Seismic Design and Retrofit D t ili F d t lDetailing ...mceer.buffalo.edu/research/HighwayPrj/Workshops/Charleston/07Des... · Seismic Design and Retrofit D t ili F d t lDetailing

Seismic Design and Retrofit D t ili F d t lDetailing Fundamentals

Reginald DesRochesf CProfessor and Associate Chair

Georgia Institute of Technology

Learning OutcomesList the types of detailing that increase a bridges displacement capacity.bridges displacement capacity.List the types of detailing to enhance a bridges ductilitybridges ductility. For displacement based design explain the

l ti hi b t th SDC t drelationship between the SDC, expected concrete strain and required detailing. List typical retrofit details along with their seismic performance benefit.

Presentation OutlineVulnerabilities of Typical BridgesVulnerabilities of Typical BridgesSeismic Detailing Fundamentals

Support Lengthpp gDetailing for Ductility

ColumnsFootingsoo gs

Seismic Retrofit FundamentalsSuperstructure

Seat Extenders Restrainers Shear Keys StoppersSeat Extenders, Restrainers, Shear Keys, StoppersSubstructure

Column Jacketing, Bent CapI l tiIsolationApplication of Fragility Curves for Seismic Retrofit

Vulnerabilities of Typical BridgesS t tSuperstructure

Brittle Steel BearingsInadequate Seat WidthsInadequate Seat Widths

ColumnsInsufficient Lap SplicesInadequate Transverse Reinforcement

Limited ductilityLimited ductilityLow shear strength

Footings with Inadequate R i f tReinforcementLiquefiable Soils Common

Presentation Outline Vulnerabilities of Typical BridgesVulnerabilities of Typical BridgesSeismic Detailing Fundamentals






Unseating at Expansion Joints

Northridge Earthquake 1994

Superstructure Expansion Joint

Pre-1971 Typical Post-1971 Typical Expansion Joint

6-inch hinge seat widthExpansion Joint

24 inch hinge seat width

Minimum Seat Width – SDC A2(1 )(4 0 20 ) 12"kSN H +

= + Δ + >(4 0.20 ) 124000ot hN H= + Δ + >

Δot = movement due to pre-stress shortening, creep, shrinkage, and thermal expansion.p, g , pHh = Largest column height w/in flexible frame (clear height – ft)frame (clear height ft).Sk = angle of skew of support (degrees)

Minimum Seat Width – SDC B, C, D, ,2(1 )(4 1 65 ) ( ) 12"kSN in+

= + Δ + Δ >(4 1.65 ) ( ) 124000ot eqN in= + Δ + Δ >

Δ t d t t h t iΔot = movement due to prestress shortening, creep, shrinkage, and thermal expansion.Δeq = seismic displacement demand of long period frame on one side of exp joint.Sk = angle of skew of support (degrees)

Minimum Seat Width – N

Minimum Seat Width – N







Improved Bridge Seismic Details

COLUMMNSS

Column VulnerabilitiesColumn Vulnerabilities

Typical Pre 1971 Caltrans & Pre 1990 CSUS Details

Non-ductile details have four main structural

CSUS Details

four main structural problems:

1- Lack of Confinement.

COL (#4 @ 12” ties)

2-Inadequate Lap Splice at the Base of the Column

LUM at the Base of the Column

3- No footing Top Steel Rebar Mat

MNS

4- Inadequate Rebar Development into the SuperstructureSuperstructure

New Column Details

COOLUMMN

Ductility/ Confinement/ Continuity

Effect of Confinement

COOLUUMNS

Tied vs. Spiral Columns

Compression Reinforcement

Confinement (SDC B, C and D)

All longitudinal bars should be enclosed by g yhoops or spirals.

#3 for # 9 longitudinal bars or smaller#5 for #10 longitudinal bars or larger#5 for bundled bars

Th i f h i h ll dThe spacing of hoops or ties shall not exceed the least dimension of the compression member or 12 inchesor 12 inches

Confinement (SDC C and D)Hoops and ties shall be arrangedHoops and ties shall be arranged

with corner ties having minimum 135 degree angles.g gNo longitudinal bars shall be further

than 6 inches clear on each side along the tie.Ties shall be located vertically not

more than half a tie spacing above the footing or other support and not

th h lf ti i b lmore than half a tie spacing below the lowest horizontal reinforcement in the supported memberthe supported member.

