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1 Seismic Design of Bridges Lucero E. Mesa, P.E.

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Page 1: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

1

Seismic Design

of Bridges

Lucero E. Mesa, P.E.

Page 2: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• AASHTO - Division IA

• Draft Specifications, 1996

• SCDOT 2001 Seismic Design Specifications

• Comparison Between LRFD & SCDOT Specs.

• SCDOT Seismic Hazard Maps

• Training and Implementation

• Conclusions

SCDOT Seismic Design Of Bridges

Overview

Page 3: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• USGS 1988 Seismic Hazard Maps

• Force based design

• Soil Classification I-IV

• No explicit Performance Criteria

• Classification based only on acceleration

coefficient

AASHTO Div IA

Page 4: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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CHARLESTON, SOUTH CAROLINA

August 31, 1886 (Intensity IX-X)

Page 5: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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Earthquake of August 31, 1886 Charleston, South Carolina

Magnitude=7.3M, Intensity = X

Page 6: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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Sandblow in Charleston

Page 7: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• 1996 USGS Seismic Hazard Maps

• Difference in spectral acceleration between South Carolina and California

• Normal Bridges : 2/3 of the 2% in 50 yr. Event

• Essential Bridges: Two-Level Analysis

Draft Specifications

Page 8: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• Force based specifications

• N (seat width)

• Soil classification: I – IV

• Draft Specifications Version of

1999

Draft Specifications

Page 9: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• Maybank Bridge over the Stono River

• Carolina Bays Parkway

• Broad and Chechessee River Bridges

• New Cooper River Bridge

• Bobby Jones Expressway

Site Specific Studies

Page 10: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• SC-38 over I-95 - Dillon County

• Maybank Highway Bridge over the

Stono River - Charleston County

SEISMIC DESIGN TRIAL

EXAMPLES

Page 11: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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SC-38 over I-95 Description of Project

• Conventional bridge structure

• Two 106.5 ft. spans with a composite

reinforced concrete deck, supported by 13

steel plate girders and integral abutments

• The abutments and the interior bents rest

on deep foundations

Page 12: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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Original Seismic Design

• SCDOT version of Div-IA

AASHTO (Draft)

• 2/3 of 2% in 50 yr

• 1996 USGS maps used

• PGA of 0.15g, low potential

for liquefaction

• Response Spectrum

Analysis

Trial Design Example

• Proposed LRFD Seismic Guidelines

• MCE –3% PE in 75 yr.

• Expected Earthquake – 50% PE in 75 yr.

• 2000 USGS maps

• PGA of 0.33g, at MCE, further evaluation for liquefaction is needed.

• Response Spectrum Analysis

SC-38 over I-95

Page 13: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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Maybank Highway Bridge

over the Stono River

Page 14: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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Highest Hazard

Lowest Hazard

Highest Hazard

Lowest Hazard

Seismicity of South Carolina 1977 to 1996

Page 15: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• 118 spans

• 1-62 flat slab deck supported by PCP

• 63-104 /33 -meter girder spans and 2 columns

per bent supported by shafts.

• The main span over the river channel consists of

a 3 span steel girder frame w/ 70 meter center

span.

• 105-118 flat slab deck supported by PCP

Maybank Highway over Stono River Description of project

Page 16: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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Original Seismic Design

• SCDOT version of AASHTO

Div. I-A (Draft)

• Site Specific Seismic Hazard

• Bridge classified as essential

• Project specific seismic

performance criteria

• Two level Analysis:

� FEE – 10% in 50 yr. event

� SEE - 2% in 50 yr. event

Trial Design Example

• Proposed LRFD Guidelines -

2002

• Two Level Analysis:

• Expected Earthquake - 50%

in 75 yr.

• MCE – 3% in 75 yr.

Maybank Highway over Stono River

Page 17: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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Table C-1. LRFD Spectral Accelerations and Site Coefficients

Earthquake Spectral Accelerations Site Coefficients

SS S1 SDS SD1 Fa Fv

Maximum Considered 1.43 0.407 1.43 0.651 1.00 1.60

Expected 0.0503 0.0104 0.0503 0.0167 1.00 1.60

SEE - Compare LRFD to Original Design Curve

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0Period, T (sec)

Spectral Acceleration, Sa (g)

LRFD CurveSite Specific Original CurveSCDOT Curve, soil type IISCDOT Curve, soil type III

* The cumulative mass participation for

mode shapes at periods indicated and

higher, is approximately 70%.

* Transverse

* Longitudinal

Page 18: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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Original Seismic Design

• Soil Classification: Type II

Trial Design Example

• Stiff Marl classified as Site Class D

Maybank Highway over Stono River

Page 19: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• The SCDOT 's new specifications adopted the

NCHRP soil site classification and the Design

Spectra described on LRFD 3.4.1

• If this structure were designed using the new SCDOT

Seismic Design Specifications, October 2001, the demand forces would be closer if not the same to

those found using the Proposed LRFD Guideline -

2002 .

Page 20: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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Cooper River Bridge

Charleston Co.

• Seismic Design Criteria- Seismic Panel

• Synthetic TH

• PGA - 0.65g

• Sa 1.85 at T=0.2 sec

• Sa 0.65 at T=1 sec

• Liquefaction

Page 21: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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Page 22: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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0

0.5

1

1.5

2

2.5

0 1 2 3 4 5

Period, sec

Spectral

Acceleration, g

Cooper River Bridge

2500 Yr - SEE for Main Piers

Page 23: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• New Specifications

• South Carolina Seismic

Hazard Maps

Need for:

Page 24: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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Page 25: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• The new SCDOT specifications

establish design and construction

provisions for bridges in South

Carolina to minimize their

susceptibility to damage from large

earthquakes.

