UIC Code
778-4 R
1st Edition, 01.07.1989. Revised Draft 10-09- 2008, 27-11-2008, 14-01-2009, 15-022009, 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, UIC Internationaler Eisenbahnverband International Union of Railways
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Summary This leaflet gives guidelines and recommendations covering procedures for the maintenance and strengthening of railway bridges. Arrangements and methods for inspection are presented; defects are described; methods for monitoring and assessment are given; and procedures for maintenance, repair, strengthening and renewal are defined. The purpose is to update the 1989 edition of UIC Code 778-4R and to implement results from a European Integrated Research Project (2003-2007) on “Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives” (TIP3-CT-2003-001653) within the 6th Framework Programme.
Table of Contents Summary ..........................................................................................................................................2 Table of Contents .............................................................................................................................2 1 - Inspection of railway bridges and detection of defects...............................................................3 1.1 - General .................................................................................................................................3 1.2 - Arrangements for inspection................................................................................................6 1.2.1 - Detail and frequency .....................................................................................................6 1.2.2 - Routine inspections .......................................................................................................6 1.2.3 - Principal Inspections .....................................................................................................6 1.2.4 - 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 ..............................................................................9 2.2.1 - 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: ..................................................................................................................20 3.2 Data processing methods:.....................................................................................................20 3.3 Sensors: ................................................................................................................................20 4 - 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...................................................................................................................................25 Appendix A – Notation .................................................................................................................27
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1 - Inspection of railway bridges and detection of defects 1.1 - General Regular inspection is a means of keeping a constant watch on the daytoday condition of structures, by noting defects as they occur and identifying the cause of any damage discovered. The actual condition must be compared with the benchmark required for the structure in service. If it is established from inspection that the structure has only minor defects, these results can be used to specify and organise the necessary maintenance work. If, however, more extensive damage is discovered, the structure must be repaired and restored to satisfactory condition, and the cause of the damage should be investigated and put to rights (see Figures 1, 2 and 3). One of the main considerations is that the structure should be in suitable condition to allow the normal movement of rail traffic over the line on which it is located ,with the required level of safety at all times. If line operating parameters are changed (for example, because of heavier axle loads or higher running speeds), then a knowledge of the actual condition will be a factor in the decision as to whether the structure needs to be strengthened or whether complete renewal is necessary. Engineers must adopt the engineering solution which will cause least disturbance to rail traffic operations. However, the overall economics of the engineering work must be taken into consideration. Those responsible for the project and bridge designers should give preference to types of construction which allow easy inspection, maintenance and repair or renovation of the structure throughout its service life. In the rest of this leaflet, reference will be made to reports produced by the EC-project “Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives”, carried out between 2003 and 2007. The reports are available from: www.sustainablebridges.net. For masonry bridges, additional information is given in UIC Code 778-3R (2009) “ Recommendations for the inspection, assessment and maintenance of masonry arch bridges”. A standard for the terminology for maintenance is given in EN 13306 (2001).
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Regular operation and maintenance Political and economical requirements (higher loads and speeds, increased traffic volume, extended service life, etc. ) Regular inspections followed by condition assessment (qualitative information)
Optional Structural Health Monitoring (qualitative information)
BRIDGE MANAGEMENT (Administration)
Regular, minor maintenance (preventive, corrective)
Bridge Management System (more/less advanced)
Figure 1. Regular operation and maintenance of bridges. If there are questions regarding safety, serviceability or durability, action can be taken according to Figures 2 and 3. From SB-GUIDE (2007).
Special stage Investigation and assessment Special inspections supported by more/less advanced tests (quantitative information)
Focused monitoring through limited time period (quantitative information)
BRIDGE ASSESSMENT (Carried out in phases)
Required performance confirmed?
Decision making and action taken
Redefine use
Intensify monitoring
Strengthening and/or repair
Replacement
Figure 2. Special stage of operation and maintenance of bridges when there is a special concern regarding . safety, serviceability or durability. After decisions are made and actions taken (the last line in the figure), the bridge is returned to regular operation and maintenance according to Figure 1. The assessment procedure is further illustrated in Figure 3 taken from SB-Guide 2007.
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Doubts
PHASE 1 - INITIAL Site visit Study of documents Simple calculation
Doubts confirmed?
Yes
PHASE 2- INTERMEDIATE Material investigations Detailed calculations/analysis Further inspections and monitoring
PHASE 3 - ENHANCED
No Compliance with codes and regulations?
Simple repair or strengthening solve the problem?
