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Hoan BridgeHoan BridgeFailure AnalysisFailure Analysis
Wisconsin Department of TransportationWisconsin Department of Transportation
City of Milwaukee, WIDecember 13, 2001
City of Milwaukee, WIDecember 13, 2001
LEHIGH FHWA LICHTENSTEIN
OUTLINEOUTLINE Introduction Issues at the Beginning Overview of the forensic
investigation Detailed Analysis Retrofitting of the structure to remain Conclusion
ISSUESISSUES Secure the area under the failed span Traffic Control and Management What caused the failure Open southbound bridge Repair/Replace existing bridges Follow-up on National Issues
CAUSES OF FAILURE?CAUSES OF FAILURE? Factors Investigated:
Structural Design of Lateral Brace System Details of Shelf Plate Connection Assembly
(Constraint) Thermal Forces Live Load Forces (Fatigue) Material Properties Weld - Fabrication Quality
Could this have been caught in inspection? Vulnerability of other bridges
OVERVIEW OF HOAN BRIDGE OVERVIEW OF HOAN BRIDGE FORENSIC INVESTIGATIONFORENSIC INVESTIGATION
Visual Examination Of Fractures Before Demolition Remove Critical Components After Demolition Evaluate Material Properties Global And Local Stress Analysis Of Detail Fractographic And Metallographic Studies Model Crack And Geometric Condition Assess Crack Instability And Arrest
Location F-7View from West
Location E-7View from West
Pier 3S Pier 2SNorth
217-0
24-6
24-6
173-88 Spaces @ 21-8 1/2 = 43-42 Sp. @ 21-8 =
65-1 1/2 108-6 1/2
Girder D
Girder E
Girder F
Floor BeamNumber 1 2 3 4 5 6 7 8 9 10 11
D6 D7 D8
E7
F7
UNIT S2A
F7
Unit S2A Northbound Traffic Lanes East
24-6 24-6
10-012-012-012-06-0
Girder E Girder FGirder D
10-5/16
WT12X55
WT12X55
WT12X55
WT12X55
1/245deg.
BTC P4E70xx
North
7/8 A-325 Bolts 15/16 Holes (typ.)
Tight Fit
SHELF PLATE DETAIL
LOCATION E-28
EXTERIOR GIRDER 108G1SECTION F-F
North
WT12X55
WT12X55
1/245deg.
BTC P4E70xx
Girder E P.P. 28Shelf Plate Weld Fracture Origin
Crack Origin
Girder E P.P. 28Gusset Plate
Crack OriginCrack Bifurcation
Crack Origin
Girder E P.P. 28Crack Origin
Cleavage Fracture Cleavage Fracture
Girder E P.P. 28Shelf Plate Fracture at Hole Repair
Girder E P.P. 28Shelf Plate Fracture at Hole Repair
Fatigue Striations Ductile Fracture
Surface Abrasion
Girder E P.P.28Bottom Flange Fracture
Girder D P.P. 28
Crack OriginsCrack Origins
D 28
Crack Origin
Bottom FlangeCrack Arrest
Girder D P.P. 28Crack Origins
Cleavage Fracture at Web EdgeCorrosion Pitted Cleavage Fracture
Girder D P.P.28Bottom Flange
SEM Crack Arrest in Weld HAZ
Girder D P.P. 28Girder D P.P. 28Crack Arrest in Bottom FlangeCrack Arrest in Bottom Flange
Crack Arrest Boundary
Cleavage Fracture at Crack Tip Cleavage/Ductile Fracture at Crack Tip
Weld
FlangeBase Metal
Girder B P.P. 26Girder B P.P. 26
Fracture Origins
Girder B P.P. 26Girder B P.P. 26
Cleavage/Ductile Fracture at Origin Corrosion Product Cleavage Fracture Near Origin
Girder B P.P. 26Girder B P.P. 26Shelf Plate
Web
Thumbnail Defect
2
2
2
3
3
3
4
4
4
5
5
5
XY
Z
XY
Z
3D Computer Model Of Failed Span/Unit S2a
Finite Element Model Of Joint Assembly
Distance from Joint Center (in)
-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20
Str
ess
(ks
i)
-20-15-10
-505
101520253035404550556065707580
X Normal Elemental StressY Normal Elemental StressZ Normal Elemental Stress
E-28 Stress onWeb Plate
FRACTURE MODELFRACTURE MODEL
ar
Test Temperature (deg. F)
-120-100 -80 -60 -40 -20 0 20 40 60 80 100 120
CV
N E
nerg
y (f
t-lb)
0
20
40
60
80
100
120
140
E-28 Web Plate
Temperature (deg. F)
-240-210-180-150-120 -90 -60 -30 0 30 60 90 120
KIc (
ksi -
in1/
2)
0
20
40
60
80
100
120
140
160KId Dynamic Load Rate
KIc Static Load Rate
E-28 Web Plate
EQUIVALENT PENNY SHAPED CRACK
ksiyy 42; t
aK arr 2
sec2
36.1 factorytriaxialit
webenterstipcrackwheninar .5.1
4
5.1sec5.1)3636.1(
2max
xxxK
.127 inksi
.4~2 int
CRACK ARREST MODELCRACK ARREST MODEL
3/4”
6”
3”
arf
1/2”
1/2”
Temperature (deg. F)
-240-210-180-150-120 -90 -60 -30 0 30 60 90 120
KIc
(ks
i - in
1/2)
0
20
40
60
80
100
120
140
160
KId Dynamic Load Rate
KIc Bridge Load Rate
KId @ NDT
