Transcript MDOT`s load rating presentation

MDOT Load Rating
Local Agency Workshop Training
Bradley 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
Coding & SI&A (Cont’d)
Item 63/65 – Operating/Inventory Method
Coding & SI&A (Cont’d)
Item 64F/66 – Operating/Inventory Rating
Can 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
Coding & SI&A (Cont’d)
Item 64MA – Michigan Operating Method
Coding & SI&A (Cont’d)
Item 64MB – Michigan Operating Rating
Can 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 trucks
Note: this is a change from past practice.
When rating factor is less than 1.0, bridge must be posted
Minimum allowable is 3 tons
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
Coding & SI&A (Cont’d)
Item 64MC – Michigan Operating Truck
Truck with lowest rating factor of 28 legal
trucks (Chapter 2 of BAG)
Coding & SI&A (Cont’d)
Item 70 – Bridge Posting
If 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
081216
1002NN
NN05NN
10NNNN
Coding & SI&A (Cont’d)
Item 193A&C – Overload Rating
Class A, B, C, or Restricted
Optional for local agency use
Summary & Assumption Sheets
Per 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
Summary & Assumption Sheets
As of July, 2012 MBIS
eliminated access to load
rating values in the SI&A
screen
Summary & Assumption Sheets
Summary & Assumption Sheets
Summary & Assumption Sheets
Must log in to MBRS to
Print
Summary & Assumption Sheets
Summary & Assumption Sheets
Summary & Assumption Sheets
Summary & Assumption Sheets
Summary & Assumption Sheets
Summary & Assumption Sheets
Coding Inconsistencies/FHWA Audit
2009 FHWA Audit, Final Report March 2010
US DOT OIG audit 2006
FHWA division Offices directed to perform in-depth reviews of
state load rating and posting practices
Findings – Conditional Compliance
Current 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 12/31/2016
Built 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 2010
Load Rating Compliance with NBIS
BA-2010-06
October 2010
Licensing and Use of AASHTOWARE Virtis Software
BA-2011-02
March 2011
Local Agency Load Rating Prioritization and Coding
BA-2012-01
July 2012
MBIS Update & Coding Revisions
Load Rating Troubleshooting
If 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 structure
Attempt to adjust distribution factors
Guide Specifications for Distribution of Loads for Highway Bridges, 1994
Calculate lever rule for cases where code equations may not apply
Other Specs/Virtis Control Options
Different methodology (LFR→LRFR, etc)
Plastic Moment Capacity (if applicable)
1979 Shear specs (if applicable)
Material Sampling (ASTM Standard)
10% increase in steel yield
20% increase in concrete compressive
Advanced Modeling
Virtis 2d/3d
Other FEM software
Load Testing
Questions?