No
Yes
No
Refined calculations/analysis Laboratory examinations and field testing Statistical modelling Reliability-based assessment Economical decision analysis
Yes Simple strengthening of bridge
Update maintenance, inspection and monitoring strategy
Yes
Sufficient load capacity? Acceptable serviceability? No
Unchanged use of bridge
Redefine use and update maintenance, inspection and monitoring strategy
Strengthening of bridge
Demolition of bridge
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 from SB-LRA (2007).
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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 of the structure. Apart from ordinary surveillance when train and track staff continuously monitor the 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-depth inspections, not necessarily covering the entire structure, but perhaps for dealing with a particular component or problem area. - General inspection: Extremely detailed inspection with examination of all parts of the bridge within 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 defects observed. In practice this means that the inspection frequency will vary according to bridge type and condition. The general inspection should result in production of a full and detailed report on the condition of the structure. The final inspection made on handover of the structure or before its commissioning, or following major repair work, provides a benchmark for the required condition. Special equipment and facilities will generally be required for these inspections, during which structures should be subjected to visual examination in order to locate any defects with the aid of special 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 bridge without using special access equipment. All defects which can be visually detected from the ground must be recorded and the condition of the structure must be evaluated in an appropriate manner. Continuous monitoring may be used to keep a check on particular developments or a new situation arising between two periodical inspections . By means of such monitoring, defects which 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 by specialist staff, who should be well experienced in carrying out examinations besides having the necessary technical knowledge. They should not only be able to identify defects but also to ensure that their development can be monitored through suitable measurements to determine movements, 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 the inspection. Likeliest causes of different damages should be recorded. Need to repair or further inspect or monitor the bridge as well as traffic limitations should be defined in the inspection report. Suitable means of access to the various parts of the structure, ranging from ladders to special scaffolding, should be arranged. Depending on the topography and on the features of the structure to be inspected (Iength, height, etc.), these aids, depending on the requirements of the railway concerned, may be subdivided as follows: - For very long viaducts spanning inaccessible terrain, it may be economical to equip the structure, at the construction stage, with an inspection platform, or at least with longitudinal rails on 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 an inspection platform at its outer end, with a system of hydraulically-operated articulated arms that can 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 are accompanied by a service vehicle of the Pemanent Way Department. - Lifting platforms mounted on rail, road or road/rail vehicles. These platforms mounted on a rail vehicle, road vehicle or road/rail vehicle, can be moved by rail or road and are provided with an inspection platform located either on the extension of a double articulated arm or on an arm with several telescopic sections. Examinations are carried out either from the inspection platform itself 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 “Monitoring tool-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 the structure; mineralogical and microscopic analyses to diagnose material conditions, ultrasonic testing 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, construction documents and the results of the acceptance inspection of the structure provide basic inputs for the 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 of the structure. They shall contain details of irregularities discovered or of the development of defects 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 – Definitions A 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 progressive deformation, 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 SBICA (2007) there is also a tool box for non destructive testing (NDT) methods with a one-page summary of each method explaining its merits and drawbacks. The background to the tool-box is described in Helmerich et al (2007, 2008a, b). Methods for masonry arch bridges are also given in UIC Code 778-3R (2009).
Table 2.1 Overview of methods and equipment
Visual and Simple Methods
Roughness depth test Liquid penetrant test Sclerometric test Hardness
External visual inspection, usually performed regularly in routine surveys or inspections, limited by human factors Internal visual inspection with devices through holes in hidden or covered parts of steel or concrete structures, experience required, inspection limited by the length of the cable Evaluation of hollows by air or fluid pressure Fluid or air permeability of concrete surfaces as measurement of durability, Depth of reinforcement in concrete structure, thickness of the concrete cover, reliable equipment available on the market Investigation of concrete surface roughness Surface cracks in welds of steel connections. Hardness of young concrete. From Greek skleroo, harden Hardness of steel
