Analysis and Testing on Dynamic Characteristics ofComposite Box-girder Bridge with Corrugated SteelWebsChen Jianbing!(I Department of Civil Engineering,Suzhou College of Science and Technology,Suzhou 215011,China2 China Communications Construction Company Highway consultansts Co.Lid(Jiangsu).nanjing 210012,China:3Transportation colege of Southeast University,Nanjing 210096,China)Abstract:Via research on a PC composite box-girder bridge with corrugated steel webs,usingjumping excitation method for the vibration characteristics test,the paper got its natural vibrationfrequency,damping ratio,vibration mode parameters and so on,according to the time-domainwaveforms,frequency spectrum and power spectra of bridge structures.Of finite element theoryto the overall structural dynamic calculation,the structural vibration frequencies and mode shapesof the top 20 bands was analyzed.Comparison of experimental and theoretical results shows thatthe combination of the tested self-vibration frequency,vibration mode and the calculated values isin good agreement,the former three-order natural frequencies of the tested value and calculatedvalue of the error value is less than 4%,and its tested results has high accuracy using Jumpingincentive bridge structure.The results provide a theoretical basis for the dynamical analysis of PCcomposite box-girder bridges of corrugated steel webs.Key words:composite box-girder bridge;corrugated steel web;natural frequency;vibration test;FEA calculationBecause the weight of traditional concrete box girder webs account for a large proportion inthe total weight of the box girder,the spanning capacity of concrete box girder bridge is subject tocertain restrictions.Corrugated steel webs play a significant role in reduce self-weightl.Thestructure has been widely used in France,Norway,South Korea,Japant2 31,and practicalapplication has aslo appeared in Chinal41.At present,further development of grider bridge withcorrugated steel webs will be a central issue for research scholars in various countries,andperformance test of grider bridge with corrugated steel webs is the key to further research andapplication.So far,girder bridge with corrugated steel webs is limited to the static characteristics,andthere are few studies of dynamics characteristics in domestic.Especially vibration characteristicsof the grider bridge with corrugated steel web bridge are rarely reported.We use finite element toanalyze vibration characteristics based on current research and girder bridge with corrugated steelwebs in this paperlsl.And the results will provide a theoretical basis and technical support forvibration performance and seismic design of grider bridge with corrugated steel webs.1 Project ProfileBohe Bridge is the first grider bridge of corrugated steel webs in China,as shown in Figure 1.It is located on Provincial road 231 Guangshan County in Henan Province.The bridge length is120m,combined span is 4x30 m,bridge width is 13+2x1.5m,design load is the road-I level.Traverse structure have four griders as shown in Figure 2,The angle of web inclination is 20,andthickness of both the top and bottom of concrete plate is 15cm,the thickness of pavement layer iscomposed of 15cm of on-site concrete and 3cm of asphalt concrete.Construction method is firstsimply supported then continuously supported,and the bridge was completed in July 2005.Fig.I Bohe BridgeFig.2 Bohe Bridge Traverse Composing2 Test of natural vibration characteristics2.1 Test instrumentSignal acquisition and analysis system employed DH-5935 dynamic signal testing analyticalsystem produced by Donghua test technology company,as shown in Figure 3.The characteristicsof DH107 acceleration sensor is the light weight and high sensitivity,the pass band is 0.2-500Hz,and the charge sensitivity is 280-360 pc/ms2,as shown in Figure 4.Fig.3 DH5936 dynamics testing analyzerFig.4 DH107 piezoelectricity acceleration transduce2.2 The measuring points arrangementThe measuring points of the continuous bridge are generally arranged at the larger peak in thevibration mode test curve,so measuring points arrangement in this experiment is according to thevibration mode characteristics of the prior theoretical analysis.Choosing the top of bridge deck ofeach span fulcrum and 1/4,1/2,3/4 span to arrange the measurement points.A total of measuringpoints is 17 and the test point arrangement diagram in Figure 5.During the test,using the clay as acoupling medium coupled to the sensor surface and structure,can make the sensor better sense thestructure vibration,make continuous operation of the sensor more stable,reliable,and reducemaintenance debugging.Fig.5 Measuring Place Location Diagram2.3 Test Methods(a)Midder span I(b)Midder span 2(c)Midder span 3(d)Midder span 4Fig.6 The Middle Section Wave,Frequency and Power DiagramThe test employ jumping excitation methodt61.The test car is at the mid-span,and itsrear-wheel slowly cross the wedge pad that its height is about 15cm,then mpac the bridge deckinstantaneously.Make the structure generate free vibration with added mass test vehicle).Andcontrol the point of jumping excitation at each mid-span.To avoid producing the phenomenon of frequency mixing,the sampling frequency must bemore than twice the maximum of frequency!71,known by the shannon Theorem.Therefore,cut-offfrequency of low-pass filter is set as 50Hz,the sampling frequency is set as 100Hz in thisexperiment.Selection of analysis points in the spectral analysis is more important,and usinghigher analysis points are beneficial for improving the accuracy of frequency and damping.Therefore,analysis points of each FFT take as N=1024 points in the experiment,and use theincreasing the data length (N =5096,8192)to confirm spectrogram of N=1024 point did not missthe important spectral line,and ensure the reliability of the spectral analysis results.Throughpractical spectrum analysis of N=1024 point,we can obtained spectrum analysis results by severalaveraging.Use power spectral density to determine the natural frequency and the amplitude sizeof each point,and also must consider the coherence function.Half-power bandwidth is determinedthe damping ratio.2.4 Test resultsVibration testing collect much groups of data.First decompose and merge the original signalcurve by using signal acquisition and analysis system,and then extract time-domain waveform,frequency spectrum and power spectra of the test in data processing,as shown in Figure 6(whereonly give one test results of each mid-span section).By using cross-power spectrum law throughDH-5935 dynamic signal analysis software,we can obtain the former 3-order natural frequency,damping and vibration mode parameters of Bohe Bridge,as shown in Table 1.