LONG TERM STRUCTURAL HEALTH MONITORING SYSTEM FOR CABLE STAYED BRIDGE IN VIETNAM
Dr. Luong Minh Chinh
Trafic work Major, Construction Faculty, Water Resources University.
175 Tay son, Đong Đa, Ha Noi. Tel: 0948060950. Email: chinhlm@wru.edu.vn
Abstract
Structural Health Monitoring System (SHMS) has been applied and developed in recent years. Most of the major
bridges in the world, especially cable-stayed bridge, are installing the Structural Health Monitoring Systems to continuously
monitoring and collecting data (the physical quantity) during the operation and exploitation time. In U.S., Japan and Europe,
the Structural Health Monitoring System applied and developed very effectively. This article introduces an overview of
monitoring systems and devices of SHMS, also shows the necessity of a SHMS system for major bridge projects in Vietnam
such as the cable-stayed bridge, serving for the management, rehabilitation and maintenance of bridge works. Based on the
documents and research results, the article aim to provide directions for establishing and training qualified staffs and experts
in this field of structural health monitoring in Vietnam.
Keywords: Structural Health Monitoring System, SHMS, Long bridge, Cable-Stayed Bridge, Measurement, data collection
maintenance,
1. General
In the design of contruction works in general and bridge design in particular, the offering assumptions to simplify the
theoretical compute model shall lead to inediquate reflection of operation status and behaviour in normal operation condition
and during exploitation stage. Dispite of many compute methods or softwares which sharply developed in recent time, for
example, the application 3D calculation method (within non-linear surface feature), but received theoretical calculation result
only indicated approximately relative to actual behaviour of structure.
One of method brink to many potentials to evaluate operation and exploitation process of bridges is intallation
devices on several equipments or elements of bridge such as monitoring devices, displacement sensors, continuous
measurement sensors for physical values of structure: from deformation state to stress state in structure components [1].
The structural Health Monitoring System (SHMS) has been started to apply and develop in the world in recent
years. The majority of bridges in the world have been installed various monitoring systems to monitor and collect data
(physical figures) during operation and exploitation stage of bridge. The monitoring systems have been applied widely and
effectively in United State, Japan and Euro. In Vietnam, Can Tho is one of the long span bridges installed BRIMOS
monitoring system provided by NTT Data company (Japan) [10].
2.
Bridge monitoring system
A long span bridge usually have complex structure, long span, result to a significant impact of temperature change,
especially for Vietnam’s temperature condition with its temperature may reach 40oC at several regions in the summer,
besides, wind effect (especially for Cable-Stayed bridge, Suspension bridge with high tower) is also significant so that the
setting up a general monitoring system as well as the collection of data, physical figures shall very necessary. To satisfy
above, the general monitoring system shall be consisted of features as bellow:
Monitoring system of structure condition(stress, displacement)
Monitoring system of aerograph (temperature, humidity, wind direction and wind speed…)
Monitoring system of picture (traffic monitoring camera, bridge operation)
Monitoring system of displacement and deformation.
Monitoring the structure status
Data transmission (to all computer)
Via GPRS, Internet or LAN
-F
- Cable tension sensor
- Tt
- Angular deformation sensor
-S
- Structural deformation sensor
-A
- Acceleration sensor
-CGD - Data collection and transmission server
- RD - Rainfall sensor
- TH
- An
- VS
- RS
- MS
- VP
- VA
- EN
Meteorological monitoring
- Temperature sensor
- Wind speed and direction sensor
- Sight distance sensor
- Road sensor
- Meteorological station
- Monitoring Camera
- Video-recording device
- Power supply
Image monitoring
Figure1. The structure of the monitoring system and associated equipments [3]
The collected data providing from monitoring equipment and sensors to be recorded by server installed on bridge, then
transfer to Internet or GSM (GPRS) storage center. The structure of the monitoring system shall be set up as Figure 1.
2.1. Monitoring system of structural status
Figure 2. Installed position diagram of sensors and monitoring devices on
Cable Stayed bridge.
For monitoring system of bridge,
the structural status monitoring system
is most important and complicate. The
change in physical figure relating to
operation status and behaviors of
structure under effect both of dead load
and live load on basis of recalculation at
some of measurement points by
measurement of sensors. The physical
figures in majority of bridges are: stress,
deformation,
displacement
and
acceleration, temperature change, wind
speed, humidity [7].
One of monitoring system SHMS
tasks are support to engineers and
experts who being monitored structural
status at execute time during the normal
operation and exploitation state of
structure and evaluate the extreme
states such as impact of whirlwind,
overload and oversize truck impact or
traffic accident occurred on bridge.
Therefore, the selection points (location) to install monitoring devices and selection of value needs to monitor and
measure at its position should be thoroughly calculated and analyzed as well as consideration of impact and effect to
