A Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Transcript of 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
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Where We Are Headed
New Features of VIRTIS 6.2Added 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 AnalysisChord member force verification for both dead and live loads
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New Truss Rating Analysis Capabilities of Br|R
New Truss Rating Analysis FeaturesAdded in VIRTIS version 6.2
Truss-Counters – tension only membersChord Member Eccentricity – at connectionsFloor Truss Beam Elements – floor trusses to be modeled using beam elements
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New Truss Rating Analysis Capabilities of Br|R
New Truss Rating Analysis FeaturesAdded in VIRTIS version 6.2
Half-Deck Configuration – user-defined deck locations along truss
Available Main Member Configurations for Truss SuperstructuresDeckThroughNew Half-Deck
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Main Member Configuration
Deck Truss ConfigurationDeck defined along truss’s upper panel points
Deck
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Main Member Configuration
Through Truss ConfigurationDeck defined along truss’s lower panel points
Deck
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Main Member Configuration
Half-Deck Truss ConfigurationDeck defined along user specified panel points
Deck Deck
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O’Neal Bridge Rating in Br|R
O’Neal BridgeFlorence, Alabama US Rte 43 over Tennessee RiverConstructed 19394 lanes of trafficLength: 2070.5’Spans: 14
6 Simply Supported Approach Spans5 Deck Truss SpansMain 3 Span Continuous Deck-to-Through Truss
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O’Neal Bridge Rating in Br|R
O’Neal Bridge ComplexitiesDeck-to-Through truss configurationUnsymmetrical deck profile
Deck
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O’Neal Bridge Rating in Br|R
Truss Modeling Assumptions
DC1 loads distributed by tributary deck area to Stringers
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O’Neal Bridge Rating in Br|R
Truss Modeling Assumptions
DC2 loads distributed uniformly to Stringers
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O’Neal Bridge Rating in Br|R
Truss Dead Load Path
String -> Floor Beam / Truss -> Main Truss
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O’Neal Bridge Rating in Br|R
Truss Live LoadLive 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
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O’Neal Bridge Rating in Br|R
Truss Live Load
Influence line method is used to determine maximum force effects
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O’Neal Bridge Rating in Br|R
Truss Modeling AssumptionsChord 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
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O’Neal Bridge Rating in Br|R
Truss Modeling Assumptions
Deck Location
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Truss Load Verification – GTSTRUDL Assumptions
Truss Load VerificationVerification of new analysis capabilities of VIRTIS
Past O’Neal Bridge Analysis Structural Evaluation of Gusset Plates
Complete in Fall of 2009GTSTRUDL analysis of main truss to determine chord member forces
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Truss Load Verification – GTSTRUDL Assumptions
Previous GTSTRUDL AssumptionsPlane Frame Structure
A truss structure cannot define axial loads that do not occur at panel pointsOccurs at floor beam locations on O’Neal Truss Panel points had moment released to simulate truss connectivity
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Truss Load Verification – GTSTRUDL Assumptions
Gross Section Properties
Similar Loading ConditionsAll 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
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Truss Load Verification – Lower Chord Members
Dead Load Comparison
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Truss Load Verification – Lower Chord Members
Live Load Comparison
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Truss Load Verification – Lower Chord Members
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Truss Load Verification – Upper Chord Members
Dead Load Comparison
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Truss Load Verification – Upper Chord Members
Live Load Comparison
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Truss Load Verification – Upper Chord Members
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Truss Load Verification – Diagonal Chord Members
Dead Load Comparison
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Truss Load Verification – Diagonal Chord Members
Live Load Comparison
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Truss Load Verification – Diagonal Chord Members
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Summary Comparision
Dead Load DifferenceLower Chord Members: 2.7%Upper Chord Members: 3.1%Diagonal Chord Members: 0.5%
Live Load DifferenceLower Chord Members: 1.1%Upper Chord Members: 1.3%Diagonal Chord Members: 1.5%
VIRTIS typically produced slightly greater member loads
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Conclusions
New features of VIRTIS 6.2 (Br | R)Beam elements in modeling of Floor TrussesHalf-Deck structure system configuration
Allows for more complex Truss Structures to be modeledO’Neal Deck-to-Through Truss Bridge
Analysis using “Half-Deck” configuration produces comparable member loads to established industry practices
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Load Rating of Deck-to-Through Truss Bridge in Br|R
Questions?
Michael Murdock, P.E.Structural Engineer TranSystems
[email protected] 804-282-1525