner.

- Principal inspection: Refined visual inspection with focus on safety every (2nd or) 3rd year .These inspections can also provide the opportunity for simultaneous special in-depthinspections, not necessarily covering the entire structure, but perhaps for dealing with aparticular component or problem area.

- General inspection: Extremely detailed inspection with examination of all parts of the bridgewithin touching distance (with hammer tapping on concrete surfaces) every 4 to 6 years.However, the inspection frequency should reflect the nature of the bridge and the defectsobserved. In practice this means that the inspection frequency will vary according to bridgetype and condition. The general inspection should result in production of a full and detailedreport on the condition of the structure.

The final inspection made on handover of the structure or before its commissioning, or followingmajor repair work, provides a benchmark for the required condition.

Special equipment and facilities will generally be required for these inspections, during whichstructures should be subjected to visual examination in order to locate any defects with the aid ofspecial examination techniques.

1.2.2 - Routine inspections

The inspector should be trained and have a basic understanding of bridges.The standard equipment includes basic tools such as hammers, cameras and lighting facilities.Foundations should be inspected at low water. Please look down.

1.2.3 - Principal Inspections

The inspector should be aware of the methods given in section 2.2 below.

A principal inspection consists of a visual examination of all accessible parts of the bridgewithout using special access equipment. All defects which can be visually detected from theground must be recorded and the condition of the structure must be evaluated in an appropriatemanner.

Continuous monitoring may be used to keep a check on particular developments or a newsituation arising between two periodical inspections . By means of such monitoring, defectswhich could become a hazard to railway operations can be monitored carefully.


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Such inspections may need to be supplemented by information from outside specialists.

Details of methods for monitoring are given in SB-MON (2007) and for masonry bridges in UIC

Leaflet 778-3 (2009).

1.2.4 - General Inspections

General inspections should be carried out by bridge experts. They should be assisted byspecialist staff, who should be well experienced in carrying out examinations besides having thenecessary technical knowledge. They should not only be able to identify defects but also toensure that their development can be monitored through suitable measurements to determinemovements, displacement, reductions in cross-section due to stress-induced corrosion. , etc.

A firstlevel assessment of the capacity of the bridge could be carried out in conjunction with theinspection. Likeliest causes of different damages should be recorded. Need to repair or furtherinspect or monitor the bridge as well as traffic limitations should be defined in the inspectionreport.

Suitable means of access to the various parts of the structure, ranging from ladders to specialscaffolding, should be arranged. Depending on the topography and on the features of thestructure to be inspected (Iength, height, etc.), these aids, depending on the requirements of therailway concerned, may be subdivided as follows:

- For very long viaducts spanning inaccessible terrain, it may be economical to equip thestructure, at the construction stage, with an inspection platform, or at least with longitudinal railson which an inspection vehicle can travel, the latter being brought on site only when required.

- Rail-mounted / lowering platforms. This equipment is mounted on a rail vehicle and has aninspection platform at its outer end, with a system of hydraulically-operated articulated arms thatcan be controlled and operated either from the platform or from the vehicle.

Such units can be used for full inspections using only one line of a doubletrack section. They areaccompanied by a service vehicle of the Pemanent Way Department.

- Lifting platforms mounted on rail, road or road/rail vehicles. These platforms mounted on a railvehicle, road vehicle or road/rail vehicle, can be moved by rail or road and are provided with aninspection platform located either on the extension of a double articulated arm or on an arm withseveral telescopic sections. Examinations are carried out either from the inspection platformitself or from the driving cab of the rail, road or road/rail vehicle.

Examples of methods are given in section 2.2 below, in SB-MON (2007), chapter 7 “Monitoringtool-box” and, for masonry bridges, in UIC Code 778-3R (2009).

Special investigations such as the analysis of vibration behaviour to assess the condition of thestructure; mineralogical and microscopic analyses to diagnose material conditions, ultrasonictesting or radiography for cables etc., are matters for teams of experts to address.

Preparations should be made beforehand to facilitate inspection, for example:- cleaning of bearing areas;


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- installation of scaffolding;- removal of certain elements to facilitate inspection of main structural components;- for piers and foundations it may be necessary to use divers.

1.2.5 - Documents

Documents such as design drawings, geotechnical surveys, calculations, constructiondocuments and the results of the acceptance inspection of the structure provide basic inputs forthe inspections. The documents shall be available during the inspections in paper or digital form(e.g in a lap-top computer)

The reports of subsequent inspections shall be based on the surveys of the actual condition ofthe structure. They shall contain details of irregularities discovered or of the development ofdefects revealed by earlier inspections.

Details shall also be given of the maintenance work necessary in the short and long term;together with any operations carried out since the last inspection.


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2 - Defects in existing bridges

2.1 – DefinitionsA list of definitions and notations is given in Appendix A

2.2 – Detection and measurements of defects

2.2.1 - Overview of methods and equipment

- Visual examination;- Detection and monitoring of cracks of all kinds by means of recording devices, strain gauges,crackwidth gauges, glued indicators, ultrasonic equipment, measuring shims, extensometers,.

etc.;- Measurement of deformation under static and dynamic loading, measurement of progressivedeformation, measurement of bearing reactions and rotations;- Levelling;- Analysis of dynamic behaviour (seismograph or accelerometer).

The following examples of available equipment are given in SB-ICA (2007), Table 5.2. In SB-ICA (2007) there is also a tool box for non destructive testing (NDT) methods with a one-pagesummary of each method explaining its merits and drawbacks. The background to the tool-box isdescribed in Helmerich et al (2007, 2008a, b). Methods for masonry arch bridges are also givenin UIC Code 778-3R (2009).