E-28 Flange Plate
Bracings Disconnected From Shelf Plate
Weigh-in-motion Testing, E. Lincoln Ave. Viaduct
0
20
40
60
80
100
120
140
0 20 40 60 80 100 120
NUMBER OF TRUCKS
GROSS VEHICLE WEIGHT, Kips
FINDINGS OF ANALYSIS A Crack-like Geometric Condition Existed At
Intersection Of Shelf Plate And Transverse Connection Plate
Geometry Resulted in High Constraint Stresses From Weight loads And Weld Shrinkage That Were 36% Greater Than Yield Strength Of Material
The Second Retrofit Hole In Center Girder E Increased Stress By 10% At Critical Point
The Bridge Strain Rate Fracture Toughness Of Girder Webs Was 120ksi - , Typical Of A36 Steel Plate
.in
FINDINGS OF ANALYSIS(continued)
Fracture Was Predicted For The Webs Of All Three Girders; Girder E Started The Failure
Only Girder D Was Capable Of Arresting The Dynamic Crack That Extended To The Flange
Flaws in the Detail Is Not Visually Detected
FATIGUE-FRACTURE FAILURE OF BRIDGES
Typical progression of failure:
• Micro-discontinuities are present in almost all large fabricated structures, usually in the welds
• With time (and traffic loads), discontinuities could develop into larger fatigue cracks
• It takes many years for fatigue cracks to grow the first few inches ---- normally can be detected visually during field inspections.
• When fatigue cracks reach a critical size, brittle fracture could result (usually on a cold night).
EFFECT OF CONSTRAINT ON FRACTURE TOUGHNESS
•As constraint is increased, fracture toughness decreases even though the inherent metallurgical characteristics of the steel are not changed
•A triaxial state of stress occurs ahead of the crack which restricts yielding and ductility in the member.
•Constraint (triaxial) played a major role in the fracture at the joints
• Fracture mechanics helps us understand and explain this failure
RetrofitRetrofitof The Hoan Bridgeof The Hoan Bridge
Approach SpansApproach Spans
Wisconsin Department of TransportationWisconsin Department of Transportation
City of Milwaukee, WICity of Milwaukee, WI
HOAN BRIDGE RETROFIT
•Removed all lateral bracings
•Removed shelf plates and grind welds smooth and flush with girder webs
•Provided positive attachment between connection plate and tension flange
•Strengthened pier diaphragms for wind forces
•Reconstructed demolished span
HOAN BRIDGE RETROFIT HIGHLIGHTS
3D Analysis & field test proved bridge can transfer wind loads without lateral bracings.
Performance of retrofit has been field tested
Eliminated fatigue/fracture prone details, driving forces, avoids progressive failure
Future maintenance inspection needs no higher than that for similar steel bridges
Lower cost/completed by year-end
Minimal disruption
RETROFITTED SECTION AT INTERIOR
(All Lateral Bracings And Shelf Plates removed)
RETROFITTED SECTION AT PIER
(Shows strengthening of end diaphragms for wind)
RECONSTRUCTION OF DEMOLISHED SPAN
•Maintained same superstructure configuration
•Omitted lateral bracings
• Improved girder design to ease fabrication and erection
•Replaced 151 ft section of new girder --- from existing splices
Conclusions
Location E-7View from West
Cause of failure determined
Replaced demolished span
Removed welded shelf plates
Removed lateral bracings
Strengthening of diaphragms
FINITE ELEMENT MODEL OF JOINT ASSEMBLY
Triaxial Constrained in a critical weld detail is the cause of failure.
ConclusionsConclusions
Facility service restored andno more problem reported
Continued inspections to monitor potential problems
Promote lessons learned
National Implications Predictive Models Have
Been Developed
Implemented Cost Effective Rehabilitation Strategies
Heightened Awareness Of Need For Inspections
Education On Use Of The Welded Shelf Plate Detail
FINITE ELEMENT MODEL OF JOINT ASSEMBLY
CHALLENGESCHALLENGES How can we improve on the detail (triaxial) Are there better tools to monitor bridges with
this type of detail What would you do differently if you were
called in? What other improvements can be made to the
improved materials (HPS) or fabrication
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