40th IABSE Symposium, 19-21 September 2018, Nantes, France.
Tomorrow’s Megastructures

Bridge Displacement Monitoring using Acceleration Measurement
and Development of Efficient Bridge Management System
Yutaro Umekawa, Hisatada Suganuma
TTES, Inc., Tokyo, Japan
Contact: umekawa@ttes.co.jp, suganuma@ttes.co.jp

Abstract
In this study, the concept of an efficient bridge management system focused on monitoring bridge
displacements, was proposed for maintaining numerous bridges of municipal government in Japan.
In order to monitor displacement easily, a displacement estimation method using measured
acceleration data was proposed. The applicability of the proposed method, then, was verified
through the field measurement using the prepared and weighed loading truck. The management
system was proposed, and its application scenario using the developed system and measurement
device, was also introduced for further actual operations in municipal government districts.
Keywords: acceleration measurement, displacement estimation, structural health monitoring,bridge management system

1

Introduction

Numerous civil infrastructures, which wereconstructed during the rapid economic growth ofJapan, have been aged over time ahead of theworld, and so much attention has been paid to themaintenance of infrastructures. There are over
700 thousand bridges in Japan and almost 70% of
the total bridges is managed by the municipal
government districts.
In addition, Japan’s population has gradually
shrunk to the date and the government finances
are severely constrained because of falling tax
revenues. Therefore, municipal governments arefacing lack of financial and human resources, aswell as technical knowledge on structures. Hence,
it is essential to manage as many bridges as
possible with the least cost and effort.
It is important to measure bridge displacement
since it can be used to ensure the applicable limitof bridges. Moreover, displacement is directly

related to the stiffness of bridges, and therefore
bridge displacement can be used to understandthe tendency of how existing bridges deteriorate
by monitoring changes of bridge displacements
induced by the known weight of the loading truck[1]. Also, displacement would be an index which iseasy to understand for administrators without
knowledge on structural engineering.
In this study, by considering the implementation
cost
andapplicabilityofdisplacement
measurement in field measurements, anacceleration based displacement monitoring
system was proposed. By the proposed method,
displacement can be estimated from one
acceleration sensor. It enables measurement of
the bridge displacements which can be easily
compared to the measurement by contact
displacement sensor. The field measurement of
the loading tests using the prepared loading truck
was conducted for the target bridge to measuredisplacements and accelerations. From the results
of
the
field
measurement,
estimated40th IABSE Symposium, 19-21 September 2018, Nantes, France.
Tomorrow’s Megastructures

displacements were compared to directly
measured displacements using a contact
displacement sensor. The accuracy of the
proposed method was verified and theapplicability of the proposed system for efficientmanagement of bridges.

displacement measurement for bridges requires
scaffoldings
toimplement
contact-type
displacement sensors. Even though there arereference free measurement systems such as a
GPS-based system and a vision-based system,
these systems are still costly and are difficult to
install [2], [3].

Finally, the bridge management system wasdeveloped in order to use this method efficiently.
The system can store the information, such asmeasured data to the registered bridges, by using
GPS location data. Moreover, the prototype
device was developed to easily measureacceleration of bridges to encourage efficient
applications.

2
2.1

Therefore, as a cost-effective and convenientmethod, displacement measurements using
acceleration data have been encouraged andproposed in the recent researches from its
easiness to implementation and cost-effectiveness.

2.2

Proposal of bridge displacement
estimation method

However, it is also difficult to estimate
displacement from acceleration. Inevitable noise
included in measured acceleration data causes alarge estimation error during integration
processes. To overcome this difficulty ofintegrating measured accelerations, Park et. al. [4]proposed an initial velocity estimation method.
Additionally, Umekawa et. al. [5] have proposed
an integration method using a wavelet
transformation. A similar approach was also taken
by Sekiya et. al. [6], proposing the method named“free vibration method” using multiple
acceleration sensor.

