1. LRFR vs. LFR Virtis Opis User Group Meeting, August 2, 2011
Bryan J. Silvis, P.E.
Senior Structural Engineer
Structure and Bridge Division

2. Presentation Overview
VDOT Load Rating Background
“LRFR Ratings on Existing Bridge Inventories – A Case Study”
Daniel Whittemore, PE,LEED AP – AI Engineers, Inc.
Prasad Nallapaneni, PE, Virginia Department of Transportation
Additions Made to Case Study
Results
Recommendations to VDOT
Miscellaneous
In Late 2004 to 2005, Department reviewed available design software for use by the Department in the transistion to LRFD. Committee established criteria for the software. (Info from BJS)

3. VDOT Load Rating Background
Decision made to move to LRFR for new structures designed in LRFD and existing inventory.
Move from Bars to Virtis:
Procured three 3-year load rating contracts
Interstate, Primary and Secondary (Interstate 90% and Primary 50% complete)
4,400 structures complete (5,000 anticipated by October when contract ends)
Preparing for another three 3-year contract to rate 5,000 more structures
In Late 2004 to 2005, Department reviewed available design software for use by the Department in the transistion to LRFD. Committee established criteria for the software. (Info from BJS)

4. IBC Presentation Methodology:
Compare rating results using the Virtis LFR engine to those using the Virtis LRFR engine in Version 6.2.
Rate AASHTO legal load vehicles (Type 3, 3-S2 and 3-3) at inventory in LFR and as legal loads in LRFR
As-built plans used for all runs
All load factors, distribution factors, etc. were calculated as the load rating method dictated.
The lowest rated structural member would control the rating regardless of location (specific member or point on a member), limit state or mode.

5. IBC Presentation Assumptions: Rating results are correct
VDOT bridges similar to those of other states
9 Bridge Types (10 structures selected for each type):
Type 1 - Simple span concrete slabs
Type 2 - Continuous concrete slabs
Type 3 - Simple span concrete T-beams
Type 4 - Simple span rolled beams
Type 5 - Continuous rolled beams
Type 6 - Simple span plate girders
Type 7 - Continuous plate girders
Type 8 - Prestressed Bulb-T’s
Type 9 - Simple span prestressed AASHTO I-beams

6. Modifications to Material Presented
Concerns:
Virtis LFR engine (PennDOT) verse Virtis LRFR engine (AASHTO)
States that post between inventory and operating (apples to apples)
Changes made for this presentation:
Worked with 3 of the 10 original files for each type
Verified data and updated rating results for Version 6.3 (BRASS in 6.2)
Added LFR operating rating results for comparison to LRFR
Added rating results using the AASHTO LFR and BRASS LFR engines
Added 10th bridge type (voided slabs – investigated 6 structures and reported 3)
Looked for similar (yellow), close (green) and differing (red) results. The colors in handout are meant as a visual aid only.

7. Simple Span Concrete Slabs

8. Continuous Concrete Slabs

9. Simple Span Concrete T-beams

10. Simple Span Rolled Beams

11. Continuous Rolled Beams

12. Simple Span Plate Girders

13. Continuous Plate Girders

14. Prestressed Bulb T’s

15. Simple Span Prestressed AASHTO I-beams

16. Concrete Voided Slabs

17. Summary LFR Engine Comparison (AASHTO, Virtis, BRASS):
Similar results between engines for Types 4, 6 and 7
Close results between engines for Types 1, 2, 9 and 10
Differing results between engines for Types 3, 5 and 8
LRFR/LFR Inventory Comparison (focus on AASHTO engine):
Average ratios for concrete structures are around 1.2 (T-beams and voided slabs), 1.5 (simple span / continuous slabs and PSC I-beams) and 1.9 (Bulb-T’s)
Average ratios for steel superstructures are around 1.3 (simple span rolled beams and plate girders), 1.1 (continuous rolled beams and plate girders)

18. Summary LRFR/LFR Operating Comparison (focus on AASHTO engine):
Average ratios for concrete structures are around 0.7 (T-beams and voided slabs), 0.85 (simple span / continuous slabs and PSC I-beams) and 1.2 (Bulb-T’s)
Average ratios for steel superstructures are around 0.8 (simple span rolled beams and plate girders), 0.65 (continuous rolled beams and plate girders)
LRFR/LFR Inventory/Operating Average Comp. (AASHTO engine):
Average ratios for steel superstructures are around 1.05 (simple span rolled beams and plate girders), 0.88 (continuous rolled beams and plate girders)

19. Recommendations made to VDOT
Move to Version 6.3 in earliest time frame possible.
Use AASHTO engines exclusively:
Have confidence in AASHTO engines
Less work/confusion involved by focusing resources on one engine
Only exception is simple span rolled beams with cover plates where recommend using the Virtis LFR engine until Version 6.4 release
For LFR rating using Version 6.2 until version change can be made:
BRASS LFR engine for Types 2, 3, 4 and 5
Virtis LFR engine for Types 1, 6, 7, 9 and 10
Engine with the higher rating for Type 8
Recommendations are under review, but so far supported.

20. Miscellaneous

21. VDOT Load Rating Website
Instructional and Informational Memorandums:
Current IIM-S&B-86, Load Rating and Posting of Structures
Current IIM-S&B-27, Bridge Safety Inspections
Frequently Asked Questions
Information on VDOT Database modifications, libraries, rating vehicles, and other miscellaneous topics
Complete Virtis examples for each bridge type are under development and will be added to the website when available.

22. Questions??
Contact