A Novel SMA Damper for Enhanced Seismic Response of Structural Systems: Some Investigations by Sujata H. Mehta

Guided by: Dr. S. P. Purohit
13EXTPHDE106


ABSTRACT:

Occurrence of frequent earthquakes demonstrate the need to conceptualize, analyze and
implement newer ways of seismic response control. Smart material based damping devices
adjust mechanical properties in real time through external power sources - voltage, current etc.
and form an active area of research. NiTi Shape Memory Alloys (SMA), a relatively newer
class of smart materials, having unique characteristics; super-elastic properties, Shape Memory
Effect (SME) along with suitable mechanical properties offer promising candidature for
implementation in damping device. The aim is to develop NiTinol SMA based supplemental
damping device to enhance the seismic performance of various structural systems. The major
objective of the present study is to implement, both passively and semi-actively, developed
novel SMA based Tension Sling Damper (SMA-TSD) with benchmark building. Nonlinear
hysteretic behavior of super-elastic SMA wire used in SMA-TSD was represented by one
dimensional Tanaka model. Control force offered by SMA-TSD was evaluated by mapping
nonlinear hysteretic behavior into linear Voigt model with equivalent stiffness and equivalent
viscous damping components and was validated for seismic inputs. Equivalent damping ratio
for SMA-TSD under seismic input was obtained by proposed instantaneous damping approach,
more appropriately simulating physical scenario, and constant damping approach.
Uncontrolled seismic response of various structural systems; SDOF system, three story
benchmark building and ten story building were determined and validated. Peak seismic
response parameters; displacement, understory drift, acceleration and damper force for these
structural systems fitted with passive SMA-TSD were determined and Performance Indices (PI)
were also evaluated. Passive SMA-TSD was modified by adding temperature controlled SMA
spring elements to adjust desired damping force in real time. Desired damper force was obtained
through an optimal control strategy, LQR. An inverse problem voltage- temperature – Shape
Recovery Force (SRF) was solved to evaluate desired damper force from semi-active SMATSD.
Benchmark building with passive SMA-TSD yields moderate reduction of ̴ 23% in peak
response parameters with proposed instantaneous damping approach and corresponding
equivalent damping ratio was found to vary between 1.9% to 20.6%. Ten story building when
fitted with one passive SMA-TSD at ground story shows moderate (5.56% -19.44%) reduction
in peak interstory drift which further reduces to ̴ 50 % with two passive SMA-TSD lower
stories. With suitable design parameters of semi-active SMA-TSD, peak seismic response of
benchmark building can be reduced substantially ( ̴71%).