FEASIBILITY OF SELF-POST-TENSIONED CONCRETE BRIDGE GIRDERS USING SHAPE MEMORY ALLOYS

Osman E. Ozbulut Assistant Professor

Department of Civil and Environmental Engineering

University of Virginia

Muhammad Sherif Ph.D. Student

6th World Conference on Structural Control and Monitoring (6WCSCM) July 16, 2014

Barcelona, Spain

Reginald Hamilton Associate Professor

Department of Engineering Science and Mechanics

The Pennsylvania State University

Asheesh Lanba Ph.D. Candidate

0 1 2 3 4 5

0

100

200

300

400

500

600

Austenite

DetwinnedMartensite

TEM

PER

ATU

RE

Austenite

Ms

Mf

As

Af

LOADING

UNLOADING

DetwinnedMartensite

Md

Partial recovery

Full recovery

No transformation

STR

ESS

STRAIN

LOADING

UNLOADING

Shape memory alloys (SMAs) are a smart class of metals that exhibit several extraordinary properties

Shape  memory  effect  (Heat-­‐ac1vated  SMAs)  

Superelas1city  (Superelas1c  SMAs)  

STRESS Detwinned

Martensite

TwinnedMartensite

HEATING

STRAIN

TEMPERATURE

TwinnedMartensite

DetwinnedMartensite

Austenite

Ms

Mf

As

Af

LOADING

HEATINGCOOLING

DetwinnedMartensite

UNLOADING

DetwinnedMartensiteAustenite

COOLING

LOADING

UNLOADING

Advantageous of SMA tendons:

ü  The  use  SMA  tendons,  which  possess  high  fa1gue  and  corrosion  resistance,  as  post-­‐tensioning  elements  in  concrete  girders  will  increase  the  service  life  and  provide  life-­‐cycle  cost  savings  for  concrete  bridges.    

ü  The  replacement  of  steel  tendons  with  SMA  prestressing  tendons  will  prevent  corrosion-­‐induced  deteriora1on  of  tendons  in  concrete  structures.    

ü  The  use  of  heat  of  hydra1on  of  grout  to  ac1vate  the  shape  memory  effect  of  SMA  tendons  will  provide  self-­‐stressing  capability.      

ü  This  will  greatly  simplify  the  tendon  installa1on.    ü  The  need  for  jacking  equipment  or  electrical  source  will  be  

eliminated.    ü  This  will  also  enable  to  form  the  reinforcement  in  any  shape  in  two  

or  three-­‐dimensional  space  without  special  devices.    ü  The  use  of  SMA  tendons  will  lead  to  beFer  control  of  the  prestress  

and  higher  levels  of  effec1ve  prestress.  During  the  service  life  of  a  bridge,  heat-­‐triggering  the  SMA  tendons  can  repair  possible  damage  observed  in  girders  and  reduce  excessive  deflec1ons.    

This study investigates self-post-tensioned beams by activating the SME of NiTiNb using the heat of hydration of grout

Self-­‐post-­‐tensioning  process    

!Austenite

DetwinnedMartensite

TwinnedMartensite

STEP 1

STEP 2

Pre-stretch original SMA while in

martensite phase

Cast concrete, and install the tendon in post-tensioning duct

Fill the duct with grout, and trigger the tendons using the

heat of hydrationSTEP 3

!

The conditions on the phase transformation temperatures and the required temperature window for self-stressing application are shown below

Phase  transforma1on  temperatures  of  SMAs    

Af

As

Ms

Mf

Temperature

Martensite fraction

100%

0%

AusteniteTwinned

Martensite

Should be over maximum ambient temperature

Should be below minimum ambient temperature

Service Temperature Should be close

to the As

The relationship between processing, microstructure, and transformation temperatures were studied

processed

Systematic experiments were conducted to characterize the shape memory effect recovery at different levels of pre-strain

Specimens  cooled  in  liquid  nitrogen  prior  to  tes1ng  in  order  to  try  and  stabilize  

martensite  in  the  matrix  at  RT  

Load Cell

Induction Heating

Coil

The material was loaded to 5.0, 8.9, 12.5, and 16.9 percent pre-strain levels and was heated to recover the residual strain

The recovery ratio and reverse transformation temperatures As and Af are plotted as a function of pre-strain level

cov *100%heatre

unlres

εε

⎛ ⎞⎜ ⎟⎝ ⎠

Recovery  Ra1o  (%):  

In order to gain insight into the transformation morphology, strain localization is characterized via DIC

0% ε (%) 20%

14 13 12 11 10 9 8 7 6 5 4 3 2 1

5 4 3 2 1 10 9 7 6 8

5.0%

16.9%

DIC Ext.

