| In the recent years, as the rapid development of national economy, the bridge construct project has realized leapfrogging development and lots of long-span bridges are built in our nation. However, the long-span bridges in service may be subject to environmental erosion and material aging and inevitably suffer from damage accumulation and load capacity descending. A structural health monitoring (SHM) system provides an efficient tool to detecting the evolution of damage and estimating performance deterioration of bridges. Shenyang Boguan Bridge is the first half-through6-span X skew arch bridge in China. To ensure the safety during its construction and service, a complete set of structural health monitoring system is designed and installed on it. Taking the Boguan Bridge as the background in this paper, the structural health monitoring of long span bridges were researched. The main contents are listed as follows:(1) Considering its novel appearance, the monitoring requirements of the bridge are put forward based on its structure features. Then the finite element software MIDAS/Civil is used to establish a refined spatial model of this bridge and the structure characteristics of the bridge are well simulated using various elements and boundary constraints. Through the static and dynamic analysis, the key or weak parts of the bridge could be mastered which lays a foundation for the rational choice and layout of sensors, as well as provides references for determining the threshold value of monitoring parameters.(2) After analyzing the functional requirements of health monitoring system, the general architecture of the system is designed, including the sensor subsystem, data acquisition and transmission subsystem, data management subsystem and condition assessment subsystem. Based on numerical simulation results, the main monitoring items of the project are determined. According to the schemes of sensor selection, the sensors of this system are determined on the basis of the comparison of the various types of sensors, laying a solid foundation for the realization of the health monitoring system.(3) On the basis of the structural characteristics and the numerical simulation results, the monitoring schemes as well as the sensor subsystem such as the placement of measuring points, protection, and realization of sensors are introduced in detail. To satisfy the high-standard requirement of the quantity, distribution, measuring accuracy and synchronism, a set of distributed data synchronous acquisition instrument for structural health monitoring is self-developed based on NI CompactRIO, which realizes the accurate synchronous acquisition between multi-type sensors and multi-terminal instruments. Considering that the data types are various, in order to guarantee the operation efficiency of the system, SQL Server2000is used as a central database, realizing the effective management and storage of data. Finally, based on the LabVIEW software platform, the monitoring system are developed and integrated, which realizes the functions of multi-type date acquisition synchronously, data storing automatically, generating reports automatically and auto-alarming, etc.(4) The preliminary stress monitor of steel-concrete connection position in construction and service has been carried out using FBG sensors. The monitoring results show that the stress amplitude under construction process is larger than that in service. Since temperature effect has a greater influence on the monitoring results, so temperature compensation must be conducted to eliminate the influence of the temperature. |
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