Thermal Heat Transfer Transient (active) thermography Pulse-phase thermography
Debonding of tiles, plaster, mortar, carbonfibre reinforced polymers (CFRP), determination of humidity/ moisture content Debonding, near surface voids with optimised contrast
External visual inspection Internal visual inspection (video scope) Void volume measurement Air (Torrent) Permeability Cover measurement
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Acoustic, Electric and Electromagnetic Methods Acoustic emission Detection of growing active cracks Modified Acoustic Emission Survey of known active cracks, in laboratory-modified AE for search of (AE) active cracks Low strain pile integrity Pile length, integrity testing Parallel seismic Pile / sheet depth Cross-hole tomography Soil, parameters, consolidation beneath embankments Cross-hole sonic logging Material quality in foundations Impulse-radar echo Radar tomography Thickness of concrete elements, grouting level of tendon ducts, localisation of rebars and tendon ducts radar Electrical 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 mortar loss Radar tomography Leaching, inner cracks from freeze-thaw-cycling, hollows, moisture (in research) Ground penetrating radar Evaluation of layers and voids in embankments and subsoil Radar scouring Scouring around stream piles Electrical conductivity Moisture content, backfill type and quality Electrical conductivity Moisture, soil type Galvanostatic 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 bridges Ultrasonic-echo (US-echo) Thickness measurement, localisation of reinforcement or tendon ducts, Dry coupling using US-array voids in RC Ultrasonic transmission Localising reinforcement or tendon ducts, voids in the concrete tomography Impact-echo Thickness measurement, localisisation of reinforcement or tendon ducts, Impact-echo Investigation of crack depth Ultrasonic-echo Residual thickness of mild and modern steel plates, weld defects, surface cracks, cracks parallel to the surface, surface crack depth, inhomogeneity Ultrasonic-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 Ultrasonic Inspection Ultrasonic-echo (masonry)
Radiographic Methods Radiography with isotopes/ steel (RI)
Ultrasonic velocity (transit time tomography), Residual stress in rivets Detection of deterioration
Detection of cracks in hidden elements and inhomogeneities in modern steel or connections (welds)
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Radiography with x-ray/ Detection of voids in RC, localisation of reinforcement and tendon ducts cobalt Spectral-chemical and Potential Methods Electrical potential field Corrosion state of reinforcement measurement Laser-Induced Breakdown Analysis of chemical elements on surface and near surface Spectroscopy Sparkle Emission Analysis of chemical elements of the steel Spectroscopy Sulphur print Chemical analysis for identification of the used iron/ steel (slightly destructive)
Advanced Data Acquisition and Evaluation Methods Automated scanning system Parallel use of different sensors for NDT-investigation of concrete bridge slabs Synthetic aperture- focusing Reverse projection of wave images technique 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 for non-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 of weldability. Attention is drawn to the difficulties involved in taking samples, and to the problem of obtaining representative 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 materials used in the structure. The problem, however, is: 1) that it is often difficult to remove a sufficient amount of steel from structural elements to provide a representative sample; 2) to identify lowstressed structural components for sampling to prevent significant weakening of the structure; 3) whether the sample taken is adequately representative of the structure as a whole (e.g. old iron or steel bridges, in which materials of varying origin have been used on construction or repair). 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 Bridges The 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 including characteristics of the material
Remarks
Visual
Contamination, loss of material, deterioration, displacements, cracks Listening for audible sounds from tapping the surface with a hammer Propagating cracks 2D/ 3 D-Localisation of active cracks Defects in thin layers
Cracks <0.1 mm, only surface observation
Depends on span
Provides an approximate understanding of the condition
Simple and inexpensive
Not for stable (not propagating) cracks ~ 10% of the distance between sensors
Research level
Max depth 10 mm, local resolution > 2mm, Only magnetisable materials Crack opening > 0,1 mm, length > 1 mm, crack hole investigation during replacement of rivets Remove old colour width > 0,1 mm Length > 1mm Maximum investigated plate thickness: 70 mm
Follow safety instructions of the railways when using hand held tools Documentation only with camera
For example:. use of reference grooves for calibration: Width x depth: 0.11mm x 0.95 mm Depth/width ratio: < 25
General inspection, in all phases of the reassessment as needed
Hammer tapping Acoustic Emission (AT) Eddy current test Magnetic particle test
Surface cracks
Colour penetration test (PT) Radiography (RT)
Surface cracks,
Ultrasonic echo (UT)
Weldroot testing, residual plate thickness, thickness of surface coating
Internal voids in sandwiched elements
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Documentation only with photography rd
Last phase (3 ) in reassessment
Ultrasonic array (UTarray)
Internal void depth and lateral dimensions, defect inhomogeneity
Multi-channel systems for adaptation to special tasks
rd
Last phase (3 ) in reassessment
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 recommendations for 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. In Table 2.3 NDT methods are given. A combination of methods is often useful.