SCDOT Seismic Design Specifications October 2001

Page 26: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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PURPOSE & PHILOSOPHY

(1.1)

• SCDOT Seismic Design Specifications replace AASHTO Division I-A SCDOT Draft

• Principles used for the development

�Small to moderate earthquakes, FEE, resisted within the essentially elastic range.

�State-of-Practice ground motion intensities are used.

� Large earthquakes, SEE, should not cause collapse.

• Four Seismic Performance Categories (SPC) are defined to cover the variation in seismic hazard of very small to high within the State of South Carolina.

Page 27: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• New Design Level Earthquakes

• New Performance Objectives

• New Soil Factors

• Displacement Based Design

• Expanded Design Criteria for Bridges

New Concepts and

Enhancements

Page 28: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• Small to Moderate Earthquakes

�Essentially Elastic

�No Significant Damage

�Functional Evaluation Earthquake

(FEE) or 10% in 50 yr. event

SCDOT Seismic Design Specifications October 2001

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• Large Earthquakes

�Life Safety

�No Collapse

�Serviceability

�Detectable and Accessible Damage

�Safety Evaluation Earthquake

(SEE) or 2% in 50 yr. event

SCDOT Seismic Design Specifications October 2001

Page 30: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• New USGS

Probabilistic Seismic

Hazard Maps

• New Design Level

Earthquakes

• New Performance

Objectives

• A706 Reinf. Steel

• New Soil Factors

• Displacement Based

Design

• Caltrans (SDC) new

provisions included

SCDOT Seismic Design Specifications Background (1.2)

Page 31: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• New Provisions meet current code objectives for large earthquakes.

� Life Safety

� Serviceability

• Design Levels

� Single Level – 2% / 50 years

� Normal Bridges

� Essential Bridges

� Two Level : 2% / 50 years and 10% / 50 years

� Critical Bridges

Upgraded Seismic Design Requirement (1.3)

Page 32: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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SCDOT Seismic Design Specifications Seismic Performance Criteria

III II I

Page 33: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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SCDOT Seismic Design Specifications October 2001

Page 34: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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VALUES OF Fa AS A FUNCTION OF SITE CLASS AND MAPPED SHORT-PERIOD SPECTRAL RESPONSE ACCELERATION SS (TABLE 3.3.3A)

Site

Class

Design Spectral Acceleration at Short Periods

SS≤≤≤≤ 0.25

SS=0.50

SS=0.75

SS=1.00

SS≥≥≥≥1.25

A

0.8

0.8

0.8

0.8

0.8

B

1.0

1.0

1.0

1.0

1.0

C

1.2

1.2

1.1

1.0

1.0

D

1.6

1.4

1.2

1.1

1.0

E

2.5

1.7

1.2

0.9

a

F

a

a

a

a

a

Page 35: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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SCDOT – Pilot WorkshopImbsen & Associates, Inc. –

I IA

1-6

Increasing

performanceIncreasing earthquake

hazard

Recent

Technology

bc

de

f

ih

gCollapse

Prevention

Limited

Damage

Essent ially

Elast ic

2% in 50 Yrs.

2/3 (2% in 50 Yrs.)

10% in 50 Yrs.

Proposed Design or Retrofit Objective

a

f, h, ia, b, c, d,

e, g

Secondary

System

Primary

SystemDesign or

Retrofit

Objective

Page 36: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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SCDOT Seismic Design Specifications October 2001

Page 37: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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DESIGN SPECTRA FOR SITE CLASS A, B, C, D AND E, 5% DAMPING (3.4.5E)

Ss=1.00g, SEE(2%/50years)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 1 2 3 4

SD_4A

SD_4B

SD_4C

SD_4D

SD_4E

Periods T (sec)

Site Class

A

B

C

D

E

SDI-SEE

Page 38: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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APPLICABILITY (3.1)

• New Bridges

• Bridge Types

�Slab

�Beam Girder

�Box Girder

• Spans less than 500 feet

• Minimum Requirements

• Additional Provisions are needed to achieve higher performance for essential or critical bridges

Page 39: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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DESIGN PHILOSOPHY AND

STRATEGIES • Specifications can be used in conjunction

with rehabilitation, widening, or retrofit

• SPC B demands are compared implicitly against capacities

• Criteria is focused on member/component deformability as well as global ductility

• Inherent member capacities are used to resist higher earthquake intensities

• Using this approach required performance levels can be achieved in the Eastern US

Page 40: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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Design Approaches

(4.7.1)

May require

closure or

removal

Not

warranted

May be higher

Significant

Plastic Action

May require

closure of

limited usage

May be Used Limited Moderate

Plastic Action

Not required to

Maintain

May be Used Limited Minimal

Plastic Action

Reparability Protection

Systems

Ductility

Demand

Design

Approach

2D

µ <

4D

µ <

Page 41: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

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• Plastic Hinge Region Lpr (4.7.7)

• Plastic Hinge Length (4.7.7)

• Seat Width SPC A and B, C, D (4.8.2)

• Detailing Restrainers (4.9.3)

• Butt Welded Hoops

• Superstructrure Shear Keys (4.10)

Other New Concepts and

Improvements

Page 42: Seismic Design of Bridges - libvolume3.xyzlibvolume3.xyz/.../seismicdesignparameterspresentation1.pdfSCDOT Seismic Design Of Bridges Overview . 3 • USGS 1988 Seismic Hazard Maps

42

Seismic Design

of Bridges

Lucero E. Mesa, P.E.

Thanks