Displacement measurement of bridge
structures

As the aforementioned background, bridge displacement is of great importance for monitoringbridge behaviours and for assessing theirstructural performance. The relationship between
the maximum bridge displacement and theloading onto the girder is as shown below:
𝛿𝑃 =

𝑃𝐿3
48𝐸𝐼

(1)

These studies have demonstrated the possibilityof estimating bridge displacements accuracy.
However, these methods do not estimate
displacements from measured accelerations
automatically.

where, the length of the bridge girder span 𝐿 , themodulus 𝐸 and the moment of inertia 𝐼. If theratio of 𝛿𝑃 to 𝑃 is the measured loading of the
prepared truck.
Therefore, the relationship between displacement
and the flexural rigidity 𝐸𝐼 is inversely
proportional as follows:𝛿𝑛𝑜𝑟𝑚𝑎𝑙𝑖𝑧𝑒𝑑 =𝛿𝑃 −1 𝐿3∝
P
48𝐸𝐼

Difficulties in bridge displacement
estimation from acceleration
measurement

Taking into account the aforementioned
integration problems and studies, this paper
presents an integration method using only one
accelerometer to estimate bridge displacement
which enables automatic displacement estimation.

(2)

2.3

Thus, the monitoring of the structural
deteriorations by monitoring the change of the
maximum displacement with regards to the
known weight of the prepared truck was madepossible.

Proposed bridge displacement
estimation method

The target displacement is a pseud static
displacement induced when only one vehicle
passes as shown in Figure 1. The bridge
displacement regarding the known weight shouldbe evaluated to monitor changes of the response

However, it is costly and not realistic to measurebridge displacements in field measurements since2

40th IABSE Symposium, 19-21 September 2018, Nantes, France.
Tomorrow’s Megastructures

A displacement is induced when the vehicle
passes onto a bridge girder and a pseudo-static
displacement which is a half-length wave andmainly lower frequency based on the passing time,causing gravity direction. This displacement can betheoretically obtained by double integration ofacceleration data.
However, measured acceleration data inherently
include sensor noise. Such sensor noise causes a
significant integration error in the process of
integrations. Therefore, the estimation error
should be removed for accurate estimation of thedisplacement.
The outline of the proposed method is as shown in
Figure 2. Firstly, measured acceleration istheoretically integrated twice to obtain
displacement (Figure 2a).

the exit of a passing vehicle is statisticallydetected in time domain from the displacement,
as the induced displacement can be considered asa local change and is distinguished from theestimation error (Figure 2b).
The estimation error can be estimated by using
the integrated result of polynomial spline
estimation (Figure 2c). Finally, the theoreticaldisplacement can be estimated by removing theestimated integration error in the time domain(Figure 2d). This applicability and accuracy of thismethod was verified by the field measurement
using the loading trucks.

Acceleration[cm/sec2]

as aforementioned equation (2). In addition,
bridges managed by the municipal districts havesmall amount of traffic, and for these reasons, theproposed method focuses on estimating thebridge displacement induced when one loading
vehicle passes through the bridge.

40
20
0
-20

-40

Hence, in this proposed method, the entrance andExit

2

Accelerometer

20

0.5

10

0

0

-0.5

-10

-1

-20
Acceleration

-1.5
-2
0

Displacement2468
10 12 14 16- pseudo-static displacement(induced displacement by passing vehicles)- dynamic displacement(bridge modes and interaction of vehicles)

1

0
-1

Exit

1

-30
-40
18

Figure 1. Outline of bridge displacement
estimation from measured acceleration

displacement
includingintegration error(c) Estimate base line
for removing
integration error

Time[sec](d) Remove the estimated base line
related to integration error

1
Displacement[mm]Entrance(b) Detect the start and the end pointof the pseudo static response

084

084

084

Time[sec](a) Integrate acceleration to displacement

Displacement[mm]Entrancemeasured acceleration

estimated displacement

0
-1
-2

Time[sec]

Figure 2. Outline of the proposed method

40th IABSE Symposium, 19-21 September 2018, Nantes, France.
Tomorrow’s Megastructures

3

Field measurement and loading
test

plate to be measured by a contact displacement
sensor that is attached and extended to theground.

