FATIGUE MONITORING OF STEEL RAILWAY BRIDGES Introduction

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					COST C25 – Fatigue monitoring of steel railway bridges




                                                                            Oliver Hechler
                                                                            ARCELOR Commercial Sections – Technical Advisory
                          13 April 2007
                                                                            Luxembourg
                                                                            oliver.hechler@arcelor.com




                             FATIGUE MONITORING OF STEEL
                             RAILWAY BRIDGES


                                          COST C25:           Sustainability of Constructions:
                                                              Integrated Approach to Life-time Structural Engineering


                                          Dipl.-Ing. O. Hechler
                                          Dr.-Ing. B. Hoffmeister
                                          Dr.-Ing. B. Kühn (PSP)
                                          Dipl.-Ing. T. Rauert




                       Introduction

                         Reasons for maintenance and strengthening:
                         • Age of existing steel bridges
                                                                                               Building investment [%]
                                                                                                   Building investment [%]

                         • Increased loads
                                                                                  100

                         • Changing demands                                        90                                 Maintenance
                                                                                   80                                 New structure
                                                                                                                          Structure
                                                                                   70

                                                                              %    60
                         Maintenance vs. New Structure:                      % 50
                                                                                   40

                         • Economic considerations                                 30
                                                                                   20

                         • Historical and social aspects                            10
                                                                                        0

                         • Sustainability and sensible                                      1977
                                                                                                    1985
                                                                                                             1995
                                                                                                   Year
                                                                                                   Year                2005
                           treatment of energy and resources                                                                        Peil U.


                         ⇒ Well targeted rehabilitation to enlarge service life




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COST C25 – Fatigue monitoring of steel railway bridges




                       Visual and technical monitoring

                                             Visual monitoring:
                                             - In Germany continuous inspections acc.
                                               to “Richtlinie 804”
                                             - Every 3 resp. 6 years


                                             Technical monitoring:
                                             - Data acquisition and procession unit
                                               ⇒ Real time information
                                                 (at special occasions or continuously)




                       Visual and technical monitoring

                          Application of technical monitoring:
                          • „Red-alert system“
                          • Supporting application for normal
                            inspections
                          • Monitoring of inaccessible areas
                          • Structural identification
                          • Application to confirm analysis
                          • Determination of input values for
                            residual life estimation models
                                                                  }    Predominantly application




ARCELOR MITTAL
COST C25 – Fatigue monitoring of steel railway bridges




                       Service life analysis with monitoring
                                                                                                  Condition assessment
                                                                                            (Inspection of the bridge condition )


                                                                                                   Should the structure be
                                                                                   YES                analysed more                        NO
                                                                                                         precisely?

                                                                           Investigation of:
                                                                  - Geometry                                                            END
                                                                  - Material parameters
                                                                  - Macroscopical material condition
                                                                  - Modeling


                                                          Identification of critical
                                                  Identification of critical componentsmembers
                                                       POSITIVE              Assessment                  NEGATIVE




                                              Long-term monitoring                           Existence of information about
                                                                                                                                                NO
                                                 not necessary                                    the loading history ?



                                                        END                                      YES
                                                                                                                             Assumptions


                                                                                       Continuous monitoring
                                                                                     + adaptive prognosis models                            Control of
                                                                                                                                    thresholds by monitoring
                                                                                                                                          (local strains,
                                                                                                                                           crack sizes)
                                                                               +         Life time prediction       -




                       Service life analysis with monitoring

                                                 Structural analysis                                                Remark:
                                                                                                                    • Schema only valid for riveted
                           Identification of members                 Identification of members in                     bridges
                                    in tension                               compression
                                                                                                                    • Welded structures:
                                                                         Stability check OK                           residual stresses due to welding
                                                                        ⇒ no failure expected                         ⇒ compression members
                                                                                                                         not fail-safe
                                        Determination of risk of breakdown using
                                 fail-safe analysis methods for the members in tension




                                      Does the failure of the member lead to the
                                    breakdown resp. partial failure of the structure?

                                                   No                  Yes




                                     Fail-safe                        Critical member




ARCELOR MITTAL
COST C25 – Fatigue monitoring of steel railway bridges




                       Service life analysis with monitoring
                                                                                          Condition assessment
                                                                                    (Inspection of the bridge condition )


                                                                                           Should the structure be
                                                                           YES                analysed more                        NO
                                                                                                 precisely?

                                                                  Investigation of:
                                                         - Geometry                                                             END
                                                         - Material parameters
                                                         - Macroscopical material condition
                                                         - Modeling


                                                         Identification of critical components


                                              POSITIVE              Assessment                   NEGATIVE




                                        Long-term monitoring                         Existence of information about
                                                                                                                                        NO
                                           not necessary                                  the loading history ?