Table 2.1 Overview of methods and equipment

Visual and Simple Methods

External visual inspectionExternal visual inspection, usually performed regularly in routine surveysor inspections, limited by human factors

Internal visual inspection(video scope)

Internal visual inspection with devices through holes in hidden or coveredparts of steel or concrete structures, experience required, inspectionlimited by the length of the cable

Void volume measurement Evaluation of hollows by air or fluid pressureAir (Torrent) Permeability Fluid or air permeability of concrete surfaces as measurement of

durability,Cover measurement Depth of reinforcement in concrete structure, thickness of the concrete

cover, reliable equipment available on the market

Roughness depth test Investigation of concrete surface roughnessLiquid penetrant test Surface cracks in welds of steel connections.

Sclerometric test Hardness of young concrete. From Greek skleroo , hardenHardness Hardness of steel

Thermal Heat Transfer

Transient (active)thermography

Debonding of tiles, plaster, mortar, carbonfibre reinforced polymers(CFRP), determination of humidity/ moisture content

Pulse-phase thermography Debonding, near surface voids with optimised contrast


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Acoustic, Electric and Electromagnetic Methods

Acoustic emission Detection of growing active cracksModified Acoustic Emission(AE)

Survey of known active cracks, in laboratory-modified AE for search ofactive cracks

Low strain pile integritytesting

Pile length, integrity

Parallel seismic Pile / sheet depthCross-hole tomography Soil, parameters, consolidation beneath embankments

Cross-hole sonic logging Material quality in foundationsImpulse-radar echo

Radar tomography Thickness of concrete elements, grouting level of tendon ducts,localisation of rebars and tendon ducts

radarElectrical conductivity Investigation of rebars and tendon ducts

Electromagnetic induction Cracks in tendon wires (slightly destructive)Impulse-radar echo Cracks from point loads, longitudinal cracks, surface cracks due to lack of

bond in more layered arches, spandrel wall separation, spalling or mortarloss

Radar tomography Leaching, inner cracks from freeze-thaw-cycling, hollows, moisture (inresearch)

Ground penetrating radar Evaluation of layers and voids in embankments and subsoilRadar scouring Scouring around stream piles

Electrical conductivity Moisture content, backfill type and quality

Electrical conductivity Moisture, soil typeGalvanostatic pulse Corrosion state of reinforcement, properties of cover concrete (moisture,

deteriorations)

Linear Polarisation Corrosion state of reinforcement, covercrete thickness (moisture,deteriorations)

Sliding collar Cable-stayed bridgesUltrasonic-echo (US-echo)Dry coupling using US-array

Thickness measurement, localisation of reinforcement or tendon ducts,voids in RC

Ultrasonic transmissiontomography

Localising reinforcement or tendon ducts, voids in the concrete

Impact-echo Thickness measurement, localisisation of reinforcement or tendon ducts,Impact-echo Investigation of crack depthUltrasonic-echo Residual thickness of mild and modern steel plates, weld defects, surface

cracks, cracks parallel to the surface, surface crack depth, inhomogeneityUltrasonic-phased array Weld defects, inhomogeneity, corrosion mapping (established by industry)

Ultrasonic emission Inclusions and segregations in steel plates

Eddy current inspection Cracks in rivet holes, cracks in very thin metallic plates

Combined UltrasonicInspection

Ultrasonic velocity (transit time tomography), Residual stress in rivets

Ultrasonic-echo (masonry) Detection of deterioration

Radiographic Methods

Radiography with isotopes/steel (RI)

Detection of cracks in hidden elements and inhomogeneities in modernsteel or connections (welds)


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Radiography with x-ray/cobalt

Detection of voids in RC, localisation of reinforcement and tendon ducts

Spectral-chemical and Potential Methods

Electrical potential fieldmeasurement

Corrosion state of reinforcement

Laser-Induced BreakdownSpectroscopy

Analysis of chemical elements on surface and near surface

Sparkle EmissionSpectroscopy

Analysis of chemical elements of the steel

Sulphur print(slightly destructive)

Chemical analysis for identification of the used iron/ steel

Advanced Data Acquisition and Evaluation Methods

Automated scanning system Parallel use of different sensors for NDT-investigation of concrete bridgeslabs

Synthetic aperture- focusingtechnique

Reverse projection of wave images

Data fusion Superposition of results from different NDT-measurements

2.2.2 – Methods for metal bridges

Examination on site:

• corrosion and reduction of cross-section:- measurements of corrosion depth using depth gauges;- measurements of residual depth by ultrasonic means or by drilling;- direct measurements of the progress of corrosive attack;

- state of corrosion protection;• detection and monitoring of cracks in the steel:

- by visual examination with or without dyepenetration technique;- detection by radiography or ultrasonic method (whenever possible) when looking fornon-visible defects;

• detection of loose connections involving rivets and bolts:

- by visual examination;- by tapping in a careful way so that the rivets do not get harmed- with a torque spanner;

• detection of cracks in welded joints:- by visual examination using a lamp, with or without dye penetration technique ;

- by radiography or ultrasonic methods in cases of doubt.

Laboratory testing to determine:fatigue, composition, tensile strength, notch ductility, elongation, micrography, testing ofweldability.

Attention is drawn to the difficulties involved in taking samples, and to the problem of obtainingrepresentative samples.

Metal sampling should ensure that, with a limited number of investigations and laboratory tests,


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the most accurate information can be obtained on the nature and characteristics of the materialsused in the structure.

The problem, however, is:

1) that it is often difficult to remove a sufficient amount of steel from structural elements toprovide a representative sample;

2) to identify lowstressed structural components for sampling to prevent significant weakening ofthe structure;

3) whether the sample taken is adequately representative of the structure as a whole (e.g. oldiron or steel bridges, in which materials of varying origin have been used on construction orrepair).

In Table 2.2 NDT methods are given. A combination of methods is often useful.

Table 2.2. Non Destructive Testing (NDT) Methods for Metal BridgesThe following table gives information about restrictions and limitation of NDT-methods, SB-ICA(2007), Table 5.4.