structures due to many calculated models and combination of various loads [Figure2].
It is necessary to pay special attention to extreme conditions [6] and
effect of outside temperature and weather change. Therefore, all sensors and
devices especially for sensors installed inside the bridge must have durability
longer than 30 years. All equipments of sensor shall be kept in closed box and
have ability to transfer the signal via 5km optic fiber cable [Figure 3]. These
advantages make wire sensor were widely applied in long-term monitoring of
bridge [4].
The changing of wire’s strain in sensor lead to vary the vibration
frequency of wire and allow to measure and monitor a lot of physical values
which needed to evaluate the operation of structures in operation and
exploitation stage.
Hình 3. Wire sensor kept in Geocon
2
closed box.
ELECTROMAGNET
MONITORING
SIGNAL
THERMISTOR
VIBRATION SENSOR WIRE
MAGNETIC FIELD
Figure 4. Working structure of wire sensor [5].
Hình 5. Inclinometer installed on bridge.
Normally, 2 deformation sensors and 2 temperature sensors [8] will be
installed at every monitoring position. This duplication of sensors will assure
accuracy and reliability of monitoring results of the system.
In order to measure and monitor angular deformations of constructions,
inclinometers with high accuracy will be installed. They are able to measure
angular deformations at ±10 seconds 0,5mm/1000m [Figure 5].
In addition, these inclinometers can be installed at bridges, where
vibration sensors [Figure 6] are necessary to be installed at a range of
positions, in order to define effects of dynamic loads and natural vibration
frequency of structures, they , will also be used to carry out modal analysis
tests of structures
Recorded in a certain period of time, for example from every 10
seconds to every 60 minutes, acquired parameters and datum from
inclinometers will be sent to the server of the pylon-based host computer,
where they will be transformed into necessary datum for monitoring by software
[Figure 7], [8].. All computers and servers installed should meet serious
requirements on quality and durability for equipments operating in extremely
severe environment. Temperature inside pylon may reach 60 Celsius degree
and humidity may be very high in hot summer days; therefore temperature
sensors and humidity sensors should be adapted to computers and ventilation
fans should be installed to cool computers.
Recorded monitoring and measurement datum will be sent from this
structure-based server to a saving and monitoring center, where they will be
previewed, analysized and estimated by experts in real time in order to assure
accuracy and identify timely problems in operation and usage of the structure.
Current systems allow expert to create system accounts in order to access and
monitor datum as well as receiving technical analysis and report.
Figure 6: Vibration sensors after
installtion
Figure 7: A server of host computer is
installed inside the pylon.
The system also creates tables and charts for every recorded physical quantity at anytime in order to supply managers with
more general view on operation and usage process of the structure [2]. Maximum and minimum values will be set up for
every recorded physical quantity in order to predict exceeding status of calculated values.
Once monitored physical quantities exceed permitted limits, the system will warn management and maintenance unit via
emails on the internet or SMS on mobile networks [5].
2.2. Meteorological monitoring system
The function of the system is provide meteorological and weather data of structural area, notice temperature indicator of
deck slab, amount of rainfall to adjust speed and volume of traffic to ensure traffic safety on bridge. The main devices of
monitoring system includes thermometer, anemometer, rain gauge, road surface sensor, road’s temperature gauge, road’s
humidity gauge and meteorological station with data transmission and collection device via cable.
3
2.3. Image monitoring system (monitoring via image)
The function of the system is transferring recorded images of structure to center of operation and data reservation base
on camera monitoring system. The image monitoring allows coordinating the traffic more effectively and detecting the
violation as well as accident to timely draw the effective treatment. The image monitoring system consist of high resolution
performance of monitoring camera which allow to monitor both in night and day with all the weather conditions, monitoring
camera of water level, devices to collect and reserve monitoring image.
2.4. Deformation and displacement monitoring system (geomatic monitoring)
Figure 9. The GPS/GNSS monitoring system of Leica Geosystems was installed on
Can Tho bridge [10].
The most different of geomatic
monitoring and the other normal
monitoring is allowed to evaluate the
dynamic changing process of structure
and determine effect of phenomenon
simultaneously. Therefore, it controlled
whole structure with ability of analysis
and emulation when incident occurred.
These
were
many
different
geomatic monitoring systems in the
world, the application of the system is
also different and base on property as
well as various distinction of each
structure. One kind of this system is
GPS/GNSS [Figure 9], [9] of Leica
Geosystem. In order to operate
accurately and effectively, the system
shall be configured, then adjusted and
programmed accurately for each
measurement time. It shall be analyzed
and evaluated objectively and accurately
the received datum
Bảng 1. Table 1. List and function of sensor ussually used in cable sayed bridge
No.
Sensor
Position
Monitoring items
GPS



