Dynamic Testing Methods of Analysis

ADVANCED DYNAMIC LOAD TESTING METHODS –PRESTRESSED CONCRETE PILESIndependent Tip and Skin Capacities

Aneesh Goly, Ph. D., P.E.

Director of Engineering & Operations

Smart Structures

Sastry Putcha, Ph. D., P.E.

Vice President

Smart Structures

Presented by:

Advanced DLT Methods – Prestressed Concrete Piles | 2

Dynamic Testing Methods of Analysis & Advancements

1968

Case Method Only Total

Resistances using Top Gauges

Signal Match Analysisfor estimation of Tip & Skin Resistanceson a single Blow

1970

EDC

Introduction2003

UF Method - Total & Tip Resistances

using Top & Tip Gauges for all Blows

2013

FDOT Method – Independent Tip & Skin Resistances

using Top & Tip Gauges for all Blows

DLT 1.0

DLT 2.0

DLT 3.0

Top only External Instrumentation

Introduction


Top Only External Gauges


Top only External Gauges

Picture Courtesy: RADISE INTERNATIONAL

Accelerometer

Strain

Transducer


Top and Tip Gauges – Embedded Data Collectors (EDC’s)


• Electronics/Sensors (strain and

accelerometer) Embedded in the pile core

at both pile ends…

• Wireless Communication and Data

Transmission from the pile

• Ruggedized Workstation to Collect Sensor

Data in Real Time

• SmartPile Software provides real-time

measured data - capacities, stresses and

integrity

• Data Portal to organize and share results

Embedded Data Collectors (EDCs)

SmartPile Workstation

Tip Gages

L

Top Gages

Internet

Wireless Data

Network


Wireless DataPort (flush mounted)

SmartPile Engineering

Workstation

Sensor Pack – Pile Top

(with combined accelerometer, temp. and strain sensing)

Sensor Pack – Pile Tip

configurable up to 3 Sensor Packs

total/system

500 foot range…

Universal Installation Bracket makes

installation quick and simple

Typical Configuration for Driven Piles

Top

Tip


Top and Tip Embedded Data Collectors (EDC’s)

Accelerometer

Positioning

FrameworkStrain Gauge

Accelerometer

Positioning

Framework

Strain Gauge –

centered in pile

core





DLT 1.0 – CASE METHOD AND SIGNAL MATCH ANALYSIS (TOP ONLY)


Case Method

• Only estimates Total axial capacity based on arbitrary damping factor value

1000

800

600

400

200

0

-200

-400

Case Method, Total Capacity =

(1 – Jc)[F1 + Z X V1]/2 + (1 + Jc) [F2 – Z X V2]/2

Jc = ?

DLT

1.0


Case Method: Damping Factor Values

Gravel 0.3 0.4

Sand 0.4 0.5

Clay 0.7 1.0

Silt 0.5 0.7Reducing

Grain Size

Increasing

Damping

factor

DLT

1.0

DLT 2.0 – UF METHOD OF ANALYSIS(TOP AND TIP SENSORS)


UF Method

The UF method utilizes both top and tip sensor packs to predict total and tip static capacities

• Total Capacity = Total Static Capacity from Case equation with Dynamic

Jc from Top and Tip gages for every blow

• Tip Capacity = Tip static capacity from Unloading Point based on Tip

gages

• Skin Capacity = Total Capacity – Tip Capacity

Tip Gages

L

Top Gages

DLT

2.0


UF Method: Total Capacity

…calculated using top and tip gauges

Dynamic Damping, Jc = - 0.09744 x In (Tip / Skin) + 0.2686

UF Method, Total Capacity = (1 – Jc)[F1 + Z X V1]/2 + (1 + Jc) [F2 – Z X V2]/2

DLT

2.0

Limin Zhang, Michael C. McVay, and Charles W. W. Ng (2001), “A possible physical meaning of Case damping in pile dynamics”, Candian Geotechnical Journal, Vol 38.


UF Tip Capacity: Unloading Point Method

At point where Fstatnamic is maximal (point 1):c = [Fstatnamic – Fstatic – (ma)tip]/vtip

At unloading point (point 2):

Fstatic = Fstatnamic – (ma)tip

DLT

2.0


UF Skin Capacity

• The University of Florida Capacity

method uses the Total Capacity

calculated using the Dynamic Jc and the

Tip Dynamic Unloading Capacity.

• Skin Capacity = Total Capacity – Tip

Capacity

DLT

2.0

DLT 3.0 – FDOT METHOD OF ANALYSIS (TOP AND TIP SENSORS)


• FDOT method determines the independent static tip and skin resistances in near real time

on every blow by analysing the data from the top and tip sensor packs embedded in the

pile.

• Tip Resistance values are evaluated based on conservation of energy method. Applied

energy as recorded in the tip gauge = static + damping + inertial energies recorded in

the tip gauge

• Skin Resistance is evaluated based on segmental skin friction method with Top & Tip

gauge data as the boundary conditions

• Total Resistance = Mobilized Tip Resistance + Mobilized Skin Resistance

FDOT Method of Analysis - Independent Tip and Skin Resistances DLT

3.0


• Knowing tip conditions (end-bearing or floating

piles)

• The pile segment beneath the tip gages and the

soil below the tip moving together is considered

a single degree of freedom system (SDOF).

• The measured tip force from the strain gage is

the external force applied to the system. Since

the applied force is measured directly, the tip

analysis is independent of the skin analysis.

• Tip static force (tip resistance) can be accurately

extracted directly from the measured dynamic

force.