Requirements for Ductile DesignMaximum axial load shall not be greater than

0.20f’ceAg.Area of longitudinal reinforcement for

compression members shall not exceed 0.04Ag.Mi i L it di l R i f tMinimum Longitudinal Reinforcement

0.007Ag for columns in SDC B, C0 01A for columns in SDC C D0.01Ag for columns in SDC C, D0.0025 for Pier Walls in SDC B, C0 005 for Pier Walls in SDC D0.005 for Pier Walls in SDC D

Inadequate Lap Splice

Splicing of Longitudinal Reinforcement in Columns (SDC C or D)

Splicing of longitudinal reinforcement shall be outside of plastic hinging zone for SDC C and D.

For SDC D, mechanical couplers must be used for splicing.

Development Length (SDC C and D)Column longitudinal reinforcement shall be extended

into footings and cap beams as close as possible to gopposite face of footing or cap beam.

Minimum anchorage length into cap beams should be 24dbl.

Confinement (SDC C and D)The maximum spacing forThe maximum spacing for

lateral reinforcement in the plastic end region shall notplastic end region shall not exceed the smallest of the following:

1/5 least dimension (Columns), 6 times the nominal diameter of

longitudinal reinforcement6 i h f i l h6 inches for single hoop

Confinement (SDC C and D)The lateral reinforcement shallThe lateral reinforcement shall

extend into footing to the beginning of the longitudinal barbeginning of the longitudinal bar bend above the bottom mat.

The longitudinal steel shall extend a distance to ensure adequate development for plastic hinge into bent cap

FProblems with Flared ColumnsFLA Strong flare createsRED

Strong flare creates shorter, stiffer columnFailure at the base ofD

C

Failure at the base of the flare is not desirable and does not agree with C

OL

gthe design assumptions

UMNN

Improved Bridge Seismic DetailsDuctilityConfinementContinuityFlare isolation

Improved Bridge Seismic DetailsFlared ColumnsFlared Columns

Improved Footing Details







Seismic RetrofittingSeismic Retrofitting Fundamentals -Fundamentals Superstructure

Seat ExtendersGoal: Provide additional support lengthRelatively inexpensive and easyRelatively inexpensive and easyConsider out-of-phase motion to determine

t t d l thseat extender length

Seat Extenders – Box Girder Bridges

Seat Extenders – Simply Supported BridgesBridges

Seat Extenders – Simply Supported Bridges Steel BracketBridges – Steel Bracket

Seat Extenders – Simply Supported Bridges Steel BracketBridges – Steel Bracket

Seat Extenders - Steel Beams

Restrainer Cables and BarsGoal: Limit movement at hinge or support adjacent girders should unseating occuradjacent girders should unseating occurRelatively inexpensive and easyC id t f h ti t d t iConsider out of phase motion to determine restrainer size and length

Restrainer Cables and Bars–Design ProcedureDesign Procedure

DesRoches and Fenves, 2000,

Restrainers - Design Procedure2 2

1 2 12 1 2

( )

2

( )eqD D D D D

D D

ρ= + +

−( )( 1) ( ) ( )

( )

( )( ) eq j r

r j r j meff r jeq j

D DK K K K

D+ = + +

1effK K

μ=

0.951 0.05 μμ

− −

effμ

ξ ξπ

= +DesRoches and Fenves, 2000

Restrainers– Multi-Step Procedure

Nr = KrDr/(fyAr)Nr KrDr/(fyAr)

Restrainers– Single Step Procedure1 2( )STEP d STEP i i d

2

1 2( )