Table 2.3. Non Destructive Testing (NDT) Methods for Masonry Bridges The 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 including characteristics of the material
Remarks
Visual
Qualitative values: geometry cracks (length, depth), heavy displacements, longitudinal/ diagonal cracks in the barrel, vegetation, drainage, humidity, heavy settlement Listening for audible sounds from hammertapping the surface
Cracks <1.0 mm, only surface observation. An endoscope may be useful
Inspection time depends on span
Provides an approximate understanding of the condition
Simple and inexpensive
Radar-echo 500 MHz, 900 MHz, (Ground penetrating radar, Georadar, Impulse radar) Radar echo 200-500Hz
Arch barrel and wing wall thickness, retaining wall inhomogeneity, embankments/ hollows, heavy deterioration Humidity, Metal inclusions (anchors) Back fill thickness, ballast thickness
Appropriate for depth maximum 2 m (lower frequencies) Defect size: in homogeneous material: ~ 5% of the depth, in heterogeneous material: ~ 10 % of the depth,
Access from one side, Use in assessment phase 3
< 5 m depth in heterogeneous material: ~ 10 % of the depth,
Ultrasonic echo (US) (US-array without coupling agent): transversal: 50 kHz longitudinal: 100 kHz Acoustic emission
Local inhomogeneity, Thickness, Metal inclusions
Depending on the condition of the masonry Defect size: 10-30 mm Train traffic noise, building activities such as drilling, anchor dysfunction or other noise can influence acoustic signal acquisition
EU-funded project Saferail has developed new wagon with 4 antennas Access from one side: Depending on the task to solve: Frequency 50-300 kHz. Assessment phase 3
Localisation of active cracks
10 % of the sensor distance in the array, Influenced by low temperature, defects, deformation rate
SIP-spectral induced polarisation
Humidity, inhomogeneity visualised in 2Dconductivity images
Flat-jack test Single or double*
Determination of stress under service in the masonry
Hole-drilling method*
Stress-strain behaviour in one single point
Hammer tapping
Method feasible, No final standards, since research is ongoing Applicable to backfill, masonry
Local near surface, information about the stress behaviour/elasticity of the masonry, locally destructive resolution ~ 0,1 N/ mm2 Only local and superficial information Accuracy of strain gauge: + 1 µε
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Standard test (Rilem, ASTM)
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, fracture and 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 for reinforcedconcrete 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), In Table 2.4 NDT methods are given. A combination of methods is often useful.
Table 2.4. Non Destructive Testing (NDT) Methods for Concrete Bridges The 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 method includingcharacteristics of the material
Remarks
Visual
Contamination, loss, deterioration, displacements, cracks
Cracks <0.1 mm, only surface observation, loose cover
Inspection time depends on span
Hammer tapping
Listening for audible sounds from hammertapping the surface
Provides an approximate understanding of the condition
Simple and inexpensive
Radar-echo 500 MHz, 900 MHz, 1.5 GHz (Groundpenetrating radar, Georadar, impulse radar) Radar transmission 500 MHz, 900 MHz, 1.5 GHz Ultrasonic echo (US) (US-array without coupling agent): transversal: 50 kHz longitudinal: 100 kHz Acoustic emission
Girder-web thickness, Slab thickness, Embankment/ Retaining wall reinforcement, Tendon ducts, Inhomogeneity, Humidity, Metal inclusions (anchors)
Appropriate for depth max. 2 m Defect size: in homogeneous material: ~ 5% of the depth, in heterogeneous material: ~ 10 % of the depth, Dense reinforcement near surface prevents deep penetration.
Access from one side, Use in assessment phase 3
Girder web thickness, Reinforcement of tendon ducts, Inhomogeneity Reinforcement, tendons location, grouting of tendons, Local inhomogeneity, Thickness, Metal inclusions
Method in course of development, better imaging of inhomogeneity expected
Research level, Access from both sides
Depth: 5-40 cm Defect size: 10-30 mm Train traffic noise, building activities such as drilling, anchor dysfunction or other noise can influence the acoustic signal acquisition,
Access from one side: Depending on the task to be solved: Frequency 50-300 kHz. Assessment phase 3
Localisation of active cracks
Method feasible, No final standards, since research is ongoing
Ultrasonic air coupling
Voids
10 % of the sensor distance in the array, Influenced by low temperature, defects, deformation rate Reflected surface waves influence the emitted waves
Impact-echo
Thickness, delamination between two concrete layers, location of voids, quantification of cracks Near subsurface voids, delamination, moisture, plaster delamination, control of strengthening measures Metal inclusions, cables, wires, tubes
Train traffic noise, building activities such as drilling, anchor dysfunction or other noise can influence the acoustic signal acquisition, Safe , no radiation, Accuracy depends on depth of the void, camera, distance and further limits, for example: 1m2: 65000 pxl: + 1 cm2 Defect size ~20 x 1-2 mm, Restriction due to radiation, no traffic during test
Surface waves may influence the result, solution: IE in transmission
Active thermography
Radiography (cobalt, γ-ray)
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Research level
No moving / scanning technique
Last phase (3rd) in reassessment
