This presentation summarizes research on using shape memory alloys (SMAs) for seismic retrofitting of reinforced concrete bridge columns. SMAs such as nickel-titanium can recover their original shape after deformation through heating. The presentation includes:
1) An overview of SMA properties and phase transformations between martensite and austenite phases.
2) A literature review of previous SMA confinement research.
3) Details of an experimental study comparing SMA spiral confinement to fiber reinforced polymer wrapping on concrete columns.
4) Test results found SMA confinement significantly improved ductility and drift capacity over FRP or unconfined columns.
5) Plans to further study SMA behavior
1. PRESENTATION ON
SMA CONFINEMENT TECHNOLOGY FOR RC BRIDGE
COLUMNS
Department of Civil Engineering
GCOEA
Presented by: Guided By:
NIDHI V.JAIN Prof. S.N.DHEPE
ID NO-16053011
2. CONTENTS
Introduction
Shape memory alloys
How do SMAs work
Literature review
Phase transformation
Properties of SMAs
Shape memory confinement
Experimental Procedure
Retrofitting techniques
Confining Techniques and loading protocol
Results and discussions
Emergency repair process
Plans for implementation
Conclusion
References
3. Introduction
In any seismic design and mitigation plan, insuring
the resilience of lifeline infrastructures against
devastating seismic events in highly populated areas is
of high priority.
Bridges are the most critical elements in any
transportation infrastructure network.
Many bridge failures in the past earthquakes were due
to the failure of one or more RC columns, which in
many cases, was due to the insufficiency of concrete
confinement.
4. This brought the need for the proper confinement of
columns to increase their strength and enhance
ductility of the structure.
For this purpose an innovative technique for seismic
retrofitting of RC bridge columns using Shape Memory
Alloys (SMAs) was suggested.
5. Shape Memory Alloys
A shape memory alloy (smart metal, memory metal,
smart alloy) is an alloy that “remembers” its original
shape and that when deformed returns to its pre-
deformed shape when heated.
Some of the commonly used SMAs are copper-
aluminium- nickel and nickel-titanium (NiTi) alloys of
which NiTi based SMAs are more preferable due to
their stability and practicability.
6.
7. How do SMAs work?
The key factor behind the unique thermo-mechanical
behavior of SMAs is the phase transformation that occurs
between the two distinct phases that exist on the atomic
level: 1) Austenitic phase, which exists at high temperatures
and 2) Martensitic phase, which exists at low temperatures.
8. Literature Review
1) Moochul Shin (2012):- Their research focused on examining the
use of shape memory alloy (SMA) spirals in the seismic retrofitting
and repair of reinforced concrete (RC) bridge columns Their
research work comprised of: 1) Performing numerical analysis on
RC columns retrofitted using SMA spirals (active confinement) and
Fiber Reinforced Polymer (FRP) wraps (passive confinement) to
examine the superiority of the suggested new confinement
technique over current confinement techniques, 2) Investigating
experimentally the thermomechanical behavior of NiTiNb SMA
which is used for this research, 3) Testing concrete cylinders
wrapped with SMA spirals and Glass-FRP (GFRP) wraps, 4)
Conducting quasi static lateral cyclic tests on four 1/3-scale RC
columns retrofitted with SMA spirals and GFRP wraps
9. 2) M. S. Alam, M. Nehdi and M. A. Youssef (2008) :-They
critically examined the fundamental characteristics of
SMA and available sensing devices emphasizing the
factors that control their properties. Existing SMA
models were discussed and the application of one of the
models to analyze a bridge pier is presented. SMA
applications in the construction of smart bridge
structures were discussed. Future trends and methods to
achieve smart bridges were also proposed.
10. Phase Transformation
Matrix of the atoms at different
phases: (a) austenite ,
(b)intermediate and(c) martensite
phase.
Four transformation temperatures.
