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lijunxue08

金虫 (小有名气)

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注册: 2013-05-11
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专业: 地理信息系统

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The GPS health monitoring system of Zhujiang Huangpu Bridge in China for the case study bridge is discussed in this section. This bridge is composed of a 705 m-long cable-stayed bridge and an 1108 m-long cable-suspended bridge. The width of deck and the height of towers for the Bridge are 34?5 and 195?476 m, respectively.There were 14 GPS units installed on the two bridges after August 15, 2009, including 13 rover stations and 1 base station as shown in Fig. 1.
The distance between base station and point (107) is 1.00 and 1.50 km from point (101) according to Fig. 1.The reference station refreshes the RTK correction
messages for the GPS monitoring stations with a frequency of 1 Hz via the optical fibre communication system. LEICA Geo-systems antennas and dualfrequency GPS receivers were used to observe the GPS satellite signals; the satellite elevation cut-off angle is 13u, at least nine satellites. The observations were split into single hour observations for the processing purposes. The data collected were mixed with that generated by the receivers’ own oscillators, and then LEICA Spider 2?1 RTK software was used to process RTK GPS data. The data collected are processed coordinates in World Geodetic System (WGS-84) and converted to the local coordinate system by the coordinate transformation, Ogundipe et al. [21] and Elsheimy [6] summarised the coordinate transformation
system which was used in this case of study. A local bridge coordinate system was established to be used in the analysis and the evaluation of the observation data.The X data represent the relative displacement changes along the longitudinal direction of the bridge; the Y data represent the relative displacement changes along the transverse direction of the bridge while the Z data represent the relative displacement changes along the altitude direction of the bridge [11]. The outputs from GPS monitoring stations include monitoring point number and RTK GPS three-dimensional coordinates,GPS time, satellite status data, GPS receiver status data,and so on, and the raw GPS outputs, if required as shown in Fig. 2. The resonant frequency of the bridge is considered a very important parameter in the bridge structural and safety analyses. The relative displacement changes of the bridge deck will be in millimetres.

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