Many research studies have been carried out based on the ambient vibration test on different types of bridge. In present study, an ambient excitation is used to find the fundamental frequency of vibration of a concrete box girder bridge. Dynamics characteristics of the bridge are identified through traffic induced vibration. The bridge vibration can be recorded for 24 hours using an accelerometer installed on the bridge. The acceleration time histories are recorded using data acquisition system (National Instruments) and recorded signal data were processed using modal analysis performed by using Stochastic Subspace Identification (Time Domain method). The vibration parameters such as modal frequencies, mode shapes and damping ratio were identified for tested bridge.

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 8, Issue 1, January 2017, pp. 504–511, Article ID: IJCIET_08_01_058
Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=1
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
EXPERIMENTAL STUDY ON CONCRETE BOX
GIRDER BRIDGE UNDER TRAFFIC INDUCED
VIBRATION
Sameer G. Patel
Research Scholar, Applied Mechanics Department,
S V National Institute of Technology, Surat, Gujarat, India
Gaurang R Vesmawala
Assistant Professor, Applied Mechanics Department,
S V National Institute of Technology, Surat, Gujarat, India
ABSTRACT
Many research studies have been carried out based on the ambient vibration test on different
types of bridge. In present study, an ambient excitation is used to find the fundamental frequency of
vibration of a concrete box girder bridge. Dynamics characteristics of the bridge are identified
through traffic induced vibration. The bridge vibration can be recorded for 24 hours using an
accelerometer installed on the bridge. The acceleration time histories are recorded using data
acquisition system (National Instruments) and recorded signal data were processed using modal
analysis performed by using Stochastic Subspace Identification (Time Domain method). The
vibration parameters such as modal frequencies, mode shapes and damping ratio were identified
for tested bridge.
Key words: Ambient vibration test, Traffic induced vibration, Modal analysis, Dynamic
characteristics and Natural frequency.
Cite this Article: Sameer G. Patel and Gaurang R Vesmawala, Experimental Study on Concrete
Box Girder Bridge Under Traffic Induced Vibration. International Journal of Civil Engineering
and Technology, 8(1), 2017, pp. 504–511.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=1
1. INTRODUCTION
Vibration parameters give important information for bridges, as extracted bridge frequency related to its
stiffness. The bridge’s fundamental frequency of fundamental mode, could be used to predict overall
structural integrity or its health condition [1-3]. Research studies shows that decrease in the frequency of
vibration indicates reduction of stiffness of the bridge due to environmental effect and long term distress
cause due to day by day increasing traffic load intensity, ground motion, settlement of bridge support or
any other damaging events. Therefore, it is necessary that the variation in frequencies of the bridge can be
monitored at regular interval of its service life span, so that remedial measures can be taken before its
normal functioning gets affected.

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Number of techniques has been developed for extracting the bridge frequencies using different
excitation sources, such as ambient vibrations [4-5], wind forces [6,7], normal traffic loads [1,3,8],
controlled traffic loads [9], forced vibrations [4,8], impact forces [10,11], among others [12]. In present
study ambient vibration test were perform as it doesn’t required to shutting down the regular traffic on the
bridge. To record the vibration data, accelerometers are mounted on the bridge at different locations of the
bridge. These sensors were connected with a data acquisition system having anti aliasing filters so that
white noise and higher frequencies can be eliminated to store the required time histories data. Results are
extracted and compared using modal analysis by Average Normalized Power Spectrum Density (frequency
domain method) and Stochastic Subspace Identification (Time Domain method).
2. DESCRIPTION OF TEST BRIDGE
The bridge selected is Chandlodiya Bridge completed in 2000. Chandlodiya Bridge is situated over
railways line of Western Railways near Chandlodiya Railway Station. It connects Gota and Akhbarnagar
area. Location of bridge is shownin Fig. 1.The bridge having combination of I - girder & Box girder type
of superstructure, which consists of total 19 spans of [12.70 m × 8( Box girder span)] + [11.0 m × 1 + 24.0
m ×1 + 11.0 m × 1 (I- girder span)] + 12.70 m × 8 [Box girder span].The bridge superstructures were
simple supported between two piers. However, the test span selected is straight and simply supported.
Therefore, seventh span of bridge was instrumented for performing ambient vibration test. The span of the
concrete box girder is 12.70 m. The cross section of the bridge has a total width of 8.275 m. Details of
bridge geometry were shown in Fig. 2.
Figure 1 Location of Chandlodiya bridge