0.500.50ff

STEP and STEP same as iterative procedure

K K η⎡ ⎤−= +⎢ ⎥mod

1 2

0.50r effK K

K KK

η+⎢ ⎥

⎣ ⎦

=mod

1 2( )eff

r

KK K

Dμ

η

=+

=0eqD

K DN

η =

r rr

y r

Nf A

=

Restrainer Cables and Bars–Properties and ModelsProperties and Models

Restrainer Cables – Box Girder BridgesBridges

Restrainer Cables – Simply Supported BridgesSupported Bridges

Cables Looped Over Bent-Cap Straight CablesCables Looped Over Bent Cap Straight Cables


Simply Supported Concrete Girder Bridge Connection Details


Simply Supported Steel Girder Bridge Connection Details


Connection Details

Restrainer Bars – Simply Supported BridgesBridges

Restrainer Bars – Simply Supported BridgesBridges

Restrainers – Vertical Tie Downs

Bumpers or StoppersGoal: Limit movement at hinge or supportGoal: Limit movement at hinge or support adjacent girdersRelatively inexpensive and easyRelatively inexpensive and easy

Bumpers or Stoppers

Shear Keys and Keeper PlatesLimit transverse a s e sedisplacement of deck relative to bent

Shear Key

beamDesigned with shearColoumb Friction Model in Designed with shear friction approach based on Priestley

Coloumb Friction Model in Transverse Direction

based on Priestley et al. (1999)

Limited Vsk<1/2Vcol

Damage due to transverse movemento e e t

0.31ｍ

Shear Keys and Keeper Plates







S i i R t fittiSeismic Retrofitting Fundamentals – SubstructureFundamentals Substructure “Detailing for Ductility”

ColumnsGoal: Improve

Shear strength deformationShear strength, deformationDuctility capacityLap SpliceLap Splice.

Approaches include:St l J k tSteel JacketConcrete JacketPre-stressed High Strength CablesComposite Jackets

Column Jacketingg

Connection DetailsConnection Details

Column Steel Jacketing

Confinement of plastic hingeConfinement of plastic hinge region

Increased compressive t th d lti t t istrength and ultimate strain

Enhanced ductility capacity Improved bond transfer andImproved bond transfer and lap splice performanceIncreased shear strengthIncreased shear strength

Steel Jacketed Column

COLLUMMNS

Pre 1971 Column Steel Jacketed Column

Modeling of Steel Jacketed ColumnIncreased compressive t th dstrength and

ultimate strain in confined concreteconfined concrete20-40% increase in column stiffnessin column stiffness for full height jacket (testing byjacket (testing by Priestley et al.)

Steel Jacket Retrofit

Concrete Overlay Jacket

Partial Height Jacket

Column Wrap - Composites

I-80 Salt Lake City

•Low Installation Cost•Lightweight

I 80 Salt Lake City

•Lightweight

I-57 Illinois

Cable Column Wrap

Bent CapspGoal: Improve

Shear strengthShear strengthDuctility capacityFlexural StrengthFlexural Strength

Approaches include:St l J k tSteel JacketConcrete JacketPre-stressed High Strength Cables

Bent Cap Retrofit - Prestressingp g


Bent Cap Retrofit - Prestressingp g


Bent Cap Retrofit – Concrete OverlayOverlay


Bent Cap Retrofit – Steel Jacketp


Bent Cap Retrofit – Steel Platesp


Seismic Retrofitting F d t l I l tiFundamentals - Isolation







IsolationGoal

Replace Vulnerable Brittle BearingsReplace Vulnerable Brittle BearingsProtect (Isolate) Vulnerable Substructure Change Vibration ModeChange Vibration Mode

Vulnerable Bearingsg

Vulnerable Bearingsg

Damage to steel and elastomeric bearingsg g

Seismic Response Modification Devices SRMD

Isolation Devices used to reduce

SRMD

used to reduce forces transmitted to the substructure systemDamping Devices used to reduce displacements

Seismic Response Modification Devices SRMD

Isolation Devices used to reduce

SRMD

used to reduce forces transmitted to the substructure systemDamping Devices used to reduce displacements

