Field Monitoring and Numerical Simulation for Performance Assessment of Integral Abutment Bridges

James M. LaFave, PhD, PEProfessor and CEE Excellence Faculty ScholarAssociate Head & Director of Undergraduate StudiesDepartment of Civil & Environmental Engineering (CEE)University of Illinois at Urbana-Champaign (UIUC) Transportation & Highway

Engineering (T.H.E.) Conference February 27th, 2018

Outline 2

Introduction – Integral Abutment Bridges (IABs)

IAB Parametric Study – Numerical Simulations Overview of modeling methodology Summary of analytical modeling results

IAB Field Monitoring of Two Highway Bridges Implementation of field monitoring systems Summary of field data

Ongoing Work

Integral Abutment Bridges (IABs)3

IABs can provide benefits in terms of decreased construction and maintenance costs

The superstructure & substructure acts as one continuous unit under thermal & other post-construction loading

Most previous IAB research has focused on substructure behavior & demand

Typical Integral Abutment Detail (IDOT Bridge Manual, 2012)

Abutment

Substructure

Superstructure

IABs in Illinois4

IDOT IAB design & construction limits have been placed on highway bridge length & skew configurations Mainly a function of pile type, based on substructure considerations

Previous research in Illinois has investigated soil-pile interaction at IAB foundations

UIUC CEE IAB Research5

Research Goals: Gain a better understanding of IAB behavior (particularly under

thermal loads and for superstructures) Improve the design and construction provisions for IDOT IABs

Two-Part Research Project: Detailed parametric study employing finite element models of

IABs Instrumentation & field monitoring of two (2) IABs in northern

Illinois

IAB Parametric Study – Numerical Simulations6

Typical IAB SAP Analytical Model

Deck and Pier: Shell elements

Girders and Piles: Frame elements

Abutments: Shell elements

Soil and Abutment Backfill:Nonlinear elastic springs

(Soil springs obtained using LPILE)

7

Nonlinear Pile Behavior:Fiber hinge elements (top 5 ft)

IAB Modeling – Primary Parameters8

Primary Parameters Are Largely Based Around Bridge Geometry:

Number of spans (1 to 20) Individual span lengths (50, 100, 150 & 200 ft) & end-span ratio Overall length (up to 1200 ft) Skew (0, 15, 30, 45 & 60 degrees) Width (36, 60 & 96 ft) Piles (HP8 HP18)

Global Movement vs. Effective Expansion Length9

Increasing EEL results in an increase in global longitudinal movement

The resulting model displacements are typically more than 90% of those corresponding to free expansion / contraction

‐5

‐4

‐3

‐2

‐1

0

1

2

3

4

5

0 100 200 300 400 500 600 700Long

itudina

l Displacem

ent (in.)

EEL (ft)

Dead

HL‐93

PosThermal

NegThermal

Free Expansion

Global Movement with Skew10

Increased bridge skew results in non-symmetric movement of the acute and obtuse corners Bridges with skew between 0° and 30° exhibit more symmetric movement For skews above 30°, movement is toward the acute corner

-100

0

100

200

300

400

500

-1000 0 1000 2000 3000 4000 5000

y-co

ordi

nate

(in)

x-coordinate (in)

150' x 2 HP14x117 45° Skew Bridge

Undeformed Deformed -80 Deformed +80

-100

0

100

200

300

400

500

-1000 0 1000 2000 3000 4000

y-co

ordi

nate

(in)

X-coordinate (in)

150' x 2 HP14x117 0° Skew Bridge

-25-20-15-10-50510152025

0 500 1000 1500 2000 2500 3000 3500 4000

Botto

m S

tres

s (k

si)

Length along bridge, in.

Bottom Flange Stress in 3-Span IAB w/ HP14x73

Dead Staged HL 93 Thermal

ThermalNeg HL 93 EXP HL 93 CON

Pure Thermal Pure ThermalNeg

-10

-8

-6

-4

-2

0

2

4

6

8

0 500 1000 1500 2000 2500 3000 3500 4000

Botto

m S

tres

s (k

si)

Length along bridge, in.

