MDOT Load Rating

MDOT Load Rating

Local Agency Workshop TrainingBradley M. Wagner, PE

Load Rating Program Manager

Overview

Michigan Bridge Analysis Guide

Coding & SI&A

Summary & Assumption Sheets

Coding Inconsistencies/FHWA Audit

Prioritization List

Troubleshooting

Michigan Bridge Analysis Guide (BAG)

MDOT Bridge Analysis Guide, 2005 Edition w/ 2009 Interim Update

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

BAG (Cont’d)

Part 2 Chapter 10 - Load Rating Aids

Chapter 11 – References

Chapter 12 – Glossary

Chapter 13 – Blank Forms

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

Coding & SI&A (Cont’d)

Item 41 – Structure Open/Posted/Closed


Item 63/65 – Operating/Inventory Method


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


Item 64MA – Michigan Operating Method


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


Item 64MC – Michigan Operating TruckTruck with lowest rating factor of 28 legal

trucks (Chapter 2 of BAG)


Item 70 – Bridge PostingIf 64MB is > 1.0, Item 70 = 5

Reflects Item 64MB NOT actual Posting

(Item 141)

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


Item 193A&C – Overload RatingClass A, B, C, or Restricted

Optional for local agency use

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


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




Must log in to MBRS to Print







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”.

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”.

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)

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

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

Questions?

Documents

MDOT Load Rating