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"Exe North bridge field testing" at ESREL2017 by Farhad Huseynov


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Abstract: Monitoring displacement of in operation bridges is practically challenging but potentially very useful for condition assessment and decision support. The primary difficulties are in finding fixed physical reference points and, for the majority short span bridges under normal operation, the mm-level magnitudes of displacement under normal operating conditions (e.g. standard truck loading). With rare possibility for physical connection between a reference and a bridge, non-contacting technologies such as GPS need to be used. Other options include total station and more exotic technologies of laser interferometer and radar have also been tried. There are drawbacks for each technology related to limited sample rate (for total station) and signal to noise ratio (for GPS) while radar and laser are expensive and require specialist users. With advances in computing power, optics-based systems are becoming popular, relying on a standard lens but with capability to track multiple positions with potential to recover deformation with high spatial resolution. This paper reports the experiences of the authors exploring the suitability of a commercially available optics-based system in terms of spatial and temporal resolution and sampling and in challenging field conditions required for long term monitoring. For example issues such as stability of camera mounting (e.g. in wind) and varying lighting conditions while not problematic in a laboratory govern performance in the field. The paper tracks a sequence of experiments moving from lab to field, ultimately moving up to a field test on a road bridge in Devon. In each case the capabilities and limitations of the system have been critically examined. The study has defined both limitations and capabilities, while defining best approaches for use and at the same time providing some useful performance data on the subject bridges.

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"Exe North bridge field testing" at ESREL2017 by Farhad Huseynov

  1. 1. EXE NORTH BRIDGE FIELD TESTING Farhad Huseynov ESREL Conference Portoroz, 2017
  2. 2. OUTLINE  Purpose of the Field Testing  Test Structure – Exe North Bridge  Instrumentation  Results and Discussions 1
  3. 3. PURPOSE OF THE TEST  Field testing can potentially reveal hidden reserves of strength in a bridge,  In particular we were interested in identifying how did the real transverse distribution factors compare to those prescribed in assessment codes  This will be examined by placing a truck at various transverse positions on the deck and examining the variation in strain transversely in a beam and slab bridge 2
  4. 4. TEST STRUCTURE – EXE NORTH BRIDGE 3 SUPERSTRUCTURE  Composite type bridge  12 girders  Steel beams embedded into RC I-girders  4 traffic lanes  Non-continuous spans, simply supported A A
  5. 5. Sensor Locations ¼ Span 4 A A INSTRUMENTATION – STRAIN TRANSDUCERS
  6. 6. 5 A A STRAIN MEASUREMENTS (¼ SPAN) Four- axle Field Test 32 tonne truck 04:00 am Sensor 5 Sensor 2 Sensor 7 Start End
  7. 7. 1 A A STRAIN & DISTRIBUTION FACTORS (¼ SPAN) DF= ε𝑖 ε𝑖 Girder Numbers LoadDistributionFactors Lane – 2 Lane – 3 Lane – 4 Girder Numbers Microstrain Lane – 1Sensor 5 Sensor 2 Sensor 7 Sensor 5 Sensor 2 Sensor 7
  8. 8. 8 A A NEXT STEPS FOLLOWING EXPERIMENTAL TESTING  Now that we had the experimental data, we wanted to compare with a theoretical study  Finite Element Model (FEM) of the bridge were developed and calibrated based on the experimental analysis  Bridge structural behaviour under static loading were investigated
  9. 9. 9 A A FE MODEL AND BOUNDARY CONDITIONS Boundary Conditions modelled Pin – Roller Pin – Pin Partially Restrained 1) 2) 3) Beams only Beams & Slab
  10. 10. Boundary Conditions Girder Numbers Microstrain Girder Numbers MicrostrainMicrostrain Girder Numbers Lane – 1 Lane – 2 Lane – 3 Lane – 4 Girder Numbers Microstrain 1 ANALYTICAL & EXPERIMENTAL COMPARISON (¼ SPAN) Field Test Pin - Roller Pin - Pin Partially Restrained Girder NumbersLoadDistributionFactors
  11. 11. 1 POSTULATED STRAIN & DISTRIBUTION FACTORS (½ SPAN) Microstrain DFs Girder NumbersGirder Numbers Pin - Roller Pin - Pin Partially Restrained Pin - Roller Pin - Pin Partially Restrained DMRB External Girders DMRB Internal Girders
  12. 12. CONCLUSIONS  Change in boundary conditions can change the stress in load carrying elements significantly (~50%)  Load is more uniformly distributed when support conditions are free to move in longitudinal direction.  Change in boundary conditions can increase transverse load distribution factors slightly  Field testing is an important topic for bridge evaluation and can reveal any hidden strength reserves 13
  13. 13. ACKNOWLEDGEMENT  This research project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska – Curie grant agreement No. 642453  Devon County Council 13
  14. 14. 13 QUESTIONS?