NDT-Method Investigated details Limitation in use.Accuracy of the method includingcharacteristics of the material

Remarks

Visual Contamination, loss ofmaterial, deterioration,displacements, cracks

Cracks 2mm,Only magnetisable materials

Follow safety instructions ofthe railways when usinghand held tools

Magnetic

particle test

Surface cracks Crack opening > 0,1 mm, length > 1

mm, crack hole investigation duringreplacement of rivets

Documentation only with

camera

Colourpenetrationtest (PT)

Surface cracks, Remove old colourwidth > 0,1 mmLength > 1mm

Documentation only withphotography

Radiography(RT)

Internal voids insandwiched elements

Maximum investigated plate thickness:70 mm

Last phase (3rd

) inreassessment

Ultrasonicecho (UT)

Weldroot testing,residual plate thickness,thickness of surfacecoating

For example:. use of reference groovesfor calibration:Width x depth:0.11mm x 0.95 mmDepth/width ratio: < 25

General inspection, in allphases of thereassessment as needed


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Ultrasonicarray (UT-array)

Internal void depth andlateral dimensions,defect inhomogeneity

Multi-channel systems for adaptation tospecial tasks

Last phase (3rd

) inreassessment

The EU (JRC) has published recommendations for the Assessment of existing steel structures together with the ECCS [EUR23252EN].

2.2.3 – Methods for Masonry Bridges

A UIC project on Masonry Arch Bridges, UIC Masonry (2008), has produced recommendationsfor inspection, assessment and maintenance of masonry arch bridges, UIC Code 778-3R (2009).

Standard methods used involve:

- In-situ visual examination (if necessary with the aid of an endoscope);

- Sampling, and laboratory tests to determine porosity, density, frost sensitivity, composition,weathering.


Table 2.3. Non Destructive Testing (NDT) Methods for Masonry BridgesThe following table gives information about restrictions and limitation of NDT-methods, SB-ICA(2007), Table 5.4. Information is also given in UIC Code 778-3R (2009) Tables 3.1- 3.6


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NDT-Method Investigated details Limitation in use.Accuracy of the method includingcharacteristics of the material

Remarks

Visual Qualitative values:geometry cracks (length,depth), heavydisplacements,longitudinal/ diagonalcracks in the barrel,vegetation, drainage,humidity, heavysettlement

Cracks


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2.2.4 – Methods for Concrete Bridges

For reinforced- concrete bridges (in-situ frames, slab bridges and girder bridges):

detection of inadequate reinforcement: number, diameter and location of bars, fractureand corrosion of reinforcement, concrete cover (depth gauge);

detection of cavities within the structure.

measurement of depth of carbonisation, measurement of cracks, strength measurement;

testing of samples in laboratory:. compressive strength, composition, density, porosity,

frost sensitivity, tensile strength, degree of weathering.

For prestressed-concrete bridges (bridges with channels/ducts, slab bridges, girder bridges,box- girder bridges, etc.):

• detection of inadequate reinforcement and of cavities in the bridge structure as forreinforcedconcrete bridges;

• detection of defects in cable ducts: incorrect alignment of ducts and faulty grouting,fracture and corrosion;

• detection of defects in prestressing strands and wires: number, dimensions, position,fracture and corrosion.

• testing of samples in the laboratory: tensile strength, fatigue, composition, elongation,flexural strength, weldability.

Additional measures for steel/concrete composite bridges:

• detection of separation between steel and concrete by radiography (in particular

gammagraphy),


Table 2.4. Non Destructive Testing (NDT) Methods for Concrete BridgesThe following table gives information about restrictions and limitation of NDT-methods, SB-ICA(2007), Table 5.4.


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NDT-Method Investigated details Limitation in use.Accuracy of the methodincludingcharacteristics of thematerial

Remarks

Visual Contamination, loss,deterioration,displacements, cracks

Cracks


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2.2.5 – Methods for Bearings and Foundations

A – Bearing defects

Bearings are treated in EN 1337 (2000), which addresses the following topics :- Bearings,- Structural members,- Structural design,- Structural systems,- Rocker bearings,- Roller bearings,- Cylindrical-roller bearings,- Mountings (bearing components),- Dimensions,- Bridges,

-Joints,- Sliding joints,- Movement joints,- Components,- Construction,- Symbols.Recommendations are also given by the Association for Bearings, see VHFL (2009).

1 - Functional defects :- examination on site, visual and aural;- measurement of the positioning and of deformation of the bearing elements;- inadequate sliding or rolling movement, excessive transverse or longitudinal displacements,

tilting or axial movement of the roller track.- dirt around bearings,

2 - Material defects :- chemical; mechanical and metallurgical testing of samples.- cracking of mechanical or elastomeric parts- corrosion

3 - Defects in bearing fasteners :- detection of loose baseplates or of bedding-mortar break-up.

B – Defects in foundations

1 - Methods applicable to all types of foundations :

- visual examination on site, where necessary after excavation of inspection pits;- measurements of tilting with the aid of plumb lines, and twist measurements using deflectionmeters (inclinometers);- measurements of twist at the bearings;- ground investigation with the aid of soil samples (penetrometer, pressure gauge);- examination of borings:


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water pressure tests, visual examination (endoscope, TV camera ), recording of the variousparameters with the aid of probes.

2 - Specific methods applicable to underwater foundations :

- visual examination and probing by divers or frogmen;- depth soundings (underwater topography) and recording of the bottom bed profile, adjacent tothe foundations, repeated at regular intervals to determine bed profile patterns;- underwater cameras and video recordings ;- use of dyes to follow the route of water courses and locate places where the water reappears.

Examples of methods for foundations and transition zones are given in SB-ICA(2007), chapter 9.

C – Waterproofing defects

- Visual examination:

• Looking for traces of water penetration, rust staining. efflorescence,stalactites, white marks along cracks or working joints;

• Localised removal of ballast to detect waterproofing defects or separation of edge sealing

• Inspection of drainage (filter system, outlets, weepholes, drains),

- Taking of samples to check permeability under hydrostatic head.

In Table 2.5 NDT methods are given.

Table 2.5. Non Destructive Testing (NDT) Methods for FoundationsThe following table gives limitation and interference of NDT-methods with railway operatinginfrastructure and rough timeconsumption (only for pure measurement without equipmentinstallation), SB-ICA (2007), Table 5.4.

