Measurement of Displacements of a Bridge

13 Vertical displacements are among the most important technical parameters to evaluate the health 14 status of a bridge structure and to verify its bearing capacity. Several methods, both conventional 15 and innovative, are used for structural displacement monitoring; no one of these does allow, at the 16 same time, precision, automation, long term and dynamic monitoring without using high cost 17 instrumentation. The proposed system makes use of a common laser pointer and image processing. 18 The measurement of the lowering is obtained by analyzing the single frames of a HD video of the 19 laser beam imprint projected on a flat target. For the processing of images, a code was developed in 20 Matlab® that provides the instantaneous displacement of a bridge, charged by a mobile load. An 21 important feature is the synchronization of the load positioning, obtained by GNSS receiver or by a 22 video. After the calibration procedures, a test was carried out during the movements of a heavy 23 truck maneuvering on a bridge. Data acquisition synchronization allowed to relate the position of 24 the truck on the deck to the displacements. The results show high accuracy and demonstrate that 25 the method is suitable for dynamic load tests, ever more adopted for the bridge controls and 26 monitoring. 27 28