Assessment of the Bill Emerson Memorial Bridge - FTP Directory ...

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3. Seismic Instrumentation System and MeasuredData Analysis3.1. GeneralField test generally provides an effective means to investigate the fundamental behaviorof cable-stayed bridges (Hu et al., 2006). Three types of field tests have been widely usedin determining the mechanical properties of long span cable-stayed bridges (Okauchi etal., 1997; Ren et al., 2005; Cunha et al., 2006; Hsieh et al., 2006; Hu et al., 2006):♦ Forced vibration tests;♦ Free vibration tests;♦ Ambient vibration tests.In forced vibration tests, bridges are usually excited by artificial means and thus bothinput and output data can be obtained. Input parameters for these tests include the type,amplitude, frequency content, duration, and time of decay of waveforms as well as thelocation of excitation loads. With a known forcing function, many of the uncertaintiesassociated with data collection and processing can be avoided. Additionally, although atany given time a structural response results from all sources of excitations, filteringtechniques can be used to separate their effects and determine part of the response to aspecific source. The amplitude of forced vibration can also be designed to be significantlyhigher than the ambient or electronic noise levels in order to increase the signal-to-noiseratio and more accurately evaluate the properties of a bridge structure. For large-scalecivil engineering structures, however, this technique is often impractical since it requiresheavy and expensive equipment to generate a controlled and significant excitation.Free vibration tests are carried out by a sudden release of a heavy load or massappropriately connected to a bridge. Over time, the potential energy originally stored inthe bridge structure gradually dissipates due to friction or heat generation, resulting in thefree vibration decay. The free vibration data can be analyzed to determine the propertiesof the structure. In the free vibration tests by Cunha et al. (2001), a suspended mass wassuddenly released from the deck of the Vasco da Gama Cable-stayed Bridge. In bothforced and free vibration tests, bridges need to be excited by an artificial means. In mostcases, traffic must be interrupted during tests, which causes inconvenience to travelers.Ambient vibration tests take advantage of natural sources of bridge vibration. Theyrequire no equipment to excite the bridge to be tested. Ambient vibration is induced bywind, minor earthquake, traffic, wave, and ground motion generated by nearbyconstruction or industrial activities. It corresponds to the real operation condition ofbridges and thus requires no traffic interruption during tests (Abdel-Ghaffer and Scanlan,1985; Brownjohn et al., 1989; Brownjohn et al., 1999; Wilson et al., 1991; Xu et al.,1997; Macdonald and Wendy, 2005). In this study, field measured data from traffic andminor earthquake are analyzed to understand the dynamics and properties of the BillEmerson Memorial Cable-stayed Bridge.16
3.2. Seismic instrumentation networkThe Bill Emerson Memorial Cable-stayed Bridge was instrumented with a real-timeseismic monitoring system named ASPEN. Accelerometers were installed insidedownholes at two nearby free fields and various parts of the bridge, including deck,towers, and foundations. In earthquake engineering, instrumentation can be grouped intothree main categories (Celebi, 2006). The first category is bridge instrumentation of thesuperstructure and substructure to capture and define (a) the overall motion of the cablestayedbridge, (b) the motion of the two towers to assess their translational and torsionalbehavior relative to the caissons and deck levels, (c) the deck motion to assess thedynamic behavior of the deck including fundamental and higher modes in threedirections, and (d) at bents of the bridge, intermediate pier locations, and bottom offoundations to understand the ground motions and interaction between foundation and thesuperstructure. The second category is instrumentation of the free fields in the vicinity ofthe bridge including those downhole measurements to assess the different groundmotions near the bridge. The third category is instrumentation array for ground failuresnear the bridge. The Bill Emerson Memorial Bridge instrumentation fell into the first andsecond categories.Data recorded from the Bill Emerson Memorial Bridge have been transmitted to andstored in the Data Management Center of the Incorporated Research Institutions forSeismology system (IRIS: http://www.iris.edu). These data are stored under the station of“NP” of the Center Recording System of the Bill Emerson Memorial Cable-stayed BridgeSeismic Monitoring System. The data transmitted to IRIS is in mini-seed format, and allstreamed data from the bridge will be stored and available for four to eight weeks. Afterthat, the stored data will be deleted except for significant earthquake data. Moreinformation about the seismic monitoring system can be found in Celebi (2004).A total of 43 stations and 84 channels of acceleration records are listed in Table 3.1. InTable 3.1, HN2 represents the transverse/lateral component perpendicular to the trafficdirection, HN3 means the traffic direction of the bridge or longitudinal component, andHNZ is the vertical component. The stations and channels are distributed on the bridge asillustrated in Figure 3.1. Each arrow in Figure 3.1 indicates one channel of accelerationdata. The seismic instrumentation system on the Bill Emerson Memorial Cable-stayedBridge continuously provides the structural vibration and soil responses at free field sites.As such, the bridge can be used for real-time monitoring of structural conditions. Thereal-time monitoring system has been reliably collecting data since February to March2004.17
Page 1 and 2: Organizational Results Research Rep
Page 3 and 4: TECHNICAL REPORT DOCUMENTATION PAGE
Page 5 and 6: Executive SummaryOpen to traffic on
Page 7 and 8: 8. All cables behave elastically un
Page 9 and 10: Table of ContentsExecutive summary.
