handout John Kulicki.pdf

8/20/2019 handout John Kulicki.pdf

1/22

Evolut ion of the AASHTO

Bridge DesignSpecifications

A Story in Two Parts

John M. Kulicki, Ph.D.,

Chairman/CEO

Modjeski and Masters, Inc.

Part 1

The AASHTO LRFD Bridge

Design Specifications:

Yesterday, Today and

Tomorrow

OHBDC – Especially 1983Edition

Spring 1986 – Gang of Four

Name 1986 Affiliation

• James E. Roberts Caltrans

• H. Henrie Henson CODOH

• Paul F. Csagoly FLDOT

• Charles S. Gloyd WashDOT

NCHRP 20-7/31 “Development ofComprehensive Bridge Specs and

Comm.”

• Task 1 - Review of other specifications for coverageand philosophy of safety.

• Task 2 - Review AASHTO documents for possibleinclusion into specification.

• Task 3 - Assess the feasibility of a probability-basedspecification.

• Task 4 - Prepare an outline for a revised AASHTOspecification.

May 1987 HSCOBS - A TurningPoint

• Findings of NCHRP Project 20-7/31 presented.

• Seven options for consideration.

• Funding requested to initiate an NCHRP projectto develop a new, modern bridge designspecification.

• NCHP Project 12-33 - “Development ofComprehensive Specification and Commentary”.

• Modjeski and Masters, Inc. began work in July,1988.


2/22


3/22

Load and Resistance FactorDesign

Σηi γ i Qi ≤ φ Rn = Rr in which:

• ηi = ηD ηR ηI ≥ 0.95 for loads for max• = 1/(ηI ηD ηR) ≤ 1.0 for loads for minwhere:

• γi = load factor: a statistically based multiplieron force effects

• φ = resistance factor: a statistically basedmultiplier applied to nominal resistance

LRFD (Continued)• ηi = load modifier

• ηD = a factor relating to ductility• ηR = a factor relating to redundancy• ηI = a factor relating to importance• Qi = nominal force effect: a

deformation stress, or stressresultant

• Rn = nominal resistance

• Rr = factored resistance: φRn

LRFD - Basic Design Concept Some Algebra

σ σ β

2Q

2 R +

Q - R =

σ σ β

γ λ

φ 2Q

2 R

ii

+ + Q

x

=

Σ

σ σ σ 2Q

2 RQ)-(R + =

x 1

= R = + + Q = R ii2Q

2 R γ λ

φ λ σ σ β Σ

Reliability Calcs Done for M and V –Simulated Bridges Based on Real Ones

• 25 non-composite steel girder bridgesimulations with spans of 30,60,90,120,and 200ft, and spacings of 4,6,8,10,and 12 ft.

• Composite steel girder bridges having the sameparameters identified above.

• P/C I-beam bridges with the same parametersidentified above.

• R/C T-beam bridges with spans of 30,60,90,and120 ft, with spacing as above.

Reliability of Std Spec vs. LRFD –175 Data Points


4/22

2006 Monte Carlo Reanalysis of1993 Beta

4 0r 5 data points each

2006 Monte Carlo Reanalysis of 1993 Beta

2006 Monte Carlo Analysis of Betafor New Bridge Data Base

Bridge Database: Beta Factors Using Monte Carlo Analysis

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

1 6 1 1 1 6 2 1 2 6 3 1 3 6 4 1 46 5 1 5 6 6 1 6 6 7 1 7 6 8 1 8 6 9 1 9 6 10 1 1 06 11 1 1 16 1 21

Full Set of 124 Database Bridges

B e t a F a c t o r

124 Bridges

Monte Carlo Analysis: B eta vs Span Length

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 50 100 150 200 250 300 350

Span Length (FT)

C o m p u t e d B e t a F a c t o r

2006 Monte Carlo Analysis

CIP Boxes

Monte Carlo Analysis: D/L Ratio vs. Beta

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0.0 1.0 2.0 3.0 4.0 5.0

Dead to Live Load Ratio (Unfactored)