Bottom Flange Stress in 3-Span IAB w/ HP14x73

Pure Thermal Pure ThermalNeg

Thermally-Induced Girder Stresses11

Girder Section: W36x194

Girder bottom stress values control for composite sections

Maximum stresses due only to thermal load are located at the abutments

Girder Bottom Stress with Skew12

‐12

‐10

‐8

‐6

‐4

‐2

0

0 50 100 150 200 250 300 350 400 450

Bottom

 stress (k

si)

y‐coordinate (in., obtuse ‐> acute girder)

4 – 100’ spans & HP14x73 (Pure Positive Thermal)

0Skew

15Skew

‐16

‐14

‐12

‐10

‐8

‐6

‐4

‐2

0

0 50 100 150 200 250 300 350 400 450

Bottom

 Stress (ksi)

y‐coordinate (in., obtuse ‐> acute girder)

4 – 100’ spans & HP14x73 & HL‐93EXP (Dead + Pos. Therm. + Live)

0Skew

15Skew

Pile Strains vs. Skew and EEL13

4x100 ft, HP14x73, EEL = 200 ft 100 ft Spans, HP14x73

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0 50 100 150 200 250 300 350

Total Strain

EEL (ft)

Max Total Strains (Pure Positive Thermal)

0 Skew

15Skew30Skew45Skew

0

0.001

0.002

0.003

0.004

0.005

0.006

0 1 2 3 4 5 6 7

Strain

Pile Number (obtuse ‐> acute pile)

Pile Peak Strain (Pure Positive Thermal)

Yield

0 Skew

15 Skew

30 Skew

45 Skew

60 Skew

General Effects of IAB Parameters14

Increase in: Effect:

EEL Increase in pile & girder demands

Pile size Decrease in pile demands, increase in girder demands

Bridge skew Increase in pile demands, decrease in girder demands

Bridge width Small increase in pile demands

End-span ratio Decrease in pile & girder demands

IAB Modeling – Secondary Parameters

Soil Foundation Stiffness Default: medium clay Variations: stiff and soft clay, dense and loose sand

Backfill Stiffness Default: uncompacted sand Variations: stiff backfill

Pile Conditions Default: H-piles, weak-axis orientation Variations: pipe piles, H-pile w/ strong-axis orientation, double H-piles

Pile-Top Relief

15

Secondary Parameters16

Pile strains increase with: Dense Sand Stiff Clay

Pile strains decrease with: Pipe Piles Pile Relief Loose Sand Soft Clay Stiff Backfill Double Piles Strong-Axis 0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0.0045

0 50 100 150 200 250 300 350

Tota

l Str

ain

EEL (ft)

Pile Strains (Pure Thermal)

Default

YIELD

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0 50 100 150 200 250 300 350

Tota

l Str

ain

EEL (ft)

Pile Strains (Pure Thermal)

Default

Clay (Stiff)

Sand (Dense)

YIELD

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0 50 100 150 200 250 300 350

Tota

l Str

ain

EEL (ft)

Pile Strains (Pure Thermal)

Default

Clay (Stiff)

Clay (soft)

Stiff Backfill

Double Piles

Strong Axis

Pile Relief

Pipe16x0.312

Pipe16x0.375

Sand (Dense)

Sand (Loose)

YIELD

Outcomes for Design17

Pile strain and girder stress nonlinear regressions:

0 0.5 1 1.5 2 2.5 3 3.5 40

5

10

15

20

25

30

35

40

Girder Stress Influence Coefficient, girder

Gird

er S

tress

(ksi

)

All Skews, R2 = 0.9229

ObservedPredicted

0200400600800

100012001400160018002000

0 20 40 60EE

L (f

t)Abutment Skew (degrees)

Pile Chart (HP14x117, D+Th+L, 5x Yield)

200 ft spans

150 ft spans

100 ft spans

50 ft spans

IDOT Pile Chart

Proposed updated pile charts:

18

IAB Field Monitoring of Two Highway Bridges19

IAB Instrumentation Goals20

Measuring strain in the concrete deck & steel girders

Checking level of embedded girder fixity

Checking for differential tilt at abutment joint

Measuring strain at pile-abutment interface

Monitoring bridge movement at various joints

Monitoring behavior of the approach slab

Bridge Instrumentation Schematics

EB I-90 Kishwaukee River

Bridge

EB I-90 Union Pacific Railroad (UPRR) Bridge

21

• 4-Span• 549 ft• 30° Skew• HLMR Guided Expansion Bearing @ Exp. Pier

• Single-Span• 184.5 ft• 42.5° Skew

Kishwaukee Bridge Instrumentation Details (similar scheme for UPRR)

