Silver Bridge

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Bridge Failures - Lessons learned

George A. Christian, P.E.Director, Office of Structures

New York State Dept. of Transportation

Bridge Engineering Course

University at Buffalo

March 29, 2010


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Bridge Failures Lessons Learned

Outline

Overview of Bridge Failures

Historic Failures in North America

Recent U.S. failures that impacted bridge engineering

practice

Lessons and Response

o

Recent NYSDOT BridgeFailure Investigations

oDealing with a failure

Part 1:

Part 2:


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My general lessons from bridge failures

Bridges can, and will fail, if not properly designed,

constructed and maintained

We may think we know everything to prevent

failures, but we do not. In hindsight, most failures could have been

prevented (but not all).

Failures generally result from a confluence ofcontributing events and/or underlying causes.

When it comes to underlying causes, history can

repeat itself.


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Honest human error in the face of the

unforeseenor the unforeseeableisultimately what brings bridges down.

J.Tarkov, Human Failure In, Bridge Failure Out,

Engineering Case Library report ECL 270, Carleton

University, CA

Two Historic Bridge Failures


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Quebec Bridge1800 ft. main span, collapsed Aug 29, 1907

Buckling Failure of compression

chord (A9L)inadequate latticing


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Quebec Bridge Collapse -Findings

Higher allowable stresses specified

Underestimated dead load ( 18% +/-)

Decision to lengthen span by 200 ft.

Error discovered but accepted

Financial pressures

Project Management issues

Ceding to Consulting Engineer reputation

Lack of experience on site

Communication failures


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Quebec Bridge Collapse -Findings

Lack of knowledge ofbehavior of large

compression members.

Lattice bracing proved to be

inadequate.


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Second Quebec Bridge - 1917

construction collapse Sept 1914


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Tacoma Narrows Bridge collapse- 1940


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Advancements in suspension bridge analysis (deflection theory)

Williamsburg Bridge

-1903

1600 ft. span, 40 ft.

deep stiffening truss

(Depth: span = 1:40)

Manhattan Bridge -1909

1470 ft. span, 27 ft. deep

stiffening truss (1: 54)


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1920s -- Highway suspension bridges become practical

Bear Mountain Bridge -1924

1632 ft. spanWurts Street Bridge,

Kingston, NY -1921

705 ft. span


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1930s--Landmark Bridges

Golden Gate Bridge - 19374200 ft. span, d:s = 1: 168

George Washington Bridge -1931

3500 ft. span, d:s = 1: 120

Originally opened with upper level

roadway only, no stiffening truss

d:s = 1: 350


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1930s: maximize structural efficiency, economy, aesthetics

Plate girder in place of truss for deck stiffening


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Bronx Whitestone

Bridge -1939

-- 2300 ft. span

-- 11 ft. girder

-- d:s = 1: 209

--77 ft. wide, w:s = 1:31

--BWB and other new

suspension bridges withshallow stiffening girders

exhibit wind-induced

Vertical oscillations

--Early retrofits

implemented


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Tacoma-Narrows Bridge--1940

--2800 ft. span--8 ft. girder

--d:s = 1: 350

--39 ft. width, w:s = 1:72

Problem with vertical

oscillations-

Retrofits:

Clamp cable to girder @midspan

Side span tiedowns

Wind tunnel studies initiated


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Torsional motion of Tacoma Narrows bridge prior to failure

Nov 7, 1940


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Lessons Learned

Lack of understanding of aerodynamics effects

Extrapolated past design successes

Economic pressures affecting design

Emphasis on structural efficiency

Lack of emphasis on designing to avoid failure

Inadequate regard to failures of 19th century flexible

suspension bridges


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Impacts of TNB failure

Intensive research on aerodynamic behavior Still no unanimous consensus on actual cause

Buffeting, Vortex shedding, Torsional flutter

Wind tunnel tests during design for all cablesupported structures (suspension and cable stayed)

Ended use of stiffening plate girders

Stiffening trusses continued to be used until 1970s


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Post-Tacoma new bridges

Tacoma-Narrows Bridge

Replacement - 1950 Mackinac Straits Bridge -1954


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Thousand Islands Bridge -Retrofits


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Deer Isle Bridge retrofits


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Bronx-Whitestone Bridge

retrofitsTower stays

Stiffening truss retrofit

Tuned mass Damper

at midspan


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Bronx-Whitestone Bridge --second retrofit 2007