0% ε (%) 15%

5 4 3 2 1

5.0 %

16.9 %

4

The constrained recovery stress were conducted on two types of specimens

!Type  A  is  a  dog-­‐bone  specimen  whose  gage  sec1on  is  57.2  mm  long  and  4.2  mm  wide,  and  strained  to  14%  strain        Type  B  is    a  flat  specimen  which  is  241  mm  long,  and  strained  to  15%  .    

In order to determine the temperature increase during grouting post-tensioning ducts, four commercially available tendon grouts were tested (1)  Euco  Cable  Grout  PTX  (Euco),  produced  by  

Euclid  Chemical;    (2)  SikaGrout  300  PT  (Sika),  produced  by  Sika  

Corp.;    (3)   Five  Star  Special  Grout  400  (Five  Star),  

produced  by  Five  Star  Products,  Inc.;    (4) MasterFlow  1205  Grout  (MasterFlow),  

produced  by  BASF  Chemical.    

0 5 10 15 20 25 30 3515

20

25

30

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45

Time (hour)

Tem

pera

ture

(°C

)

EucoS1S2S3S1−AmbientS2−AmbientS3−Ambient

0 5 10 15 20 25 30 3515

20

25

30

35

40

45

50

55

Time (hour)Te

mpe

ratu

re (°

C)

SikaS4S5S6S4−AmbientS5−AmbientS6−Ambient

Temperature  measured  in  different  commercially  available  grouts  during  curing    

0 5 10 15 20 25 30 35 40 4515

20

25

30

35

40

45

Time (hour)

Tem

pera

ture

(°C

)

Five Star

S7S8S7/8−Ambient

0 5 10 15 20 25 30 35 40 4515

20

25

30

35

40

45

Time (hour)Te

mpe

ratu

re (°

C)

MasterFlow S9

S10S11S12S9/10/11/12−Ambient

Temperature  measured  in  different  commercially  available  grouts  during  curing    

SUMMARY  OF  GROUT  TEMPERATURE  TEST  RESULTS  

To investigate the bond behavior of SMA bars with grout, pull-out tests were conducted

! !

τ =T

πdbl b

T  =  the  tensile  load  on  the  SMA  bar      db  =  the  nominal  bar  diameter    lb  =  the  embedment  length  of  the  bar    

0 10 20 30 400

0.2

0.4

0.6

0.8

1

1.2

1.4Bo

nd S

tress

(MPa

)

Slip (mm)

Loaded End

0 10 20 300

0.2

0.4

0.6

0.8

1

1.2

1.4

Bond

Stre

ss (M

Pa)

Slip (mm)

Free End

0 10 20 30 400

0.2

0.4

0.6

0.8

1

1.2

1.4

Bond

Stre

ss (M

Pa)

Slip (mm)

Loaded End

0 10 20 300

0.2

0.4

0.6

0.8

1

1.2

1.4

Bond

Stre

ss (M

Pa)

Slip (mm)

Free End

Bond  stress-­‐slip  rela1onship  for  SMA  bars  at  free  end  and  loaded  end  for        (a)  Specimen  1    

 

(b)  Specimen  2    

Beam tests will be conducted in Fall

Material characterization tests were conducted on two types of NiTiNb SMAs. It was shown that a recovery stress more than 500 MPa could be achieved after cooling to ambient temperature.

The increase in temperature during the hydration of four commercially available grouts was evaluated. At three different tests of Sika grout, an average of 28°C temperature increase was observed.

Pullout tests were conducted on cylindrical specimens to investigate the bond between the grout and SMA bar.

0 5 10 15 20 25 30 3515

20

25

30

35

40

45

50

55

Time (hour)

Tem

pera

ture

(°C

)

SikaS4S5S6S4−AmbientS5−AmbientS6−Ambient

!

ACKNOWLEDGEMENTS

This study has been supported by the Mid-Atlantic Universities Transportation Center (MAUTC) Pooled Research Program issued by

the Research and Innovative Technology Administration of the US DOT (Grant No. DTRT12-G-UTC03).

FEASIBILITY OF SELF-POST-TENSIONED CONCRETE BRIDGE GIRDERS USING SHAPE MEMORY ALLOYS

Osman E. Ozbulut Assistant Professor

THANK YOU !

Muhammad Sherif Ph.D. Student

6th World Conference on Structural Control and Monitoring (6WCSCM) July 16, 2014

Barcelona, Spain

Reginald Hamilton Associate Professor

Asheesh Lanba Ph.D. Candidate