Measuring system of strain monitoring of bridge structural components and bridge clearance

Анотація

At present, the automated systems of strain monitoring (ASSM) are in demand; they are widely implemented and used in Ukraine and abroad. The aim of this paper is to determine the most effective methods and measuring systems to monitor the strains of bridge components and bridge clearance. On the basis of the application of optic methods and systems to measure bridge structure strains and the principle of laser beam sweep in horizontal and vertical planes, this paper describes the devices, which are designed by the authors of the article, to monitor bridge structure strains and bridge clearance that can be used in the ASSM. The proposed devices have a laser (laser diode) that permanently radiates a beam in an infrared (IR) range of a certain wavelength. An optical collimator and a scanning unit to radiate a laser beam towards photodetectors, which are fixed on a bridge span girder, are installed sequentially with a laser. It guarantees the parallelism of a laser beam. The laser, optical collimator and the unit of laser beam sweep are installed on a platform that is fixed on a step motor shaft at a certain distance from a bridge. The laser beam sweep unit, which uses the programmer of the step motor control unit, turns the shaft and the platform one-step (angle) further. The step motor is a mass production motor having a step of 0.9⁰ or 1.8⁰. A laser beam, which sweeps vertically, sequentially runs through all the n photodetectors, which are fixed on a bridge span girder, and the n photodetectors, which are fixed at a certain distance from the bridge in the same plane as the n photodetectors on the bridge span girder. The time span of a beam moving from one photodetector to the other photodetector corresponds to the length of a bridge clearance; the difference between the time of laser beam moving from one photodetector to the other photodetector without bridge strain and with bridge strain determines the value of a bridge structure strain. The described devices can be used in the ASSM; it enables us to effectively monitor the state of a bridge structure, shift and buckling that take place as a result of natural and climatic effects, intensive traffic as well as in cases when trains and aircraft apply large dynamic loads.