Research On The Realization And Application Of Structural Dynamic Monitoring System For Long-span Bridges Under Construction

Construction progress of large bridges is complicated with excessive influential factors and the quality control is strict. The structure and morphology parameters that reflect the safety status of the bridge structures will change significantly with the construction progress. The way of which to evaluate the periodic alignments, internal force and its safety and to acquire the state and the response behavior under severe conditions are of great signification for large bridges under construction or after it is open to traffic. Long-term continuous monitoring with bridge structure dynamic monitoring system serves as the best way to insure the structure safety. Under this circumstance, a bridge structure dynamic monitoring system based on GPS and georobot was developed and this paper researched the key problems. The key research contents and main achievements of this article are as follows.(1) With a systematical review of the development courses of structure monitoring techniques and the summarization of its state of the art and achievements, the key problems of dynamic monitoring for large structures or long-span bridges under construction were proposed.(2) The influential factors of safety of large bridges under construction or after it is open to traffic are analyzed and the contents and methods of bridge structure dynamic monitoring were introduced. The general layout and the monitoring points alignments of the bridge structure dynamic monitoring system were researched. A real-time dynamic monitoring system based on GPS and georobot were developed, which was able to operating continuously and automatically. The key problems of the monitoring system such as its hardware design and integration, the software design and development, the data transmission and processing and its data management and storage methods were researched in detail.(3) Two monitoring modes of the georobot based dynamic monitoring system, which are called fixed-point tracking and the specified period scanning respectively, were put forward. Their monitoring schemes for the towers and the cantilever beams under construction were researched. Then the characteristics and the applicabilities were analyzed.(4) Considering the consecutive operation of the monitoring system, adaptive and robust data filtering methods were of great importance. Empirical Mode Decomposition (EMD) based data filtering methods were researched for its being considered an ideal method in many research domains for non-stationary and non-linear data analysis characteristics.(5) Vondrak filter was researched thoroughly for the time series acquired by the monitoring system. Aiming at the shortcoming of its artificial selection of the smoothing factor, a methods based on Helmert variance component estimation was developed, which could estimate an optimal smoothing factor for the input time series. A punishment function was introduced for the realization of robust Vondrak filter, which was able to restrain gross errors automatically during a filtering process.(6) Kalman filter was researched for the time series position data acquired by the monitoring system in real-time and an adaptive memory attenuated filter algorithm was utilized for the divergence restraining of it. In order to eliminate the outliers mixed in the monitoring data series, an iteration algorithm of the weight function based on the robust estimation theory was utilized, which benefited the real-time data processing of the automatic dynamic monitoring system.(7) Online modal parameter identification for bridge safety estimation based on the time series of the monitoring system were researched. As time domain modal parameter identification methods was sensitive to the noise mixed in the time series, the EMD based filter was utilized to preprocess the data for its powerful ability for discrimination of the modal and noise hiding in the data. Considering the shortcomings of the Random Decrement Technique (RDT) for acquiring free decay response signal, some key parameter settings were thoroughly researched and the EMD based filter was employed to improve it and the results showed improved. With all of the key problem researched thoroughly, a method that synthetically utilized the EMD, modified RDT and the Ibrahim time domain method for modal parameter identification was put forward for the first time. Program codes of the above algorithm were developed and integrated into the software module of the structure dynamic monitoring system.(8) Relying on the construction progress of Sutong Bridge, which is the largest cable-stayed bridge on the earth, this article analyzed the structure behavior characteristics of the towers and cantilever beams utilizing the structure dynamic monitoring system. The author also researched the structure dynamics of the bridge under all kinds of disadvantageous loads such as extreme construction conditions, thermal loading effects and strong winds, which provided scientific evidences for the safety assessment and the construction of the main-span closure for Sutong Bridge.