Bridge Failures - Lessons learned

Recent NYSDOT Bridge Failure Investigations

George A. Christian, P.E.

Director, Office of StructuresNew York State Dept. of Transportation

Bridge Engineering Course

University at Buffalo

March 29, 2010

2

I-787 - Dunn Memorial Bridge InterchangeAlbany, NY

partial collapse at pier 11- August 2005

I-787 Ramp NB to South Mall

Expressway WB

(BIN 109299A)

3

BIN 109299A

4

Structure Layout (looking east)

5

Overview of Failure

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High Rocker Bearings

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History of Misalignment of High Rocker Bearings at Pier 11

1987 Inspection

Temp. @ 45 °F

1999 Inspection

Temp. @ 70 °F

8

2003 Inspection – Span 12 East Bearing

Temp @ 45 F

Lifted 0.25 ft.(3 in.) - Eccentricity = 3.4 in.

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How did the bearings get misaligned?

Superstructure Displacements:• Survey of adjacent piers (w/ fixed bearings)

– Pier 10 displaced north 1.6 inches.

– Pier 12 displaced north 1.0 in (avg.) 1.7 inches on east side.

• History of Pier 13 joint

– Joints ‘reset’ (vertical) in 1990

– Joint was closed in 1990

– Closed in 1995 thru present

• Longitudinal forces due to braking, centrifugal force

10

Condition of Rocker Bearings• Susceptible to corrosion, debris when continually

tilted

• Corrosion, debris prevents rocking back toward vertical

– Under rocker

– Pin corrosion

• Contact surfaces flatten or “dish”

• Result: Bearings become resistant to horizontal movement, especially back toward being plumb . Transfers longitudinal forces to substructure

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Corrosion & Flattening

12

Frozen Pins

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Rocker and Pintle Corrosion – Span 11 Bearing

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Pier 11

• Height: 82.3 feet

• 13.9’ x 6.44’ at base

• 9’ x 4’ at top of stem

• Stem rebar: 46 -# 8 bars

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Pier 11: Lack of Elastic Range

• Cracks 40 ft. up north face

• Rebounded 51/2 in. when ‘released’

• The pier failed in flexure

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Comparison of Adjacent Piers

PIER

NO.

HGT. BASE REINFORCING STEEL

No.-Size Bars Area

BEARINGS

FIX OR EXP

9 67.47’ 131.4” x 71.2” 42 - # 8 33.18 Fix - Exp

10 72.79’ 132.6” x 72.6” 36 - #11 56.16 Fix

11 82.31’ 166.6” x 77.3” 46 - # 8 36.34 Exp - Exp

12 83.38’ 155.3” x 77.6” 42 – #11 65.52 Fix

13 84.75’ 156.4” x 84.2” 42 - #11 65.52 Exp - Exp

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Pier 11 Design Check

• Designed per 1965 AASHO code

• Meets strength req. for code assumptions

– Allowable / Actual ratio = 0.98 =1.0 (OK)

• No provision for large flexural displacements

• Equivalent Column with 1% reinforcing.

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Results of Pier Analysis

• Limited elastic range - yields at 5.5” deflection

• Cracking at 2.5” deflection

• No capacity increase beyond cracking

Old Pier 11 (AC-12)

0

20

40

60

80

100

120

140

160

0 5 10 15 20

Longitudinal Pier Cap Displacement [in.]

Lo

ng

itu

din

al P

ier

Ca

p F

orc

e [

kip

s]

f’c=9210 psi

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Forces Needed for Failure

• Thermal: limited by resistance of bearing

– Up to 0.58 x Dead Load if sliding assumed: approx. 200 kip from Span 12 only

– Limited range of movement

• Corrosion Build-up:

– Develops horizontal component of vertical dead, live load reactions

– Larger range of movement

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Probable Failure Sequence

• Bearings tilted to north > 20 years ago

• Bearings begin to resist horizontal mov’t.

