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