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 deflection meters (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 various parameters 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 to the 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 Foundations The following table gives limitation and interference of NDT-methods with railway operating infrastructure and rough timeconsumption (only for pure measurement without equipment installation), SB-ICA (2007), Table 5.4. NDTMethod
Investigated details
Limitation in use. Accuracy of the method including. characteristics of the material
Remarks
Radar echo Radar echo array 200-800 MHz
Soil layers, thickness, scour, humidity track-bed condition
Penetration depth depending on frequency: Max. depth 10m,
According to requirements for the test and resolution
SIP Spectral
Sonic-velocity evaluation along a profile on masonry surface Integrity of pile foundations, pile length Pile length
Borehole tomography Parallel seizmic method
max. + 5 % of the penetration depth Calibration by means of coring, humidity influences the precission, limited resolution To measure the integrity, sensors are lovated in a tube paralle to the investigated pile Influence of construction quality (concrete), stiffness of soil has to be taken into account
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According to requirements for the test and resolution
According to requirements for the test and resolution According to requirements for the test and resolution
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 conveniently treated. 2 - Serious defects without short-term effects on the stability of the structure, but which may lead to increasingly costly maintenance work if not rectified swiftly. Short-term may here mean a period of a couple of months. 3 - Serious defects with short-term effects on the carrying capacity of the structure, thus leading 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 (Defects and 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 FEMmodel), 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 and analytical 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-state harmonic), - Natural frequencies (Response spectrum method), - Damping (Decay curve method, Half-power bandwidth method, Phase method, Multiple-mode decay method, Ambient vibration method), - Modal parameters (Peakpicking method, Stochastic subspace identification)
3.3 Sensors: -Accelerations (Piezoelectric accelerometers, Capacitive accelerometer, Force balanced accelerometer), - Displacements (Inductive linear position sensors, Vibrating wire displacement sensors, Microbend displacement sensor, Pulse time-of-flight deformation sensor, Capacity non-contact displacement sensor, Eddy-current displacement sensor), - Strains (Electrical resistance strain gage, Bragg grating strain gage, Fabry-Perot interferometer strain 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 the contents is given below. The bridge assessment in many aspects is very similar to the bridge design. The same basic principles lie at the heart of the process. Nevertheless, an important difference lies in the fact that when a bridge is being designed, an element of conservatism is generally a good thing that can be achieved with very little additional costs. When a bridge is being assessed, it is important to avoid unnecessarily conservative measures because of the financial implications that may follow 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 additional recommendations or guidelines are required that will lead to less conservative assessment of their loadcarrying capacity. Such guidelines have already been proposed for assessment of highway bridges in Europe. However, there is a lack of this type of documents that can be applied for the assessment of railway bridges. Guide SB-LRA(2007) provides guidance and recommendations for applying the most advanced and beneficial methods, models and tools when assessing the loadcarrying capacity of existing railway 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-bridge interaction), - 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 Bayesian updating 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 the EC 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); Basic information for bridge assessment (Chapter 4); Load and dynamic effects (Chapter 5, Annex 5.1); Concrete, Metal and Masonry Arch Bridges (Chapter 6, 7 and 8 and Annexes 7.1 8.1 and 8.2); Foundations and transition zones (Chapter 9); Improvement of assessment using information 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 of original methods and models that have been developed, obtained or systematised through research 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 in working condition. The maintenance work to be carried out can be divided into preventive maintenance on the one hand, and minor repair work on the other hand, with the aim of rectifying minor faults or delaying the 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 vegetative growth on the masonry facings, the replacement of ashlars or bricks in cases of isolated damage, and the repair of damaged concrete edges; - on masonry: repointing, injection, application of coating products in connection with general surface 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 of loose bolts; - maintaining the drainage of masonry structures in working condition so as to prevent penetration 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 on the bearing seating and the deck.
