Load testing on existing prestressed concrete bridges to determine long-term effects on strain measurement

Structural Health Monitoring is an effective tool for extending the life of aging bridges with load-bearing capacity deficits. To interpret and verify the data from sensor systems on structures, in-field load tests for calibration can be used. Such tests were performed for a long-term monitoring project on two prestressed highway slab bridges in Munich. The sensor system was designed to detect fractures in prestressing steel and concrete cracks and to derive a site-specific traffic load model. To achieve this, fiber optical sensors based on the Rayleigh backscattering technology were used for crack detection, while permanent strain gauges provided continuous traffic load measurements. For calibration purposes, it was possible to compare the results from different sensor types. The strain levels recorded are low and the test results indicate that strain gauges are highly accurate under different environmental conditions, while fiber optic sensors are less accurate. During the calibration process, longterm effects were identified that did not significantly affect the data.