NDT- Method

Investigateddetails

Limitation in use.Accuracy of the methodincluding. characteristics ofthe material

Remarks

Radar echoRadar echoarray

200-800MHz

Soil layers,thickness, scour,humidity

track-bed condition

Penetration depth depending onfrequency:Max. depth 10m,

max. + 5 % of the penetrationdepth

According to requirements for the test andresolution

SIPSpectral

Sonic-velocityevaluation along aprofile on masonrysurface

Calibration by means of coring,humidity influences theprecission, limited resolution


Boreholetomography

Integrity of pilefoundations, pilelength

To measure the integrity,sensors are lovated in a tubeparalle to the investigated pile


Parallelseizmicmethod

Pile length Influence of construction quality(concrete), stiffness of soil has tobe taken into account



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2.3 - Classification of defects

A distinction is made between four groups of defects:

1 – Minor defects, rectification of which may be postponed until they can be convenientlytreated.

2 - Serious defects without short-term effects on the stability of the structure, but which maylead to increasingly costly maintenance work if not rectified swiftly. Short-term may here mean aperiod of a couple of months.

3 - Serious defects with short-term effects on the carrying capacity of the structure, thusleading to traffic restrictions.

4 - Defects requiring immediate action.

The classification can also be based directly on safety levels (where severity could be clarified)or on the cost of repair.

One example of a system to classify defects is given in SB-ICA(2007). In chapters 3 (Defectsand degradation processes) and 4(Condition rating) and in Appendix 2 (defect catalogue),defects are described according to their position L (geometrical data as input to the FEM-model), their intensity I (for example as a relation between designed and current cross section)and defect extend R (relation between damaged and integer element).

For masonry bridges examples are given in UIC Code 778-3R (2009).


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3 - Monitoring

Monitoring is mostly used in special cases, for example.

- In the construction phase to check strains and deformations- Before and after strengthening of a bridge to check the effect of the strengthening- On important and new types of bridges to check their behaviour and to calibrate numerical andanalytical models for bridges for their load bearing capacity and life-cycle length- On damaged bridges to check the bearing capacity- To check the influence of increased speed and/orheavier loads on an existing bridge- To check if maintenance procedures are efficient

Examples of methods are given in SB-MON (2007), chapter 7” Monitoring tool-box”.

3.1 Testing methods:- Ambient vibration testing,- Free vibration testing,- Impact hammer testing,- Linear exciter testing,- Rotating unbalanced exciter testing,- Displacement measurements via inclinometers and curvature measurements.

3.2 Data processing methods:- Transfer functions or Frequency response functions (Periodogram method, Steady-stateharmonic),- Natural frequencies (Response spectrum method),- Damping (Decay curve method, Half-power bandwidth method, Phase method, Multiple-modedecay method, Ambient vibration method),- Modal parameters (Peakpicking method, Stochastic subspace identification)

3.3 Sensors:-Accelerations (Piezoelectric accelerometers, Capacitive accelerometer, Force balancedaccelerometer),

- Displacements (Inductive linear position sensors, Vibrating wire displacement sensors,Microbend displacement sensor, Pulse time-of-flight deformation sensor, Capacity non-contactdisplacement sensor, Eddy-current displacement sensor),- Strains (Electrical resistance strain gage, Bragg grating strain gage, Fabry-Perot interferometerstrain gage, Interferometric deformation sensors),- Temperatures (Thermocouples, Bragg grating temperature sensor, Resistance thermometers)


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4 - Methods for Load and Resistance Assessment

Methods for load and resistance assessment are given in SB-LRA (2007). A summary of thecontents is given below.

The bridge assessment in many aspects is very similar to the bridge design. The same basicprinciples lie at the heart of the process. Nevertheless, an important difference lies in the factthat when a bridge is being designed, an element of conservatism is generally a good thing thatcan be achieved with very little additional costs. When a bridge is being assessed, it is importantto avoid unnecessarily conservative measures because of the financial implications that mayfollow the decision of rating the bridge as deficient. Therefore, the design codes (e.g. EC codes)may not always be appropriate for assessment of existing bridges, and some additionalrecommendations or guidelines are required that will lead to less conservative assessment of

their loadcarrying capacity. Such guidelines have already been proposed for assessment ofhighway bridges in Europe. However, there is a lack of this type of documents that can beapplied for the assessment of railway bridges.

Guide SB-LRA(2007) provides guidance and recommendations for applying the most advancedand beneficial methods, models and tools when assessing the loadcarrying capacity of existingrailway bridges. This includes:- systematised step-level assessment methodology,- advanced safety formats (e.g. probabilistic or simplified probabilistic)- refined structural analysis (e.g. non-linear or plastic, dynamic considering train-bridgeinteraction),- better models of loads and resistance parameters (e.g. probabilistic and/or based on the

results of measurements) and- methods for incorporation of the results from monitoring and on-site testing (e.g. with Bayesianupdating of the concrete strength with values from different testing series).

Guide SB-LRA(2007) has been compiled with the aim of following somehow the structure of theEC codes : it is divided into 10 chapters and 12 Annexes concerning: Assessment procedure(Chapter 2); Requirements, safety formats and limit states (Chapter 3, Annexes 3.1-3.7); Basicinformation for bridge assessment (Chapter 4); Load and dynamic effects (Chapter 5, Annex5.1); Concrete, Metal and Masonry Arch Bridges (Chapter 6, 7 and 8 and Annexes 7.1 8.1 and8.2); Foundations and transition zones (Chapter 9); Improvement of assessment usinginformation from testing and monitoring (Chapter 10, Annex 10.1).In most of the topics related to railway bridge assessment, the Guide uses state-of-the-art

knowledge and current best practice. Nevertheless, in many subjects it proposes the use oforiginal methods and models that have been developed, obtained or systematised throughresearch performed within the project.

