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FAQs: I get a very low rating factor for an existing bridge. What is wrong?

Question

I get a very low rating factor for an existing bridge. What is wrong?

Answer

Typically, a very low rating factor for an existing bridge is caused by missing data or an inaccurate model of the superstructure created based on the data entered into BrR. The following steps can be taken to track down the cause of the low rating:

 
1.      The first thing to do to determine the cause of a low rating factor is to view the analysis results report in BrR by selecting the View Analysis Report toolbar button, or Bridge/Tabular Report from the command menu.
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      The Analysis Results window will open displaying the controlling rating factors, their location and the controlling limit state. To obtain more information about the controlling location, create a Point of Interest in BrR for that location if one does not exist yet. Then run the analysis engine again to obtain detailed computation information in the analysis engine output for that location.
 
2.      The analysis engine input and output files can be viewed from within BrR by selecting the View Analysis Output toolbar button, or Bridge/Output from the command menu.
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     This will open a window in which an input file, output file, or log file can be selected for viewing. The log file contains the input file along with any warning or assumption messages about how the BrR data was exported to the analysis engine input file.
 
3        Select the output file and search the output file for the controlling Point of Interest. Review the specification check computations to determine what is controlling at that point. Check if the correct section properties are used for this point. Many times low rating factors are caused by improper modeling of composite/non-composite section properties. If incorrect composite sections are used, review the deck and shear connector input data. Other items that should be reviewed are the dead and live load forces.
 
4.      Select the log file for viewing in the View Analysis Output window.
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      Then review any warnings or assumptions listed in the file to determine if the BrR input data was correctly exported to the analysis engine input file.
 
5.      Use the Validate function in BrR to check for any errors or missing input data. To access the Validate window, the name of the bridge, the superstructure definition, the member, or the member alternative must be highlighted. Then select the Validate toolbar button, or Bridge/Validate from the command menu.
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A window will be displayed which lists any warning or error messages related to the input data.
 
6.      A report of the BrR input data can be created by the Report Tool.
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See Can I print a copy of my BrDR input? for details on how to view the input data. Review the input data for errors or missing data.
 
After these steps, if you feel that the data has been input correctly into BrR and there is an error in either exporting the BrR data into the analysis engine input file or in the analysis engine computations, report this low rating as an issue on the BrDR technical support site: http://aashto.mbakercorp.com. Be sure to include the bridge as an exported XML file as an attachment when you submit the issue.
 
 

Category

Technical

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Created at 5/28/2015 10:03 AM by Uong, Ethan
Last modified at 3/3/2016 1:28 PM by Uong, Ethan