                                               END                                       YES
                                                                                                                     Assumptions


                                                            Continuous monitoring +
                                                                    Continuous monitoring
                                                                                                                                    Control of
                                                                  + adaptive prognosis models
                                                          adaptive propagation models                                       thresholds by monitoring
                                                                                                                                  (local strains,
                                                                                                                                   crack sizes)
                                                                       +         Life time prediction       -




                       Service life analysis with monitoring

                        Classic approach:                                                                                      Application of monitoring:
                                                                                                                               Optimisation of input
                             Action model                                                                                      parameters for the specific
                                                                       Action Monitoring
                              e.g. traffic                                                                                     damage model in service
                                                                                                                               life analysis

                           Structural model
                            static, dynamic
                                                                 Performance Monitoring


                            Strains at critical
                                 details
                                                                       Stress Monitoring


                            Damage model                               Health Monitoring




ARCELOR MITTAL
COST C25 – Fatigue monitoring of steel railway bridges




                       Service life analysis with monitoring
                                                                                          Condition assessment
                                                                                    (Inspection of the bridge condition )


                                                                                           Should the structure be
                                                                         YES                  analysed more                        NO
                                                                                                 precisely?

                                                                  Investigation of:
                                                         - Geometry                                                              END
                                                         - Material parameters
                                                         - Macroscopical material condition
                                                         - Modeling


                                                         Identification of critical components


                                              POSITIVE              Assessment                   NEGATIVE




                                        Long-term monitoring                         Existence of information about
                                                                                                                                        NO
                                           not necessary                                  the loading history ?



                                               END                                       YES
                                                                                                                              Thresholds,
                                                                                                                     Assumptions


                                                                              Continuous monitoring
                                                                                                                            assessment of
                                                                            + adaptive prognosis models                     operating time
                                                                                                                                     Control of
                                                                                                                             thresholds by monitoring
                                                                                                                                   interval
                                                                                                                                   (local strains,
                                                                                                                                    crack sizes)
                                                                          Life life analysis
                                                                     Servicetime prediction
                                                                      +                     -




                       1st Application of monitoring: Support

                         Steel railway bridge
                                                                                                  Result:
                                                                                       Cracks in connection angle,
                                                                                             failure of bolts
                                    Problem:
                                 Friction due to
                                    corrosion




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COST C25 – Fatigue monitoring of steel railway bridges




                       1st Application of monitoring: Support
                                                                       Monitoring:
                         Steel railway bridge                       Strain gauges as
                                                                         sensors




                                                    Location of strengthening

                                                                                                       Monitoring:
                                                                                                      Stress in bolts




                       2nd Application of monitoring: Rail

                         Steel railway bridge
                                                                    Problem:
                                                              Fatigue of rail due to
                                                              bearing defect (gap)




                         Monitoring:
                         - „Red-alert system“
                                                                            Assessment of application of monitoring:
                         - Measuring during train crossing
                                                                            - „Red-alert system“ in rail traffic
                           (otherwise sleep mode)
                                                                              complicated
                         - Fine wires (electrical wire) at                    ⇒ backup capacity required
                           location of crack initiation
                                                                            - Suggestion: Exchange or
                         - Fibre optical sensors                                          strengthening of rail




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COST C25 – Fatigue monitoring of steel railway bridges




                       3rd Application of monitoring: Station

                         Problem:
                         -  Inaccessible bridge construction
                            ⇒ Problem of inspection acc. to RiL 804

                         Concern:
                         - Corrosive atmosphere

                         Monitoring:                                                     Sensor and
                         Continuous monitoring of micro climate:                         memory module
                         - Air and surface temperature
                            ( period > 1 year )

                         Thresholds of parameter monitored:
                         -   Minimal temperature –10°C
                         -   Relative humidity < 60% (dry air)




                       3rd Application of monitoring: Station

                                                       Measurement point 1



                                                                      60% relative humidity




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COST C25 – Fatigue monitoring of steel railway bridges




                       3rd Application of monitoring: Station

                                                                    Measurement point 1:
                                                                    (Represent most of locations):


                                                               ⇒
                                                                    No threshold exceedance
                                                                    Measurement point 2:
                                                                    (Critical location)
                                                                    frequent, long lasting exceedance of
                                                                    humidity threshold


                         Assessment of monitoring:
                         Monitoring is reasonable:
                         - Evaluation of condition at any time
                         - Low manpower needed
                         - Confirmation of calculation parameters for further investigation
                           ⇒ Elongation of required inspection periods acc. to RiL 804