For masonry arch bridges, guidelines are also given in UIC Code 778-3R (2009)


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5 - Maintenance, repair / strengthening and renovation

5.1 - Maintenance

Maintenance covers all measures undertaken with the object of maintaining the structure inworking condition.

The maintenance work to be carried out can be divided into preventive maintenance on the onehand, and minor repair work on the other hand, with the aim of rectifying minor faults or delayingthe occurrence or development of more serious defects.

Maintenance work may include:

- work not directly related to the stability of the structure, such as the removal of vegetativegrowth on the masonry facings, the replacement of ashlars or bricks in cases of isolateddamage, and the repair of damaged concrete edges;

- on masonry: repointing, injection, application of coating products in connection with generalsurface damage;

- the cleaning of metal parts of the structure, where dirt collects and pro-motes oxidation(excrements, birds' nests, earth, sand...);

- for steel superstructures, partial or complete repainting (after removal of rust) at intervals

determined by the harshness of the environment. Replacement of loose rivets, tightening ofloose bolts;

- maintaining the drainage of masonry structures in working condition so as to preventpenetration of water or the buildup of water pressure;

- monitoring the functioning of collecting drains and the drainage to the main outfall;

- maintenance of bridge bearings which, if not functioning properly, can have adverse effects onthe bearing seating and the deck.

5.2 - Repair

Repair covers all measures aimed at restoring the structure to working condition. Suchmeasures are directed at the cause of defects and are thus designed to prevent their furtherdevelopment. For this work to be carried out efficiently, a thorough examination of the structureis required. Although experience from earlier cases and the review of previous data are of greatvalue, it should not be forgotten that every structure needing repair is a unique case

Repair work may include for example

- on masonry bridges: rejointing, injection and application of surface coating in case of extensive


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superficial damage

- on metal bridges: the replacement of damaged metal components, arresting the further growth

of cracks by stop hole drilling to reduce the stress concentration at the crack tip and thanbridging of cracks by cover plates using rivets or high-strength friction-grip bolts;

- on concrete bridges: the renovation of the concrete surface by application of shotcrete orinjected mortar, or cast-insitu concrete;

- re-waterproofing and installing new drains

- repair of expansion joints;

- treatment of cracks in concrete or masonry by injection, sealing, bridging, installation ofanchors/bolts, wedges and cramps;

- installation of tie bars or prestressed tie rods;

- replacement or repair of materials underperforming technically;

- replacement of the whole bearing or of bearing components, injection of synthetic resinbeneath the bearing plates, repair of bearing supports;

- stabilisation of retaining walls by buttressing.

Occasionally, comprehensive repairs have to be delayed for financial or other reasons, e.g. toavoid disruption of railway operations by civilengineering work. In such cases where only

minimal repairs can be undertaken it should be appreciated that this will inevitably lead topremature renewal of the structure. A shorter interval between inspections may help reduceuncertainties and problems until proper repair has been undertaken

5.3 - Strengthening

Work of this kind is undertaken in particular to ensure the safety and regularity of rail traffic inresponse to railways' current demand for: - heavier axle loads for freight traffic ;- higher maximum speeds for both freight and/or passenger traffic, on existing lines.

In order to achieve the first objective, it is frequently necessary to increase the carrying capacityof the structure; the second objective, depending on the new speed planned, may occasionallynecessitate bridge-widening.

Older concrete bridges may be strengthened by means of additional reinforcement, for exampleby using the technique of bonded plates, sheets or bars of steel or Carbon Fibre ReinforcedPolymers (CFRP), see SB-STR (2007).

If necessary, it is possible:

- to strengthen masonry arches by means of a saddle or adding a new ring, and also by tyingin


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the spandrel walls. The height of the haunches may also be increased by injection.- to strengthen prestressed concrete superstructures by additional prestressing.- to reinforce steel decks by replacement of weak components, bracing components with

inadequate resistance to flexural buckling, fining additional components.- to reinforce walls and abutments by ground anchoring at the rear, soil injection, or load transferto root piles.- to protect and improve underwater foundations by means of concrete or sheetpile enclosures,and to protect and stabilise the ground in the vicinity of water courses by stone pitching, gabionsor drainage blankets.

Methods for strengthening are given in SB-STR (2007). This Guide contains a graphic indexwith typical structures plus examples of areas in need of strengthening and of possible methods.Methods for masonry arch bridges are also given in chapter 5 of UIC Code 778-3R (2009)

5.4 - Renewals

Renewals cover the replacement of a complete structure or of decks if necessary wherebecause of the poor condition of the structure, strengthening cannot provide an economicalsolution ensuring traffic safety under the required operating conditions.

On main lines, the replacement of steel decks with small spans up to, say, 15 m is generallymore economical than strengthening, especially if there are restrictions imposed on maintainingrail traffic movements.


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Bibliography

EN 1337 (2000) Structural bearings. General design rules. EN1337-1:2000

EN 13306 (2001): Maintenance terminology. European standard, CEN, 54pp.

Helmerich, R., Bien, J., Cruz, P.J.S. (2007):A guideline for railway bridge inspection andcondition assessment including the NDT toolbox Proceedings: Sustainable Bridges -Assessment for Future Traffic Demands and Longer Lives,,pp 93-104; Wroclaw : DolnoslaskieWydawnictwo Edukacyjne. ISBN 978-83-7125-161-0

Helmerich, R., Niederleithinger, E., Trela, Ch., Bien, J., Bernardini, G. (2008a):Complex multi-tool inspection of a masonry arch bridge using non-destructive testing Proceedings: Bridge Maintenance, Safety, Management, Health Monitoring and Informatics -IABMAS 2008, July 13-17, 2008, Seoul, South Korea, 8 pp; CRC Press; Editor: InternationalAssociation for Bridge Maintenance and Safety – IABMAS. ISBN 978--0-415-46844-2

Helmerich, R., Niederleithinger, E., Algernon, D., Streicher, D., Wiggenhauser, H (2008b):Bridge Inspection and Condition Assessment in Europe . Scientific journal: TransportationResearch Records, Taylor & Francis, Washington D.C., USA.