5.2 - Repair Repair covers all measures aimed at restoring the structure to working condition. Such measures are directed at the cause of defects and are thus designed to prevent their further development. For this work to be carried out efficiently, a thorough examination of the structure is required. Although experience from earlier cases and the review of previous data are of great value, 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 than bridging 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 or injected 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 of anchors/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, beneath the bearing plates, repair of bearing supports;
injection of synthetic resin
- stabilisation of retaining walls by buttressing. Occasionally, comprehensive repairs have to be delayed for financial or other reasons, e.g. to avoid 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 to premature renewal of the structure. A shorter interval between inspections may help reduce uncertainties 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 in response 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 capacity of the structure; the second objective, depending on the new speed planned, may occasionally necessitate bridge-widening. Older concrete bridges may be strengthened by means of additional reinforcement, for example by using the technique of bonded plates, sheets or bars of steel or Carbon Fibre Reinforced Polymers (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 transfer to 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, gabions or drainage blankets. Methods for strengthening are given in SB-STR (2007). This Guide contains a graphic index with 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 where because of the poor condition of the structure, strengthening cannot provide an economical solution 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 generally more economical than strengthening, especially if there are restrictions imposed on maintaining rail 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 and condition assessment including the NDT toolbox Proceedings: Sustainable Bridges Assessment for Future Traffic Demands and Longer Lives,,pp 93-104; Wroclaw : Dolnoslaskie Wydawnictwo 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: International Association 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: Transportation Research Records, Taylor & Francis, Washington D.C., USA. SB-GUIDE (2007): Overall Project Guide: “Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives” – a project within EU FP7. 28pp. Available from: www.uic.asso.fr or www.sustainablebridges.net. [cited 30 XX 2008] SB-ICA (2007): Guideline for Inspection and Condition Analysis of Railway Bridges. Prepared by Sustainable Bridges – a project within EU FP6. 259 pp. Available from: www.uic.asso.fr or www.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 Systems for Reinforced Concrete Bridges, SB-5.2-S3, 23 pp; Estimating Reliability of Monitoring systems for 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 of steel railway bridges. UIC, 2nd edition, 1.1.1997 UIC Code 778-2R (1997): Recommendations for determining the carrying capacity of existing metal 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 maintenance of 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 supporting the 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 arch bridges. 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 bridges. 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. UIC Report - Ozaeta, R. G, Martín-Caro, J.A., Brencich, A. (2007): Guide to the execution and control of masonry arch repairs. UIC Report - Steffens, K., Gutermann, M. (2006): Guide to the load test of masonry arch bridges. UIC Report - Orban, Z. (ed.) (2006): Recommendations for the non-destructive testing of masonry arch bridges. UIC Report - UIC Code 778-3R. (1994): Recommendations for the assessment of the loadcarrying capacity of 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 the International Union of Railways, Paris. UIC Masonry (2008): Improving Assessment, Optimisation of Maintenance and Development of Database 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 von Fahrbahnübergängen 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 and Condition-assessment of railway bridges including Non Destructive Testing (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 the terminology and understanding of non-destructive evaluation of the current state of an investigated bridge. Amended from SB-ICA (2007). Table A1. Terms and procedures for inspection and condition assessment English Terms Acoustic emission (AT)
Acoustic methods
Array
Artefacts
A-scan
Assessment
B-scan
Definition Acoustic Emission is the class of phenomena whereby an elastic wave, in the range of ultrasound usually between 20 KHz and 1 MHz, is generated by the rapid release of energy from the source within a material. The elastic wave propagates through the solid to the surface, where it can be recorded by one or more sensors. Acoustic methods are non-destructive testing methods for the investigation of the current condition of the inner structure by implementing an acoustic sound as impact (single wave) by an hammer impact or an acoustic wave, induced by acoustic sensors (ultrasound) recording and processing the reflected or transmitted waves. Each material needs sensors developed for characteristic frequencies. Acoustic methods can be applied in echo mode (transmitter and receiver are on the same side of en structural element, recording reflected waves) or in transmission mode (transmitter and receiver are on opposite sides of an element). Array is a set of sensors. Usually, sensors can be applied as a group of sensors, transmitters or receivers. Known procedures are US-array measurement, phased array for investigation of cracks in steel or concrete structures. The set-up of a group of acoustic emission sensors is also named array. Ultrasonic phased arrays are well introduced to quality assurance systems of industrial steel structures. They are investigated for use in concrete bridges. Non real phenomena in images calculated as inverse processing of NDT-data sets, artefacts actually result from an inauspicious algorithm or geometry, data density or quality. Experience is required to distinguish real defects from artefacts. Acoustic, thermal or electromagnetic data obtained with non-destructive testing methods recorded in time domain for one single point on the surface of a structure. A set of activities undertaken to characterise current state and the reliability of a structure in comparison with a required state. See → condition assessment and → structural assessment. Image of a vertical section perpendicular to the investigated surface below a line scan recorded in time domain