C o m p u t e d B e t a F a c t o r

2006 Monte Carlo Analysis

⎟⎟

⎠

⎞⎜⎜

⎝

⎛ ⎟

⎠

⎞⎜

⎝

⎛ ⎟

⎠

⎞⎜

⎝

⎛

Lt

K

L

S

2900

S + 0.075 = g

3

s

g

0.10.20.6

Major Changes• Revised calculation of load distribution

Circa1990


5/22

Distribution Factors Revisited (2005)On-Going Work – NCHRP 12-62

Moment in the Interior Girder, 1 Lane Loaded, Location 104.00y = 1.8817x+0.0388R

2 = 0.4005

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Rigorous Distribution Factor

A A S H T O S t a n d a r d D i s t r i b u t i o n F a c t o

r

Moment in the Interior Girder, 1Lane Loaded,Location 104.00y= 0.9729x +0.1378R

2 = 0.3521

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Rigorous Distribution Factor

L R F D D i s t r i b u t i o n F a c t o r

Courtesy of Prof. Jay Puckett

Major Changes (Continued)• Combine plain, reinforced and prestressed

concrete.• Modified compression field/strut and tie.

• Limit state-based provisions for foundationdesign.

• Expanded coverage on hydraulics and scour.

• The introduction of the isotropic deck design.

• Expanded coverage on bridge rails.

• Inclusion of large portions of the AASHTO/FHWA Specification for ship collision.

Major Changes (Continued)• Changes to the earthquake provisions to

eliminate the seismic performancecategory concept by making the method ofanalysis a function of the importance of thestructure.

• Guidance on the design of segmentalconcrete bridges – from Guide Spec.

• The development of a parallelcommentary.

New Live Load Model – HL93• Continuation of a long story

1912 Article Published inTransactions of ASCE,

Henry B. Seaman

• It would thus seem that 80 lb/sf wouldbe a maximum load, if indeed it shouldnot be much less, for long spans.

Bridge Engineering, Published in1916, J.A. Waddell

Waddell discusses the source of distributed

load used in the design of bridges:

Some people have the idea that a herd ofcattle will weigh more per square foot than a

crowd of people, but such is not the case, asthe actual limit for the former is about 60 lb/ft2.

L.R. Manville and R.W. Gastmeyer,

Engineering News, September 1914

“The customary loading assumed for the design of

highway bridges in the past has been a certainuniform live load alone, possibly a typical heavywagon or road-roller, or a uniform live load with aconcentration….But these older types of loading are inadequate

for purposes of design to take care of modern

conditions; they should be replaced by some

types of typical motor trucks.”


6/22

L.R. Manville and R.W. Gastmeyer,Engineering News, September 1914

3k4k6k4k

14k12k

8'12'12'12'12'12'

5k16k18k24k20k28k

5'6'6'6'6'6'

4-Ton10-Ton12-Ton14-Ton17-Ton20-Ton

1923 AREA Specification

4k6k

8k

14'

16k24k

32k

5.5'

10-Ton15-Ton

20-Ton

VERY CLOSE!!


8k14'

32k19'

8k14'

32k19'

8k14'

32k

20-Ton 20-Ton 20-Ton

15'

800 lb per ft


8k

14'

32k

19'

8k

14'

32k

19'

8k

14'

32k

15'15'

20-Ton 20-Ton 20-Ton 800 lb per ft800 lb per ft

Shoemaker’s Truck Train andEquivalent Load (Bold Added)-1923

• The 7.5-ton [capacity] truck, which weighs

about 15 tons when loaded to capacity andwhich can be overloaded to weigh about

20 tons, is the heaviest commonly used.

• A large part of traffic, however, is carried intrucks of 5 tons capacity or less. It wouldnot appear to be necessary, therefore, toprovide for a succession of 20-ton loads.

Shoemaker’s Truck Train andEquivalent Load - 1923

15-Ton 15-Ton 20-Ton 15-Ton 15-Ton

6k14'

24k30'

6k14'

24k30'

8k14'

32k30'

6k14'

24k30'

6k14'

24k

600 lb/ft

28,000 lb

By 1929 lane load becomes what we have today


7/22

1928-1929 ConferenceSpecification

6k14'24k

30'6k

14'24k

30'8k

14'32k

30'6k

14'24k

30'6k

14'24k

15-Ton 15-Ton 20-Ton 15-Ton 15-Ton

640 lb/ft

18,000 lb for Moment

26,000 lb for Shear

1941 AASHTO----HS20(Almost)

640 lb/ft32,000 lb for Moment

40,000 lb for Shear

8k

14 '

32k

14 '

32k

H20 - S16

1941-1944 Rebellion & Chaos!!