SB-GUIDE (2007): Overall Project Guide: “Sustainable Bridges – Assessment for Future TrafficDemands and Longer Lives” – a project within EU FP7. 28pp. Available from: www.uic.asso.fr orwww.sustainablebridges.net . [cited 30 XX 2008]

SB-ICA (2007): Guideline for Inspection and Condition Analysis of Railway Bridges . Prepared bySustainable Bridges – a project within EU FP6. 259 pp. Available from: www.uic.asso.fr orwww.sustainablebridges.net . [cited 30 XX 2008]

SB-LRA (2007): Guideline for Load and Resistance Assessment of Railway Bridges .Prepared by Sustainable Bridges – a project within EU FP6, 428 pp. Available from:www.uic.asso.fr or www.sustainablebridges.net . [cited 30 XX 2008]

SB-MON (2007): Guideline for Monitoring of Railway Bridges . Prepared by Sustainable Bridges – a project within EU FP6. 93 pp.. Background documents for: Steel railway bridges, SB-5.2-S1,53 pp; Structural Damping of Railway Bridges, SB-5.2-S2, 29 pp; Corrosion Monitoring Systemsfor Reinforced Concrete Bridges, SB-5.2-S3, 23 pp; Estimating Reliability of Monitoring systemsfor Bridges, SB-5.2-S4, 20 pp. Available from: www.uic.asso.fr or www.sustainablebridges.net .[cited 30 XX 2008].

SB-STR (2007): Guide for use of Repair and Strengthening methods for Railway Bridges.Prepared by Sustainable Bridges – a project within EU FP6. 63 pp. Available from:www.uic.asso.fr or www.sustainablebridges.net . [cited 30 XX 2008].

UIC Code 778-1R (1997): Recommendations for the consideration of fatigue in the design ofsteel railway bridges. UIC, 2nd edition, 1.1.1997

UIC Code 778-2R (1997): Recommendations for determining the carrying capacity of existingmetal structures. UIC, 1st edition of 1.7.86 and 1 Amendment


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UIC Code 778-3R (2009): Recommendations for the inspection, assessment and maintenanceof masonry arch bridges. Approved by the Panel of Structural Experts in February 2008, 163 pp.Update of an earlier version from 1.7.1995. The following reports were produced:

- Bien, J, Kaminski, T, Rawa, P. (2006): Technology and pilot version of expert tool supportingthe evaluation of the degradation level for masonry bridges with damages . UIC Report - Brencich, A., Gambarotta, L. (2006): Guide to the high-level assessment of masonry archbridges . UIC Report- Gilbert, M. (2006): Guide to use of RING 2.0 for the assessment of railway masonry arches .UIC Report- Harvey, W. J. (2007): Review of the MEXE method . UIC Report - Harvey W J. (2007b): Rule of thumb method for the assessment of arches. UIC Report (draft)- Harvey W J. (2007c): Guide to the assessment of masonry arch bridge s. UIC Report - Ingenieurbüro A. Pauser. (2005): Guide to the assessment of circular masonry arch bridges .UIC Report- Ingenieurbüro A. Pauser. (2005): Guide to the destructive testing of masonry bridges . UIC

Report- Ozaeta, R. G, Martín-Caro, J.A. (2006): Catalogue of Damages for Masonry Arch Bridges . UICReport- Ozaeta, R. G, Martín-Caro, J.A., Brencich, A. (2007): Guide to the execution and control ofmasonry arch repairs . UIC Report- Steffens, K., Gutermann, M. (2006): Guide to the load test of masonry arch bridges . UICReport - Orban, Z. (ed.) (2006): Recommendations for the non-destructive testing of masonry archbridges . UIC Report- UIC Code 778-3R. (1994): Recommendations for the assessment of the loadcarrying capacityof existing masonry and mass-concrete arch bridges , Paris.- UIC Report. (2004): Assessment, Reliability and Maintenance of Masonry Arch Bridges (ed.

Orban, Z., UIC Masonry Arch Bridges Study Group ). State-of-the-Art Research Report of theInternational Union of Railways, Paris.

UIC Masonry (2008): Improving Assessment, Optimisation of Maintenance and Development ofDatabase for Masonry Arch Bridges. A research project of the International Union of Railways,see http://masonry.uic.asso.fr

ECCS-JRC Joint report: Recommendations for the assessment of existing steel structures (2008), EUR 23252 EN. http://eurocodes.jrc.ec.europa.eu/doc/background/EUR23252EN.pdf

VHFL (2009): Guidelines for Bearings (In German). Vereinigung der Hersteller vonFahrbahnübergängen und (Brücken)Lagern (Association of Bearing Producer). See www.vhfl.de


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Appendix A – Notation

Definitions and short characteristic of the terms for inspection andCondition-assessment of railway bridges including Non DestructiveTesting (NDT) methods in bridge engineering

The following table lists terms and procedures for inspections and condition assessment(ICA) of railway bridge structures. They may give a rough overview about theterminology and understanding of non-destructive evaluation of the current state of aninvestigated bridge. Amended from SB-ICA (2007).

Table A1. Terms and procedures for inspection and condition assessment

English Terms Definition Acousticemission (AT)

Acoustic Emission is the class of phenomena whereby an elasticwave, in the range of ultrasound usually between 20 KHz and 1MHz, is generated by the rapid release of energy from the sourcewithin a material. The elastic wave propagates through the solid tothe surface, where it can be recorded by one or more sensors.

Acousticmethods

Acoustic methods are non-destructive testing methods for theinvestigation of the current condition of the inner structure byimplementing an acoustic sound as impact (single wave) by anhammer impact or an acoustic wave, induced by acoustic sensors(ultrasound) recording and processing the reflected or transmittedwaves. Each material needs sensors developed forcharacteristic frequencies. Acoustic methods can be applied in echomode (transmitter and receiver are on the same side of en structuralelement, recording reflected waves) or in transmission mode (transmitterand receiver are on opposite sides of an element).

