Heat Activated Prestressing of SMA Wires for Seismic Retrofitting of RC Beam-Column Joints

Raj Suhail

Research output: Other contribution


Shape memory alloys (SMAs) possess several unique material properties that have great potential in civil engineering, especially for seismic applications. Besides other features SMAs have extraordinary ability to undergo reversible hysteretic shape change known as the shape memory effect. The shape memory effect of SMAs can be utilised to actively confine concrete sections to improve their shear strength, ductility and energy dissipation capacity. In this research an attempt has been made to exploit the shape memory feature of NiTiNb SMA for seismic retrofitting of non-seismically detailed (NSD) reinforced concrete beam-column joints (BCJs). Two novel retrofitting schemes were designed and experimentally tested on full scale BCJ specimens under reverse cyclic loading. The retrofitting schemes essentially involve heat activated prestressing of NiTiNb SMA wires to provide active confinement to the joint region of NSD-BCJs.

In view of the complex material behaviour of SMAs, a detailed material characterization of NiTiNb SMA wire was carried out prior to full-scale testing of retrofitting schemes. A series of tests were conducted to study the influence of transformation temperatures, pre-strain, strain rate and pre-strain history on heat activated prestress, commonly referred to as recovery stress. Full-field strain contour maps of the specimens were obtained using digital image correlation technique to gain a deeper insight into the strain localization, observed in NiTiNb SMAs during stress induced martensitic phase transformation, and its effect on recovery stress. Furthermore, prior to full-scale testing, small-scale experimental tests on shape modified concrete prisms confined with NiTiNb SMAs spirals were carried out to evaluate the efficacy of active confinement achieved by heat activated prestressing of NiTiNb SMA confinement. In addition to experimental testing, a comparative study of different constitutive models for non-linear finite element analysis of reinforced concrete BCJs is also carried out.

The results from the material characterization of NiTiNb SMA wires show that NiTiNb SMAs have great potential in civil engineering, especially in heat activated prestressing applications. The experimental tests of the proposed retrofitting schemes, which exploited the unique feature of NiTiNb SMA wires, showed a significant enhancement in the strength and energy dissipation capacity of the NSD-BCJs as compared to the as-built specimen. However, this study revealed that several issues related the practical implementation of the NiTiNb SMA wires require special attention, which are discussed in detail in this thesis. Some new aspects from a civil engineering perspective are also highlighted in this study.
Original languageEnglish
TypePhD Thesis
Publication statusPublished - Jul 2018


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