Prestressing effect of cold-drawn short NiTi SMA fibres in steel reinforced mortar beams

This study investigated the prestressing effect of cold-drawn short NiTi shape memory alloy (SMA) fibres in steel reinforced mortar beams. The SMA fibres were mixed with 1.5% volume content in a mortar matrix with the compressive strength of 50 MPa. The SMA fibres had an average length of 34 mm, and they were manufactured with a dog-bone shape: the diameters of the end- and middle-parts were 1.024 and 1.0 mm, respectively. Twenty mortar beams with the dimensions of 40 mm × 40 mm × 160 mm ( B  ×  H  ×  L ) were prepared. Two types of tests were conducted. One was to investigate the prestressing effect of the SMA fibres, and the beams with the SMA fibres were heated at the bottom. The other was to assess the bending behaviour of the beams prestressed by the SMA fibres. The SMA fibres induced upward deflection and cracking at the top surface by heating at the bottom; thus, they achieved an obvious prestressing effect. The beams that were prestressed by the SMA fibres did not show a significant difference in bending behaviour from that of the SMA fibre reinforced beams that were not subjected to heating. Stress analysis of the beams indicated that the prestressing effect decreased in relation to the cooling temperature. (paper)