3. Sameer G. Patel and Gaurang R Vesmawala
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Figure 2 Geometry of tested bridge span
3. TEST INSTRUMENTATION
Uniaxial accelerometers were used to measures of vibration signals. For experimental study,
accelerometers having a sensitivity 100mV/g and measurement range ±50g. For attachment of
accelerometers to object mounting pads are used which are fixed with the bee wax or adhesives. These
sensors are connected with data acquisition system consist of NI cDAQ 9174 and acceleration measuring
Modules NI 9234 (National Instruments, USA) through LabVIEW software. NI cDAQ 9174 can connect
to a host computer over USB. LabVIEW program were used to acquire acceleration data. These data are
recorded in hard drive in form of .lvm file format and other file format. For processing the recorded data
for identify modal parameters we are using system identification tool. After obtaining a set of time
histories, it helps to extract and visualize useful modal parameters information from acquired time- and
frequency-domain experimental data.
Figure 3 Test instrumentation on Test Bridge

4. Experimental Study on Concrete Box Girder Bridge Under Traffic Induced Vibration
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Figure 4 Location of accelerometers on test bridge span
4. TECHNIQUES USED FOR MODAL ANALYSIS
The Stochastic Subspace Identification (SSI) technique is becoming a consolidating method, being one of
those methods more indicated for identification of systems submitted to natural excitation condition [5].
This method identifies a stochastic state space model from output-only measurements. Since it is
practically impossible to measure the operational forces, output-only system identification techniques are
required in the system identification analysis of such vibration response data. Among the different system
identification techniques proposed for civil engineering monitoring applications the stochastic subspace
identification (SSI) method is a reliable output-only identification technique which compares favourably to
other available methodologies. For a more in-depth look at the SSI method the reader may refer to the
work by Peeters [13].
+ + = =
where M, C2, K = mass, damping, and stiffness matrices; F(t) = excitation force; and U(t) =
displacement vector depending on time t. The force vector F(t) is factorized into a matrix B2 describing the
inputs in space and a vector u(t). Although equation represents quite closely the true behavior of a
vibrating structure, it is not directly used in SSI methods. So the equation of dynamic equilibrium (given
equation) will be converted to a more suitable form: the discrete-time stochastic state-space model. The
state-space model originates from control theory, but it also appears in mechanical/civil engineering to
compute the modal parameters of a dynamic structure with a general viscous damping model [14]. Solution
of the above equation is given in detail in the literature [15-16].
5. RESULTS OF DYNAMIC RESPONSE OF THE TEST BRIDGE
The vertical ambient vibration responses of the bridge shown in fig.5, recorded over entire span of the
bridge, using the acceleration. Each record with a sampling rate of 1000 Hz was taken. In the SSI method,
dynamic characteristics are obtained from collection of all vibration signals as a singular value. It means
that the number of measurement steps in each measurement test setup using references accelerometers
affects the stabilization behavior. Singular values of spectral density matrices, stabilization diagrams of
estimated state space models. Initial eight modes are taken for study. The fundamental frequency is
identified as 3.450 Hz in bending mode. However, the peak associated with the second frequency 5.915Hz
and so on as shown in Fig.7.

5. Sameer G. Patel and Gaurang R Vesmawala
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Figure 5 Acceleration time history of Ambient Vibration of Chandlodiya Bridge
Figure 6 Hourly Based Identification of Natural Frequency of Chandlodiya Bridge
Figure 7 Modal frequencies identification by SSI Method

6. Experimental Study on Concrete Box Girder Bridge Under Traffic Induced Vibration
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Table 1 Results of Mode & Modal frequencies & Damping ratio from AVT of Chandlodiya Bridge
Mode Modal Frequencies (Hz) Damping ratio ξ (%)
1 (Fund.) 3.450 6.142
2 5.915 1.646
3 7.779 0.982
4 9.287 0.259
5 11.576 1.386
6 12.766 1.383
7 14.481 0.797
8 16.112 0.593
Figure 8 Mode Shapes of the Chandlodiya Bridge

7. Sameer G. Patel and Gaurang R Vesmawala
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6. CONCLUSION
The experimental study of a post tension concrete box girder type of the bridge was carried out under
ambient loading condition and following conclusions are drawn:
From experimental study, Band pass filter is applied on the acceleration analog signal between 0.05 Hz
to 50 Hz. Acceleration time histories were recorded using sampling rate 100 Hz. The first modal
frequency of the bridge is evaluated 3.450Hz with 6.142 % damping at first mode by Stochastic Subspace
Identification technique (SSI method). Remaining modal frequencies are obtained below 20 Hz.
The fundamental frequency of the bridge model is evaluated experimentally and it is found 3.450 Hz in
first bending mode and total 8 mode shapes are obtained in study below frequency of 20 Hz. These mode
shapes correspond to the bending, tortional or combine effect. This test demonstrated that ambient
vibration measurement system is used effectively to determine the vibration properties of bridges. During
the test, any kind of traffic shutdown need not be necessary. These experimentally determined vibrational
characteristics can be use in future for health monitoring purposes.
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