Study On Opto-electronic & Combinatorial Measurement Technology Of Multi-dimensional Displacement For Long-span Arch Bridges

Influenced by long-term fatigue and other occasional damage during their service period, the structural reliability of bridge will be declined, and which will result in potential security problems. Therefore, more and more attention was paid on the structural health monitoring of bridge. As a result, some bridge structural health monitoring with modern sensing systems were developed and implemented on some long-span bridges and some interesting results were obtained; however, the state of art in structural health monitoring system is far behind the diversiform needs of bridges. So there are still some key problems for health monitoring of bridges need to further research. Among them, an important prarameter-displacement/deformation (which can indicate status of bridges) is one of the research hotspot.Arch bridges are famous for its reasonable structure, good looking, easy to achieve long span, but it is very hard to set up their mechanical model, because of their complicate structure, and then structural health monitoring for arch bridges becomes a big problem. Among all bridge collapse disasters in Mainland China, one third were happened on arch bridges, because the absence of inner structural/safety information during their service time. In an arch bridge, the arch and the girders are the key components to endure internal force, and their strain condition could be showed as their global deformation. If the deformation is in normal range, the inner force of the arch and girders should also be in the normal range; correspondingly, a out-range deformation usually represents an abnormal force on these components, and which will lead to bridge damage. From this point of view, displacement or deformation can be used as a key parameter to evaluate health status of arch bridges. The arch bridge has very complicated 3D deformation, because it is a large combination structure with one main arch and hundreds of support girders and beams. Real-time, high accuracy and large measurement range 3D deformation monitoring is a new challenge to current deformation measurement technology, but it is a very important science and engineering problem deserves careful study.The main contents of this dissertation are stated in detail as following:①Mechanics prosperities of arch and girder of Caiyuanba Yangtze River Bridge were analyzed. A method for multi-dimensions displacement monitoring of long-span arch bridges based on combination measurement technology is proposed. The main idea is: a total station system was adopted used to monitoring the three-dimension deformation of the arch; and a connected pipes system was used to detect vertical displacement direction for girder. Some key problems for these two measurement technique were studied.②For displacement deformation monitoring in three-dimensions of arch, the most important error reason is the shift of total station. A three dimensions movement model of instrument base was set up, according to measurement principle of total station. Coordinates of deformation points are calculated. Methods to calculate the instrument base shift were proposed based on the analysis instrument base movement properties. Furthermore, the influence of atmosphere refraction was analyzed, methods to address this problem were also proposed. At last, an automatic protection device was designed for prisms, and it can open automatically during measurement and close in other times.③For vertical displacement monitoring of girder, measuring precision and liquid fluctuation in connected pipes are the key problems need to be studied. Mathematics model of liquid flow based on multi-channels connected pipes was set up with hydromechanics knowledge. Properties of liquid fluctuation in time domain were analyized. According to properties of liquid fluctuation, a wavelet threshold algorithm was proposed to eliminate the fluctuation noise.④Signal distortion of opto-electronic liquid sensor was analyized, and corresponding measurement software was analyzed in detail, the liquid sensor which can be used to measuring displacement signal in static state and in low frequency dynamic state together are developed.⑤Lots of experiments were designed and carried out to demonstrate the validity of our combination measurement technique for arch bridges. A series of experimental results with two Leica TC 405 total stations show that, a three dimensions movement model of instrument base is correct and the improved measurement method to compensate movement of total station is feasible. For connected pipes system, experiments results showed that the static accuracy and quasi-dynamic accuracy of opto-electronic liquid sensor 0.1mm and 0.25mm respectively. A series experiments results for connected pipes system showed, connected pipes system is suitable to measure static displacement and very low frequency dynamic displacement at the same time. With improved wavelet threshold algorithm, the measurement error is less than 4mm for a ten minutes continuous time.⑥At last, total station and connected pipes system are applied on Chongqing Caiyuanba Arch Bridge spans across the Yangtze River. The on site load experiment results also demonstrated the feasibility of multi-dimensional deformation measurement by the combination of total station technique and connected pipes system. The method to compensate total station instrument base shift was also verified by the load experiments. The experimental data also showed that the displacement measurement with connected pipes system has very good accuracy. A mutual proved analysis between the vertical displacement measured by total station and connected pipes, and it raise the reliability of the data.