Vibration-based output-only bridge monitoring of the Floßgrabenbrücke (Zeitz)

The University of Applied Sciences Leipzig has started a series of experimental studies to monitor the structure of the Floßgrabenbrücke, a bridge in Näthern near Zeitz. This was made possible with the kind support of the Road Construction Administration of Saxony-Anhalt. In the first phase, four of the seven spans were equipped with a measurement system, specially developed by the I4S (Institute for Statics, Structural Dynamics, System Identification and Simulation). Eight acceleration sensors are installed per span. The sensors are uniaxial IEPE sensors of the type PCB393A03. To monitor the environmental conditions, four temperature sensors are installed inside the box girder and a weather station at the top of a column. The scope of this first phase is to test the continuous use of the monitoring system and to gain further knowledge and understanding about the test structure.

The bridge is divided into seven spans, with the outer spans having a length of 44.00 m and the middle span of 54 m. The construction height is 2.60 m with a width of 12.00 m. The superstructure is constructed as a trapezoidal, single-cell, torsion-resistant composite-steel box girder with an in-situ concrete slab.

The bridge is still open to traffic and Fig. 2 shows exemplary acceleration data due to traffic load and first identified modal shapes for a single span (span 4).

The TU Braunschweig (Institute of Flight Guidance and Institute of Geodesy and Photogrammetry) carried out laser measurements and photogrammetric drone images, from which point clouds were generated. These serve as preparatory work for planed image-based deformation measurements and automated detection of surface damages.