r - The Hong Kong Polytechnic University

manner for statistical analysis, (iv) able to use contemporary commercially available sensors, (v) able to carry
out additional measurements by removable/portable sensors, and (vi) able to carry out cross-calibration of
different sensors at same (key) locations. The criteria for sensor selection should be based on: (i) operational
bandwidth, (ii) magnitude and frequency response within the operational bandwidth, (iii) accuracy and
resolution, (iv) type of input or excitation energy, (v) type of output energy, (vi) output signal type, (vii) physical
dimensions, weight and materials, (viii) further signal conditioning requirements, (ix) operating environment
conditions, (x) installation constricts, (xi) special contractual requirements on component being monitored, and
(xii) costs.
A total number of 1781 sensors (of which, 400 nos. of them has been used since the construction stage) in
fifteen types are deployed to monitor the structural performance of Stonecutters Bridge and its environment.
These 1781 sensors are classified into 15 types and they are: anemometers, barometers, rainfall gauges,
temperature sensors, hygrometers, corrosion cells, accelerometers, dynamic strain gauges, static strain gauges,
global positioning systems, tiltmeters, dynamic weigh-in-motion stations, video cameras, articulation sensors
and tensio-magnetic gauges. The layout of sensory systems in Stonecutters Bridge is shown in Figure 5. The
details and locations of sensors for monitoring are tabulated in Tables 1 to 4. The arrangement and/or
deployment of different types of sensors are made reference to their intrinsic characteristics of measurements
and requirements of data processing, analysis and /or derivation. Detailed discussions are given in Paragraph
3.3.2.
3.2.2 Portable Data Acquisition System (PDAS)
The portable data acquisition system is composed of two portable PC-based data logging systems. The first (or
PDAS-1) is used for the collection, processing and analysis of time-series acceleration and dynamic strain data
received from the portable servo-type accelerometers (a total of 48 nos.) installed on stay cables during vibration
measurements and the dynamic strain gauges (a total of 400 nos. – which had been used for construction
monitoring during the bridge construction stage and are deployed for re-usage in the bridge operation stage)
installed at ten locations inside five steel deck segments at main span. The PDAS-1, which is a 24-bit data
logging system with 48 nos. of simultaneous sampling data channels (at 200 kHz per data channel), is equipped
with Dewetron products, i.e. Dewe-5000 Industrial PC as the PCI-Controller plus Dewesoft 6 Professional
Edition as the application software for data triggering and management, ORION-1624-S1 as the
analogue-to-digital converter for data storage and transmission, DAQP-LV-S1 as the signal conditioner for
acceleration data filtering and amplification, DAQP-Bridge-A-S1 as the signal conditioner for dynamic strain
data filtering and amplification, and associated facilities such strain gauge adapter, rack, power cables, signal
cables, batteries and battery charger. Dewetron products are selected because they had comparative better
performance than other products (in terms of 24-bit simultaneous data acquisition capability and more compact
in design – 16 nos. of simultaneous sampling data channels per card-device) during the system installation
design stage (~2005/2006).
The second (or PDAS-2) is used for the collection and analysis of corrosion data received from corrosion cells
(a total of 33 nos.) installed in concrete tower-bases, pier-base, and concrete cross-girder in side-span. It is
composed of two identical portable corrosion monitoring data loggers, and each logger is equipped with Camur
II System for the measurement of open circuit potential, macrocell current, concrete resistivity, concrete
temperature and concrete relative humidity and Gamry G300 with DC105 Corrosion Techniques Software for
linear polarization resistance measurement.
3.2.3 Data Acquisition System (DAS)
The data acquisition system is composed of eight types, namely, (i) DAS for Static and Dynamic Signals, (ii)
DAS for DWIMS (dynamic weigh-motion stations) Signals, (iii) DAS for GPS Signals, (iv) DAS for Fiber
Optic Signals, (v) DAS for Vibrating-Wire Strain Gauges, (vi) DAS for Tensio Magnetic Gauges, (vii) DAS for
corrosion signals, and (viii) DAS for Video Signals (or the video signal converters). Installation design is
required for the first type only. As the remaining types of DAS are proprietary DAS and are supplied directly
from the sensor-suppliers, the installation design is therefore not required, and only the DAS for Static and
Dynamic Signals is described here.
The first DAS is composed of 8 nos. data acquisition units. Of which, 4 nos. are installed at upper level of the
cross girders in main span and the remaining 4 nos. are installed inside the tower-shafts). Due to the same
reasons as mentioned in the paragraph for PDAS-1, Dewetron products are also applied to the four major types
of hardware devices in all data acquisition units. They are : (i) PCI-Controller – Dewe-808 Industrial PC, (ii)
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