Tip Gages

L

Top Gages

SDOF Applied force(strain gage)

FDOT Method: Tip ResistanceDLT

3.0


“Estimating static tip resistance of driven piles with bottom pile instrumentation” , Tran, McVay, Herrera, and Lai, Canadian Geotechnical

Journal, Vol 49., April 2012

Energy Method For Accessing Damping and Static forces

DLT

3.0


• Model the pile tip as a SDOF

• Nonlinear stiffness k

• Model updating by Genetic

Algorithm

Displacement, u(x,t)

Sta

tic

Tip

Res

ista

nce

k

Max(u)

1

k2

k3

k4

l1 l3l = Max(u)- l - l2 1 3

A

B

Max(u)/2

range 1

Max(u)/2

range 2

Tran K.T., McVay M., Herrera R., and Lai P. (2012), “Estimating Static

Tip Resistance of Driven Piles with Bottom Pile Instrumentation”,

Canadian Geotechnical Journal

FDOT Method: Tip ResistanceDLT

3.0


EDC Blow 777 Forces vs. Time at Pile Tip of Pier 8 Pile-300.00

-200.00

-100.00

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

-0.01 7E-17 0.01 0.02 0.03 0.04 0.05

Fo

rce

(kip

s)

Time (sec)

Inertia Force

Static Resistance

damping force

applied force

predicted gage force

Where damping

and inertia forces

are zero, static

force is equal

to applied force.

0 0

Force & Energy Method For Accessing Damping and Static forces

DLT

3.0


Dixie Highway 24” x 50’

0

200

400

600

800

1000

1200

1400

1600

0 5 10 15 20 25 30

Sta

tic

Tip

Re

sist

an

ce (

kN

)

Displacement (mm)

Blow 1

Blow 2

Blow 3

Blow 4

Blow 5

Static LoadTest

Matching Forces: Inertia, Damping & Static

FDOT Method - Tip Resistance: Florida pile

Zero velocity point

Dynamic = Static

DLT

3.0


Knowing boundary conditions at both ends of a pile

helps simulate wave propagation along the pile

accurately

• The difference between top and tip downward

forces is the dynamic side friction, which is the sum

of static side friction and side damping

• Static side friction can be accurately extracted from

the dynamic side friction.

)()(1

0),0(

straintgx

u

xattv

)()(2

),(

straintgx

u

lxattlv

Side friction

Side damping

FDOT Method: Skin ResistanceDLT

3.0


B

Cc

B

fb

Ea

where

bt

uc

t

u

x

ua

srs 44

.

2

2

2

2

22

qKf

and

unloadingfortxuuKf

qtxuwithloadingforf

qtxuwithloadingfortxuK

f

u

u

us

)],()[max(

),(

),(),(

Tran K.T., McVay M., Herrera R., and Lai P. (2012), “Estimation of Nonlinear Static Skin Friction on Multiple Pile Segments Using Measured Hammer Impact Response at the Top and Bottom of the Pile”,

Computers and Geotechnics

Model 1-D wave propagation in pile

FDOT Method: Skin ResistanceDLT

3.0


0 2 4 6 8 10 12 14 16 18 200

100

200

300

400

500

600

700

800

Displacement, mm

Skin

Fric

tio

n, kN

segment 4

segment 2

segment 3

segment 1

total

Displacement, u(x,t)

Loading

Quake q

Un

it S

kin

Fri

ctio

n, fs

Ult

imat

e U

nit

Sk

in F

rict

ion

, fu

KK

Max(u)

Seg

men

t le

ng

th

Lm

To

tal

pil

e le

ng

th, L Fs,m

Fd,m

)()(1

0),0(

straintgx

u

xattv

)()(2

),(

straintgx

u

lxattlv

FDOT Method: Skin Resistance

• Model updating by Genetic Algorithm

• Matching estimated to measured particle velocities at top and bottom of pile

DLT

3.0


0 0.01 0.02 0.03 0.04 0.05 0.06 0.07-1

0

1

2

3

Time, s

Top

Ve

locity, m

/s

Observed

Estimated

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07-1

0

1

2

3

Time, s

Botto

m V

elo

city, m

/s

Observed

Estimated

Skin Friction of Dixie Highway, Pile 1

0

100

200

300

400

500

600

700

800

900

1000

0 2 4 6 8 10 12 14 16 18 20 22 24

Displacement, mmS

kin

Fric

tio

n, k

N

Blow 1

Blow 2

Blow 3

Blow 4

Blow 5

Load Test

0 20 40 60

0

2

4

6

8

10

12

14

0 20 40 60

SPT 'N'

De

pth

, m

Ultimate unit skin friction, kN/m2

a) Dixie Highway, pile 1

blow 1

blow 2

blow 3

blow 4

blow 5

SPT

Finesand

Cemented sand & shell

0 20 40 60

0

2

4

6

8

10

12

14

0 20 40 60

SPT 'N'

De

pth

, m

Ultimate unit skin friction, kN/m2

b) Dixie Highway, pile 2

blow 1

blow 2

blow 3

blow 4

blow 5

SPT

Cemented sand & shell

Finesand

Dixie Highway 24” x 50’

FDOT Method - Skin Resistance: Florida PileDLT

3.0


www.smart-structures.com

Aneesh Goly, Ph.D., P.E.

Email: [email protected]

Presented by:

4152 W Blue Heron Boulevard

West Palm Beach, Florida 33404

Phone: (561) 988-0070


Sastry Putcha, Ph.D., P.E.


Documents

Dynamic Testing Methods of Analysis