MDOT Load Rating
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Transcript of MDOT Load Rating
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MDOT Load Rating
Local Agency Workshop TrainingBradley M. Wagner, PE
Load Rating Program Manager
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Overview
Michigan Bridge Analysis Guide
Coding & SI&A
Summary & Assumption Sheets
Coding Inconsistencies/FHWA Audit
Prioritization List
Troubleshooting
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Michigan Bridge Analysis Guide (BAG)
MDOT Bridge Analysis Guide, 2005 Edition w/ 2009 Interim Update
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BAG (Cont’d)
Part 1 Chapter 1 – Introduction Chapter 2 – Michigan Legal Loads Chapter 3 – Legal Loads in other States…. Chapter 4 - General Analysis Procedures Chapter 4a – Load Factor Rating and Load And Resistance Factor Rating Chapter 5 – Analysis Vehicle Selection Chapter 6 – Live Load Distribution Chapter 7 – Posting Procedures Chapter 8 – Overload Procedures Chapter 9 – Calculation Examples
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BAG (Cont’d)
Part 2 Chapter 10 - Load Rating Aids
Chapter 11 – References
Chapter 12 – Glossary
Chapter 13 – Blank Forms
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Coding & SI&A MDOT SI&A Coding Guide
Current version August 26, 2009 Update to be released in 2012
Load Rating Items Item 41 – Structure Open/Posted/Closed Item 63 – Federal Operating Rating Method Item 64F – Federal Operating Rating Item 64MA – Michigan Operating Method Item 64MB – Michigan Operating Rating Item 64 MC – Michigan Operating Vehicle Item 65 – Federal Inventory Rating Method Item 66 – Federal Inventory Rating Item 70 – Bridge Posting Item 141 – Posted Loading Item 193 A & C – Overload Class
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Coding & SI&A (Cont’d)
Item 41 – Structure Open/Posted/Closed
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Coding & SI&A (Cont’d)
Item 63/65 – Operating/Inventory Method
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Coding & SI&A (Cont’d)
Item 64F/66 – Operating/Inventory RatingCan be metric tons or rating factor
LRFR Rating MUST be rating factor
Must correspond with Item 63/65
Metric tons, not English.
Rating Factor of 1.0 = 32.4 mTons (not 36)
Minimum allowable is 2.7 mTons (or 3 english ton equivalent)If less, close the bridge, and record 0.00
If temporarily supported, must be coded for un-supported case (item 103 = T)
Record 99.9 if live load is negligible
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Coding & SI&A (Cont’d)
Item 64MA – Michigan Operating Method
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Coding & SI&A (Cont’d)
Item 64MB – Michigan Operating RatingCan be English tons or rating factor
Rating factor is preferred
Must correspond to item 64MA
Based on the lowest rating factor of the 28 Michigan Legal trucksNote: this is a change from past practice.
When rating factor is less than 1.0, bridge must be posted
Minimum allowable is 3 tonsIf less, close the bridge, and record 0.00
If temporarily supported, must be coded for un-supported case (item 103 = T)
Record 99.9 if live load is negligible
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Coding & SI&A (Cont’d)
Item 64MC – Michigan Operating TruckTruck with lowest rating factor of 28 legal
trucks (Chapter 2 of BAG)
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Coding & SI&A (Cont’d)
Item 70 – Bridge PostingIf 64MB is > 1.0, Item 70 = 5
Reflects Item 64MB NOT actual Posting
(Item 141)
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Coding & SI&A (Cont’d)Item 141 – Posted Loading
Leave blank if structure not posted
Bridge must be posted if item 64MB < 1.0
4 Options for Posting – Includes 6 digits
Minimum posting is 3 Tons Gross
081216081216 1002NN
1002NN
NN05NN
NN05NN
10NNNN
10NNNN
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Coding & SI&A (Cont’d)
Item 193A&C – Overload RatingClass A, B, C, or Restricted
Optional for local agency use
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Summary & Assumption SheetsPer AASHTO MBE 2.5.1.2:
“A general statement of the results of the analysis with note of which members were found to be weak, and any other modifying factors that were assumed in the analysis, should be given.”
Calculations must include:Analysis methodology
Assumptions
Factors that affect the rating (condition, unique loads)
Results – to include controlling members
MDOT MBIS/MBRS Summary and Assumption Sheets Meet these requirements
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Summary & Assumption Sheets
As of July, 2012 MBIS eliminated access to load rating values in the SI&A screen
As of July, 2012 MBIS eliminated access to load rating values in the SI&A screen
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Summary & Assumption Sheets
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Summary & Assumption Sheets
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Summary & Assumption Sheets
Must log in to MBRS to Print
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Summary & Assumption Sheets
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Summary & Assumption Sheets
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Summary & Assumption Sheets
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Summary & Assumption Sheets
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Summary & Assumption Sheets
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Summary & Assumption Sheets
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Coding Inconsistencies/FHWA Audit
2009 FHWA Audit, Final Report March 2010US DOT OIG audit 2006FHWA division Offices directed to perform in-depth reviews of state load rating and posting practices
Findings – Conditional ComplianceCurrent practices “are generally in compliance with NBIS and AASHTO requirements”.Many MDOT bridges in the database “may not be load rated in compliance with NBIS” and “as many as 2,900 bridge load ratings must be revised”.Many local agency bridges in the database may not be in compliance with NBIS “as many as 4,100 or more”.
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Prioritization List
Tier 1 – No Rating – Due 12/31/2012 Nulls in load rating values
Item 63 or 65 = 5 (no rating)
Item 64f = 66
Tier 2 – Poor Condition – Due 12/31/2014 Deck, superstructure, substructure OR culvert
ratings equal to 4 or less AND
Deterioration indicator in MBIS equals “No”.
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Prioritization List (Cont’d)
Tier 3 – Other Irregularities – Due 12/31/2016Built after 1993 AND ASR (Item 63 or 65 equal 2 or 7)
Built after 2010 AND not LRFR (Item 63 or 65 not equal to 3 or 8)
NHS bridge AND ASR (Item 63 or 65 equal 2 or 7)
Fed Operating is greater than 3X Fed Inventory (Item 64F > 3*Item 66)
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Load Rating Bridge Advisories
BA-2010-03 August 2010Load Rating Compliance with NBIS
BA-2010-06 October 2010Licensing and Use of AASHTOWARE Virtis Software
BA-2011-02 March 2011Local Agency Load Rating Prioritization and Coding
BA-2012-01 July 2012MBIS Update & Coding Revisions
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Load Rating TroubleshootingIf an analysis yields low rating results AND the results are not consistent with
field observations (consider whether bridge has ever seen full legal load)…….
Review model & verify field conditions of structureAttempt to adjust distribution factors
Guide Specifications for Distribution of Loads for Highway Bridges, 1994Calculate lever rule for cases where code equations may not apply
Other Specs/Virtis Control OptionsDifferent methodology (LFR→LRFR, etc)Plastic Moment Capacity (if applicable)1979 Shear specs (if applicable)
Material Sampling (ASTM Standard)10% increase in steel yield20% increase in concrete compressive
Advanced ModelingVirtis 2d/3dOther FEM software
Load Testing
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Questions?
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