Hui Lv

The increasing incidence of urban fires poses significant threats to structural integrity, underscoring the urgent need for concrete materials with enhanced mechanical properties post-fire. Incorporating recycled waste steel fibers (WSF) from industrial byproducts into concrete not only bolsters its crack resistance but also advances circular economy principles by transforming industrial waste into valuable resources. Although a large amount of research has focused on native steel fiber-reinforced concrete, there is still a lack of systematic exploration on the optimal dosage and effectiveness of waste steel fibers in slowing down the strength degradation of concrete after high-temperature action. In this study, two grades of concrete (C40 and C60) containing 0%, 1%, and 2% WSF by volume were subjected to heating cycles ranging from 200 °C to 800 °C. Post-cooling evaluations encompassed mass loss quantification, cube compressive strength testing (using 100 mm³ specimens), and splitting tensile tests conducted at a loading rate of 0.1 MPa/s. Results indicated that mass loss escalated to 11% at 800 °C, with C60 experiencing a 12% higher loss compared to C40. Compressive strength decreased by 15% for every 200 °C increment; however, the inclusion of 1% WSF significantly minimized this degradation, preserving 44.5% (for C40) and 37.8% (for C60) of the original strength at 800 °C. Notably, the splitting tensile strength of 1% WSF-reinforced C60 concrete exceeded that of plain concrete by 39.4% after exposure to 800 °C, demonstrating its superior crack-bridging capabilities.

To explore the axial compressive mechanical properties of steel tube recycled steel fiber reinforced concrete short columns (STRSFRCSCs), axial compression tests were conducted on ten STRSFRCSCs and two steel tube reinforced concrete short columns (STRCSCs), mainly analyzing the effects of recycled steel fiber (RSF) content, steel content, and concrete strength grade on their mechanical properties. The results showed that different RSF contents had no significant effect on the failure mode of the specimens, while the concrete strength grade and steel content had a significant effect on the failure mode. When the steel content was 2.84%, the specimens experienced shear failure, while when the steel content was 4.24%, they experienced waist drum failure. As the RSF content increased, the peak strain during the loading process of the specimens decreased, and the transverse deformation coefficient at the peak decreased. The addition of RSF significantly improved the ductility performance of the specimens. When the volume fraction of RSF was 2%, the bearing capacity of the specimens increased the most, reaching 13.4%, and the ductility coefficient gradually increased. The axial compressive bearing capacity and combined elastic modulus of the specimens increased with the increase in concrete strength grade, RSF content, and steel content.

Building upon the analytical study of the structural configuration and prestress state of the drum-shaped quad-strut cable dome, we conducted further investigation into its structural configuration. By employing the nodal equilibrium equations to solve the prestress state analysis of the cable dome, we compared the effects of two different cable laying methods on the prestress state of the cable dome structure. These methods include equal length of the radial horizontal projection of the upper chord ridge cables and equal radial chord length of the upper chord ridge cables. The analysis results show that the radial length of the top chord and its corresponding radial horizontal projection length of the cable dome structure can effectively reflect the trend of the prestress state of the structural configuration. Furthermore, by using a rise-to-span ratio of 0.11 as a threshold, the cable dome configuration is categorized into the flat spheroidal structural configuration and the small hemispheroidal structural configuration. When the structure is analyzed using a small rise-to-span ratio, the difference in prestress calculations between the two structural configurations is found to be less than 10%. Additionally, the structure exhibits a more uniform distribution of prestress, with the prestress gradually increasing from the inner circle to the outer circle. However, when the rise-to-span ratio increases, the difference between the prestress calculation results of the two configurations also increases, emphasizing the need to deploy upper chord ridge cables based on equal radial chord lengths (arc lengths). The research presented in this paper provides a novel insight into the structural topological form and prestress state calculation of cable domes with this configuration.

The drum-shaped honeycomb-type cable dome departs from traditional concepts and incorporates the idea of multiple strut configurations. It is the most diverse type of cable dome structure. Both cables and struts serve as the main load-bearing components. Analyzing the effects of local component failure is crucial for designing large-scale cable domes able to resist continuous collapse. A numerical analysis model using the ANSYS finite element method with a 120 m span is established. Dynamic analysis methods are employed to study the response of structural internal forces and displacements during the failure of different component types. By defining the internal force dynamic coefficient and change coefficient, the structural continuity collapse resulting from component failure is determined based on computational results and observation of structural deformations. Furthermore, the importance of the various components within the overall structure is classified. The research findings indicate that the failure of individual components does not cause overall instability of the structure. The importance level of the ring cables and some upper chord ridge cables is higher than that of the inclined cables. Class a struts have a higher importance level than class b struts. Additionally, the importance level of outer ring components is higher than that of inner ring components.