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significant vibration at approximately 3.187 Hz. The approach spans is muchstiffer than the cable-stayed span. Their interaction during earthquakes is weak.7. Based on sensitivity analysis, the key parameters affecting the modal properties ofthe bridge are the mass density of concrete and boundary conditions. The massdensity of concrete, specified in bridge drawings, appear underestimated by 6.7%.They need to be increased in order to match the natural frequencies of the 3-Dmodel with their respective measured data. Except for expansion conditions, theuse of other boundary conditions at bases of all piers changes the naturalfrequency of the main bridge by less than 5%.8. The computed natural frequencies of the 3-D FE model agree well with thosefrom field measured data. The maximum error of the first 31 significant modes iswithin 10%. For mode shapes, however, slight differences exist between thecomputed and the measured values. One of the reasons for these differences isthat the exact locations of all accelerometers deployed on the bridge are unknown.Nevertheless, the mode assurance criterion index between a computed modeshape and its corresponding measured one is above 0.888 for the first eightmodes. This indicates that the 3-D FE model is fairly accurate for engineeringapplications.9. Time history analysis indicates that an earthquake excitation of higher peakacceleration does not necessarily induce a stronger response. The maximumresponse does not necessarily occur in the same direction of the bridge underdifferent earthquake excitations but depends on the earthquake characteristics, themodal properties, and mass distribution.10. 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.11. The solid section of both towers at the lower portion is generally more criticalthan the hollow section of the upper portion above the cap beams. The in-planebehavior of two towers is always in elastic range under the design earthquakewith a wide margin of safety. Similarly, 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, likelyexperiences moderate yielding out of plane during the design earthquake thoughthe safety of the bridge is not a concern.7.2 Future researchThe seismic instrumentation system was installed and put in operation in December 2004.Since then, acceleration data from ambient vibration have been collected continuouslyfrom the Bill Emerson Memorial Cable-stayed Bridge. The current study only addressedone way of using these data for structural assessment of the bridge under a projecteddesign earthquake.94
The vast arrays of acceleration data can also be used to address a number of issues relatedto engineering seismology, engineering design, bridge maintenance, bridge security, andbridge management. In a long term, these potential uses include, but are not limited to,1. Assess the bridge structural condition in near real time to compliment themandatory once-every-two-years inspections of the bridge so that the problemareas, if any, can be readily probed and examined in a cost-effective way.2. Evaluate the bridge structural condition in a short time immediately after acatastrophic earthquake event to assist in decision making for emergency trafficuses or general public transportation in a much shorter time than traditional visualinspections may take.3. Validate design assumptions made during the design of the cabled-stayed bridge.Several structure details are unique features to the Bill Emerson Memorial Bridge.Due to complexity and large scale of the Bridge, these unique features generallycannot be validated to the full extent with laboratory tests. The acceleration datameasured from the bridge are valuable to accomplishing this importantengineering task.4. Collect the load data of small and moderate earthquakes for bridges in the CentralUnited States and study the free field response of soil deposits and the spatialdistribution of ground motions.5. Monitor the security and safety of the critical transportation system incombination with other visual tools that may be installed in the future such asblast effects and vehicle impact.This study provides a 3-D baseline model of the cable-stayed bridge that has beenvalidated against the field measured traffic data and those data recorded during the May 12005 earthquake. This model can be applied to develop a system identification schemefor potential damage detection using emerging technologies, such as neural network, andvibration-based techniques. Further development in this direction will address the firsttwo applications of the measured data from the above list. With strong motion datacollected in the future, the 3-D model can also be expanded to fully validate designassumptions, which is the 3 rd application, and to study the seismic behavior of the bridgeunder real earthquakes.95
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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 and 106: Tensile stress (MPa)800750700650600
Page 107: 7. Conclusions and RecommendationsB
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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