A Load Rating of a 3 Span Continuous Deck-toThrough 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
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
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
AASHTOWare BrDR 2013 User Group Conference
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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
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
AASHTOWare BrDR 2013 User Group Conference
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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
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Main Member Configuration
Deck Truss Configuration
Deck defined along truss’s upper panel points
Deck
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Main Member Configuration
Through Truss Configuration
Deck defined along truss’s lower panel points
Deck
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Main Member Configuration
Half-Deck Truss Configuration
Deck defined along user specified panel points
Deck
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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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-toThrough Truss
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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O’Neal Bridge Rating in Br|R
O’Neal Bridge Complexities
Deck-to-Through truss configuration
Unsymmetrical deck profile
Deck
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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O’Neal Bridge Rating in Br|R
Truss Modeling Assumptions
DC1 loads distributed by tributary deck area to Stringers
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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O’Neal Bridge Rating in Br|R
Truss Modeling Assumptions
DC2 loads distributed uniformly to Stringers
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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O’Neal Bridge Rating in Br|R
Truss Dead Load Path
String -> Floor Beam / Truss -> Main Truss
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
AASHTOWare BrDR 2013 User Group Conference
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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
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
AASHTOWare BrDR 2013 User Group Conference
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O’Neal Bridge Rating in Br|R
Truss Live Load
Influence line method is used to determine maximum force effects
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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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
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
AASHTOWare BrDR 2013 User Group Conference
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O’Neal Bridge Rating in Br|R
Truss Modeling Assumptions
Deck Location
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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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
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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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
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
AASHTOWare BrDR 2013 User Group Conference
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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
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Truss Load Verification – Lower Chord Members
Dead Load Comparison
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Truss Load Verification – Lower Chord Members
Live Load Comparison
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Truss Load Verification – Lower Chord Members
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Truss Load Verification – Upper Chord Members
Dead Load Comparison
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Truss Load Verification – Upper Chord Members
Live Load Comparison
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Truss Load Verification – Upper Chord Members
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Truss Load Verification – Diagonal Chord Members
Dead Load Comparison
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Truss Load Verification – Diagonal Chord Members
Live Load Comparison
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Truss Load Verification – Diagonal Chord Members
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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Summary Comparision
Dead Load Difference
Lower Chord Members:
Upper Chord Members:
Diagonal Chord Members:
2.7%
3.1%
0.5%
Live Load Difference
Lower Chord Members:
Upper Chord Members:
Diagonal Chord Members:
1.1%
1.3%
1.5%
VIRTIS typically produced slightly greater member loads
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
AASHTOWare BrDR 2013 User Group Conference
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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
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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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
Load Rating of a 3 Span Continuous Deck-to-Through Truss Bridge in Br|R
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