China Zhongtie Major Bridge Engineering Group, Shanghai # 2 Engineering Co., Shanghai Urban Construction Group. Officially opened in December, 2005
The Donghai Bridge, China’s first sea-crossing bridge, opened in 2005 and cost $1.2 billion to complete. The six-lane bridge provides China with direct access to Yangshan Island from Shanghai, and proves to be a unique structure for monitoring with a full length of 32.5 km and an S shape to provide a safer driving route in typhoons and high waves known to affect the region.
They implemented a structural health monitoring (SHM) system to provide quantitative data for assessing the extent of damages and deterioration, evaluating structural performance, responding to unexpected catastrophic events, and researching bridge design and construction technologies. JUST ONE Technology based in Shanghai was selected to implement the SHM system using an NI PXI-based data acquisition (DAQ) system and NI LabVIEW software.
They used the NI PXI-based DAQ system because of its ruggedness and compact size that allows it to reside in protected areas of the bridge. As a result, it has successfully battled the humidity, dust, shock, and chemical erosion the bridge has experienced since installing the system. Using LabVIEW, engineers can perform vital, real-time analysis as well as offline processing of the signals produced due to the wealth of sensors distributed along the bridge.
Hardware System Setup
Monitoring the Donghai Bridge requires using more than 500 accelerometers spread across each segment of the bridge to acquire the frequency response from environmental stimuli. Also, the bridge is equipped with wind meters and load cells to record environmental conditions associated with the frequency response. Each segment of the bridge contains a data acquisition station where data is collected by NI PXI-4472B dynamic signal acquisition (DSA) devices from surrounding accelerometers.
Additionally, we used the NI PXI-6652 synchronization module, NI PXI-6602 counter module, and NI PXI-8187 chassis controller to address the challenge of synchronizing data acquisition.
In the Donghai Bridge setup, we connected a GPS unit to each PXI chassis using pulse per second (PPS) and IRIG-B timing signals for signal synchronization and timestamping, respectively. The PPS signal transmits 10 million pulses per second to provide the base clock for sampling on each chassis. This allows the acquisition modules to achieve a resolution down to 100 ns for accurate and synchronized sampling across all of the channels on the bridge.
Software System Setup
After acquiring raw data using the Donghai Bridge system, we have to analyze and process it to provide information to the user. We conduct offline processing by transmitting the data back to a central monitoring center where we can perform processor-intensive operations while online processing is carried out directly on the PXI controller.
Offline Analysis
The main components of offline processing for the Donghai Bridge are multichannel signal spectrum analysis and modal analysis. We perform both of these calculations at an off-site location where more powerful computers running LabVIEW, the LabVIEW Advanced Signal Processing Toolkit, and the LabVIEW
System Identification Toolkit process the data.
Because the typical method of performing modal analysis-applying forces to a structure and measuring the response is not viable for a large, distributed structure like the Donghai Bridge, we performed operational modal analysis instead. With this method, the natural forces from the environment and the work load applied to the structure serve as the stimuli. The signals measured by the bridge sensors serve as the response signals. Then, modal parameters are calculated using the stochastic subspace identification (SSI) algorithm, which is the method used to employ the output-only system identification technique, implemented in the LabVIEW Advanced Signal Processing Toolkit.
Online Analysis
To monitor the bridge’s immediate structural health status, the Donghai Bridge system calculates resonance frequencies in real time as accelerometer data is collected. Because we process data in real time and in parallel with data acquisition, the resonance frequency calculations must be efficient and quick. The SSI algorithm is an ideal method for performing these calculations but requires too many calculations to be conducted in real time. To overcome this, we implement the SSI algorithm in a recursive fashion called recursive stochastic subspace identification (RSSI). As data is collected, the values are entered into the algorithm and a new set of resonance frequencies is calculated. After an initialization period, the RSSI algorithm can run quickly enough to provide real-time frequency values.
Conclusion
The Donghai Bridge data acquisition and processing system built with NI PXI components provides a complete solution for monitoring one of the largest bridges in the world. LabVIEW, in conjunction with the LabVIEW Advanced Signal Processing and LabVIEW System Identification toolkits, allowed two engineers with no previous LabVIEW experience to develop the entire Donghai Bridge monitoring system in just three months. Due to this system’s ease of use and NI world-class support, the entire bridge is monitored by three engineers, keeping maintenance costs at a minimum.
With accurate GPS synchronization and timestamping, NI PXI dynamic signal acquisition hardware, and LabVIEW, their team successfully created a rugged, modular, reliable, low-maintenance, and accurate monitoring system for the Donghai Bridge..
veri best
ReplyDelete