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A Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R

A Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R AASHTOWare BrDR 2013 User Group Meeting. Michael B. Murdock, P.E. Structural Engineer August 6, 2013. Where We Are Headed. New Features of VIRTIS 6.2

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A Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R

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  1. A Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R AASHTOWare BrDR 2013 User Group Meeting Michael B. Murdock, P.E. Structural Engineer August 6, 2013

  2. Where We Are Headed • New Features of VIRTIS 6.2 • Added truss analysis capabilities in fall 2010 (now known as Br|R) • Load Rating • O’Neal Deck-to-Through Main Span Truss for ALDOT • Verification of Truss Analysis • Chord member force verification for both dead and live loads

  3. New Truss Rating Analysis Capabilities of Br|R New Truss Rating Analysis Features Added in VIRTIS version 6.2 Truss-Counters – tension only members Chord Member Eccentricity – at connections Floor Truss Beam Elements – floor trusses to be modeled using beam elements

  4. New Truss Rating Analysis Capabilities of Br|R New Truss Rating Analysis Features Added in VIRTIS version 6.2 Half-Deck Configuration – user-defined deck locations along truss Available Main Member Configurations for Truss Superstructures Deck Through New Half-Deck

  5. Main Member Configuration Deck Truss Configuration Deck defined along truss’s upper panel points Deck

  6. Main Member Configuration Through Truss Configuration Deck defined along truss’s lower panel points Deck

  7. Main Member Configuration Half-Deck Truss Configuration Deck defined along user specified panel points Deck

  8. O’Neal Bridge Rating in Br|R • O’Neal Bridge • Florence, Alabama • US Rte 43 over Tennessee River • Constructed 1939 • 4 lanes of traffic • Length: 2070.5’ • Spans: 14 • 6 Simply Supported Approach Spans • 5 Deck Truss Spans • Main 3 Span Continuous Deck-to-Through Truss

  9. O’Neal Bridge Rating in Br|R • O’Neal Bridge Complexities • Deck-to-Through truss configuration • Unsymmetrical deck profile Deck

  10. O’Neal Bridge Rating in Br|R • Truss Modeling Assumptions • DC1 loads distributed by tributary deck area to Stringers

  11. O’Neal Bridge Rating in Br|R • Truss Modeling Assumptions • DC2 loads distributed uniformly to Stringers

  12. O’Neal Bridge Rating in Br|R • Truss Dead Load Path • String -> Floor Beam / Truss -> Main Truss

  13. O’Neal Bridge Rating in Br|R • Truss Live Load • Live load does not follow same load path as dead load for truss • Live load distribution to truss is based on live load distribution factors • Factors are manually calculated according to the lever rule

  14. O’Neal Bridge Rating in Br|R • Truss Live Load • Influence line method is used to determine maximum force effects

  15. O’Neal Bridge Rating in Br|R • Truss Modeling Assumptions • Chord members were defined using built up members with gross section properties • Member connections are “Riveted” • All connections are modeled as k=1.0 • Deck location was defined using “Mid” panel points along vertical chord members

  16. O’Neal Bridge Rating in Br|R • Truss Modeling Assumptions Deck Location

  17. Truss Load Verification – GTSTRUDL Assumptions • Truss Load Verification • Verification of new analysis capabilities of VIRTIS • Past O’Neal Bridge Analysis • Structural Evaluation of Gusset Plates • Complete in Fall of 2009 • GTSTRUDL analysis of main truss to determine chord member forces

  18. Truss Load Verification – GTSTRUDL Assumptions • Previous GTSTRUDL Assumptions • Plane Frame Structure • A truss structure cannot define axial loads that do not occur at panel points • Occurs at floor beam locations on O’Neal Truss • Panel points had moment released to simulate truss connectivity

  19. Truss Load Verification – GTSTRUDL Assumptions • Gross Section Properties • Similar Loading Conditions • All dead loads manually calculated and applied as point loads except truss selfweight • Similar to VIRTIS approach • Live load is determined through an influence line approach comparable to VIRTIS approach

  20. Truss Load Verification – Lower Chord Members • Dead Load Comparison

  21. Truss Load Verification – Lower Chord Members • Live Load Comparison

  22. Truss Load Verification – Lower Chord Members

  23. Truss Load Verification – Upper Chord Members • Dead Load Comparison

  24. Truss Load Verification – Upper Chord Members • Live Load Comparison

  25. Truss Load Verification – Upper Chord Members

  26. Truss Load Verification – Diagonal Chord Members • Dead Load Comparison

  27. Truss Load Verification – Diagonal Chord Members • Live Load Comparison

  28. Truss Load Verification – Diagonal Chord Members

  29. Summary Comparision • Dead Load Difference • Lower Chord Members: 2.7% • Upper Chord Members: 3.1% • Diagonal Chord Members: 0.5% • Live Load Difference • Lower Chord Members: 1.1% • Upper Chord Members: 1.3% • Diagonal Chord Members: 1.5% • VIRTIS typically produced slightly greater member loads

  30. Conclusions • New features of VIRTIS 6.2 (Br | R) • Beam elements in modeling of Floor Trusses • Half-Deck structure system configuration • Allows for more complex Truss Structures to be modeled • O’Neal Deck-to-Through Truss Bridge • Analysis using “Half-Deck” configuration produces comparable member loads to established industry practices

  31. Load Rating of Deck-to-Through Truss Bridge in Br|R • Questions? Michael Murdock, P.E. Structural Engineer TranSystems mbmurdock@transystems.com 804-282-1525

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