Experimental study on growth of time-dependent strain in SMA reinforced PSC beams

Gradual changes occur in the internal forces and deflections of reinforced pre-stressed concrete (PSC) flexural members owing to the combined effects of concrete creep and shrinkage, and relaxation of pre-stress. For wide-scale use of PSC members in civil engineering applications (e.g. long-span bridge girders), this long-term behaviour must be minimised. The ability of shape memory alloy (SMA) bars to restrict the growth of time-dependent and thermal strains in reinforced PSC beams was investigated up to concrete age of 350 days using four laboratory-scale models. It was observed that the growth of time-dependent strain was less in the treated PSC beams reinforced with a combination of SMA and conventional steel bars than in controlled PSC beams with only conventional steel bars. Analysis of the results of the experimental beams showed that the presence of SMA bars increases the cracking moment and effective moment of inertia of the treated specimens. This makes the treated beams stiffer and restricts the growth of time-dependent strain and deflections. The experimentally obtained strain values were compared with predicted strain values of similar size and grade of plain concrete (PC) beam using model code ACI 318, and it was found that the strain in treated PSC beams was less than that in PC beams.