1. Veermata Jijabai Technological
Institute Mumbai
Shape Memory Alloys and it’s
Applications in Civil
Engineering
Seminar on
Under The Guidance
of Dr. Priyanka
Jadhav
By
Pankaj Dhangare
M. Tech I(Structural)
Roll No-142040013
3. Introduction
SMAs are the Materials which have the ability
to return to a predetermined shape when heated
or cooled.
When it is heated above its transformation
temperature it undergoes a change in crystal
structure which causes it to return to its original
shape.
The most common shape memory material is
an alloy of nickel and titanium called Nitinol
This particular alloy has very good electrical
and mechanical properties, long fatigue life,
and high corrosion resistance
4. History
1932: Chang and Read recorded the first
observation of the shape memory
transforation.
1938: Greninger and Mooradian observed the
formation and disappearance of martensitic
phase by varying the temperature of a Cu-Zn
alloy.
1951: Shape memory effect was observed
1962-63: Ni-Ti alloys were first developed by
the United States Naval Ordnance
Laboratory.
Mid-1990s – Memory metals start to become
widespread in medicine and soon move to
5. Literature reviews
"Applications of Shape Memory Alloys in Civil
Engineering Structures - Overview, Limits and New
Ideas” by JANKE, L., et al.(2005). "Materials and
Structures” 38(June 2005): 578-592.
A basic description of SMA highly non-linear material
behaviour in terms of shape memory effect and
superelasticity.
It is followed by a brief introduction to Ni-Ti and Fe-Mn-Si
SMAs.
Pre-existing and new applications in the fields of damping,
active vibration control and prestressing or posttensioning of
structures with fibres and tendons are being reviewed with
regard to civil engineering.
New ideas for using SMAs in civil engineering structures are
proposed such as an improved concept for the active
confinement of concrete members.
6. Literature reviews….
“Applications of Shape Memory Alloys in Civil
Structures” by Song, G., Ma, N., and Li, H.-N. (2006).,
Engineering Structures, 28, 1266-1274.
The shape memory effect (SME) and pseudoelasticity,
two major properties of SMA associated with the
thermal-induced or stress-induced reversible hysteretic
phase transformation between austenite and martensite
are reviewed.
These unique properties enable SMA to be used as
actuators, energy dissipaters and dampers for civil structure
control.
Various applications in civil structures.
7. Literature reviews….
“APPLICATION OF SMART MATERIALS IN CIVIL
ENGINEERING STRUCTURES,” by T.S.
Thandavamoorthy(2013) , Research in Civil Engineering
Structures-05 251-263.
He described the characteristics of smart materials, the use of
SMA in construction and research, and their beneficial
aspects by reviewing the available information.
He considered Shape Memory Alloy as SMART MATERIAL or
INTELLIGENT MATERIAL.
11. Properties….
Austenite and Martensite – Two phases
exhibited by SMA’s in solid state.
If deformed in martensite phase, the
parent shape is regained upon heating.
As and Af are the temperatures at which
transformation from martensite to
austenite starts and finishes.
Transition dependant on temperature and
stress.
Repeated use of shape memory effect
leads to functional fatigue.
12. Properties….
Pseudo-Elasticity
o Occurs without temperature change.
o Based on stress induced mechanism
o This property allows the SMA’s to bear large
amounts of stress without undergoing permanent
deformation.
13. Working principle
A molecular
rearrangement in the
SMA’s austenite and
martensite phase is
responsible for its
unique properties.
Martensite is relatively soft and occurs
at lower temperatures.
Austenite occurs at higher
temperatures.
14. Working principle…..
The shape of austenite structure is cubic.
No change in size or shape is visible in
shape memory alloys until the Martensite
is deformed.
To fix the parent shape, the metal must
be held in position and heated to about
500°C.
The high temperature causes the atoms
to arrange themselves into the most
compact and regular pattern possible
resulting in a rigid cubic arrangement
(austenite phase).
15. Applications
General applications
• Eyeglass Frames
• Helicopter blades
• Dental wires
Applications in civil engineering/
structure
1. Reinforcement
SMA’s are particularly beneficial for
construction in seismic regions.
If SMA is used as reinforcement, it will yield
when subjected to high seismic loads but
will not retain significant permanent
deformations.
16. Applications….
2. Prestressing
The benefits of employing SMAs in
prestressing include:
i. No involvement of jacking or strand-cutting
ii. No elastic shortening, friction, and
anchorage losses over time
SMA strands are used in pre tensioning
and post tensioning.