Array Array is a set of sensors. Usually, sensors can be applied as a groupof sensors, transmitters or receivers. Known procedures are US-arraymeasurement, phased array for investigation of cracks in steelor concrete structures. The set-up of a group of acoustic emissionsensors is also named array. Ultrasonic phased arrays are wellintroduced to quality assurance systems of industrial steelstructures. They are investigated for use in concrete bridges.

Artefacts Non real phenomena in images calculated as inverse processing ofNDT-data sets, artefacts actually result from an inauspicious algorithm orgeometry, data density or quality. Experience is required todistinguish real defects from artefacts.

A-scan Acoustic, thermal or electromagnetic data obtained with non-destructivetesting methods recorded in time domain for one single point on the surfaceof a structure.

Assessment A set of activities undertaken to characterise current state and thereliability of a structure in comparison with a required state. See→ condition assessment and → structural assessment.

B-scan Image of a vertical section perpendicular to the investigated surfacebelow a line scan recorded in time domain


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Bridge conditionassessment

Also condition appraisal: Process of evaluation of the local and/orglobal state of bridge conservation expressed in the form ofcondition rating, either numerical (scale: 0-5, 1-10, 1-100 or other) or

linguistic (good, poor, acceptable, etc.);Bridge defect : Difference between the designed and the real state of a structural

element, effect diminishing the technical condition of the bridgeBridge safety/structuralassessment

Process of evaluation of remaining bridge safety measured in termsof partial safety index, reliability index or probability of failure,

Bridgeserviceability

Measure of differences between current and designed values ofbridge service parameters, e.g. load capacity, clearance, maximumspeed, etc.

Bridge technicalcondition

Measure of differences between current and designed values ofbridge technical parameters, e.g. geometry, material characteristics,etc.

CFRP CarbonFibre Reinforced Polymers. Often used as extra reinforcement whenbridges are strengthened

C-scan Image of processed NDT-data sets characterising a horizontal depthslice of the inner structure, parallel to the investigated surface.Data set is usually taken from 3-dimensional data sets of recordedand processed data as impulse radar-echo, active thermography,ultrasonic-echo or impact echo.

Condition Current state of a structure, characterised by quality of design,execution quality and aging processes influenced by external loadingand environmental influences.

Conditionassessment

(Also: condition appraisal) is a judgement about the condition of abridge compared to its initial state or designed plan enabling the

authorities to compare it to other bridges.The condition assessment is a tool for a detailed appraisement of abridge itself as input to a ranking in a bridge management system.The inventory of existing standard methods for Conditionassessment and inspection of railway bridges together with a toolbox of established and new innovative Non-Destructive testingtechniques will form the basis for a proposal of a Unified ConditionAssessment procedure for railways in Europe

Conditionrating

Indicates the global state of conservation of one bridge structure andits evaluation using weighted factors, indices or percentagesaccording to its value in comparison with the theoretical initial value.

Condition

ranking

Comparison of the bridge ratings in the bridge stock of an

infrastructure owner. Condition ranking based on current condition-rating systems is a tool for bridge owners when ranking their bridge assetin order to coordinate their maintenance strategy or manage thebridge stock. Currently used condition rating systems do notdeliver data for the structural assessment of bridges.

Corrosiondetection

Surface investigation of reinforced concrete bridges, e.g. with electro-chemical potential methods in order to detect early characteristicsanticipating corrosive processes.

Damage Difference between current state of the bridge and the designedstructure. Damage can be caused by low quality during theconstruction process or during service life.


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Contrary to defects, damage describes a process.

Defect When describing current condition related deficiencies in a bridge –

the term defect is used, rather than the word "damages" nowfrequently used. One exception to this general rule is the expression"fatigue damage" which is in normal usage (Network rail).

Data Fusion Super positioning of data from different (NDT-)data sets obtained forthe same geometrical structural points to receive a more refined and morerealistic visualised image.

Datareconstruction

Data obtained from running radar antennas appears as hyperbolas.The back-calculation of the measured data to the real geometricalshape reflecting the electro-magnetic wave is called reconstructionof data

Degradation Timedependent (deterioration, aging) or non-time dependent (trafficimpact, earthquake) process causing a defect of structure.

Duty survey Continuous visual survey of the infrastructure by track staffEddy- currenttest (EDT)

Eddy-current testing uses electromagnetic induction to detect flaws (voids)in conductive materials. Basically, an eddy is the swirling of a fluid and thereverse current created when the fluid flows past an obstacle.

Endoscope Instrument for looking at internal parts of an object. From Greek endon =within and skopeo = look at

Electrochemicalinspections

Corrosion detection plays a role in servicelife prediction of concretestructures. Potential mapping or Laserinduced breakdownspectroscopy enable researchers to earlydetect incipientcorrosionprocesses.

Electromagneticmethods (EM)

Electromagnetic methods use electromagnetic waves to produceimages. Impulse radar measurement belongs to the group of

electromagnetic waves. The more the obtained data is focused on theinvestigated objects and the closer the measurement grid, the better are theresults.Simple electromagnetic methods are magnetic powder inspectionapplied to steel bridges or application of the cover meterElectromagnetic methods use impulse-radar-echo waves orinduce magnetic fields in structures.

Experts opinion(E)

In case of doubts during reassessment of structures (in phase 2), thestructural engineer can ask for a refined investigation. Specialknowledge and experience is required.

GeneralInspection

Extremely detailed inspection involving examination of all parts of thebridge within touching distance (with hammer tapping on concrete surfaces)

every 4 to 6 years. However, the frequency of inspection should reflect thenature of the bridge and the defects observed. Less detailed examinationsare made during Routine and Principal Inspections

Impact echo With sensors in echo arrangement : Acoustic wave excitation andreceiver are on one side of a structural element. Surface wavesmay badly affect the result. Advantage is the accessibility from onlyone side.With sensors in transmission arrangement: Acoustic wave excitationfrom one side and the receiver on the opposite side of a structuralelement. Advantage is that surface waves do not disturb the result.