• Superstructure longitudinal displacements began to move pier instead of Span 12 bearings

• Bearings resist movement moving back toward vertical– Increased southward tipping of Span 12 and 11 bearings

• Instability point reached – bearings tipped

• Forces (displacements) sustained to deflect pier 16 + in. (bearings tipping and spans falling on tipped bearings)

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22

23

24

25

26

27

28

29

30

31

32

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Underlying Cause of Failure

1. Rocker bearings becoming misaligned

2. Rocker bearing not functioning properly

3. Pier 11 was flexible in direction longitudinal to the bridge

4. Pier 11 stem was “lightly” reinforced, and not elastically ductile

• 1, 2 and 3 were required for failure to occur. 4 may have been required, but contributed to extent of failure

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35

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Follow up actions

• Reviewed all high rocker bearings with low inspection ratings (CR 3 or less)

• Inspected those overextended

• Preventive interim retrofits – bolsters

• Technical Advisory: INSP 05-001

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Follow up actions

• Bolsters installed as an extraordinary precautionary measures on 10 bridges

• Alerted other owners of bridges not under DOT’s inspection jurisdiction

• Corrective action:– Dunn Complex, bearing replacements

Marcy Pedestrian Bridge CollapseOctober 2002

South Abutment

North Abutment

Bracket

Field Splice

Span = 171 ft.

Acknowledgements

• Sponsored by New York State DOT

• P.I.—Weidlinger Associates, Inc.

• Material testing and weld inspections by ATLSS Research Engineering Center, Lehigh University

Outline

1. Collapsed Bridge

2. Review of Bridge Design

3. Analysis of Bridge Failure

4. Demolition

5. Laboratory Testing

6. Conclusions

7. Recommendations

8. NYSDOT Actions

9. Applications—Tub girders and beyond

Tub Girder Cross Section

Intermediate

Diaphragm

14.0 ft (4.27 m)

6.3

ft

(1.9

3 m

)

4.3 ft (1.3 m)

Collapsed Bridge

North Abutment

South Abutment

Screed

Collapsed Bridge

South Abutment

Exp. Bearing

Collapsed Bridge

North AbutmentFixed Bearing

2. Review of Bridge Design

Objective: Evaluate the adequacy of the bridge design

2.1 Design Codes

• NYS Standard Specifications for Highway Bridges with

provisions in effect as of April 2000.

• AASHTO Standard Specifications for Highway Bridges, 16th

Ed. LFD (1996) with 1997, 1998 & 1999 interim

• ·AASHTO Subsection 10.51 Composite Box Girders (LFD) …. “This section pertains to the design of … bridges of moderate length supported by two or more single cell composite box girders…..”

2.3 Finished Bridge

• Design assumption: Two I-girders

• Conclusions: The bridge, as designed, would have been sufficient to resist its design loads if it had survived its construction.

2.4 During Construction

Failure Modes:

• b/t of top flange;

• Top flange buckling (between

intermediate diaphragms)

• Global Torsional buckling

Intermediate

DiaphragmTop

Flange

3. Analysis of Bridge Failure

Objective: To find and prove the cause of failure

Metal Form

Angle

Bottom Flange

Bracket

(3' apart)

Form/Catwalk

Tie-rod

(4' apart)

Web Concrete

Top Flange

Web

HangerWest

Operator

Drum

C.L. Bridge

Engine

Screed

East

3.1 Deck Construction Facilities:

Top

Top Steel Plate

Bottom Steel Plate

Elastomer

Steel

Plates

a). Expansion Bearing

Top Steel Plate

Bottom Steel Plate

b). Fixed Bearing

Steel Pin

kESkES

kEC

X

Y

Z kBRG=kES+kPIN

kFS

kEC

X

Y

Z

FD

Nonlinear Spring

kPIN

3.3 Elastomeric Bearings

0

10000

20000

30000

40000

50000

0 1 2 3 4 5 6 7 8 9 10

Deformation, mm

Fo

rce

, N

36 mm dia

Applied Force

SteelPlate

Force-Deformation CurveFixedBoundary

94m

m

3.4 Fixed Bearing Steel Pin Model

End

Diaphragm

Top Flange

Top Flange

Web

Diaphragm

Strut

3.5 Global Model

SW+DL (rebar, form, etc.)Concrete Screed

Steel girder

North

Abutment

-10.0

-9.0

-8.0

-7.0

-6.0

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

0.0 10.0 20.0 30.0 40.0 50.0

Concrete Pour Length, m

Gir

der

Ro

tati

on

, D

egre

e

As-built

As-designed (ideal)

Y

Rotation

42'

105'

3.6 Analysis Results

Middle Screw

Location

Edge Screw

Location3.7 Corrugated Metal Form

Form Thickness = 1.2 mm (3/64 in.)Top Flange

F

Fixed Boundarya

Weak Form: a=1/2" (12 mm)Fy = 40 ksi (275 MPa)

Strong Form: a=3/4" (20 mm)Fy = 45 ksi (310 MPa)

3.9 Form Connection Model

-10.0

-9.0

-8.0

-7.0

-6.0

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0Concrete Pour Length, m

Gir

de

r R

ota

tio

n,

De

gre

e

As-designed (ideal),

No form

As-built

No form

Strong form,

as-built

Weak

form,

as-built

42' 82'95' 105'

