Investigation on the effects of activation strategies and service temperature on the pre-stress levels of Fe-SMA-to-glass adhesively bonded joints

Glass beams have been widely used as structural elements. However, glass is brittle, and the load-carrying capacity of glass beams after cracking is quite low. Adhesively bonded pre-stressed iron-based shape memory alloy (Fe-SMA) tendons can effectively increase the initial glass cracking load, the post-cracking load-carrying capacity, and the deformability of glass beams. Activation, which involves controlled heating followed by natural cooling, is one of the key processes of such an application to attain the target pre-stress levels. The effectiveness of activation depends on the activation length (over which the Fe-SMA strips were activated), anchorage length and activation temperature. A deep understanding of the activation strategy is crucial for maximizing pre-stress levels while avoiding premature failures such as glass breakage or debonding during activation. In this study, first, activation strategies for Fe-SMA-to-glass adhesively bonded joints were investigated experimentally by considering various activation temperatures and activation lengths, aiming to attain high pre-stress levels while avoiding glass breakage and debonding. Second, the effect of elevated service temperature (50 °C and 80 °C) on the pre-stress loss was investigated for the same specimens. Third, a finite element model was developed to investigate the different activation strategies further. The results showed that (1) the segmented activation strategy improved stress concentration compared with the single-cycle activation strategy, (2) the pre-stress was completely lost when the service temperature was 50 °C and 80 °C, (3) longer activation lengths resulted in a relatively lower pre-stress level, and (4) increasing the activation temperature substantially raised the pre-stress level. The findings in this research will contribute to the efficient design and application of pre-stressing glass elements using adhesively bonded Fe-SMA tendons.