Pylon tops
Midpoint of main span girder
Basic point (reference)
Displacement types
Wind gauge


Pylon top
Midpoint of main span girder
Velocity/ wind direction
3
Udometer

Midpoint of main span girder
Precipitation
4
Cable accelerometer

Longest cable
Cable force
5
Cable force meter

Mobile equipment
Cable force
Deformeter


The edge of pylon base
Midpoint of main span girder
Pylon stress
Deck slab stress
7
Smart camera

Cross beam on pylon top
Bridge condition
8
Water level camera

Pylon edge
Water level
9
Seismometer

Pylon leg
Seismic impact
10
Joint gauge

Expansion joint
Expansion due to temperature
Thermometer





Pylon top
Midpoint of main span girder
Inside fake cable
Inside pylon
Midpoint of main span girder
Air temperature
Air temperature
Fake cable temperature
Temperature in pylon
Temperature in deck slab
Cable in anchorage pylon dynamometer

Cable in anchorage pylon
Cable in anchorage pylon force
1
2
6
11
12
4
13
14
15
1 axial accelerometer

Midpoint of main span girder
Deck slab vibration
2 axial accelerometer


Midpoint of main span deck slab
Top of pylons
Deck slab vibration
Pylon vibration
Multi-dimension shape sensor

Inside pylons
Pylon shape
3. Actual application of monitoring system
Monitoring system is designed for each bridge based on structure properties of each construction, required financial
situation of Client. Bridge monitoring system must have high durability; ensure high accuracy during exploitation time. The
cost of whole monitoring system is not big when compare with total cost of bridge construction, it’s about 0.3% - 1.5% total
investment value of bridge construction depends on the complexity of monitoring system [6]. Management and operation cost
for monitoring system is not big in compared with total cost of construction maintenance, but monitoring system requestvery
high requirements on human and experience of management experts.
The biggest advantage of bridge monitoring system is that it can continuously monitor activities and changing of
structure for safety and efficient in exploitation and operation. Based on data analyzing and evaluating, we can make correct
decision for bridge maintenance. Monitoring results allow us to evaluate the correction of assumptions which were shown in
design and construction procedure. The frequency of monitoring allows us to control the behavior of construction under
different load combination impact; helps experts determine aging procedure of structures to make solution for avoiding and
rising life exploitation of bridge construction.
4. Conclusion
Bridge monitoring system is a complex system combined of many elements from construction structure monitoring,
aerograph monitoring, image monitoring to geo-mathematics monitoring. To integrate above elements to a finish system,
ensure in supplying accurate data for management, operation and exploitation phase in effective way with low cost and rising
construction durability we need the cooperation of many experts in different sector, with deep and wide knowledge in
construction. Monitoring work play an important role in erection, construction and operation procedure; it allows verifying
assumptions which were shown in design phase and can be impact in implementation cost of construction. So that, the
development and application of modern methods, advanced techniques to monitor bridge construction for implementation,
study and manage, operate construction in safety and efficiency way is very necessary and imperative.
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