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Bridge condition assessment
Bridge defect: Bridge safety/ structural assessment Bridge serviceability Bridge technical condition CFRP C-scan
Condition
Condition assessment
Condition rating Condition ranking
Corrosion detection Damage
Also condition appraisal: Process of evaluation of the local and/or global state of bridge conservation expressed in the form of condition rating, either numerical (scale: 0-5, 1-10, 1-100 or other) or linguistic (good, poor, acceptable, etc.); Difference between the designed and the real state of a structural element, effect diminishing the technical condition of the bridge Process of evaluation of remaining bridge safety measured in terms of partial safety index, reliability index or probability of failure, Measure of differences between current and designed values of bridge service parameters, e.g. load capacity, clearance, maximum speed, etc. Measure of differences between current and designed values of bridge technical parameters, e.g. geometry, material characteristics, etc. CarbonFibre Reinforced Polymers. Often used as extra reinforcement when bridges are strengthened Image of processed NDT-data sets characterising a horizontal depth slice of the inner structure, parallel to the investigated surface. Data set is usually taken from 3-dimensional data sets of recorded and processed data as impulse radar-echo, active thermography, ultrasonic-echo or impact echo. Current state of a structure, characterised by quality of design, execution quality and aging processes influenced by external loading and environmental influences. (Also: condition appraisal) is a judgement about the condition of a bridge 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 a bridge itself as input to a ranking in a bridge management system. The inventory of existing standard methods for Condition assessment and inspection of railway bridges together with a tool box of established and new innovative Non-Destructive testing techniques will form the basis for a proposal of a Unified Condition Assessment procedure for railways in Europe Indicates the global state of conservation of one bridge structure and its evaluation using weighted factors, indices or percentages according to its value in comparison with the theoretical initial value. Comparison of the bridge ratings in the bridge stock of an infrastructure owner. Condition ranking based on current conditionrating systems is a tool for bridge owners when ranking their bridge asset in order to coordinate their maintenance strategy or manage the bridge stock. Currently used condition rating systems do not deliver data for the structural assessment of bridges. Surface investigation of reinforced concrete bridges, e.g. with electrochemical potential methods in order to detect early characteristics anticipating corrosive processes. Difference between current state of the bridge and the designed structure. Damage can be caused by low quality during the construction process or during service life.
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Contrary to defects, damage describes a process. Defect
Data Fusion
Data reconstruction
Degradation Duty survey Eddy- current test (EDT) Endoscope Electrochemical inspections
Electromagnetic methods (EM)
Experts opinion (E) General Inspection
Impact echo
Impulse radar
When describing current condition related deficiencies in a bridge – the term defect is used, rather than the word "damages" now frequently used. One exception to this general rule is the expression "fatigue damage" which is in normal usage (Network rail). Super positioning of data from different (NDT-)data sets obtained for the same geometrical structural points to receive a more refined and more realistic visualised image. Data obtained from running radar antennas appears as hyperbolas. The back-calculation of the measured data to the real geometrical shape reflecting the electro-magnetic wave is called reconstruction of data Timedependent (deterioration, aging) or non-time dependent (traffic impact, earthquake) process causing a defect of structure. Continuous visual survey of the infrastructure by track staff Eddy-current testing uses electromagnetic induction to detect flaws (voids) in conductive materials. Basically, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. Instrument for looking at internal parts of an object. From Greek endon = within and skopeo = look at Corrosion detection plays a role in servicelife prediction of concrete structures. Potential mapping or Laserinduced breakdown spectroscopy enable researchers to earlydetect incipient corrosionprocesses. Electromagnetic methods use electromagnetic waves to produce images. Impulse radar measurement belongs to the group of electromagnetic waves. The more the obtained data is focused on the investigated objects and the closer the measurement grid, the better are the results. Simple electromagnetic methods are magnetic powder inspection applied to steel bridges or application of the cover meter Electromagnetic methods use impulse-radar-echo waves or induce magnetic fields in structures. In case of doubts during reassessment of structures (in phase 2), the structural engineer can ask for a refined investigation. Special knowledge and experience is required. Extremely detailed inspection involving examination of all parts of the bridge within touching distance (with hammer tapping on concrete surfaces) every 4 to 6 years. However, the frequency of inspection should reflect the nature of the bridge and the defects observed. Less detailed examinations are made during Routine and Principal Inspections With sensors in echo arrangement : Acoustic wave excitation and receiver are on one side of a structural element. Surface waves may badly affect the result. Advantage is the accessibility from only one side. With sensors in transmission arrangement: Acoustic wave excitation from one side and the receiver on the opposite side of a structural element. Advantage is that surface waves do not disturb the result. Geo-radar: Ground Penetrating Radar
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Inspection
Magnetic Particle Test (MT) , Non-Destructive Testing(NDT)
Permeability
Phased array
Polarisation
Potential field
Principal Inspection Probability of Detection(POD)
Radiographic methods