17. Applications….
3. Braces for frame structures
The SMA wire braces are installed diagonally in the frame
structures.
As the frame structures deform under excitation, SMA
braces dissipate energy through stress-induced Martensite
transformation (in the superelastic SMA case) or Martensite
reorientation (in the Martensite SMA case).
18. Applications….
4. Damping element for
Bridges(restrainer)
One of the main problems of bridges
during earthquakes is their unseating
because of excessive relative hinge
opening and displacement
These limitations can be overcome
by introducing SMA restrainers as
they have larger elastic strain range
and can be brought back to its
original position even after
deformation.
19. Applications….
5. SMA for structural self-Rehabilitation
The IRC(Intelligent Reinforced Concrete ) uses
stranded Martensite SMA wires for post-
tensioning .
By monitoring the electric resistance change of
the SMA wires, the strain distribution inside the
concrete can be obtained. In the presence of
cracks due to explosions or earthquakes, by
electrically heating the SMA wires, the wire
strands contracts and reduce the cracks.
This self-rehabilitation can handle macro-sized
cracks.
The concrete structure is intelligent since it has
the ability to sense and the ability to self-
20. Applications….
A small concrete block
with SMA post-tensioned
Test Set up of beam
reinforced with SMA wire.
A model by G. Song et. al(2006)
22. Applications….
6. SMA as FRP
SMA-FRP reinforcing bars behave in a ductile manner and are
capable of dissipating energy.
It was found that SMA-FRP bars have more potential to
improve the ductility and energy dissipation capability of
concrete structures compared to conventional FRP bars.
7. SMA as fibers
The most crucial limitation of concrete is its low tensile
strength, compared to its compressive strength, which results
from the propagation of micro-cracks.
This may be prevented by using prestrained SMA wires that
are embedded in the concrete matrix.
Upon activation, these wires regain their original shape, and
consequently, initial compressive stresses are transmitted to
the concrete matrix.
23. Advantages
Bio-compatibility
Diverse Fields of Application
Good Mechanical Properties (strong, corrosion
resistant)
Disadvantages
These alloys are still relatively expensive to
manufacture and machine compared to other
materials such as steel and aluminum.
Most SMA's have poor fatigue properties; this
means that while under the same loading
conditions (i.e. twisting, bending, compressing) a
steel component may survive for more than one
hundred times more cycles than an SMA
element.
24. Case study
1. Retrofitting Of the Basilica of San
Francesco at Assisi, Italy
The Basilica of San Francesco was restored after being strongly
damaged by an earthquake of 1997 Umbria-March earthquake
(Castellano 2000).
The gable was completely disconnected from the roof and was then
linked to the roof again by means of Shape Memory Alloy Devices
(SMAD’s). Each SMAD is designed to take both tension and
compression forces, while consisting of SMA wires which are only
subjected to tension.
In order to reduce the seismic forces transferred to the tympanum, a
connection between it and the roof was created using superelastic
SMAs
The SMA device demonstrates different structural properties for
different horizontal forces. Under extremely intense horizontal loads,
the SMA stiffness increases to prevent collapse.
25. SMA Devices in the Basilica of St Francesco of
Assissi
Below figure shows the SMDs used in the retrofit.
26. Case study
2. Retrofitting of the bell tower of the Church
of San Giorgio at Trignano, Italy
The S. Giorgio Church, located in Trignano,
Italy, was struck by a 4.8 Richter magnitude
earthquake on October 15, 1996, resulting in
significant damage to the bell tower within the
church.
Following the earthquake, the tower was
rehabilitated using SMAs.
The upgrade was carried out linking top and
bottom of the tower by means of hybrid
tendons.
Four vertical prestressing steel tie bars with
SMA devices were placed in the internal
corners of the bell tower to increase the flexural
resistance of the structure.
27. Case study
• The retrofit was tested by a minor m=4.5 Richter
magnitude earthquake on June 18, 2000, with the same
epicenter as the event in 1996. After the main shock, the
tower was investigated and no evidence of damage was
present (DESROCHES and SMITH 2003).
Bell tower with tendons and SMA devices
28. Conclusion
SMA’s have the potential to be used
effectively in seismic regions.
The high cost of SMAs is a major limiting
factor for its wider use in the construction
industry.
Their capability to allow the development of
smart structures with active control of
strength and stiffness and ability of self-
healing and self-repairing opens the door for
exciting opportunities, making them the
construction material of the future.
