The mechanical property of prestressing steel wire during and after heating is the key factor in the design of fire resistance and after-fire damage evaluation of prestressed structures. Tensile experiment of 16 prestressing steel wires ( f ptk = 1770 N/mm 2 , d = 5 mm, low relaxation of stress) at high temperature and tensile experiment of 14 prestressed steel wires after heating are carried out. According to the experiment, the shapes of stress-strain curves of steel wire at high temperature go smooth and the mechanical property indexes of the steel wire such as strength, modulus of elasticity, etc., degenerate continuously as temperature increased. According to the experiment after heating, the mechanical property of steel wire varies little when the highest temperature that the steel wire has ever been heated to is lower than 300°C; while the stress-strain curves of steel wire become more ductile and the mechanical property indexes of the steel wire degenerate gradually when the highest temperature is higher than 300°C. By applying the theory of viscoelastic mechanics, stress-strain curves of steel wire at high temperatures without loading rate influence are obtained. The law of mechanical property indexes of the wire is presented. The mathematical models of the stress-strain relationship of the pre-stressed steel wire are established. All can serve as basic data for the analysis of fire resistance and after-fire damage evaluation of pre-stressed structures.

No abstract

The multistage centrifugal pump is the critical component of mineral resources lifting in deep-sea mining. The reflux of nodules in the lifting pipe caused by the emergency pump stop can easily cause the pump to clog. In this paper, coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM co-simulations) are used to clarify the solid-liquid two-phase flow in two-stage centrifugal pumps under different particle sizes (10–20, 20–30, 30–40, 40–50 mm) with constant particle concentration. The movement and accumulation behaviour of particles in different flow fields (pipeline to pump, the first to the second pump stage) is investigated. Meanwhile, the effect of particle size and particle reflux velocity on the blockage of the flow channel in the pump was investigated. Particle accumulation in the pump was observed to determine the key factors affecting the pump’s reflux capacity. The residual mass of particles in the pump at different particle sizes was counted. Simultaneously, the percentage of residual mass of 10–20 mm particles in the pump was compared between the experiment and the simulation with an acceptable tolerance of within 10%. In addition, pressure changes in the blockage-prone section were also investigated. A comparison between experiments and simulations verifies the consistency of the trend on the pump inlet pressure when clogged with 50 mm particles. It was found that larger particles in the range of 10–30 mm can better ensure the pump’s reflux performance.

The Y-shaped elbow is used as a connecting pipe between the buffer and the lift pipe in the deep-sea mining system. After being mixed with seawater in the Y-shaped elbow, nodule particles are lifted to the sea surface mining ship via the lift pump. In this paper, we employ a computational fluid dynamics and discrete element coupled method (CFD-DEM) to study the characteristics of particle transport in the Y-shaped elbow. Considering a large diameter of the particles, we discuss the behavior of particles and fluid under different conveying velocities. In addition, the simulation was verified based on the experiment. The results show that the simulation agrees well with the experiment. On this basis, the distribution and motion characteristics of the particles in the Y-shaped elbow were obtained. The interaction between fluid and particles is also discussed. These findings suggest that the particles can be successfully transported when the pump runs at medium to high frequencies. The particles are basically moving along the pipe wall and slower than the fluid flow. Moreover, it was found that the particle motions are more complex with the increasing of conveying velocities, and it is closely related to the secondary flow of fluid. Some suggestions on the actual particle transportation can be put forward based on the research in this paper.