A Novel SMA Damper for Enhanced Seismic Response of Structural Systems: Some Investigations

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%).