• Much disagreement over HS Loading

• “An Analysis of Highway Loads Based onthe Special Loadometer Study of 1942” by

Dr. A.A. Jakkulka

• Recommended HS20 Truck “Because itwas the more common stress producingtruck on the road”

1941-1944 Rebellion & Chaos!!

At the December 1944 Bridge CommitteeGroup Meeting, a progress report on a truckloading study conducted at Texas A and MCollege was presented. The minutes of themeeting state that:

the discussion that followed ….soondeveloped into a “free for all” over “them”good old fighting words “what design loadingshould be used.” After the meeting got down tonormalcy again, Mr. Paxon presented…

1944 Agreement• No HS Lane Load---use H20 Lane Load

• Variable axle spacing adopted – more

closely approximates “the tractor tailorsnow in use”

• HS20-S16-44…..44 added to reduceconfusion from so many changes

Live Load Continued to beDebated

• Early 1950’s – Discussion to remove the

lane load as too heavy and wasteful forcontinuous spans

• Throughout 50’s there are discussionsabout increasing the design truck

• 1958 – Decision to do nothing until after AASHO Road Tests are completed.


8/22

Live Load Continued to beDebated

• Late 60’s – H40, HS25 and HS30 discussed• 1969 – SCOBS states unanimous opposition to

increasing weight of design truck – “wastefulobsolescence” of existing bridges

• 1978 – HS25 proposed again

• 1979 – HS25 again – commentary –

– need for heavier design load seems unavoidable

– HS25 best present solution

– 5% cost penalty

• Motion soundly defeated

“Exclusion Loads” – Based on TRBSpecial Report 225, 1990

EXCL/HS20 Truck or Lane or 2 – 110 kN Axles @ 1.2 m

Selected Notional Design Load

HL-93

EXCL/HL 93 – Circa 1992

B I N G O ! !

NCHRP 12-33 Project Schedule• First Draft - 1990 – general coverage

• Second Draft - 1991 – workable

• Third Draft - 1992 – pretty close• Two sets of trial designs - 1991 and 1992

• Fourth Draft - 1993 – ADOPTED!!

• 12,000 comments

• Reviewed by hundreds

• Printed and available - 1994


9/22

Implementation Starts Slowly• Lack of software.

• Early lack of training – but several thousand havetaken NHI courses with more to come.• Perceived difficulties

– Load distribution – Shear in concrete – Foundations – Load cases seemed numerous but that may

be because they are all stated – Continual changes – more later

• Similar story with EUROCode plus nationalissues.

Implementation (Continued)• Down size, right size, capsize.

• To SI or not to SI? That’s the question.

• But things are moving, especiallycompared to other major changes.

• Federal deadline: 2007.

• By 2007:

– 5,000 LRFD bridges

– More than half of states doing part or allLRFD

First LRFD Major Bridge Opened1997

Upgrades and Changes to 1990Technology

• 1996 foundation data reinserted.

• New wall provisions – ongoing upgrade.

• 2002 upgraded to ASBI LFRD Segmental GuideSpecs.

• MCF shear in concrete simplified and clarifiedseveral times – major update in 2002.

• Load distribution application limits expandedseveral time in 1990’s due to requests to liberalize.

• More commentary added.

Upgrades and Changes• 2004 – major change in steel girder design

in anticipation of………

• 2005 – seamless integration of curvedsteel bridges ending three decade quest

Curved Girder Leaders• Dr. Bill Wright

• Dr. Don White

• Mr. Mike Grubb

• Dr. Dennis Mertz

• Mr. Ed Wasserman


10/22

Upgrades and Changes (Continued)• 2005 – P/C loses updated

• 2006 – complete replacement of Section 10 –Foundation Design

• 2006 – more concrete shear options

• 2007 - big year

– Streamline MCF for concrete shear design

– 1,000 year EQ maps and collateral changes

– Seismic Guide Spec - displacement based

– Pile construction update

• 2008 - Coastal bridge Guide Spec

HSCOBS Asserts Ownership

• LRFD Oversight Committee – Circa 2002“The mission… is to promote LRFD as thenational standard for bridge design and develop astrategic plan to successfully implement LRFD by2007 for all new bridge designs.

