FEASIBILITY OF SELF-POST-TENSIONED CONCRETE BRIDGE GIRDERS ... · (3) &Five&Star&Special&Grout&400&...
Transcript of FEASIBILITY OF SELF-POST-TENSIONED CONCRETE BRIDGE GIRDERS ... · (3) &Five&Star&Special&Grout&400&...
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
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0
100
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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.
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Time (hour)
Tem
pera
ture
(°C
)
EucoS1S2S3S1−AmbientS2−AmbientS3−Ambient
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25
30
35
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55
Time (hour)Te
mpe
ratu
re (°
C)
SikaS4S5S6S4−AmbientS5−AmbientS6−Ambient
Temperature measured in different commercially available grouts during curing
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20
25
30
35
40
45
Time (hour)
Tem
pera
ture
(°C
)
Five Star
S7S8S7/8−Ambient
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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
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0.2
0.4
0.6
0.8
1
1.2
1.4Bo
nd S
tress
(MPa
)
Slip (mm)
Loaded End
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0.2
0.4
0.6
0.8
1
1.2
1.4
Bond
Stre
ss (M
Pa)
Slip (mm)
Free End
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0.2
0.4
0.6
0.8
1
1.2
1.4
Bond
Stre
ss (M
Pa)
Slip (mm)
Loaded End
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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