Limin Lu

For coastal structures susceptible to corrosion, the structural fire behavior of them should be considered as a coupled damage of corrosion and high temperature. As the interfacial bond characteristics between the reinforcements and the concrete directly influence the mechanical properties of reinforced concrete structures, it is essential to release the residual bond‐slip property between corroded steel bars and concrete after exposure to high temperatures. This study examined the coupled effects of steel corrosion rates (1%, 3%, 6%, and 10%) and temperature levels (20, 100, 300, 500, and 700°C) on bond properties through center‐pullout tests on steel bar‐embedded basalt fiber reinforced concrete (BFRC) specimens. Moreover, a constitutive model was established to characterize the bond‐slip relationship between corroded steel bars and BFRC, taking temperature and corrosion rate as parameters. The results showed that at the temperatures of 100–300°C, the corrosion rate had a significant influence on the bond performance of BFRC specimens, with the severity of the effects initially increasing then continuously decreasing with the addition of corrosion rate. When above 500°C, the beneficial effect of mild corrosion vanished, exhibiting severe bond deterioration under combined thermal‐corrosion damage. The addition of basalt fibers showed limited effect on constraining the degradation of bond performance after the coupled damage. The findings of this research provide critical insights for the prediction of structural fire performance of corroded reinforced concrete structures.

The end restraint strength of the reinforced concrete (RC) beams under the fire conditions may greatly influence the inner force redistribution and the structural behavior of the beams, even the stability of the whole structure. The structural fire behavior of two full‐scale frame beams with different end restraint strength under load were studied based on experiment and simulation. The temperature field, reinforcement strain, beam deflection, end axial displacement, and rotation angle of the structure during the whole heating and cooling process were measured. The influence of end restraint strength on the structural behavior was analyzed. The results show that the vertical displacement, axial force, end bending moment, and angular displacement first increase rapidly, then decrease gradually and become stable in the whole process; the lateral displacement increases first and then stabilizes; the change of axial and rotational deformations appeared to be non‐proportional with the corresponding restraining forces, reflecting that the axial and the rotational restraint strength at the ends of the beams decreased with the rise of temperature. The restraining strength of beams that submitted to fire globally decreased faster, and leading to a severe fire response and an earlier failure of the structure. The analysis results and the conclusions will supply scientific basis for the fire‐resistance design and safety evaluation on complex structures.

Chloride ion penetration frequently leads to steel corrosion and reduces the durability of reinforced concrete. Although previous studies have investigated the chloride ion permeability of some fiber concrete, the chloride ion permeability of the basalt fiber reinforced concrete (BFRC) has not been widely investigated. Considering that BFRC may be subjected to various exposure environments, this paper focused on exploring the chloride ion permeability of BFRC under the coupling effect of elevated temperatures and compression. Results demonstrated that the chloride ion content in concrete increased linearly with temperature. After exposure to different elevated temperatures, the chloride ion content in BFRC varied greatly with increasing stress. The compressive stress ratio threshold for the chloride ion penetration was measured. A calculation model of BFRC chloride ion diffusion coefficient under the coupling effect of elevated temperatures and mechanical damage (loading test) was proposed.

The durability of subsea tunnels under the coupled action of stress and chloride ions was analyzed to estimate the service life and provide a theoretical foundation for durability design. The influence coefficient of the stress on chloride ion transmission at lower stress levels was discussed according to the material mechanics, and was verified by experimental data. A stress calculation model of a subsea tunnel’s lining section is proposed based on the plane-section assumption. Considering the space-time effect of the convection velocity, a partial differential equation was constructed to calculate the chloride ion transfer condition under the coupled action of stress-convection-diffusion. The numerical solution of the partial differential equation was solved and the sensitivity of the parameters was analyzed. The subsea tunnel’s time-varying reliability index was calculated following the Monte Carlo method, and was used to predict the service life. The results show that the chloride ion concentration calculated by considering the coupled action is larger and the reliability index is lower than calculated only considering diffusion. Our findings contribute to the conclusion that durability designs of subsea tunnels should consider the coupled action of stress-convection-diffusion. An effective method to improve the service life of a subsea tunnel is to reduce the water–binder ratio or increase the thickness of protective cover.