Slide 1

Report
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?

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