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?