Extending the Life of a Bridge – Harmsenbrug measurements
In the last week of October, 2013, a cable-stayed steel box girder bridge near Rotterdam in the Netherlands was instrumented.
Ttwo monitoring systems were applied: (i) a Bridge WIM (B-WIM) system on the section of the bridge over the road over the road and (ii) a more traditional monitoring system based on strain gauges on the section of the bridge over the canal and inside the pylon.
The bridge consists of 3 separate bridges:
HI. Cable stayed bride
HII. Draw bridge
HIII. Orthotropic bridge
The central section of the third part of the bridge (HIII) is instrumented with the B-WIM system, which provides information of the weight of the heavy vehicles. 28 strain sensors are located under the central point of the lower part of each stiffener.
In addition to 28 B-WIM sensors installed on HIII, a set of strain gauges are installed on HI to validate the developed numerical model of the bridge. The sensors are located at sections that feature predominantly global effects.
A total of 24 Sensors were located on the main deck, in two cross sections, where the load effects of passing vehicles are expected to reach maximum values. The strain gauges were installed directly on the plate in between stiffeners. In addition to the main deck, 4 additional strain gauges were placed inside the pylon to record strains due to moment and shear. For this purpose, strain gauges in two directions were used. Due to the presence of the entry door, changing plate thickness and local stress distributions at the connection between deck and pylon, the strain gauges are located at the second level of the pylon. These sensors can be easily accessed and are in a protected environment. The information provided by these sensors is being used to validate the global model but also allow validation of a refined model of the pylon, if necessary.
Measurements have been collected from October 30th 2013 to November 12th 2013 which corresponded to the passage of over 8 000 trucks.
Due to the complexity of the bridge model, the assessment is divided into two parts. First there is a global assessment of the structure, considering the main structural members (pylon and girder). Secondly a fatigue analysis will be performed over the orthotropic deck which is generally more difficult to predict and where the associated uncertainties are higher. The FE model represents the global response of the bridge, which is being validated with measurements. For the fatigue assessment, some particular locations and members will be selected to perform a detailed analysis, based on a locally refined version of the global model. A fatigue damage accumulation analysis will be performed to estimate and predict damage at all points on the bridge – direct measurement points and virtually monitored points.