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: 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-53AsphaltSmall34’-0”Welded steel plateNone CL-179AsphaltSmall31’-6”Welded steel plateNone CL-406Asphalt“Car hauler”42’-0”Large beam, plate4 FO-25TimberSmall70’-0”Steel beamsNone FO-54SteelSmall81’-0”Steel beamsNone FO-256SteelSmall82’-0”Steel beams4 VE-24ConcreteLarge50’-0”1 steel beamNone

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 Sealing WiringData-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 % CL % FO % FO % VE %  Measured = stress in loaded girder/total stress between girders  Lever Rule is reasonably conservative for typical bridges

Distribution Factor - Comparison Bridge Loaded Girder: Measured Loaded Girder: Lever Rule Increase Lever Rule by 10% % Difference CL % CL %  Special cases: Increase lever rule by 10%  CL-406: “Car hauler”  CL-179: “Unknown” geometry ?

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?