21. Maximum and normalized
strength, ductility and drift ratios
of the four columns
As- built GFRP SMA HYBRID
Max. Strength
(Kips)
7.76 7.84 8.27 8.00
Normalized
strength
1 1.01 1.07 1.03
Ductiltity
Ratio
2.8 3.3 8.0 6.7
Normalized
ductility
1 1.18 2.85 2.39
Drift ratio 2.8% 3.5% 12% 10%
22. • The results demonstrated that the SMA and SMA/GFRP columns exhibited a
slight increase in strength, a significant increase in flexural ductility and
ultimate drift capacity compared to the as-built column, while the GFRP
column showed only a moderate enhancement in ductility and drift capacity.
• When assessing the damage of the four tested columns during and after testing
revealed that the damage sustained by both SMA and SMA/GFRP columns was
far less than that sustained by the GFRP column, although the 75% increase in
maximum drift on the SMA-retrofitted columns.
• These results clearly show that the SMA retrofitting technique is very effective
in increasing the ductility, drift capacity and energy dissipation ability of
insufficient RC columns. It is also capable of mitigating the damage sustained
by RC columns during extreme seismic events.
23. Plans for implementation
This analysis helped in proving the concept of using thermally
prestressed SMA spirals for retrofitting vulnerable RC bridge columns. The
product (i.e. SMA spiral) is ready for immediate use in retrofit and emergency
repair projects.. Among the issues which are currently being investigated is:
Understanding the behavior of the spirals and the actively confined concrete
under real seismic loading (i.e. strain rate effects).
Studying the durability of the spiral under harsh environmental conditions.
Searching for other cost-effective SMAs with thermomechanical
characteristics suitable for the application of interest.
Modeling the behavior of the actively confined concrete using SMA spirals.
This will help in studying the impact which this new retrofitting/repair
technique has on the entire bridge system.
Studying the feasibility of using the same concept studied in this project in
retrofitting/repairing non-circular columns.
24. Conclusion
This analysis and research work explored a new application of SMAs
that could potentially transform how RC bridges are retrofitted and/or
repaired.
The results of the analysis clearly proved the superiority of the
proposed SMAs spirals compared to the currently used FRP jackets in
terms of: (1) Increasing the flexural ductility of the columns (more than
2.4 times the ductility obtained from using GFRP jacket). (2) Limiting
the damage sustained by the columns even under excessive lateral
drifts (14 %-drift).
Furthermore, the amount of SMA used to reach such superior
behavior was relatively small and the amount of time and labor
required for installing the SMA spirals were minimal.
25. Unlike using prestressed strands or FRP jackets, installing the thermally
prestressed SMAs will require minimal labor and hardware. Further, in
contrary with FRP jackets, the proposed SMA spirals do not require any
curing time, which makes the spirals very suitable for emergency repairs
following a major earthquake or a collision accident.
This analysis has provided bridge engineers with an effective and easy tool
for applying the concept of active confinement on-site. This very concept
can be used to mitigate the effects of various man-made and natural
hazards (e.g. earthquakes, impacts, blasts, etc.) on bridges.
26. References
1.O.E.Ozbulut, S. Hurlebaus & R.DesRoches (2011) “Seismic response control using shape
memory alloys : A Review”. Journal of Intelligent Materials and Structures, 22, 1531-1549.
2. Shin M, Andrawes B (2014) “Parametric study of RC bridge columns actively confined with
shape memory alloy spirals under lateral cyclic loading” Journal of Bridge Engineering.19.
3. Chen Q, Shin M, Andrawes B (2014) “Experimental study of non – circular concrete elements
actively confined with shape memory alloy wires” Construction and Building Materials. 61:
303-311.
4. Shin M, Andrawes B (2011) “ Emergency repair of severely damaged reinforced concrete
columns using active confinement with shape memory alloys” Smart Materials and Structures
.20.
5. Shin M, Andrawes B (2011) “ Seismic repair of RC bridge piers using shape memory alloys”
Structures Congress 2011- Proceedings of the 2011 Structures Congress. 2056-2065.
6. M. S. Alam, M. Nehdi and M. A. Youssef (2008) “ Analytical prediction of the seismic
behavior of superelastic shape memory alloy reinforced concrete elements” Engineering
Structures 30 (12), 3399-3411.
