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

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To further investigate the relative flexibility of the bridge in three directions, the verticalacceleration record taken during the El Centro earthquake or during the Arkansasearthquake was input into the FE model in all three directions. The peak displacements atmidspan of the main bridge are listed in Table 6.3. It can be observed that the maximumdisplacement of the bridge does not occur in the same direction under the twoearthquakes, which further confirm the importance of ground motion characteristics.Under an El Centro type of earthquake record, the vertical direction appears to be moreflexible as it has the largest displacement. Under the earthquake record obtained at thebridge site, the transverse displacement is lightly larger than displacements in otherdirections, and thus more flexible. This general trend that the bridge is more flexible invertical and transverse directions is consistent with the natural frequency distribution asdemonstrated in Table 5.1.However, the peak displacements in three directions are overall in the same order whilethose due to the El Centro type of earthquake are quite different. The significantdifference between the two is attributable to the variation of their ground motioncharacteristics. As shown in Figures 6.2 and 6.4, the frequency bandwidth is muchnarrower for the vertical ground motion from the El Centro earthquake. Therefore, theresponse due to the El Centro earthquake is more sensitive to the major difference indynamic characteristics of the bridge in three principal planes (longitudinal, transverse,and vertical) as indicated by the natural frequencies in Table 5.1. On the other hand, therock motion at the bridge site has much wider frequency contents, which can excite mostof the vibration modes in all three principal planes and result in more uniform peakdisplacements in three directions.Table 6.3Peak displacement at midspan of the bridge (mm)Earthquake Longitudinal Transverse VerticalEl Centro 10.40 33.90 64.30Station D1 -32.26×106.3 Evaluation of the bridge-32.58×10 2.18×10 -3As shown in Section 3, several instrumentation stations exist at the bottom of towers,including D1, D2, and D3. At each station, three accelerometers were installed along thetransverse, longitudinal (traffic), and vertical directions of the bridge. It was observedfrom the measured data that the accelerometers at Station D3 did not work properlyduring the May 1, 2005 earthquake. The measured data at D1 and D2 indicate that theyhave similar wave forms and peak values, which are expected due to their installation onrock. The peak value of the measured accelerations at D1 and D2 are very small as it wasdue to a minor earthquake of magnitude M4.1. As a result, the components of themeasured acceleration at D1 are all scaled up by 10,000 times in order to approximatelyrepresent an M7.5 design earthquake for the bridge (Woodward-Clyde Consultants 1994).The measured earthquake records generally reflect the regional geologic conditions andseismic characteristics of the NMSZ. The three original acceleration components from84
Station D1 (before amplification) and their Fourier spectra are shown in Figures 6.4, 6.5and 6.6, respectively. From these figures it can be inferred that the amplified peakacceleration is 0.57 g in transverse and longitudinal directions and 0.42 g in the verticaldirection. The Fourier spectra indicate that the rock motions have wide frequency rangeswith their dominant frequency at approximately 10 Hz. The amplified three-componentrock motions will be used as inputs to the FE model of the cable-stayed bridge to assessthe structural conditions of main components in this section.Considering their critical role in maintaining the structural integrity of the bridge, twotowers and all cables are evaluated. Time history analysis was conducted to characterizethe stress distribution on towers. To mimic the actual excitation condition, the 3-D FE ofthe cable-stayed bridge was subjected to the amplified rock motions in three directionssimultaneously. Normally, the maximum moment will possibly occur at the bottoms ofthe two towers, B and D, and at the intersections of tower columns and cap beams, A andC, as shown in Figure 6.11.At the lower part of Towers 2 and 3 up to the cap beams, the cross sections of all columnsare 3.66 m × 6.71 m (12 ft × 22 ft) in solid shape as shown in Figure 6.12(a). In the planeof each tower is a solid 2.44 m (8 ft)-wide RC wall, which will strengthen the in-planebehavior of the tower. Therefore, the out-of-plane behavior of the tower is expected to bemore critical at its bottom portion up to the cap beam. Above the cap beam, the crosssection of all columns is also in rectangular shape but with a hole in the center as shownin Figure 6.12(b). The hollow sections start at joints 374, 417, 432, and 475 in the FEmodel as shown in Figure 6.11,To determine the bending capacity of each section, moment curvature analysis wasperformed to evaluate the load-deformation behavior of a RC section, using the nonlinearstress-strain relationships of concrete and steel materials. In this study, the Whitney stressblock for concrete along with an elasto-plastic reinforcing steel behavior is used. Theflexural strength of each section was evaluated using the software XTRACT developedby Imbsen & Associates, Inc (http://www.imbsen.com). In the analysis of the solidsection, the concrete wall was neglected since the 2.44 m (8 ft) RC concrete wallbasically behaves like an infilled wall. The dimension and reinforcement distribution inboth solid and hollow sections are based on the bridge drawings. The solid sections at Band D are reinforced with 356 No. 35 (#11) bars and the top hollow sections at A and C isreinforced with 464 No. 28 (#9) bars.85
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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
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
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: Displacement (m)0.30.20.10-0.1-0.2X
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 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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