3.1

Target Bridge and field measurement

The contact displacement sensor was also
installed as a reference data to verify estimation
results using acceleration data by comparing these
data. These sensors were connected to the samedata logger with a sampling frequency of 100 [Hz].

The target bridge is a steel girder bridge as shownin Figure 3. The span length is 24 [m] and theeffective width is 4.9 [m]. The target bridge wasselected as local bridges have commonly short or
medium length span (~30m), and are located in
low-traffic area.

Loading test was conducted using a 2 axles Truckand a passenger car, which were prepared for
inducing enough large displacement. The total
weights of these vehicles are 6.2 [ton] and 1.5[ton]. The passing speed of the loading truck was
set to over 20 [km/h] considering the span of thebridge to accelerate.

The MEMS acceleration sensor was attached tothe installation point, lower flange of the girderwith a magnetic base plate. The carbon rod
connected with a universal joint, was attached at
the same location. The top of this rod has theSide View

Cross Sectional View
24[m]
12[m]

4.9[m]
3[m]MEMS acceleration sensor
Contact displacement sensor(a). MEMS Acceleration Sensor（For Displacement Estimation）(b). Contact displacement sensor（Reference）

Installation
point

Target bridge and Installation
location.

Loading truck(a) MEMS sensor and theuniversal joint clamp
connected with a carbon
rod.

(b) Contact displacement
sensor using a carbon rod
connected with a universal
joint clamp

Passenger car

Figure 3. Target bridge and the detail of measurement equipment (steel girder bridge)
4

40th IABSE Symposium, 19-21 September 2018, Nantes, France.
Tomorrow’s Megastructures

In the case of the loading truck, the maximum
displacement was 1.64 [mm]. The frequency ofthis induced pseudo-static dis-placement was
roughly 0.05 [Hz] (passed time = 9 [sec]). In thisfrequency band, it is difficult to obtain theaccurate integration results since the larger
integration error occurs when the frequency ofnoise is lower than 1 [Hz]. In other cases of apassenger car, the maximum displacement wasaround 0.3 [mm]. This result showed the highaccuracy even for small displacement. It is difficultfor other displacement sensors to measureaccurately this order of small displacement, andtherefore these results demonstrated the highapplicability
forestimating
even
small
displacements.
The estimation errors were calculated by threetimes of standard deviation (3σ) of the difference
between measured and estimated displacementsin each case. It showed that the displacements
could be estimated from a measured acceleration
data with high accuracy as described in Table 1.
Although there are still a few errors between thetwo data, the difference was caused bydifferences between sensor specifications of theapplicable frequency bandwidth. Thus, thisaccuracy can be considered sufficient formeasuring bridge displacements instead of using acontact displacement sensor.
Hence, from the conducted loading tests, theapplicability and the accuracy of this proposed
method was verified by comparing to measuredisplacements as referential data. This developed
method was implemented in the proposed bridge
management system to apply this method easily.

Truck

0.5

10

0

0

-0.5

-10

-1

-20
Measured
Estimated -30
Acceleration -40

-1.5
-2
0

2

4

6

Acceleration[cm/sec2]

20
Passing time : 9[sec]8 10 12 14 16 18
Time[sec]

Passenger car
0.2

5
Passing time : 4[sec]

0.1
0

0

-0.1
-0.2

-5

-0.3

-0.4

Measured-0.5

Estimated
Acceleration

-0.6
0

2

4

6
8
Time[sec]

10-10

Acceleration[cm/sec2]

The displacement induced by the loading truck
was measured by a contact displacement sensor,
and estimated from measured acceleration databy the proposed method. The verification results
were as shown in Figure 4. These results showhighcorrelation
betweenthebridgedisplacements derived from the measured andtheoretical acceleration data by using the
proposed method.

