IFMASS10

245

–

The time lag to apply the wind load displacement of bridge should be < 10~15s.

–

The accuracy of displacement should be 1~2 cm.

–

The data are processed in the central control room.

–

Data should be transmitted in wireless way.

–

The data needed include: 1. displacement real-time record; 2. time-displacement curve

(t-x, t-y, t-z); 3. 2-D deformation figure; 4 rotation of the tower; 5 dynamic vibration

simulation animation; 6 frequency spectrum analysis.

The components of here applied GPS automatic monitoring systems are:

–

GPS monitoring station.

–

Hardware: NOVATEL RT-12, 12-channel GPS receiver, which can process double

frequency kinematic monitoring. The difference accuracy is 1~2 cm, the data output

frequency is 4 Hz, and the antenna can avoid multi-path effects.

–

Monitoring software: developed by Tsinghua University can accomplish the parameter

setup of GPS real-time carrier phase difference; datum station difference signal transmit

monitoring and satellite situation monitoring.

–

Data transmitting system: wireless multi-to-one communication method is adopted. The

difference signal sent from the datum station is 279 bits; the sampling frequency of

flowing station is 0.25 Hz. The signal sent back is 35 bits per group.

–

Software system includes four softwares: for database management, for bridge displace-

ment real-time monitoring, for bridge safety analysis and for general control.

–

The time-displacement curves are plotted each day. It was found a linear regression

between displacement and temperature.

Figure 6: GPS displacement monitoring system in real time /8/

As concluded, GPS is an effective method for the safety monitoring of large span

bridges and has advantages as real-time, distinctness, and no influence to the traffic. Cost

of GPS and total station is compared in Table 1. GPS is proven that can work under any

weather condition including fog, rain and typhoon.

Table 1: Comparison of cost between GPS and former total station method in yuans, CNY, /8/

Item cost (x10

CNY)

GPS method

Total station method

Equipment

220

Labor

Traffic stop

400 (8 nights)

Total cost

222

431

CNY (1 chinese yuan) = $US 0.146156 on 2008.12.12