Monitoring of Ahvenkoski Highway Bridge

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 Sensor length: 25 or 100 cm os3610, 25 cm in steel bars 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 Main girders, lower flange, 3 pcs (m2, m4, m6) Crossmembers, lower flange, 3 pcs (m11, m12, m15) Kotka 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) ¼ Span 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

Mesurement case Monitoring station FBG interrogator Channel mux 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 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

Strain [µstrain] Temperature [ C] Curves showing similar shapes of strain and temperature sensors, temperature compensated curve also included -150 Kompensoitu Kompensoimaton Lämpötila 12-200 9-250 6-300 3-350 0-400 -3-450 -6 Time [day/div]

Stress [N/mm2] Temperature [ C] Example curves of embedded strain sensors M20 ja M21 during concrete casting of bridge deck Concrete pouring Concrete shrinkage Time [h]

Stress [N/mm2] Bridge loading test 4 log trucks, á 76 tn 12 loading stages, 9 static, 3 dynamic 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 Media- Converter PC Fibre to camera Mass storage Interro gator Fibre to sensors On/off 220V UPS Power switch controlled by text message

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