To investigate fire‐resistance behaviors of simple supported reinforced concrete (RC) beams with three faces exposed to fire, six full‐scale specimens were designed in accordance with the principle of “strong bending and weak shearing.” One beam was treated as the control case of room temperature while the other five beams were exposed to high temperature. Parameters related to shear capacity were discussed, such as longitudinal reinforcement ratio and stirrup ratio. The experimental results show that brittle shear failure under room temperature may transfer to shear‐bend failure at high temperature due to thermal expansion and strength degradation of concrete and steel. The greater the longitudinal reinforcement ratio, the longer the failure time of specimens. It indicates that the pinning action of longitudinal reinforcement can significantly improve the shear capacity of beams under high temperature. In addition, the configuration of stirrup reinforcement can effectively reduce the brittle change of vertical deflection when the beam enters the failure stage.

The mechanical properties of concrete and steel are seriously degraded under high temperature, so that reinforced concrete (RC) members after fire may not be able to satisfy the prescribed performance. In this study, 27 full-scale RC beams were carried out shear tests to investigate the shear behaviour after fire. A total of 20 beams were subjected to fire on three sides in accordance with ISO 834 standard fire curve, and the remaining 7 beams (which were not subjected to fire) were employed as a reference. The influences of fire time, stirrup ratio, shear span ratio, longitudinal reinforcement ratio, and preloading (40% loading level) were considered. The experimental results indicated that the shear failure mode of the RC specimens after fire exposure was similar to that of the reference specimens. Both the residual shear load bearing capacity and stiffness of the RC beams decreased after being subjected to fire. The loss of shear bearing capacity increased with the heating time. In addition, the ultimate load bearing capacity of specimens with stirrups subjected to the same fire exposure time decreased with an increasing shear span ratio.

The presence of loose medium backfill above the horizontal pillar will technically hinder the efficient recovery of the pillar since the improper design and preserved roof protection layer height will potentially lead to casualties and equipment damage caused by large area collapse of filled tailings as well as roof fall accidents. In this study, a safe and efficient technique for the recovery of isolated pillars under loose tailings backfill was carried out via field investigation, theoretical analysis, numerical simulation, and analytic hierarchy process using the isolated pillars in the 855 middle sublevel of Hongling Zinc-Lead Mine, Chifeng, Inner Mongolia, as a practical engineering background. Current studies have revealed that the optimal scheme for an isolated horizontal pillar recovered via the cut-and-fill stoping of a drift vertical to ore body strike involves preserving a 1.0-m roof protection layer above the crown pillar combined with a spaced mining extraction sequence. This design minimizes ore dilution and losses during the pillar extraction process under safe operation. Our research results provide theoretical and technical support for the safe and efficient recovery of isolated pillars under loose tailings backfill in similar mines.

An important task in the development of the construction industry is to find rational technologies, materials and solutions that ensure energy efficiency in construction and create conditions for obtaining energy-saving products and structures for various construction projects. At the same time, the issue of structures made of the same material, but having a difference in their properties and characteristics in thickness, the so-called variatropic building material, which, due to differences in structure and properties, ensures variatropic properties of the building structure itself, has been poorly studied. The goal of this study was to eliminate a significant scientific deficit, consisting in the absence of a systematized knowledge base on the structure and thermophysical properties of variatropic products and structures made of concrete or reinforced concrete. The modeling was performed in the ANSYS environment (Ansys version 2024 R1). An element selected for modeling was a ring-section heavy concrete pillar with an outer diameter of 450 mm and an inner diameter of 150 mm. Variatropy was specified by conventionally dividing the element’s cross-section into several layers with different physical and mechanical properties: three for centrifuged concrete and four for vibrocentrifuged concrete. In the course of modeling, the authors determined the main initial data for the calculations, and based on the results of the calculations, dependencies were established confirming the improvement of the concrete’s heat-insulating properties due to the use of centrifugal compaction technology. The phenomenon of variatropy leads to an increase in heat-transfer resistance – from 13% for centrifuged concrete to 23% for vibrocentrifuged concrete in comparison with vibrated concrete. At the same time, vibrocentrifuged concrete turned out to be 8% more efficient than centrifuged concrete in terms of “heat-transfer resistance”. The conducted modeling shows that variatropic concrete is promising for further research and practical application in terms of its thermophysical characteristics.

To investigate the shear capacity of indirectly loaded reinforced concrete beams under and after fire exposure, load tests were conducted on eight full-scale specimens exposed to fire testing in a furnace chamber, and the effects of additional transverse reinforcement in the junction region between the primary and secondary beams on the shear capacity, fire resistance, failure modes and deflection were analysed. The results indicate that the slopes of the diagonal cracks in post-fire tested reinforced concrete beams without additional transverse reinforcement were shallower than those of a similar reference beam not exposed to fire, and that the ultimate capacities of reinforced concrete beams with additional transverse reinforcement decreased obviously after fire exposure. However, beams with additional transverse reinforcement exhibited increased fire resistance times and reduced strains in their reinforcement, indicating the benefit of conservatively providing such reinforcement. The findings of this study are expected to provide a reference for the improved fire-resistant design of indirectly loaded beams.

Building fire is one of the most frequent disasters. The mechanical properties of concrete and steel will deteriorate to different degrees under fire exposure, thus weakening the bearing capacity of reinforced concrete (RC) members. Therefore, it is of great theoretical and practical significance to carry out research on the bearing capacity of RC members subjected to fire. To study the residual shear capacity of post-fire RC beams under indirect loading, static load tests were carried out on six full-scale RC beams to investigate the development of diagonal cracks and failure modes under an indirect load. Numerical models were established with ABAQUS to study the effect of the shear span-to-depth ratio and stirrup ratio on the residual shear capacity of the tested beams after fire exposure, and the shear capacity calculation method of indirectly loaded beams after high temperature is proposed. The results indicate that although the fire had no obvious affect on the failure mode of the beam under indirect loading, the fire aggravated the failure degree of the beams without additional transverse reinforcement. Moreover, the ultimate bending capacity of beams with additional transverse reinforcement decreased obviously after fire. The residual shear capacity of indirectly-loaded beams subjected to fire decreased compared with the directly-loaded beams due to the variation in the shear span-to-depth ratio and stirrup ratio. The shear capacity theoretical calculation results of the indirectly-loaded beam after high temperature were in good agreement with the tested results, and the average absolute error was 3.88%. Therefore, this calculation method for an indirectly loaded beam with a shear span-to-depth ratio less than 3.0 after fire as proposed in this paper was effective. The findings of this study are expected to provide a reference for the improved fire-resistant design of RC structures under indirect loading.