Transcript Slide 1
Session 10
Purdue
Research
Updates
Use of railroad
flatcars
as bridges on
low-volume
roads
Dr. Robert Connor
Ryan Sherman
Jason Provines
Purdue University
Wednesday, March 9, 2011
Topics
Introduction
Field instrumentation
Load rating procedure
Future tasks
Introduction
Typical RRFC
1 main longitudinal
girder
2 smaller exterior
girders
Bridges
Span up to 90’
Single or multi-span
2 or 3 flatcars wide
○ Longitudinal connection
Railroads to County Roads
Retired from railroad industry
Age: 40-50 years
○ No specs prior to 1964
○ Fatigue considerations
Derailment
Economics
Attractive option for county roads
Easy installation
Span up to 90 feet
Low maintenance & cost
Examples of RRFC Bridges
They even make models!
Load Rating RRFC Bridges
Not typical bridges
Past methods
Arkansas State University
○ FE modeling
○ Not using anymore
Iowa State University
○ 3 distribution factors
○ Need experimental data
Use field instrumentation
Field Instrumentation Objectives
Understand how flatcars distribute live load
Let the cars tell us
Transverse distribution
○ Between cars & within car
Use field data to develop accurate load
rating method
Bridges for Instrumentation
133 bridges in
Indiana
7 selected for
instrumentation
Longer, single spans
Deck type
Cross section
Longitudinal
connection
Low load rating
Access
Bridges for Instrumentation
Bridge
Deck
Type
Exterior
Girder Size
Span
Length
Longitudinal
Connection
Load Posting
(tons)
CL-53
Asphalt
Small
34’-0”
Welded steel plate
None
CL-179
Asphalt
Small
31’-6”
Welded steel plate
None
CL-406
Asphalt
“Car hauler”
42’-0”
Large beam, plate
4
FO-25
Timber
Small
70’-0”
Steel beams
None
FO-54
Steel
Small
81’-0”
Steel beams
None
FO-256
Steel
Small
82’-0”
Steel beams
4
VE-24
Concrete
Large
50’-0”
1 steel beam
None
Field Instrumentation
Strain Gage Plans
What are we looking for?
Load distribution
○ Overall (global) behavior – main girders
○ Local behavior – stringers & ext. girders
Location of gages & test trucks
103 gages on 7 bridges
TYPICAL GAGE PLAN
Strain Gage Installation
Welding
Wiring
Sealing
Data-logger
Controlled Load Testing
3 testing lanes
Left
Right
Center
3 testing speeds
Crawl
Static
Dynamic
Axle dimensions & weights
Load Test Data
Real time data
Does it make
sense?
Troubleshooting
Where do we
start?
Load Rating Main Girders
What is total moment on bridge?
How much moment applied to each girder?
Distribution factor
How to calculate stress on girder?
Effective section
Difference between actual stress vs. calculated stress?
Stress reduction factor
Distribution Factor - Comparison
Bridge
Loaded
Girder:
Measured
Loaded
Girder:
Lever Rule
%
Difference
FO-54
0.75
0.84
+12%
CL-53
0.69
0.76
+10%
FO-256
0.66
0.72
+9%
FO-25
0.84
0.86
+2%
VE-24
0.82
0.90
+10%
Measured = stress in loaded girder/total
stress between girders
Lever Rule is reasonably conservative for
typical bridges
Distribution Factor - Comparison
Special cases: Increase lever rule by 10%
Bridge
Loaded
Girder:
Measured
Loaded
Girder:
Lever Rule
CL-179
0.88
0.84
0.92
+5%
CL-406
0.93
0.86
0.95
+2%
CL-179: “Unknown” geometry
?
Increase
%
Lever Rule
Difference
by 10%
CL-406: “Car hauler”
Effective Section
Have moment, now calculate stress
Need section properties
What cross section to use?
Effective Section
Typical flatcar without composite deck
Main
girder + 2 stringers/side
Use section properties to get stress
Effective Section
Flatcar with composite concrete deck
Entire car including composite deck
Is it composite?
Rivet heads
Stress Reduction Factor
Have stress, now match actual with calculated
Statics over-predicts stress
Typical flatcar with no composite deck
Stress multiplied by 0.85
○ Reasonably conservative
Composite concrete deck
No reduction in stress
“Car hauler”
No reduction in stress
Summary of Main Girders
Distribution factor
Lever rule is reasonably conservative
10% increase
○ “Unknown” geometries
○ “Car haulers”
Effective section
No composite deck
○ Main girder + 2 stringers/side
Composite concrete deck
○ Entire car including composite deck
Stress reduction factor
Typical flatcar with no composite deck
○ 0.85 reduction
Flatcar with composite concrete deck or “car hauler”
○ No reduction
Future Tasks
Continue with load rating procedure
“Fine tune” process for main girders
Develop similar method for stringers & deck?
Implementable
○ Applicable to Indiana inventory
○ Simple, yet not overly conservative
Develop inspection methods/criteria
Factors specific to RRFCs
Develop acquisition guidelines
Field experience & load test results
Questions?