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TRUSS GUSSET PLATES TRUSS GUSSET PLATES
Wahid Albert, PENYSDOTOffice of StructuresOctober 2008
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BACKGROUND
Truss Gusset Plates and Connections of Truss Members to the Gusset Plates are Ordinarily Stronger than the Truss Members to which they are Connected. For this Reason, Load Ratings of Trusses Have not Usually Included a Check of the Gusset Plate Capacity
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BACKGROUND
I-35W Bridge over the Mississippi River in Minneapolis, Minnesota Collapsed on August 1, 200713 Fatalities, 100 Injuries
NTSB Preliminary Finding on Jan 15, 2008: Under-designed Gusset Plate
http://www.ntsb.gov/Recs/letters/2008/H08_1.pdf
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FHWA TECHNICAL ADVISORY (T 5140.29)
RECOMMENDATIONSJANUARY 18, 2008
Check the Capacity of Gusset Plates as Part of the Initial Load Ratings
Check the Capacity to Account for Modifications that Result in Significant Changes in Stress Levels
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NYSDOT’S IMPLEMENTATION PLAN
Identify Truss Type Structures Carrying Highways in New York State
Identify Bridges with Stress Increase in their Gusset Plates
Check Capacity of Gusset Plates for the Identified Bridges
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TRUSS GUSSET PLATE SCREENING
Screening to Include:Bridges Whose Gusset Plates Have Been Subjected to Increased Stresses Due to Increased Applied Loads (Dead or Live)
Bridges Whose Gusset Plates Have Lost Capacity Due to Deterioration or Damage
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CAUSES of DEAD LOAD INCREASE
Increased Deck ThicknessDeck Overlay IncreaseBridge Deck WideningWidening Roadway Width (Curb to Curb, Rail to Rail)Addition of Sidewalk OverhangAddition of Major UtilitiesAddition of Concrete Barrier to Replace Rail
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CAUSES of LIVE LOAD INCREASE
Current Live Loading > Design Live LoadingIncrease in Number of Lanes Since Original ConstructionIncrease in Deck Roadway Width (Increased LL Distribution to Trusses)Known to be in an Area of Increased Overweight Loads
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TRUSS GUSSET PLATE SCREENING
605 Truss Structures Carrying Highways in NYS(NYCDOT and Authorities not Included)
350 out of 605 (58 %) are Locally Owned
145 Bridges with Stress Increase in Gusset Plates that Required Analysis
42 out of 145 Requiring Analysis (29 %) are Locally Owned
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STATE and LOCAL SUMMARY
24%24%Percentages145605Sub Total
50.0%121116.7%161012.8%1294914.7%1175837.1%2670710.7%328618.2%844554.0%4787417.1%741316.0%850219.4%211081
AnalysisAnalysisPopulation% RequiringRequiringTrussRegion
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LOCAL SUMMARY
12%12%Percentages42350Sub Total
0.0%00110.0%00109.9%881913.2%538832.7%185579.1%222610.7%32850.0%02448.0%22534.2%12425.7%3531
AnalysisAnalysisTrusses
% RequiringRequiringLocalRegion
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NYSDOT ISSUANCETechnical Advisory (TA 08-001)Load Factor Design (LFD) Analysis for Existing Trusses
Structures Design Advisory (SDA 08-001)Load and Resistance Factor Design (LRFD) for New and Replacement Trusses
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WHAT TO CHECK?Combined Flexural and Axial LoadsShear on Both the Gross and Net SectionsUnsupported Edge DistanceEdge Slenderness RatioThe Resistance of FastenersBlock Shear Rupture ResistanceAnalysis of Whitmore SectionGusset Plates in Compression
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LRFD LIVE LOAD CASES FOR NEW AND REPLACEMENT BRIDGES
HL-93 & NYSDOT Design Permit Vehicle Live Loads :
The Higher Loaded Chord is Maximized with Concurrent Forces in the Other Members.
The Higher Loaded Diagonal is Maximized with Concurrent Forces in the Other Members.
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LFD LIVE LOAD CASES FOR EXISTING BRIDGES
HS-20 Truck or Lane Load:
Case I: The Maximum Truss Member Tensile Forces.
