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The 81 m long Lehnen Bridge built in 1969 with precast elements, is part of the A5 La Neuveville-Biel/Bienne national road in Switzerland.
Due to critical stresses in the transverse reinforcement of the bridge, mageba was commissioned by the bridge owner (ASTRA Federal Roads Office) to perform an on-site temporary monitoring including stress and fatigue analysis.
The evaluation showed that the stress values of the rebar were significantly below the failure criterion according to the local technical standards resulting in reduced strengthening works for the client.
The monitoring includes real-time measurements on the rebar to verify fatigue. Thus, critical locations have been identified, concrete has been locally removed to apply strain gauges on the rebar, to finally connect them to the ROBO-CONTROL monitoring box.
To calibrate the measurements, a load test with a 20 t truck was conducted.
Measurements were taken 24/7 for three months of continuous monitoring at a frequency of 100 Hz in order to get an in-depth understanding of the actual stress ranges of the rebar.
The raw data was processed and presented in a histogram showing the measured stress ranges.
Finally, the damage accumulation was calculated using the SIA standard.
ROBO-CONTROL Portable SHM system
Tüscherz – Alfermée
Federal Roads Office
Gruner Wepf AG, Zurich