Full Scale Testing of TrunnionHubGirder Assemblies of Bascule Bridges

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Full Scale Testing of Trunnion-Hub-Girder
Assemblies of Bascule Bridges

• Department of Mechanical Engineering
• College of Engineering, USF

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Outline of Presentation

• Purpose
• Problem Definition
• Previous Work
• Experimental Set-up
• Quarter Scale Model
• Full Scale Models
• Results
• Conclusions/Recommendations

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PURPOSE

• Problems involved with Trunnion-Hub Assembly
• Christa McAuliffe (Hub Crack)
• Venetian Causeway (Trunion stuck in hub)
• FDOT wanted a complete numerical and experimental
  study to find
• Why these assemblies failed?
• How they could be avoided in the future?

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PROBLEM DEFINITION

• FN2 or FN3 interference fit on the TH and HG
• Existing Procedure is AP1

• AP1
• Step1.Trunion cool down
• Step2.Trunion warm-up in hub
• Step3.Trunion-Hub cool down
• Step4.Trunion-Hub warm-up into girder

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Alternative to existing procedure is AP2

• AP2
• Step1.Hub cool down
• Step2.Hub warm-up in girder
• Step3.Trunion cool down
• Step4.Trunion warm-up in Hub-Girder

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Interference fits

• Trunion,hub and girder are assembled with FN2 or
  FN3 interference fits
• Shrink fitting is carried out by cooling in
  liquid nitrogen
• Cool down in liquid nitrogen produces thermal
  stresses
• Interference between the trunion-hub and the
  hub-girder produces structural stresses

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Stresses

• 1.Thermal Stresses (thermal gradients)
• 2.Structural Stresses (interference)

• 1.Transient Stresses
• (during the assembly
• procedure)
• 2.Steady State Stresses
• at the end of the
• assembly procedure

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PREVIOUS WORK

• Denninger(2000)
• Steady State Stresses
• Theory of elasticity (compounded cylinders)
• Steady state stresses were found to be within
  safe limits of ultimate strength

• Ratnam(2000)
• Transient stresses
• FEA (ANSYS)
• 3 different bridges
• AP2 was better than AP1

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EXPERIMENTAL WORK

• Set-up
• Strain gages
• Thermocouples
• Data acquisition system and LabVIEW

• Objectives
• Measure stresses during each step of the two
  assembly procedures
• Use recorded stresses to compare the two
  procedures.
• Validate results of steady state and transient
  stresses from the earlier two studies

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Sensors

• Strain Gages
• Cryogenic strain gages
• WK-06-125RA-350
• M-bond 610 (bonding agent)
• N-1(moisture proofing agent)

• Thermocouples
• Type-E thermocouples
• Highest millivolt output per degree change in
  temperature
• 5TC-TT-E-20-120
• CY-20 cryogenic epoxy

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Data Acquisition

• SCXI-1000 chassis with three SCXI-1122 modules
• 48 channels
• 12 thermocouples and 12 strain gage rosettes
• Fastest scan rate (one channel/sec)
• Cool down times are of the orders of minutes,
  while warm-up times are of the order of hours

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Strain-Temperature.vi
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QUARTER-SCALE MODEL

• Trunion cool down
• Trunion shrink fitted into hub
• Trunion-Hub cool down

Shrunk Trunion

• Hub

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Geometry of Quarter Scale Model
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Pool Boiling during trunion cool down

• Source Barron(1999)

• h increases by 100 factor

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Temperature and Hoop Stress during Trunion Cool
Down
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Hoop Stress on Quarter Scale Hub
Trunion warm-up into Hub

• Trunion-Hub Cool Down

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Comparison of Steady State Hoop Stresses on Hub
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Fracture Toughness
Source Steel Castings Handbook, Steel Founders
of America
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Critical Crack Length

• Stress Intensity Factor
• KI 1.125 ? (? a)1/2
• For Example, if ? 30 ksi
• Critical Crack Length at Ambient Temperature
• KIc 80 ksi in1/2
• a 1.79 in
• Critical Crack Length in Liquid Nitrogen
• KIc 27 ksi in1/2
• a 0.20 in

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Conclusions of Quarter Scale Model

• Pool Boiling
• Critical region (Hub inner diameter)
• Maximum hoop stress occurred during
• Trunion-Hub cool down

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Two nearly identical sets of trunion, hub and
girder
FULL-SCALE MODEL

• Assembly Procedure 1 (AP1)
• Trunnion in Hub
• Trunnion-Hub in Girder

• Assembly Procedure 2 (AP2)
• Hub in Girder
• Trunnion in Hub-Girder

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Pictures of Full Scale
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Geometry of Full Scale Model
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RESULTS
Hoop Stress on Hub Inner Diameter for AP1
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Hoop Stress on Hub Inner Diameter for AP2
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Comparison of Hoop Stress on Hub Inner Diameter
during AP1 and AP2
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Comparison of CCL

• Experiment CCL
• FEA CCL

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Comparison of Von-Mises Stress on Hub Inner
Diameter during AP1 and AP2
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Summary of comparisons of AP1 and AP2
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CONCLUSIONS

• AP1 versus AP2
• Steady state stresses equal
• AP2 is the better alternative compared to AP1
• Quicker, but possibly costlier
• Lower transient (thermal) stresses
• Higher critial crack length (CCL)
• FEA versus Experiment
• Excellent agreement at steady state
• Good agreement during transient

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RECOMMENDATIONS

• In General
• Enforce no taper on hub
• Combined heating cooling
• Heat to 200F
• Cool in dry ice / alcohol
• If LN, eliminate thermal shock by gradual cooling
• Refrigeration ? Dry ice / alcohol ? LN
• If AP1
• No sudden LN immersion
• Combine heating with gradual cooling
• If AP2
• Gradually cool hub
• Collaboration between contractors

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FUTURE CONSIDERATIONS

• Effect of THG geometry (Optimize)
• Thickness
• Width
• Diameter ratios
• Eliminate fit at HG
• Bolts take bridge load
• 17th St Causeway