Research on compensating vertical prestress loss of concrete box-girder webs based on the self-prestressing characteristic of Fe-SMA

The excessive loss of vertical prestress is a primary factor contributing to web cracking in large-span prestressed concrete box girders. The self-prestressing characteristics of iron-based shape memory alloys (Fe-SMAs) after heat activation offer significant potential for the timely and efficient supplementation of vertical prestress loss. Therefore, the effects of stress supplementation introduced by the self-prestressing of Fe-SMA rebars were investigated using six scaled concrete plates. This analysis focuses on the influence of the vertical prestressing rebar type and spacing on the compressive stress field. The self-prestressing of the Fe-SMA rebars stabilized after approximately 4 h of Fe-SMA activation. Furthermore, unlike the conventional prestressing rebar, the self-prestressing of the Fe-SMA rebar was relatively uniformly distributed along its entire length. When both types of bars were positioned at the same position in separate specimens, the difference between the maximum and minimum values of stress on the specimen with only Fe-SMA rebars was only 6.98% of that in the specimen with only screw-threaded steel bars. Overall, by strategically and vertically equipping the web with Fe-SMA rebars, the vertical prestress loss of the box web can be effectively supplemented in a timely manner.