Transcript
Monitoring of Ahvenkoski Highway Bridge
Summary • Goal: examine whether the structural elements supported by the steel arch behave according to the FEM simulations and to determine the stresses caused by concrete shrinkage and thermal elongation • In addition the officials wish to monitor overloads and special transportation • Customer: Road Administration of Finland
• Monitoring period: 2013 – 2026 • Sensors: 23 x strain + 12 x temperature + IP-camera • Fibre-optic FBG-sensors and instruments (Micron Optics, Inc. /USA) • Internet website: alarms, long-term saving of measurement data, reports
Measurement instrument Micron Optics sm130-700 • Accuracy: 1 pm, correspond to < 1 in strain measurement • Sampling rate: max 1000 Hz, in this project 62.5 Hz • 4 channels, typically 8 FBGsensors / channel
sm130-700
• 3 internal references need no other calibration • Channel number expanded to 16 by sm041 -multiplexer sm041
Strain sensors Micron Optics os3600 and os3610 • FBG-type fibre sensor • Sensitivity: < 1 • Strain: ± 2500
os3610, 25 cm in steel bars
• Sensor length: 25 or 100 cm • Operating temperature: -40 … +80 °C (IP67) • Need pre-elongation • Multiplexable sensors less cables needed • Integrated temperature compensation • Calibrated sensors
os3600, 100 cm embedded to concrete
Position of strain sensors, lower truss Helsinki
• • •
Kotka Main girders, lower flange, 3 pcs (m2, m4, m6) Crossmembers, lower flange, 3 pcs (m11, m12, m15) Torsion truss, 2 pcs (m7, m8) Ground support T3
¼ Span
Position of strain sensors, upper truss Helsinki
• • • • •
Main girders, upper flange, 3 pcs (m1, m3, m5) Crossmembers, upper flange, 3 pcs (m13, m14, m16) In arch’s pull and compression rods, 2 pcs (m9, m10) Concrete deck, lower surface, 2 pcs (m22 ja m23) Inside concrete deck, 2 pcs (m20 ja m21)
¼¼Span Span
Kotka Ground support T3
Position of strain sensors, steel arch • Steel arch, 2 pcs (M18, M19) • Pull cable, 1 piece (M17)
¼ Span
Ground support T3
Sensor assembly • •
Photograph of a strain sensor on upper flange of a crossmember (M16) Sensor (25 cm) attached to L-shaped welded steel plates with aid of threaded rod, nuts and brackets
L-shaped steel plates
Strain sensor
Bracket
Nuts
Sensor assembly …
Sensor attached to a rebar
Sensor attached to a pull cable
Sensor attached on lower surface of concrete deck
Complete sensor assemblies
Monitoring station Mesurement case •
Measurement instruments are located in a monitoring station which is about 1 km to Helsinki from Ahvenkoski bridge
•
Equipped with aircondition system monitoring station provides UPS secured electricity and 100 Mbit/s internet connection for remote management of the measurement system
FBG interrogator
Channel mux
Modem
Network memory unit, 4 TB, RAID
Measurement PC
Measurement stages 1. Steel truss on waterside in unloaded state (5/2013) 2. Concrete casting (7/2013) 3. Removing of auxiliary supports and assembly of pull cables (10/2013) 4. Bridge loading test (6/2014) 5. Long-term monitoring 2014 – 2026
Curves showing similar shapes of strain and temperature sensors, temperature compensated curve also included Kompensoimaton
Lämpötila 12
-200
9
-250
6
-300
3
-350
0
-400
-3
-450
-6
Time [day/div]
Temperature [°C]
Strain [µStrain]
Kompensoitu -150
Example curves of embedded strain sensors M20 ja M21 during concrete casting of bridge deck
Stress [N/mm2]
Concrete shrinkage
Time [h]
Temperature [°C]
Concrete pouring
Bridge loading test • •
4 log trucks, á 76 tn 12 loading stages, 9 static, 3 dynamic
Stress [N/mm2]
Loading test, log truck 76 tn sensor M6 (outermost main girder, lower flange) speed test 45 km/h + sudden stopping in the middle of bridge
Sudden stopping
Time [s]
Overview of monitoring system Firewall and router MediaConverter Fibre to camera
PC
Mass storage
Fibre to sensors
Interro gator
On/off Power switch controlled by text message
220V UPS
Most important features of Web-portal • Real-time measurement results
• Real-time video picture • Saving of sensor data and video capture after trigger event e.g. overloaded truck
• Sensor history • Rainflow analysis • Standard reports
• Mobile support (Android, iOS)
View of Webpage
Challenges of monitoring • How to keep reference value stable for over 10 years? Integrated calibration unit (3 pcs) Measurement of absolute values (possibility to change instruments) Careful sensor assembly
• Huge amount of sensor data (> 2000 measurements / s) Real-time calculation, only results above certain limits are registered (e.g. log trucks, tank cars etc.)
• Long-term saving of measurement data Saving data to several physical locations (cloud servers etc.)
• How to distinguish slow structural changes from normal thermal lengthening? Comparing measurement results with FEM analysis