(GPR) or Impulse Radar is a geophysical, non-destructive technique based 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. Gathering of data from the existing bridge via regular visual control usually based on rules or standards and its translation to the inspection records (bridge book, sheets, digital files). Inspection is a regular visual control of the bridge condition. All railway authorities plan their inspections on the basis of national rules, Use of magnetised particles in a suspension to find surface cracks Investigation of structures or structural elements using waves to receive data visualised in images to obtain information about the inner structure. Acoustic, electromagnetic, thermal or microwaves can be used. The structure’s integrity is not affected. Density of the concrete surface against air or water penetration. Low permeability of concrete is the best guarantee for its durability. If no gas or water can penetrate the concrete, the chloride transfer or carbonation process is interrupted. Impermeability can be tested with pressurised water, and permeability by means of a permeability test. A set of ultrasonic transducer and/or receiver elements in which the timing of the elements' excitation can be individually controlled to produce certain desired effects, such as steering the acoustic beam axis or focusing the beam to find voids or inhomogeneities. The EM field contains electric and magnetic field vectors which are orthogonal to each other and to the direction of translation. By convention, the EM field solutions are characterised by the direction of the electric field vector. When the time variation of the fields is sinusoidal, the concepts of linear, circular and elliptical polarisations arise. In practice, using dipole antennas between parallel and perpendicular polarization in relation to the antenna, movement will be distinguished. The potential field on a surface changes if corrosion occurred inside the structure. It is measures non-destructively from the concrete surface. The test is sensitive to humidity Refined visual inspection with focus on safety carried out every (2nd) or ( 3rd) year. More in-depth examinations are made during General Inspections. 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 probability of not overlooking an existing defect (probability of detection, POD) and correct sizing of the defect. However simple this definition may appear, it encompasses many complex issues ranging from the specification of the nature of defects to influencing factors related to the inspection instrumentation, product nature, the involved human factor and the available expertise for inspection data processing and assessing. Radiographic inspection is more important for the assessment of steel structures than for voluminous and massive concrete bridges. It is the only reliable method for the assessment of weld defects or of damages in sandwiched elements, as built-up sections in riveted
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Routine Inspection
Resistance Assessment
SAFT
Special investigation
Strength Assessment:
Survey
Thermography
Time of flight areas (TOF) Tomography
Ultrasonic
girders. While in some countries the application of radioactive sources is restricted by safety measures, others apply e.g. Iridium sources successful in experts’ opinions for detail investigation. Annual inspection from ground level by trained examiners. It is carried out in accordance with national standards or rules of infrastructure owners. More in-depth examinations are made during Principal and General Inspections. 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 material testing, and structural analysis.) Synthetic Aperture Focusing Technique is a digital signal processing method (DSP) for ultrasonic testing (SAFT UT). It provides an accurate measurement of the spatial location and extent of flaws contained in objects such as structural components and welds and nuclear-power reactor systems. Transit-time for the ultrasonic beam to travel to and from a point is a hyperbolic function of the probe position and target depth. When the equation of this hyperbola is known, A-scan signals can be shifted in time and added together. In case of doubts during inspection of any level, a special investigation can be required. The inspector (professional bridge engineer) determines the scope for special investigations or expert opinions. 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 material testing, and structural analysis.) Also Routine surveillance or standard visual inspection from the ground level , for example performed half-yearly or yearly. The inspector has to follow national requirements on his training level. Active and passive thermography allow the reliable detection of humidity in a structure, investigation near surface damages as debonding, especially after repair or strengthening measures with thin layered materials (e.g. CFRP) or cavities near the surface. The evaluation of images of surfacetemperature data obtained as cooling down behaviour characterises near-surface integrity Time between emitting and receiving an acoustic or electromagnetic wave which is a measure of an inhomogeneity, if the wave velocity increases compared to the homogeneous material Tomography is a term describing the reconstruction of 2D- or 3D structure from data obtained from NDT-measurements (acoustic, electromagnetic or radiographic) using transmitters and receivers on neighboured or opposite sides of a structure, while at least one of the sensors is moved along the surface. Several dozens to hundreds of transmitter/ receiver positions are used. A term referring to acoustic vibration frequencies greater than about 18,000 Hertz. Ultrasonic waves have a wide diversity of applications over an extended range of intensity, with cutting, cleaning, and the
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Ultrasonic-echo (US-echo)
Visual inspection
y
destruction of tissue as one extreme and non-destructive testing (NDT) at the other end. Analysis of acoustic waves received on the same surface from which they where emitted, reflected from back wall, defects or cavities in structural materials. Advantage: Accessibility from only one side of a structural element. Gathering of data from the existing bridge via regular visual control, today usually based on national rules or standards and its translation to the inspection records (bridge book, sheets, digital files). If tools such as endoscopes are used to document the structure, the inspection is called indirect or internal. Computer program used for the analysis of wave propagation in structures.
Application With effect from 1 May 2009 All UIC railways.
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