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

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different earthquake excitations but depends on the earthquake characteristics, themodal properties, and mass distribution.2. Although less obvious, time history analysis generally confirms the conclusiondrawn from the modal properties of the bridge that the bridge is most flexible invertical direction and then in transverse direction.3. All cables behave elastically under a design earthquake. Their factor of safety islarger than 2.35 at all times. On the other hand, the cable subjected to least stressis always in tension, ensuring no slack occurrence during the earthquake.Therefore, cables can be simplified as linear elements for seismic analysis.4. The solid section of both towers at the lower portion is generally more criticalthan the hollow section of the upper portion of the towers above the cap beams.The in-plane behavior of two towers is always in elastic range under the designearthquake with a wide margin of safety. For out-of-plane behavior, the upperportion of the towers above the cap beams remains nearly elastic with asignificant margin of safety. The lower portion of the towers, however, issubjected to moderate yielding out of plane during the design earthquake thoughthe bridge safety is not a concern.92
7. Conclusions and RecommendationsBill Emerson Memorial Cable-stayed Bridge is one of very few long-span bridges in theU.S. that are instrumented with a real-time seismic monitoring system. This systemconsists of 84 accelerometers deployed on the bridge and on two nearby free fields.Based on the traffic and earthquake data, this study mainly develops and validates arealistic 3-D FE model of the bridge as well as assesses the seismic condition of thebridge under a projected design earthquake.7.1 Main findingsThe main topics addressed in this report include: (1) automatic retrieval of peakaccelerations and measured data analysis, (2) 3-D FE bridge model with explicitmodeling of all main components, (3) sensitivity study and validation of the 3-D FEbridge model, and (4) seismic behavior and assessment of the bridge structure. Based onthe comprehensive analysis of the cable-stayed bridge, the following conclusions can bedrawn:1. A Java-based system was developed to automatically compile the peak groundand structural accelerations measured from the bridge. The system can beseamlessly integrated with the data management system at the ISIS website. Theoutput of this system is a string of peak acceleration data every hour or other timewindows, which can be pulled into an Excel sheet for further processing.2. The peak-picking method in frequency domain can be conveniently applied toanalyze a huge set of field measured data from the seismic monitoring system.The vibration characteristics of the bridge such as natural frequencies and modeshapes were extracted.3. One rigid link element must be introduced in the FE model at each end of a cablein order to model the actual length and configuration of the cable as specified inas-built drawings. Cables significantly influence the stiffness of the bridgesystem. Their sagging should be taken into account in the modeling of the cablestayedbridge to account for geometric nonlinear effects.4. Extra attention must be paid to the modeling process of bearings at each pier bothin the main span and in the approach span of the bridge. They play an importantrole in seismic behaviors of the complex cable-stayed bridge.5. The 3-D response and behavior of the cable-stayed bridge are evident. Most of thevibration modes are coupled with others. The dynamic characteristics (frequencyand mode shapes) of the bridge indicate that the cable-stayed structure is mostflexible in vertical direction and least flexible in longitudinal direction. Thisobservation is generally supported by time history analysis.6. The 31 significant modes of vibration up to 14.09 Hz include more than 70%mass participation in translational and rotational motions along any of threedirections. The fundamental frequency is 0.339 Hz, corresponding to verticalvibration of the main bridge. Cables begin to vibrate severely at a naturalfrequency of 0.842 Hz or higher. The Illinois approach spans experience93
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Organizational Results Research Rep
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TECHNICAL REPORT DOCUMENTATION PAGE
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Executive SummaryOpen to traffic on
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8. All cables behave elastically un
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Table of ContentsExecutive summary.
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List of Figure CaptionsFigure 1.1 A
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Figure 5.30 29 th mode shape (1.032
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1. Introduction1.1. GeneralCable-st
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Figure 1.1Artist rendering of the B
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Expansionand lateralearthquakerestr
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3. Evaluate the model by conducting
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2. Automatic Retrieval of Peak Acce
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2.2.3. Map/Find stationsClicking th
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2.2.5. Displaying seismogramsTo dis
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Figure 2.8Directory chooser2.2.6. S
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3.2. Seismic instrumentation networ
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The main bridge from Bent 1 to Pier
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(a) South side of deck at support o
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(a) North side of deck at middle of
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The seismic responses at the top (T
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Polyreference Complex Exponential (
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are evaluated and presented in Figu
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0.353.50.330.252.5Amplitude0.20.15A
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1 x 10-4 Frequency(Hz)Amplitude0.90
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Amplitude0.20.180.160.140.120.10.08
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Amplitude0.20.180.160.140.120.10.08
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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
Page 85 and 86: The FE model of the bridge was vali
Page 87 and 88: 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
Page 93 and 94: (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
Page 103 and 104: symmetric about the centerline of t
Page 105: Tensile stress (MPa)800750700650600
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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