1

Displacement[mm]Verification of estimated displacement
by using the proposed method

Displacement[mm]

3.2

-15
12

Figure 4. The results of bridge displacement
estimation.

Table 1. The evaluation of estimated results
and its accuracy
Total
Measured Estimated 3σ
Case Type Weight[mm][mm] [mm]
[ton]
1

1.60

1.64

0.20

2

1.68

1.62

0.24

1.64

1.74

0.25

4

1.76

1.75

0.30

5

1.52

1.52

0.29

6

1.80

1.90

0.22

7

0.33

0.36

0.07

0.29

0.32

0.08

0.32

0.36

0.07

3
Truck

8
9

Car

6.2

1.5

40th IABSE Symposium, 19-21 September 2018, Nantes, France.
Tomorrow’s Megastructures

3.3

displacement at both side, should be measured
and the passing position of the loading truck isalso needed to monitor the effect on rotation of
the girder.

Effect on bridge displacement ofpassing position

The accuracy and applicability of the proposed
method was verified as aforementioned. However,
the maximum displacement had some variations
even though the same truck passed through thebridge. This variation was caused by the passing
position of the loading truck, and this effect was
confirmed in the other target bridge.

Cross Sectional View
MEMS
sensorpedestrian0

Max displacement[mm]

The other field measurement was conducted andthe target bridge was a two-span problem bridgewith tow-lane road and a sidewalk as shown in
Figure 5. Each span length is 28.9 [m] and two
MEMS sensors were install to each side of thewheel guard at the mid span. The loading truck
was a 3 axle dump truck and 20[ton].

Lane1

The loading truck passed through lane 1 and lane
2 several times, and the bridge displacement at
the sensors attached, were estimated using the
proposed method. The results show that the
maximum bridge displacement on both sides wasaffected by the passing position of the loading
truck as shown in Figure 6.

-1

Lane1

-2

Lane 2-3

Max displacement
[mm]

MEMS
sensor

The maximum bridge displacement when theloading truck passed on lane 2 was bigger thanwhen the loading truck passed on lane 1. These
results demonstrated that the rotation of thegirder to transverse direction strongly happened
because of the loading position.

Lane 2pedestrian

0

-1

Lane1

-2

Lane 2-3

Figure 6. Effect on bridge displacements ofpassing positions of the loading truck

Therefore, it could be confirmed that the bridge

Data logger

Plan view
29 [m]〃

29 [m]

〃

〃

〃

MEMS
sensora) Measurement equipment

Lane 2 →← Lane 1
Sidewalk

MEMS sensor

loading truck : 20[t]b) Loading test and prepared truck

Figure 5. Target bridge and the detail of measurement equipment (2-span prebeam bridge)
6

40th IABSE Symposium, 19-21 September 2018, Nantes, France.
Tomorrow’s Megastructures

4

Application of the proposed bridge
management system

4.1

Preparation for bridge displacement
measurement

The proposed bridge management system
requires only one acceleration sensor, and it waspossible to provide the information on bridge
natural frequencies of bridges and displacements
induced by passing vehicles.
As acceleration can be installed on the girderusing the base plate anchored to wheel guard ofbridges as shown in Figure 7a, and this plate
enables measurement of the acceleration from on
the bridge.

4.2

Operation scheme of the proposedsystemThe actual application scheme of this proposedsystem is as shown in Figure 6. The brief outline of
the actual operations of this proposed system is asfollows:
1)
The base plate is attached to the center ofwheel guards of bridges to enable acceleration
measurement from over bridges. Then, an
acceleration sensor is attached to the base plate,
before the field measurements using the preparedtruck are conducted.

measured at each bridge. The total weight of theloading truck should be measured beforehand.
Then, the measured data is uploaded and stored
to Could server through IoT communication withGPS location information. The simultaneously
uploaded measured data are analyzed by Cloudcomputing engine including the proposed analysis
algorithm.
This system can be considered capable ofsupporting the problems such as cost, humanresource, and technical shortage in municipal
government districts. In addition, the proposed
bridge management system was developed as the
WEB application [7] as shown in Figure 5b.

