EXPERIMENTAL STUDY ON CONCRETE BOX GIRDER BRIDGE UNDER TRAFFIC INDUCED VIBRATION

Transcription

1 International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 1, January 2017, pp , Article ID: IJCIET_08_01_058 Available online at ISSN Print: and ISSN Online: 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 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 editor@iaeme.com

2 Experimental Study on Concrete Box Girder Bridge Under Traffic Induced Vibration 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 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 m m 1 (I- girder span)] 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 m. The cross section of the bridge has a total width of m. Details of bridge geometry were shown in Fig. 2. Figure 1 Location of Chandlodiya bridge editor@iaeme.com

3 Sameer G. Patel and Gaurang R Vesmawala 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 editor@iaeme.com

4 Experimental Study on Concrete Box Girder Bridge Under Traffic Induced Vibration 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, C 2, 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 B 2 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 Hz in bending mode. However, the peak associated with the second frequency 5.915Hz and so on as shown in Fig editor@iaeme.com

5 Sameer G. Patel and Gaurang R Vesmawala 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 editor@iaeme.com

6 Experimental Study on Concrete Box Girder Bridge Under Traffic Induced Vibration Table 1 Results of Mode & Modal frequencies & Damping ratio from AVT of Chandlodiya Bridge Mode Modal Frequencies (Hz) Damping ratio ξ (%) 1 (Fund.) Figure 8 Mode Shapes of the Chandlodiya Bridge editor@iaeme.com

7 Sameer G. Patel and Gaurang R Vesmawala 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 % 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 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. REFERENCES [1] Ward HS. (1984), Traffic Generated Vibrations and Bridge Integrity. Journal of Structural Engineering, ASCE, 110(10), pp [2] Kato M, Shimada S. (1986), Vibration of PCBridgeduring Failure Process. Journal of Structural Engineering, ASCE, 112(7), pp [3] Mazurek DF, DeWolf JT. (1990), Experimental Study of Bridge Monitoring Technique. Journal of Structural Engineering, ASCE, 116(9), pp [4] Fujino Y, Abe M, et. al. (2000), Forced and Ambient Vibration Tests and Vibration Monitoring of Hakucho Suspension Bridge. Transportation Research Record, 1696(2), pp [5] Chang CC, Chang TYP, Zhang QW. (2001), Ambient Vibration of Long-Span Cable-Stayed Bridge. Journal of Bridge Engineering, ASCE, 6(1), pp [6] Brownjohn JMW, Bocciolone M, Curami A, Falco M, Zasso A.(1994), Humber Bridge Full-Scale Measurement Campaigns Journal of Wind Engineering and Industrial Aerodynamics, Vol. 52, pp [7] Xu YL, Zhu LD, Wong KY, Chan KWY.(2000), Field measurement results of Tsing Ma Suspension Bridge during Typhoon Victor. Structural Engineering and Mechanics, 10(6), pp [8] Farrar CR, James III CH. (1997), System Identification from Ambient Vibration Measurements on a Bridge. Journal of Sound and Vibration, 205(1), pp [9] Paultre P, Proulx J, Talbot M. (1995), Dynamic Testing Procedures for Highway Bridges Using Traffic Loads. Journal of Structural Engineering, ASCE, 121(2), pp [10] Douglas BM, Reid WH. (1982), Dynamic Tests and System Identification of Bridges. Journal of the Structural Division, ASCE, 108(10), pp [11] Huang CS, Yang YB, Lu LY, Chen CH. (1999), Dynamic Testing and System Identification of a Multi- Span Highway Bridge. Earthquake Engineering and Structural Dynamics, Vol. 28, pp [12] Salawu OS, Williams C. (1995), Review of Full-Scale Dynamic Testing of Bridge Structures. Engineering Structures, 17(2), pp [13] Peeters B. (2000), System Identification and Damage Detection in Civil Engineering. Ph.D. dissertation, Katholieke Universiteit Leuven. [14] Ewins DJ. (1984), Modal Testing: Theory and Practice, Research Studies Press, New York. [15] Juang JN (1994), Applied System Identification, Prentice-Hall, EnglewoodCliffs, N.J, USA editor@iaeme.com

8 Experimental Study on Concrete Box Girder Bridge Under Traffic Induced Vibration [16] Yu DJ and Ren WX (2005), EMD-Based Stochastic Subspace Identification of Structures from Operational Vibration Measurements. Engineering Structures, 27(12), pp [17] Patil Yashavant S. And Prof. Shinde Sangita B., Comparative Analysis and Design of Box Girder Bridge Sub-Structure With Two Different Codes. International Journal of Advanced Research in Engineering and Technology (IJARET), 4(5), 2013, pp [18] Ubaid Illahi, Burhan-ul-Wafa, Danish Zaffar Wani and Raqeeb Nabi Khan, Traffic Flow Analysis & Efficiency of Geometric Design of a T - Intersection, A Case Study, International Journal of Civil Engineering and Technology, 7 (1), 2016, pp editor@iaeme.com