22

Modeling of Site Bridges

SAP2000 was also used to model each instrumented bridge

Boring logs were utilized to determine backfill and foundation soil properties at each site

Soil softening was included to represent pile-top relief: Kishwaukee Bentonite slurry UPRR MSE wall effects

23

Displacements – Kishwaukee 24

Approach Slab Behavior25

Strains are not uniform throughout the approach slab

Average strain indicates a clear trend with change in temperature

Abutment Cold Joint Rotations 26

Middle band = 74% of data Middle band = 86% of data

UPRR Kishwaukee

Girder Differential Rotations27

Middle band = 68% of dataMax rotation: 0.33°

Middle band = 49% of data Max rotation: 0.1°

UPRR Kishwaukee

Kishwaukee Field vs. Model Abutment Rotations28

Pile Strains29

Pile top strains from the field data are closer to pure weak-axis flexure than combined flexure

Strong-axis bending causes a separation in magnitude between strain gage pairs

31

42

bf/4

Bridge

Axial force causes a shift in the magnitude of tensile vs. compressive strain

Kishwaukee – Obtuse Pile Top Strains

30

Axial contribution causes upward shift in magnitude; strong-axis bending causes a separation between gage pairs

Girder Demands

Top-flange and web gages trend well over time and with temperature Bottom-flange measurements typically deviate from expected trends over

time, after the first fall/winter/spring

31

T

B

bf/4

M

Seasonal Girder Stresses

After the first year of data collection, bottom-flange stresses deviate from model predictions, while top-flange stresses stay similar as before

The highest girder stresses are seen near the abutments:

32

33

Overall Conclusions for IABs34

IAB Analysis (Parametric Study) Bridge expansion & contraction are about 90% of the magnitude of free

expansion & contraction Thermally-induced stresses in the superstructure should be considered when

proportioning girders (especially in end-spans) An allowance for moderate inelastic deformation in pile foundations may

broaden the range of acceptable bridge layouts

IAB Instrumentation (Field Monitoring) Field results were used to validate parametric study analytical models and to

better understand IAB & approach slab performance Pile strains in the field closely follow predicted analytical trends Girder bottom flanges exhibit the highest thermal stress ranges

Ongoing Work – IAB Approach Slab Research35

Research Goals: Identify the fundamental cause of cracking

issues in IAB approach slabs Develop improved design criteria and

procedures to mitigate cracking

Three Main Components: Investigation of existing IAB approach

slabs Numerical modeling parametric study Field instrumentation & monitoring of two

Illinois Tollway IAB approach slabs

Approach slab embedded strain gage instrumentation

Initial Approach Slab Model

IAB Seismic Research 36

Research Goals: Assess the behavior of IABs

to a 1000-year return period seismic event

Form recommendations to improve seismic design & construction of IABs, with a focus on southern Illinois

Two Main Components: Develop 1000-year return

period hazard ground motions for southern Illinois

Model IABs in OpenSees and assess their seismic behavior

Ground motions developed for Cairo, IL

0 1 2 3 4 50

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Period, T (sec)S

pect

ral A

ccel

erat

ion,

Sa (g

)

Mean

Schematic of the three‐span IAB used for modeling in OpenSees

0 20 40 60 80 100Time (s)

-6

-4

-2

0

2

4

6

Tota

l Tra

nsve

rse

Bas

e S

hear

(N)

106

Total base shear in a three-span steel IAB during a ground motion

Acknowledgements37

Illinois Department of Transportation (IDOT)

Illinois Tollway

Illinois Center for Transportation (ICT)

ICT R27-115 Technical Review Panel – Chair: Mark Shaffer (IDOT)

Co-PI & UIUC CEE Professor Larry Fahnestock

Gabriela Brambila, Joseph Riddle, Matthew Jarrett, Jeffrey Svatora, Beth Wright & Huayu An (former UIUC CEE Graduate Student Researchers)