Impulse radar Geo-radar: Ground Penetrating Radar


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(GPR) or Impulse Radar is a geophysical, non-destructive techniquebased on transmitting electromagnetic (EM) waves (short impulses)into material and receiving reflected waves to detect structures and

changes in dielectric material properties within the material.Inspection Gathering of data from the existing bridge via regular visual control

usually based on rules or standards and its translation to theinspection records (bridge book, sheets, digital files). Inspection is aregular visual control of the bridge condition. All railway authoritiesplan their inspections on the basis of national rules,

Magnetic ParticleTest (MT)

Use of magnetised particles in a suspension to find surface cracks

, Non-DestructiveTesting(NDT)

Investigation of structures or structural elements using waves toreceive data visualised in images to obtain information about theinner structure. Acoustic, electromagnetic, thermal or microwavescan be used. The structure’s integrity is not affected.

Permeability Density of the concrete surface against air or water penetration. Lowpermeability of concrete is the best guarantee for its durability. If nogas or water can penetrate the concrete, the chloride transfer orcarbonation process is interrupted. Impermeability can be testedwith pressurised water, and permeability by means of a permeability test.

Phased array A set of ultrasonic transducer and/or receiver elements in which thetiming of the elements' excitation can be individually controlled toproduce certain desired effects, such as steering the acoustic beam axis orfocusing the beam to find voids or inhomogeneities.

Polarisation The EM field contains electric and magnetic field vectors which areorthogonal to each other and to the direction of translation. Byconvention, the EM field solutions are characterised by the direction

of the electric field vector. When the time variation of the fields issinusoidal, the concepts of linear, circular and elliptical polarisationsarise. In practice, using dipole antennas between parallel andperpendicular polarization in relation to the antenna, movement willbe distinguished.

Potential field The potential field on a surface changes if corrosion occurred insidethe structure. It is measures non-destructively from the concretesurface. The test is sensitive to humidity

PrincipalInspection

Refined visual inspection with focus on safety carried out every (2nd) or ( 3rd) year. More in-depth examinations are made during General Inspections.

P robability o fD etection(POD)

POD is a term that describes the reliability of inspection techniques.Two main elements affect PoD; the technique and the human factor.

Broadly speaking the inspection reliability is defined as the probabilityof not overlooking an existing defect (probability of detection,POD) and correct sizing of the defect. However simple this definition mayappear, it encompasses many complex issues ranging from thespecification of the nature of defects to influencing factors related tothe inspection instrumentation, product nature, the involved human factorand the available expertise for inspection data processing and assessing.

Radiographicmethods

Radiographic inspection is more important for the assessment ofsteel structures than for voluminous and massive concrete bridges. Itis the only reliable method for the assessment of weld defects or ofdamages in sandwiched elements, as built-up sections in riveted


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girders. While in some countries the application of radioactivesources is restricted by safety measures, others apply e.g. Iridiumsources successful in experts’ opinions for detail investigation.

RoutineInspection

Annual inspection from ground level by trained examiners. It is carried outin accordance with national standards or rules of infrastructure owners.More in-depth examinations are made during Principal and GeneralInspections.

ResistanceAssessment

When numerically determining the carrying capacity (or resistance)of a bridge - Strength (or resistance) Assessment. (This essentiallyconsists of measurements, the determination of physical materialproperties either from generic tables or material testing, andstructural analysis.)

SAFT Synthetic Aperture Focusing Technique is a digital signal processingmethod (DSP) for ultrasonic testing (SAFT UT). It provides anaccurate measurement of the spatial location and extent of flaws

contained in objects such as structural components and welds andnuclear-power reactor systems. Transit-time for the ultrasonic beamto travel to and from a point is a hyperbolic function of the probeposition and target depth. When the equation of this hyperbola isknown, A-scan signals can be shifted in time and added together.

Specialinvestigation

In case of doubts during inspection of any level, a specialinvestigation can be required. The inspector (professional bridgeengineer) determines the scope for special investigations or expertopinions.

StrengthAssessment:

When numerically determining the carrying capacity(or resistance) of a bridge - Strength (or resistance) Assessment.(This essentially consists of measurements, the determination of

physical material properties either from generic tables or materialtesting, and structural analysis.)

Survey Also Routine surveillance or standard visual inspection from the groundlevel , for example performed half-yearly or yearly. The inspector hasto follow national requirements on his training level.

Thermography Active and passive thermography allow the reliable detection ofhumidity in a structure, investigation near surface damages asdebonding, especially after repair or strengthening measures withthin layered materials (e.g. CFRP) or cavities near the surface. Theevaluation of images of surfacetemperature data obtained ascooling down behaviour characterises near-surface integrity

Time of flight

areas(TOF)

Time between emitting and receiving an acoustic or electromagnetic

wave which is a measure of an inhomogeneity, if the wave velocityincreases compared to the homogeneous material

Tomography Tomography is a term describing the reconstruction of 2D- or 3Dstructure from data obtained from NDT-measurements (acoustic,electromagnetic or radiographic) using transmitters and receivers onneighboured or opposite sides of a structure, while at least one ofthe sensors is moved along the surface. Several dozens to hundredsof transmitter/ receiver positions are used.

Ultrasonic A term referring to acoustic vibration frequencies greater than about18,000 Hertz. Ultrasonic waves have a wide diversity of applicationsover an extended range of intensity, with cutting, cleaning, and the


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destruction of tissue as one extreme and non-destructive testing(NDT) at the other end.

Ultrasonic-echo

( US-echo)

Analysis of acoustic waves received on the same surface from which

they where emitted, reflected from back wall, defects or cavities instructural materials. Advantage: Accessibility from only one side of astructural element.

Visualinspection

Gathering of data from the existing bridge via regular visualcontrol, today usually based on national rules or standards and itstranslation to the inspection records (bridge book, sheets, digitalfiles). If tools such as endoscopes are used to document the structure, theinspection is called indirect or internal.

y Computer program used for the analysis of wave propagation instructures.

ApplicationWith effect from 1 May 2009All UIC railways.