Replaced Concrete

deck with Orthotropic

steel deck

Removed Stiffening

Trusses

Added lateral bracingto lower flanges

Added wind fairings

on stiffening girders

Diagonal stays and

tuned mass damper

remain

Reduce Dead load,

improve torsional stiffness,

improve aerodynamic behavior


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Recent U.S. bridge Failures of significance(and one less significant failure)

Last 30 years

Had Significant impact on Federal and State agencybridge management and safety practices

NTSB findings and recommendations


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Silver Bridge over Ohio RiverPoint Pleasant , WV Gallipolis, OH

Built 1928 , collapsed Dec. 15, 1967


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Silver Bridge collapse

Collapse initiated by eyebar fracture

Initiated at a crack Stress corrosion cracking

High residual stress

corrosion fatigue

At time of design these phenomena werenot known to occur with materials and

conditions present.

Higher traffic loads than when

originally designed New high strength steel had low

toughness

Flaw was inaccessible to inspection

Lack of Redundancy


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Silver Bridge Collapse

consequences

Burning Question : How many other bridges canhave a similar fate??

Resulted in Federal National Bridge Inspection

Standards regulations National bridge inventory

Biennial inspections

Inspector qualifications Reporting requirements

New research: fracture mechanics, materials


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Mianus BridgeI-95 over Mianus River, Greenwich, CT.

Built 1958 , collapsed June 1983


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Mianus River Bridge collapse

Failure of pin and hanger assembly supporting suspended span Hanger displaced laterally, worked off the pin

Transferred (eccentric)load to other hanger

Hanger worked outward, fractured pin

Underlying causes

Corrosion- unmaintained

drainage system

Lack of redundancy

Skew


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Mianus Bridge Collapse

Consequences

Fracture Critical Inspection requirements

Visual hands on every 2 years

NDT methods

Pin and Hanger inspection NDT methods

improved


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Mianus Bridge Collapse Consequences

New York DOT Response

Add redundancy to all 2 and 3girder Pin and Hanger bridges

(approx. 24 bridges)

Over time, these bridges (or

superstructures) have beenreplaced or made redundant /

continuous


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Mianus Bridge Collapse Consequences

New York DOT Response

Detailed Inspections of 3 and 3 welded girderbridges (hands-on and NDT)

Found many fatigue prone details, cracks

Removed flaws, tab plates, drilled out cracks

Some prioritized for replacement

Lesson in 1960s welding

became popular and economical,

however effects of fatigue andunintended structural participation

was not fully recognized.


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A near collapse

Hoan Bridge, Milwaukee, WIBuilt 1970, Failure on Dec. 13, 2000

Brittle fractures that originated

at a lateral bracing system

connection to the girder, where a

horizontal shelf plate intersects atransverse connection plate with

intersecting and overlapping

welds.

2 of 3 girders completely

fractured full depth


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Hoan Bridge Failure

Connection detail provided high tri-axial

constraint at the web, resulted in very highstress concentration (1.6 x Fy).

Very small initiating crack in web,

critical crack size not detectable.

Cold weather contributed to

brittle behavior of steel.

Steel toughness met spec.

requirements

Hoan Br idge Forensic I nvestigation,

Failur e Analysis F inal Report;

Federal Hwy. Admin. and Wisconson DOT,

2001


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(The one less significant failure)

New York County Road Bridge Failure -1986

Significant section losson trusses ( up to 50%)

Lack of redundancy

Excessive dead load:

Timber deck replaced bya steel pan deck with

asphalt

50 psf from 20 psf

Shows importance

of load ratings

Bridge should have

been closed

200 ft. deck truss span one lane bridge

Load posted for 8 tons

Failure initiated by 16 ton truck crossing

the bridge


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Schoharie Creek BridgeNYS Thruway over Schoharie Creek

Built 1954, Collapsed April, 1987


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Schoharie Creek Bridge failure(NTSB Findings)

Caused by scour undermining pier foundation

50 year flood event

Spread foundations on dense glacial till

Inadequate rip rap protection

Inadequate rip rap size

Damage from prior flood events

Rip rap not maintained


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Schoharie Creek Bridge failure

Contributing

causes- Lack of:

Redundancy

ductility in piers

resiliency

f


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Follow Up Actions in NY

Improved hydraulic and scour evaluations

Post flood inspections

Flood warning action plan

Bridge Safety Legislation Uniform Code of bridge inspection

Codified inspection requirements

Structural integrity evaluations

NYSDOT oversight of Authorities, local owners NYSDOT authority to close unsafe bridges

Priority given to bridge inspection program

S h h i C k B id f il


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Follow Up Actions in NY

Bridge Safety Assurance (BSA) Initiative

Program of assessment of bridges vulnerability

to structural failure due to their inherent

characteristics or due to extreme events Assessments are made for individual failure

modes

Identify causes of failure beyond condition

(Why do Bridges Fail?)