Page 11 and 12: List of Figure CaptionsFigure 1.1 A
Page 13 and 14: Figure 5.30 29 th mode shape (1.032
Page 15 and 16: 1. Introduction1.1. GeneralCable-st
Page 17 and 18: Figure 1.1Artist rendering of the B
Page 19 and 20: Expansionand lateralearthquakerestr
Page 21 and 22: 3. Evaluate the model by conducting
Page 23 and 24: 2. Automatic Retrieval of Peak Acce
Page 25 and 26: 2.2.3. Map/Find stationsClicking th
Page 27 and 28: 2.2.5. Displaying seismogramsTo dis
Page 29: Figure 2.8Directory chooser2.2.6. S
Page 33 and 34: The main bridge from Bent 1 to Pier
Page 35 and 36: (a) South side of deck at support o
Page 37 and 38: (a) North side of deck at middle of
Page 39 and 40: The seismic responses at the top (T
Page 41 and 42: Polyreference Complex Exponential (
Page 43 and 44: are evaluated and presented in Figu
Page 45 and 46: 0.353.50.330.252.5Amplitude0.20.15A
Page 47 and 48: 1 x 10-4 Frequency(Hz)Amplitude0.90
Page 49 and 50: Amplitude0.20.180.160.140.120.10.08
Page 51 and 52: Amplitude0.20.180.160.140.120.10.08
Page 53 and 54: 1.20.80.400 100 200 300 400 500 600
Page 55 and 56: 4. Finite Element Modeling of Bill
Page 57 and 58: Since the cable stays are connected
Page 59 and 60: Table 4.3Initial property of cables
Page 61 and 62: Table 4.4Spring and damping coeffic
Page 63 and 64: (a) View of the entire bridge(b) Vi
Page 65 and 66: 4.6. RemarksA detailed 3-D FE model
Page 67 and 68: knω = (5.4)nm nSimilarly, when dam
Page 69 and 70: mainly corresponds to the vertical
Page 71 and 72: thFigure 5.10 9 mode shape (0.740Hz
Page 73 and 74: thFigure 5.19 18 mode shape (0.947H
Page 75 and 76: Figure 5.27 26 th mode shape (0.977
Page 77 and 78: When the bridge deck moves up and d
Page 79 and 80: 1.1Frequency (Hz)0.90.70.5BC Case 1
Page 81 and 82:
1.1Frequency(Hz)0.90.70.5Plus 0Plus
Page 83 and 84:
no difference among the three cases
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The FE model of the bridge was vali
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10.6TestFE model0.2-0.20 100 200 30
Page 89 and 90:
1.20.80.40-0.4TestFE model0 100 200
Page 91 and 92:
differences is that the exact locat
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(a) Vertical acceleration time hist
Page 95 and 96:
The FE model of the cable-stayed br
Page 97 and 98:
Displacement (m)0.30.20.10-0.1-0.2X
Page 99 and 100:
Station D1 (before amplification) a
Page 101 and 102:
ending of the tower as shown in Fig
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symmetric about the centerline of t
Page 105 and 106:
Tensile stress (MPa)800750700650600
Page 107 and 108:
7. Conclusions and RecommendationsB
Page 109 and 110:
The vast arrays of acceleration dat
Page 111 and 112:
14. Cunha A, Caetano and Delgado T.
Page 113 and 114:
42. Song, W., Giraldo, D.F., Clayto
Page 115 and 116:
Figure A.2 Vertical stiffness and d
Page 117 and 118:
A.2 Group Interaction FactorThe cro
Page 119 and 120:
For a group of piles with identical
Page 121:
Missouri Department of Transportati
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