…to develop a strategic plan to identify andprioritize educational and training needs….

Where Do We Go From Here?

Future as Seen in 1993 – ContinuedDevelopment

• Quantifying Redundancy.

• Expanded database of loads, etc.

• Refinement of foundation provisions.

• Simplification of load distribution.

• Improvements in reliability procedures.

• Joint probability procedures

– LL with EQ?

– Ship and scour?

– EQ and scour?

– Ice and wind? – Etc.

Calibration of Service Limit State• Deformation, cracking, service stress limits.

• What quantitative criteria can be established?

• What is the structural penalty for violating a non-strengthlimit state?

• How often can the limit state be exceeded in the designlife?

• What is an appropriate reliability index?

• What is the appropriate loading in terms of magnitude,configuration, and placement? How does this relate tomultiple presence factors?

• Should permit loads and illegal loads be considered?

• Will SHRP 2 and NCHRP 12-83 do it??

Other Limit States??• Does current design address the real culprits?

• Where are owners spending maintenance $$?

• Do we know the impact of changes?

Will FHWA LTBP Tell Us??


11/22

Rehabilitation

• Applying new standards to existing bridgeshas always been a challenge.

• Are other limit states or load combinationsor reliability targets appropriate for rehab?

• Do we need and “Application Manual” forrehab?

Bridge Security

– Per 2003 BRC recommendations, T–1formed several years ago

– Much research ongoing

– ASCE Committee on Bridge Securityformed – James Ray, Chair

– First fledgling steps towards specificationson ballot – NCHRP 12-72

Quantification of Redundancy• 2005 – T-5 commits to work with

results of:

– NCHRP 406 – redundancy of super

– NCHRP 458 – redundancy of sub

– Goals:

• Multiplier table for routine girder bridges.

• Process for evaluating more complexbridges for a reliability index in damaged

state.

Joint Probability of Occurrence• 2005 – T-5 also commits to continued review

of:

– FHWA Synthesis Report on ExtremeLoading Combinations by Nowak, Knott andDumas, August, 1996

– NCHRP 489 – extreme events, 1999

• 2005 T-5 presentation by Sue Hida onCALTrans in-house study of joint probability ofscour and EQ-----non-issue.

• Focus shifting to “all hazard “ approach.

Fatigue and Fracture• Should new load histograms be obtained?

– Traffic changes after 1970’s oil embargo

– Increases in legal loads – CB’s, etc.

– Load bandwidth increase

• Having said that – still seeing little loadinduced damage

• Have we given up on F and F Specchanges for HPS?

Perfection is Still an Illusive Goal

But Improvement is Possible andDemanded by Society


12/22

Summary• The object was to switch to a more robust, more

expandable, more adaptable platform---------likeWindows vs. DOS.

• As with the switch to Windows, there were sometransitional learning curves and headaches----butmany developers can see benefits, users can seethe logic.

• It is unrealistic to expect the LRFD Specs to becomestatic-----researches will always have new ideas,nature will continue to teach us lessons.

• But LRFD was intended to adapt and grow!

Net Effect So Far

‘94‘06‘04 ‘09

“Accessory For 5th Edition???

Thank You

And A Special “Thank You”To All Who Helped Over The

Last Two Decades!!

But Some Must Be Mentioned• NCHRP – Ian Friedland, Scott Sabol,

Dave Beal

• SCOBS – Bob Cassano, Clellon Loveall,Jim Siebels, Dave Pope, Mal Kerley

• Panel – Jim Roberts, Chairman

• AASHTO – Kelley Rehm, Ken Kobetsky

• Modjeski and Masters – Dennis Mertz,

Wagdy Wassef, Diane Long


13/22

Part 2

Bridge Failures and

Design Specifications

First Problem—Defining Failure

The easy definition:• Any unplanned occurrence in construction

or service

• Now lets get realistic

First Problem—Defining Failure• Collapse – event easy to identify and agree on

– cause is something else

• Inability to serve intended function – Lack of sufficient service strength

– Misalignment

• Unsightly defect – Cracks

– Misalignment

– Discoloration

• Disproportionate future maintenance• Shortened service life

How Does Profession React?• Research• Additions to design spec to design avoidance• Changes to material specs

• Changes to fabrication or construction specs• Add to non-spec “body of knowledge”• Operational changes

• Policy changes• Retrofits• Mixtures

Lets look at some examples!!