Bridge Failures in the US: 1966 2005


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Bridge Failures in the US: 1966-2005

Cause of Bridge Failures from 1966 to 2005

Figure courtesy of J-L Briaud, Texas A&M University


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NYSDOT Bridge Failure Database


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Sytematic evaluations of bridges based on individual

failure modes.

Hydraulics Steel Details

Overload Concrete Details

Collision Earthquake

Evaluate statewide bridge population:

Screen Assess Classify

Vuln. Classifications consider failure likelihood andconsequence.

Evaluation data needs collected during bridge

inspections

NYSDOT Bridge Safety Assurance Initiative

Vulnerability Assessments


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Scour repairs

Steel Detail Retrofits

Add Redundancy

BSA Retrofits

Vulnerability score may

influence rehab / replace

decision


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I-35W over Mississippi RiverBuilt 1967 , collapsed Aug 1, 2007


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Inadequate load capacity of gusset plates at U10 joints,

attributed to design error Substantial increases in weight of the bridge from prior

modifications

Concentrated construction loads combined with traffic

I-35W over Mississippi River

NTSB Findings



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Inadequate Gusset plate thicknesses at U10 and L11

(NTSB) Contributing Cause: Failure of designer Quality

Control Procedures

Deficiency seems evident in hindsight.

Lesson: Design errors can slip through.

NTSB


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Bowed gusset plates suggested problem for further investigation.

NTSB

(NTSB) Contributing cause: Inadequate attention to gusset plates by

transportation agencies during inspections.


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Response by DOTs and FHWA

Inspections of all non-redundant deck truss bridges

(How many other bridges can have a similar fate?)

Guidance on construction loads and stockpiling on bridges

Gusset plate analysis

Include gusset plate analysis in load capacity evaluations

Evaluate gusset plates on all bridges that have undergone a substantial

change in load.

Gusset Plate Analysis Research NCHRP 12-84

FHWA Advisory on non-destructive testing of gusset plates



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I 35W over Mississippi River

NYSDOT actions

Inspected 50 deck truss bridges in NYS

Analyzed Gusset Plates on 133 Trusses that had undergone asubstantial change in load.

Developed analytical tools for gusset plate design and load

capacity checks (LFD and LRFD)

Did not find design errors

similar to I-35W

Found problems due to

deterioration

Developed gusset repair and

replacement procedures

Closed / replaced 1 bridge

due to gusset evaluations

NYSDOT G t


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NYSDOT Gusset

repairs

Failures Caused by Extreme Events


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Failures Caused by Extreme Events Earthquakes

Collisions

Vessel Vehicle

Storm surge

Fire


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Failures Caused by Extreme Events

Lessons learned result in improved design

specifications, detailing practices

Seismic research,

AASHTO seismic specifications

AASHTO Guide specs. for Vessel Collision

AAHSTO Guide specs. For Bridges Vulnerable to Coastal Storms

--NCHRP 12-85:Highway Bridge Fire

Hazard Assessment

--NCHRP 12-72:

Blast Resistant Highway

Bridges- Design and

Detailing Guidelines


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Failures during Construction

When a bridge may be

most at risk to a

structural collapse.



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Rt 470 / I-70 overpass, Golden CO; May 15, 2004

Probable Cause of Failure (NTSB Report):

Failure of temporary bracing system due toinsufficient planning.

Contributing causes:

--girder installed out of plumb.

--inadequate standards for temporary bracing

--inadequate oversight

Only ifs ---Problem reported by passerby, but miscommunication occurred.

---Subsequent girder erection was delayed

(NTSB) Recommendations / Lessons:

Improve standards for temporary works and erection procedures (FHWA, State

DOT, AASHTO, OSHA)

-Prequalification

-Submit written plan, dwgs.

-Certified by a P.E

Failures during construction


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Potential Issues

Bridges are often in their most failure vulnerable

state during construction

Considering construction states during design

Design focuses on completed structure in service

Specs may be vague in addressing construction states Division of responsibility between designer and

contractor/erector.

Designer responsibility for a constructible bridge

Contractor responsible for means and methods for

construction.

l d


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Lessons

Must provide a constructible design Contract documents show one feasible method of

construction (plans or notes)

Design specs shall address constructability

Design loads, limit states during construction

Structural construction operations shall be designed,

certified by a P.E., submitted for approval

Temporary structures, temporary works Erection Drawings

Structural lifting


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Questions?

Documents

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