                       4th Application of monitoring: Filler Beam Bridge

                         Problem:
                         - Resonance effect due to high
                            speed trains

                         Aims:
                         - Determination of “real” stiffness
                         - Determination of “real” damping
                         - Contribution of ballast
                            (effective contribution
                            to stiffness, coupling of two
                            bridge halves for each track)




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COST C25 – Fatigue monitoring of steel railway bridges




                       4th Application of monitoring: Filler Beam Bridge

                         Performance monitoring:
                         Structural identification
                         - Mixed traffic, high-speed line
                            Cologne-Aachen (250 km/h
                            ICE/TGV)
                         - Built in 2000 next to an
                            old steel bridge
                         - Span width 24,6 m
                         - 2 parallel bridges, separated
                            by a gap
                         - For each bridge a different type
                            of concrete is used (B25/B35)




                       4th Application of monitoring: Filler Beam Bridge




ARCELOR MITTAL
COST C25 – Fatigue monitoring of steel railway bridges




                       4th Application of monitoring: Filler Beam Bridge




                       4th Application of monitoring: Filler Beam Bridge




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COST C25 – Fatigue monitoring of steel railway bridges




                       Assessment of monitoring

                                                                                       Modified risk analysis using
                                         Classic risk analysis
                                                                                               monitoring




                                                                                       Assessment of the modified
                                Assessment of global risk (IG)
                                                                                           global risk (IG,mod)




                                                    Result                               Comparison IG vs. IG,mod




                                                                                       Assessment of the benefit
                                                                                         by applying monitoring




                       Assessment of monitoring

                             Structure        Environment                Risk          Modified risk analysis using
                         S1     S2     S3     E1     E2       E3    R1    R2     R3            monitoring
                         1      1        1     1        1     1     1     1      1
                              Dim.               Except.             Pol. risks
                         2      2        2     2
                                                  event 2
                                                    2               2     2      2    Definition of reduction factors xij
                         Fab. and
                         9  9    9             9        9     9     Eco.9risks
                                                                    9        9
                          erection              Nat. ph.                              Remark:
                        αS1     αS2    αS3    αE1    αE2      αE3   αR1 αR2 αR3
                                                                      Human
                                                                                      The reduction factors have to be
                         Condition
                            α                  corrosion
                                                   α                     risks
                                                                           α
                                 S                        E                R          checked for each monitoring task
                                                                                      (engineer, bridge owner, expert)
                                     Global risk-coefficient:
                                                    3                                                            3
                                             αG = ∏ αLi                                         αG,mod(αLj) = ∏(xij ⋅ αLj)
                                                    i=1                                                         j=1


                                        10 ln(αG )                                                   10 ln(αG,mod )
                                IG =               , 0 < IG< 10                         I G,mod =                   , 0 < IG,mod< 10
                                       ln(maxαG )                                                   ln(max αG,mod )




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COST C25 – Fatigue monitoring of steel railway bridges




                       Assessment of monitoring
                                 Bridge                                                        Train station
                                                        Risk assessment scale
                                αG = 26244                           10         387 420 489       αG = 729
                                 IG = 5,15                           9          53 624 632
                                                                                                  IG = 3,33
                                                      Extreme high   8          7 422 429
                             ⇒ Very high risk                        7          1 027 372
                                                                                                ⇒ High risk
                                                                     6          142 203
                                                       Very high
                                                                     5          19 683


                              αG,mod = 10078             High        4          2 724
                                                                                              αG,mod = 186,62
                                                                     3          377
                               IG,mod = 4,66            Medium                                  IG,mod = 2,64
                                                                     2          52

                               ⇒ High risk                Low        1          7
                                                                                              ⇒ Medium risk
                                                       Very Low      0          1

                                                          Risk            IG   αG
                             Monitoring acc. to                                               Monitoring acc. to
                             risk assessment                                                  risk assessment
                               questionable                                                      reasonable




                       Summary and Prospect

                         •    Trend to well targeted rehabilitation to enlarge service life of steel
                              railway bridges

                         •    Combination of theoretical and experimental investigations by
                              monitoring ⇒ optimised condition assessment

                         •    Existence of various monitoring systems to specific monitoring
                              tasks (fiber optic sensors preferred, MEMS in development)

                         •    „Red-alert system“ assessed to be critical for steel railway bridges
                              without backup capacity

                         ⇒ Monitoring as alternative resp. support of conventional normal
                           inspections

                              Risk analyse for more than one critical member per structure to be
                              developed




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