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

More documents

Recommendations

Info

Conclusions and recommendationsBased on the comprehensive analysis of the cable-stayed bridge, the followingconclusions can be drawn: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. They 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. Cables and bearings significantly influence the stiffness of the bridge system. Thesagging of cables should be considered in the modeling of the cable-stayed bridgeto account for geometric nonlinear effects. Bearings play an important role inseismic behaviors of the complex cable-stayed bridge.4. 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.5. 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 experiencesignificant vibration at approximately 3.187 Hz. The approach spans are muchstiffer than the cable-stayed span. Their interaction during earthquakes is weak.6. 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%.7. 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 due in part to unknown exact locations of allaccelerometers. Nevertheless, the mode assurance criterion index between acomputed mode shape and its corresponding measured one is above 0.888 for thefirst eight modes. This indicates that the 3-D FE model is fairly accurate forengineering applications.v
8. 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.9. 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. For out-of-plane behavior, the upper portion of thetowers above the cap beams remains nearly elastic with a significant margin ofsafety. The lower portion of the towers, however, likely experiences moderateyielding out of plane during the design earthquake though the safety of the bridgeis not a concern.Future researchThe current study only addressed one way of using the recorded data for structuralassessment of the bridge under a projected design earthquake. The vast arrays ofacceleration data can also be used to address a number of issues related to engineeringseismology, engineering design, bridge maintenance, bridge security, and bridgemanagement. 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 biennial inspections of the bridge so that the problem areas, if any, canbe 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 firstvi
Page 1 and 2: Organizational Results Research Rep
Page 3 and 4: TECHNICAL REPORT DOCUMENTATION PAGE
Page 5: Executive SummaryOpen to traffic on
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 and 30: Figure 2.8Directory chooser2.2.6. S
Page 31 and 32: 3.2. Seismic instrumentation networ
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
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 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
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?