Case II: The Maximum Truss Member Compressive Forces.
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SECTIONS OF INTEREST
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FREEBODY DIAGRAM
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MEMBER FORCES
For Each LL+I Case:Factored Member ForcesHorizontal ComponentsVertical Components
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FORCES & STRESS
Forces Acting on Section:Axial ForceShear ForceBending Moment
Stress Along Section:Axial StressMaximum Shear StressFlexural Stress
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GUSSET PLATES UNDER COMBINED FLEXURAL AND AXIAL LOADS
FHWA Guide: The Maximum Elastic Stress may beTaken as φf Fy
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GUSSET PLATES IN SHEAR
Gross Shear Yield SectionsGross Shear Yield Sections
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GUSSET PLATES IN SHEAR
Net Shear Fracture Sections
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UNSUPPORTED EDGE DISTANCE
Allowable Length of Unsupported Edges
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EDGE SLENDERNESS RATIO REQUIREMENT
Allowable Slenderness Ratio
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MEMBER CONNECTION DESIGN
Strength Limit State for Not Less than The Larger of:
The Average of The Factored Axial Force and The Factored Axial
Resistance of the Member OR
75 % of the Factored Axial Resistance of the Member
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THE RESISTANCE OF FASTENERS
Plate Bearing FailuresFasteners SShear
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BLOCK SHEAR RUPTURE RESISTANCE
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WHITMORE SECTION
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ANALYSIS OF WHITMORE SECTION
Allowable Tensile Force on Gross Section (Yielding Resistance)
Allowable Tensile Force on Net Section (Fracture Resistance)
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GUSSET PLATES IN COMPRESSION
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EFFECTIVE LENGTH FACTOR, KValue of K will Depend on the Anticipated Buckled Shape
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"k"
"k" Value Vary from 0.65 to 2.1 in Most Cases, k = 1.0 (Pinned-Pinned)
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SAMPLE PHOTOS
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GUSSET PLATES IN COMPRESSION
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REPAIR EXAMPLEREPAIR EXAMPLE
ROUTE 23 OVER SCHOHARIE CREEKROUTE 23 OVER SCHOHARIE CREEK
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CONNECTION IN 3DCONNECTION IN 3D
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CONNECTION IN 3DCONNECTION IN 3D
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DAMAGED PLATEDAMAGED PLATE
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ANGLES REPAIRANGLES REPAIR
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WOOD BLOCKWOOD BLOCK
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STRONGBACK BEAMSTRONGBACK BEAM
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STRONGBACKSTRONGBACK
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DETAILSDETAILS
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STAGING AREASTAGING AREA
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RIVETS REMOVALRIVETS REMOVAL
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RIVETS REMOVALRIVETS REMOVAL
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NEW PLATE INSTALLEDNEW PLATE INSTALLED
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CHORD CONNECTIONCHORD CONNECTION
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DIAGONAL & DIAPHGRAM DIAGONAL & DIAPHGRAM CONNECTIONCONNECTION
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UNDER TRUSS VIEWUNDER TRUSS VIEW
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BOTTOM LATERAL PLATEBOTTOM LATERAL PLATE
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UPDATE
NYSDOT Continues to Analyze the Identified State and Local Trusses
Emergency Repairs Were Done to 4 Trusses out of 23 that Were Analyzed
16 % of Trusses Analyzed;13 % Needed Repairs
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1. Technical Advisory (TA 08-001) Load Factor Design (LFD) Analysis for Existing Trusseshttps://www.nysdot.gov/divisions/engineering/structures/manuals/technical-advisory/repository/TA_08-001-Truss_Gusset_Plate_Analysis.pdf
2. Structures Design Advisory (SDA 08-001) Load and Resistance Factor Design (LRFD) for New and Replacement Trusses:
https://www.nysdot.gov/divisions/engineering/structures/repository/manuals/SDA-08-001_Gusset_Plate_Design.pdf
3. FHWA TECHNICAL ADVISORY (T 5140.29) http://www.fhwa.dot.gov/legsregs/directives/techadvs/t514029.htm
4. National Transportation Safety Board Safety Recommendationhttp://www.ntsb.gov/Recs/letters/2008/H08_1.pdf
WEB REFERENCES