Y

Rotation

3.11 Force-Rotation Curve

4. Demolition

• Remove debris safely;

• Sample materials;

• Preserve evidence

Temp. Support

Cut Location

Objectives

5. Laboratory Testing

• Verify Analysis Assumptions

• Check whether materials conform to contract specifications

Objectives:

0

2000

4000

6000

8000

10000

12000

0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25

Lateral Deformation, mm

Fo

rce, N

Force-Deformation Curve

of Form Connections

Strong Form Model

Weak Form Model

Lab Results

5.1 Form Connection Tests

Form connection test

Gage 12

Steel PL

Form

Screw

0

2000

4000

6000

8000

10000

12000

0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25

Lateral Deformation, mm

Fo

rce, N

Force-Deformation Curve

of Form Connections

Strong Form Model

Weak Form Model

Lab Results

5.1 Form Connection Tests

Form connection test

Gage 12

Steel PL

Form

Screw

b. Bearing Model

Fixed Boundary

a. Damaged Fixed Bearing

5.2 Bearing Inspection

6. Conclusions

• The bridge failed in a global torsional mode;

• Stay-in-place forms greatly delayed the collapse, but were not strong enough to prevent it;

• Progressive failure of form connections that initiated the failure sequence

• The bridge would have buckled even if the two deck haunches were identical

7. Recommendations

• Clarify applicable codes;

• Add a new code provision that requires full length lateral bracing to be installed between top flanges unless proven unnecessary by analysis

8. NYSDOT Actions

• Reviewed similar ongoing projects in NYS.

• Required bracing systems for similar bridges in NYS—(NYSDOT “Blue Page”)

• Sought recommendations from AASHTO regarding code revisions.

AASHTO LRFD Specs. – 3rd Edition (2004)

• Art. 6.11: Provisions for single or multiple closed-box or tub girders

• Art. 6.7.5: Lateral Bracing– 6.7.5.3: Top lateral bracing shall be provided

between flanges of individual tub sections. The need for a full-length system shall be investigated…

– If a full length lateral bracing system is not provided, the local stability of the top flanges and global stability of the individual tub sections shall be investigated for the assumed construction sequence

Centroid @ +36.3”Shear Ctr. @ -36.0”Izz = 36 in^4Iyy = 205,817 in^4

Centroid @ +37.3”Shear Ctr. @ -12.2”Izz = 114,870 in^4Iyy = 212,572 in^4

1/16” Top Plate

Lateral Torsional Stability of Open-tub girders

Application to I-Girder Bridges

Application to I-Girder Bridges

Twin I-Girders: No bottom lateral bracing

Iyy = 15,470 in^4 Izz = 472 in^4

Centroid @ +19.96”Shear Ctr. @ -19.06”Izz = 472 in^4Iyy = 296,426 in^4

Twin I-Girders: With bottom lateral bracing

LTB with Non-linear Plate Model

0.0

0.5

1.0

1.5

2.0

2.5

0.0 20.0 40.0 60.0 80.0

Transverse Displacement at Midspan [in.]

De

ad

Lo

ad

Fa

cto

rTwin I-Girders: With bottom lateral bracing

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LTB with Non-linear Plate Model

No Lateral Bracing

0.0

0.5

1.0

1.5

2.0

0.0 20.0 40.0 60.0 80.0 100.0

Transverse Displacement at Midspan [in.]

De

ad

Lo

ad

Fa

cto

r

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Twin I-Girders: No bottom lateral bracing

Twin I-Girder Behavior--summary

• More stable than open tub girder.

• Lateral or lateral-torsional behavior (vs. global torsional)

• Bottom lateral system effective for lateral resistance

• Consider top and bottom laterals for long, narrow spans

• No “spec-ready” equations for checking global behavior (Single Tubs or Twin-I systems)

Dealing with a bridge failure

• Expect your inspection program to come under scrutiny

• Expect safety of other bridges to be questioned

• Expect requests for data on failed bridge and other bridges

• Establish point of contact for all media questions.

• Make “public” info. Easily available –

Dealing with a bridge failure

• Work with your lawyers, (but do not expect them to always have the same priorities).

• Establish protections for privileged material, e.g. ongoing investigations.

The Paradox of Failure

“When it comes to bridge

design, collapse is a most

reliable teacher.”

Henry Petroski

“Success Through Failure; The

Paradox of Design”

One Final Lesson

Questions?