Abstract
Deck inclination and vertical displacements are among the most important technical parameters to evaluate the health status of a bridge and to verify its bearing capacity. Several methods, both conventional and innovative, are used for structural rotations and displacement monitoring; however, none of these allow, at the same time, precision, automation, static and dynamic monitoring without using high cost instrumentation. The proposed system uses a common laser pointer and image processing. The elastic line inclination is measured by analyzing the single frames of an HD video of the laser beam imprint projected on a flat target. For the image processing, a code was developed in Matlab® that provides instantaneous rotation and displacement of a bridge, charged by a mobile load. An important feature is the synchronization of the load positioning, obtained by a GNSS receiver or by a video. After the calibration procedures, a test was carried out during the movements of a heavy truck maneuvering on a bridge. Data acquisition synchronization allowed us to relate the position of the truck on the deck to inclination and displacements. The inclination of the elastic line at the support was obtained with a precision of 0.01 mrad. The results demonstrate the suitability of the method for dynamic load tests, and the control and monitoring of bridges.
Highlights
The possibility to perform fast and accurate image processing, thanks to the power of the most recent computers, allows us to conceive new exciting applications of this technology in several fields and, in particular, for the monitoring of large structures
In light of the results of the test carried out on a real case, we can conclude that the method proposed allows one to obtain the displacement at an arbitrary point of a bridge using the load position measured by GNSS or a camcorder video and rotational angle at an end measured synchronously by laser projection-sensing technology
The rotations are obtained with the precision required for load tests and monitoring
Summary
The possibility to perform fast and accurate image processing, thanks to the power of the most recent computers, allows us to conceive new exciting applications of this technology in several fields and, in particular, for the monitoring of large structures. The projection of the tangent to the elastic line of a girder, materialized by a light beam, on an image sensor or on a target, can be effectively used for this purpose. Nowadays this is possible in a cheap and simple way thanks to laser technology. Several laser pointers, characterized by a low cost, small dimensions and weight, low power, limited beam divergence, and good pointing stability, are presently available on the market All these characteristics allow the development of a technique for monitoring large structures, and in particular, bridges. The deflections of the girders are measured by using levels or Sensors 2018, 18, 338; doi:10.3390/s18020338 www.mdpi.com/journal/sensors
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