A Comparison of AASHTO Bridge Load Rating Methods (2011) / Chapter Skim
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5To successfully complete the objectives of this project, a 1,500 bridge BRIDGEWare database needed to be established. Ideally the database would reflect the cross section of bridges found in the FHWA NBI database and would include as many material types and bridge configurations as possible.
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Using this software, an initial sample bridge domain was developed based on these comparisons. The sample was intentionally left larger than 1,500 bridges needed as additional winnowing of the data would take place in the second phase of the research.
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that bridge type and span length. This is done by creating several tabs within the spreadsheet to hold a pool of available bridges by span length and moving the selected bridges to a "final" bridge tab.
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Process 12-50 is available in NCHRP Report 485: Bridge Software -- Validation Guidelines and Examples. A process was added internally to Virtis for this project to move the Process 12-50 files produced by BRASS to a central location and to modify the internal values for the "SubdomainID" to uniquely identify the records produced with the specific girder in Virtis.
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2.2 Development of Live Load Vehicle List 2.2.1 Introduction The vehicle loadings obtained by the NCHRP Project 1278 Survey were used to investigate the resulting shears and moments in comparison to the HL-93 live load. The vehicles were divided into geographical regions, which allow an envelope of actions to be obtained.
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10 Figure 5. Reliability Index Output (RIO)
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• −Msuppt -- negative moment at the interior support for continuous spans (considers one truck and two "spaced" trucks) ; • Vab -- shear at exterior supports; and • Vba -- shear at interior support.
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Graphing the ratio versus span length was completed to aid in eliminating vehicles that did not follow the trends observed within each region. An example of this is shown for the southwest region in Figures 9 and 10.
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13 Figure 11. Northwest region live loads including AASHTO legal loads for simple span moment.
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14 Figure 13. Simple span moments ratioed to HL-93 for regional vehicles and AASHTO legal loads.
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15 Figure 15. Southwest region vehicles.
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