Fire-Induced Failure of Long-Term Service and Fresh Concrete Beams Subjected to Fire

In engineering, reinforced concrete beams are subjected to natural erosion and the working stress state. However, previous studies regarding structural fire have focused on new concrete beams, and most results are obtained from no-stress-state tests. Hence, research that considers the natural erosion and working stress states of beam members in fire is lacking. In this study, fire experiments were performed to investigate the differences between long-term service concrete beams and new elements under loads. A technique using ARAMIS three-dimensional (3D) optical strain measurement was adopted; it provides increased sample throughput and 3D measurements that indicate the change in strain more intuitively. Results show that the moisture content of concrete determines the spalling degree of concrete under the influence of working stress. With the increase of concrete moisture content, the range of temperature of heated and backfire surface increases and the spalling phenomenon is more obvious, especially when the moisture content exceeds 2.5%. In addition, the long-term service specimens are affected by fire more easily, thereby accelerating the destruction process owing to the degree of carbonation.