LRFD FOUNDATION DESIGN FOR FLYOVER 13 OVER I-95 AND I-73

April 4, 2013 Geo3 T2 Conference

Sanjoy Chakraborty PhD, PE

I-73 Phase 1 Overview

• I-95 to US-501 • $166 Million Construction Cost • About 5.7 mi of Interstate Hwy. • 10 Bridges • Partial Interchange at I-95

Bridge 4B Design

• Ramp from I-95 South to I-73 South • Crossing over I-95 and I-73 • 2,514 ft. in length • 8 spans • Post-tensioned concrete segmental box girder • Hammerhead piers on drilled shaft groups • Steel piles at abutments

Bridge 4 Design

Geotechnical Design Procedure

• Geotechnical Exploration and Laboratory Testing • Conduct Site Response Analysis

– Design Acceleration Response Spectra – Design Acceleration Time History Data Sets – Analysis of Seismic Hazards

• Design of Bridge Foundations • Design of Embankments and Retaining Walls • Foundation Substructure Analysis

• Dynamic Stiffness and Damping compatible with Superstructure Model

Bridge 4 Design

Geotechnical Exploration

• Preliminary (Right-of-way) Phase – 5 SPT borings – Seismic CPT soundings – Deep boring to 500 feet with shear wave velocity

measurements • Final (Construction Plans) Phase

– Borings at abutments and interior bents – Borings at approach embankments and MSE wall locations

• Laboratory Testing

Bridge 4 Design

Subsurface Conditions

• 25 to 40 feet of Pleistocene soils – Sands with clay and silt – Measured SPT from WOH to 26

• 10 to 25 feet of Bear Bluff soils – Sands with clay and silt, some fat clay – Measured SPT from 3 to 28

• Black Creek soils to bottom of borings – Sands and silty sands, low plasticity fines, some cementation – Measured SPT from 5 to 86

Bridge 4 Design

Site Response Analysis

• SEE and FEE Design Scenarios • SHAKE Analysis – South Carolina Soils • Development of site specific Acceleration Response Spectra

– Horizontal – Vertical

• Development of spatially incoherent and spectrum compatible acceleration time histories for SEE – 3 sets total – Horizontal and vertical components – Developed at support locations (abutments and interior bents)

Bridge 4 Seismic Analysis

Design Response Spectra : 5% Damping

Bridge 4 Seismic Analysis

Site Response Analysis

Development of Spectrum Compatible Horizontal and Vertical Acceleration Time Histories

• Variability – subsurface conditions

• Spatial variability of motion – wave passage effects

• Incoherency of motion

Bridge 4 Seismic Analysis

Subsurface Variability

Bridge 4 Seismic Analysis

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.0 1.0 2.0 3.0 4.0

Spec

tral

Acc

eler

atio

n (g

's)

Period (sec)

Design Horizontal Acceleration Response Spectra at GROUND SURFACE Damping = 5 %

Boring BA-09 Boring BA-10 Boring BA-11 Boring BA-12 Boring BA-13

Bridge 4 Seismic Analysis

Wave Passage Effects

• Spatial Variability of Motion • Incoherency of Motion

Summerville

Myrtle Beach

Bridge

Columbia

Spatial Variability

Bridge 4 Seismic Analysis

Incoherency of Motions

Seismic Hazards

• Idriss and Boulanger, 2008 Monograph + SCDOT GDM • Site Specific Demands from SHAKE (CSR) • Liquefaction and Cyclic Softening • Seismically Induced Settlements • Horizontal Movements • Residual Shear Strengths • Downdrag loads • Mitigation at abutments – earthquake drains

Bridge 4 Design

Design of Bridge Foundations

• AASHTO LRFD 2010 + SCDOT GDM • Driven pile group at abutments • Drilled shaft group at interior bents • Limit States

– Service – Strength – Construction (Strength) – Extreme Event

Bridge 4 Design

Design of Bridge Foundations

• Group analysis using FB-Multipier – Movements : Service – Shaft demands : Strength and Extreme Event – Equivalent linear stiffness – compatible with superstructure

analyses

• Shaft axial resistance – AASHTO + SCDOT Resistance Factors – Load test data – Group effects – Downdrag from seismic settlements

Bridge 4 Design

FB-Multipier Models

Bridge 4 Design

Shaft Axial Resistance – Bent 4 Diameter = 7.0-ft

Bridge 4 Design

-20

-10

0

10

20

30

40

50

60

70

80

90

100

110

0 500 1000 1500 2000 2500 3000 3500 4000

Drill

ed S

haft

Tip

Ele

vatio

n (ft

)

Factored Axial Resistance, Redundant Design (kips)

Strength Limit StateExtreme Event LS with Downdrag

Drilled Shaft Design

Bridge 4 Design

Bent

Strength Limit State Extreme Event Limit State : SEE

Maximum Factored Load (kips) Minimum Tip

Elevation - Strength (ft)

Maximum Factored Load

(kips)

Minimum Tip Elevation

EE (ft)

Required Minimum Tip Elevation (ft) Construction Strength

2 2,406 2,545 6 2,570 9 6

3 2,406 2,545 15 2,570 18 15

4 2,518 2,939 0 3,681 -6 -6

5 2,518 2,939 9 3,681 12 9

6 2,518 2,939 -3 3,681 -3 -3

7 2,390 2,484 9 2,603 40 9

8 2,390 2,484 17 2,603 42 17

Foundation Model for Time History Analysis

• Equivalent static stiffness for SEE loads

– 6x6 stiffness matrix for group – Iterations for compatibility

• Frequency dependent damping

– Shear wave velocity/Shear Modulus profile – Frequency dependent damping ratio/dashpots – Horizontal, rocking, vertical and cross-coupling terms

Bridge 4 Seismic Analysis

Shear Wave Velocity Model

Bridge 4 Seismic Analysis

0

20

40

60

80

100

120

140

0 500 1000 1500 2000 2500

Dept

h fr

om G

roun

d Su

rfac

e (fe

et)

Shear Wave Velocity (ft/sec)

BA-09BA-10BA-11BA-12BA-13Vs Match

Shear Wave Velocity Model based on SHAKE site-specific analyses models

Shaft Head Damping – Lateral Swaying

Bridge 4 Seismic Analysis

Shaft Head Damping – Vertical (Axial)

Bridge 4 Seismic Analysis

Seismic Analysis of Superstructure

• Michael Baker Corp. and CDM Smith – Response Spectrum – Pushover – Time History

• Multiple iterations to achieve compatibility between substructure and superstructure models

Bridge 4 Seismic Analysis

I-73/I-95 Interchange Bridge 4B

• Questions?

Bridge 4 Design