4.3

Development of the prototype device

In order to increase the applicability of this system
for the municipal government districts, it was
important to develop the measurement system touse easily. The prototype device was developed asshown in Figure 6. This device includes MEMS
accelerometer, a GPS module and an IoT module.
The sensor can be connected to the internet. The
measured data can be uploaded, and results canbe stored to the WEB application system. These
procedures can be operated simply by pressing aswitch or button. This system and device enables
measurement of the bridge displacement andvibration with low cost and effort, making it
possible to measure tens of bridges in a day.

2)
The prepared loading vehicle passes
through bridges, and acceleration data are
Application Scheme① Installation of Base Plate

Data Standardization② Loading Test / Measurement / Data Transmission

M2M Communication（3G/LTE)

Cloud / Data Store

Loading Test
Data logging with GPS dataa) Installed the base plate
and the attached sensor

Secure Network
Big Datab) The stored displacement
data with GPS information

Figure 7. The application scheme of the proposed bridge management system

40th IABSE Symposium, 19-21 September 2018, Nantes, France.
Tomorrow’s Megastructures

5

Conclusion

The purpose of this study was to propose a bridge
displacement estimation method by using one
acceleration data to develop a convenient
displacement measurement method.

With regards to infrastructure, the same situationas Japan would happen in the world sooner orlater. Hence, this proposed system can beconsidered effective to maintain large number ofbridges not only in Japan but also in the world.

6

References[1]

Yokoyama. H., Ishio. M., and Tamakoshi. T.,
2016., Experimental Study on determinationof the degree of deterioration of RC roaddeck slab using the impact load, Journal of
Structural Engineering, pp.1194-1201.

[2]

Nakamura, S. 2000 GPS Measurement ofWind-Induced Suspension Bridge Girder
Displacements, Journal of StructuralEngineering, pp.1413-1419.

[3]

Lee J-J., and Shinozuka M., 2006, A vision
based system for remote sensing of bridge
displacement, NDT & E International 39,
pp.425-431.

[4]

2)
The accuracy of the proposed methodwasverifiedbycomparing
estimateddisplacements to measured displacements.

Park K-T., Kim S-H., Park H-S., and Lee K-W.,
2005, The determination of bridge
displacement using measured acceleration,
Engineering Structures 27, pp. 371–378.

[5]

3)
The concept of the efficient bridge
management system was introduced. Then, theactual operating procedures have also been
introduced. In addition, the bridge management
system and the measurement device weredeveloped to encourage efficient applications.

Umekawa. Y., Sasaki. E., 2015, Evaluation of
Vehicular Induced Displacement by Using
Wavelet Transformation from WirelessAcceleration
Measurement,
IABSE
Symposium Report, IABSE Workshop
Helsinki.

[6]

Sekiya, H.; Kinomoto, T.; Miki, C. 2016,“Techniquefor Determining Bridge
Displacement Response Using MEMS
Accelerometers”, Sensors, v16, 1882.

[7]

Infra Studio: http://infra-studio.com/

A bridge estimation method was proposed, andapplied for measured accelerations of the target
bridge. The results have then been verified bycomparing estimated displacements to measured
displacements using a contact displacement
sensor. In addition, to apply this proposed method
as a bridge management system, the actual
operation procedure was proposed and thisprocedure made it possible to measure morebridges in a day. In addition, the bridge monitoring
system which includes data storage and analysis
engine was developed. The results can besummarized as follows:1)
A bridge displacement estimation method
was proposed, and its applicability was verified
through field measurements using preparedloading trucks.

Micro Computer + IoT, GPS module
Battery

MEMS sensor

Figure 8. The prototype device for efficientmeasurement of acceleration data