Isolation - BasicsSa

T1 T2

Period TPeriod, Tacceleration response spectrum

SdSd

Period, Tdisplacement response spectrum

Effect of Damping lower damping

S

higher damping

T1 T2Sa

acceleration response spectrumPeriod, T

Sd

Period, Tdisplacement response spectrump p p

Types of SRMDsypIsolation Devices

Elastomeric BearingsElastomeric BearingsLead-rubber bearingsF i ti P d l B iFriction Pendulum BearingsSliding Bearings

Damping DevicesHysteretic Dampers (Lead Bar)Fluid Viscous DampingVisco-elastic Damper

Isolation – Typesyp

Elastomeric Sliding Friction PendulumElastomeric Sliding Friction Pendulum

Elastomeric Bearings

L d Fill dLead Filled Elastomeric Bearing

Elastomeric Bearing

Friction Pendulum Bearings

Friction – PendulumIsolation Bearing

Friction Pendulum Bearingg

Fluid Viscous Damper & Lock-up DeviceDevice

Dampers







Bridge Fragility CurvesExpert OpinionEmpiricalFragility = P[D≥ds|IM=y]

AnalyticalNon-linear time history approachhistory approach

[ ] 1CDPfp ≥= Cf

Very few studies developing fragilities p g gfor retrofittedretrofittedbridges

Methodology for Fragility Development

Bridge Vulnerability

Given Seismic Event

What is the probable bridge performance overbridge performance over a range of potential EQ

intensities?

Bridge Fragility CurvesMSSS SteelSSS Stee

88%

40%

25%

8%

Nine Bridge Classes Considered

Bridge Fragility Curves - ComparisonsNine Bridge Classes Considered

Typical Bridge Classes & RetrofitsSteel Steel

Jacket

Shear Key

Restrainer Cable

Shear Key

Cable

Elastomeric Bearing

Seat Extender

Motivation: Probable Performance

Gi S i i E tGiven Seismic Event

What is the impact ofWhat is the impact of retrofit on the probable bridge performance over a range of potential EQa range of potential EQ

intensities?

Approach: Bridge Fragility CurvesB id F ilit CBridge Fragility Curve

Fragility = P[D≥ds|IM=y]

Assess bridge performanceEvaluate & select retrofit measuresRegional seismic risk analysesPerformance-based retrofitPerformance based retrofit

Retrofitted MSSS Steel Fragility

Applications of Retrofitted B id F ilit CBridge Fragility Curves

Retrofit Selection based on Median Value ImprovementpPerformance-Based Retrofit in Support of Seismic Retrofit Manual Dual-LevelSeismic Retrofit Manual Dual Level EvaluationCost Benefit AnalysesCost-Benefit AnalysesRegional Seismic Risk Assessment

Performance-Based RetrofitPerformance Based Retrofit

Performance-Based Retrofit

Identify viable retrofit ystrategy based on performance pobjectives

Objective: jLimit slight damage (design level pga=0.7g)

Performance-Based RetrofitIdentify viable retrofit ystrategy based on performance pobjectives

Objective: jLimit slight damage (design level pga=0.7g)P[Slight|PGA=0.7]

AB 1.0 RC 1 0RC 1.0 EB 0.8SE 1.0 SJ 1.0

0.7g

Performance-Based RetrofitIdentify viable retrofit ystrategy based on performance objectivesp j

Objective: Limit slight damage (design level pga=0.7g)

Objective:Avoid complete damage (design level pga=0.7g)

Performance-Based RetrofitIdentify viable retrofit ystrategy based on performance objectives P[Comp|PGA=0.7]

AB 0 30p j

Objective: Limit slight damage

AB 0.30 RC 0.20 EB 0.18 SE 0.12SJ 0.21

(design level pga=0.7g)Objective:

Avoid complete damage (design level pga=0.7g)

Retrofitted Bridge Fragility CurvesRetrofitted Bridge Fragility Curves




Seismic Design and Retrofit D t ili F d t lDetailing ...mceer.buffalo.edu/research/HighwayPrj/Workshops/Charleston/07Des... · Seismic Design and Retrofit D t ili F d t lDetailing

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