Sunshine Skyway 1980 Sunshine Skyway• Vessel hit side span pier which was

not protected

• Response – design – 1994 Guide Specification

– Written and adopted

– Partly incorporated into

AASHTO LRFD 1st Edition


14/22

Sunshine Skyway• Basic parameters

( ) ( ) ( ) ( ) AF = N PA PG PC

( ) ( ) ( ) ( ) ( ) B C XC DP A = B R R R R R

Human factors and serendipity

hard to eliminate

Webber Falls

MM-62

MM-60

Pier 3 Pier 2 Pier 1Pier 4

West Abutment

Pier 1

Webber Falls

Pier 3 Pier 2 Pier 1Pier 4

Webber Falls

Webber Falls

• Special structural features – Barge reversed-back exerts more load

– Corner hit-less energy absorption – Hit weakest pier

• Reactions – Ops and Policy-Recommendation for alarms if

active controls not sense in some period of time

– Retrofit-similar bridges got pier protection added

Webber Falls - Retrofit


15/22

2009 - Now There Is A Choice Silver Bridge

Silver Bridge• Reaction

– Fracture Control Plan

• Materials-fracture toughness

• Fabrication-welder quals and testing

• Documentation

• Weld repairs

– Design Specifications

• Identification of FCM and tension components

• Toughness requirements identified but not used

in design calcs

Silver Bridge• Reaction (cont.)

– Policies

• NBIS with special requirements for FCM’s

• Redundancy stressed

• Permit numerical demonstration of redundancy

– Retrofits

• Sister bridge demolished and replaced

• Some redundancy enhancement

I-794 Hoan Bridge(December 2000)

I-794 Hoan Bridge


16/22

I-794 Hoan Bridge

Web Plate

Gusset Plate

Welds Touching or Overlapping

in Web Gap

Stress Concentration Triaxial Constraint = HIGH RISK

I-794 Hoan Bridge

• All fractures were brittle (cleavage) initiationat the intersecting welds

• No fatigue crack growth was detected in theweb at any shelf plate detail

• The shelf plate lack of direct connection to thetransverse connection plate created a largegeometric crack like condition

• Failure analysis showed that the crack likegeometry and the high triaxiality resulted infracture on the upper shelf

I-794 Hoan Bridge

• Response

• FHWA memorandum cites two criteria

that can indicate fracture vulnerability – 1) Intersecting / overlapping welds

– 2) Evidence of rapid crack growth

• Body of knowledge-detailing guidance

– ¼” RULE: Intersecting weld toes must

have at least ¼” of clear separation toe-to-toe to allow relief of constraint

Static Wind - Tay Bridge

Dynamic Wind - First Tacoma

NarrowsWind - Response

• Research - Identify quasi-static pressure

and understand dynamic phenomena

• Design Spec – “static” wind pressure and

overturning line load• Body of knowledge on dynamic actions

– Section models

– Aeroelastic models

– Terrain models

– Computational methods

– A variety of potential fixes


17/22

Section Model Japanese Aeroelastic Tests

Wind/Rain - Cables What Causes Cable Vibration?• Classic analysis says that a steady wind

will impose a steady force/constantdeflection of the cable. However, – General experience - cable stay vibrations build up

to violent movements under the combined effect ofrain and wind, both being light to moderate in theirintensities.

– Some bridges show excessive vibration withno rain, possibly due to vortex shedding.

– There are other various phenomena

which may also be responsible.

Reducing Cable Movement• Various methods used to

control cable movement – Use of energy absorbing pads

between cables and end ofanchor pipes.

– Cross-tying the cable together.

– Modifying the cable shape to

change the aerodynamic

conditions.

– Installation of energy absorbers

(or dampers) on the cables to

reduce the cable vibration.

Cable Damper Retrofit• Cable dampers are double-acting,

linear, fluid viscous mechanical devices: – Dampers mounted to the cables in the tower head.

– Steel collar at cable attachment point.

– Steel bracket assembly attaches other end of

damper to stationary steel anchor pipe.

CNEW

CABLECOLLAR

NEW DAMPER

BRACKET ASSEMBLY

NEW CABLE

DAMPER

NEW U-BOLT

ANCHOR PIPE

CSTAYCABLE

TOWER CORE

L

L


18/22

FatigueYellow Millpond Bridge

Fatigue• Response research on resistance and

loads• Much added to body of knowledge

Fatigue• Response – Design Spec

CAFT (Typ.)

( ) ( )n

f F γ Δ ≤ Δ

( )( ) ( )365 75SL

N n ADTT =

( )

1

3

n

AF

N

⎛ ⎞Δ = ⎜ ⎟⎝ ⎠( ) ( )TH n F F Δ=Δ

Distortion Fatigue

Distortion Fatigue

• Response

– Research

– Body of knowledge from case studies

– Specification – verboten details

– No quantification in spec so far

Earthquakes - San Fernando 1971


19/22

San Fernando 1971 San Fernando 1971• Response

– Research• Lab tests, particularly on column cyclic behavior

San Fernando 1971• Response (cont.)

– Capitalize on building research – ATC 2, NEHRP

– Shear failures

– Bond and development



• ATC 6 Document lead to

Div. I-A of Std Spec

• SSPC

• Design Spectrum

• Site factors

• R factors

2/ 3

1.22.5sm

m

AS C A

T = ≤

2.01.51.21.0S

IVIIIIII

Soil Profile Type

Site

Coefficient



• Methods of analysis

• Seat widths

• Confinement

• Plastic hinging

• Bond and development

THTHMMMMMMSM/UL4

THMMMMMMMMSM/UL3

MMMMMMSM/ULSMSM/UL2

******

No seismicanalysisrequired

1

irregular regular irregular regular irregular regular

Critical BridgesEssential BridgesOther Bridges

Multispan Bridges

Single-Span

Bridges

Seismic

Zone

Northridge 1994


20/22


21/22

Pensacola, FLBay Saint Louis, MS

Biloxi, MSBiloxi, MS

TASK ORDER DTFH61-06-T-70006 (2006)

DEVELOPMENT OF GUIDE SPECIFICATIONS

AND HANDBOOK OF RETROFIT OPTIONS

FOR BRIDGES VULNERABLE TO COASTALSTORMS

Modjeski and Masters, Inc.

Moffatt & Nichol, Inc.

Ocean Engineering Associates, Inc.

Dennis R. Mertz

D’Appolonia

Status Report in 2007 General Session

Wave Tank Studies 2009 Coastal Guide Specification

Past Reactionary Cycle Has Often

Been Iterative

ResearchEvent

Application

ApplicationResearch

Event

Is There A Better Way?• Can we make a summary of past events

more accessible? – HDR FHWA report

– On line summaries – like crash tested railings?

• Can we be proactive?

• “What iffing” by think tanks? – Would this uncover yet unseen phenomena?

– Can we deduce behavior w/o experiments?

– Can we calibrate design or analysis model w/oexperiential data?


22/22

Is There A Better Way?

• The problem: – So far nature has been asking the

questions and we have been trying to findanswers.

– For proactive response we would have toknow the fundamental questions!

• Difficult ------ but maybe we should at

least try to get ahead of the need some

how.

A Modest Proposal• Maybe it would be worth a trial

workshop to see what might evolve! – High level, innovative thinkers

– Not just bridge people

– Meet several times – give time to think

• Objective: What “big thing” are we

missing?

• We have spent money on more

speculative ideas!!

Lets at least try to get ahead

of events!!

Thank you

Some graphics provided by:Dr. J. Fisher Mr. D. Barrett

Dr. D. Mertz Mr. J. O’Conner Dr. R. Connor Dr. Z. Savor Dr. Z Prucz Dr. D. Sheppard

handout John Kulicki.pdf

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