High-strength concrete (HSC) has a high compressive strength, high density, excellent durability, and seepage resistance, but its deformation ability is weak. Adding fibers can improve the physical and mechanical properties of HSC. Additionally, the HSC structure may face the threat of fire. In the process of fire extinguishing, the damage mechanism of high-temperature-resistant concrete is complicated due to the different contact conditions with water at different locations. Hence, it is essential to conduct pertinent research on the behavior of fiber-reinforced HSC with different cooling methods after high-temperature action. In this paper, polyvinyl alcohol fiber (PVA fiber) was selected to be added into the HSC to carry out high-temperature experimental research, so as to explore the apparent changes, failure pattern, and mass loss rate of the fiber-reinforced HSC using different cooling methods and analyze the influence of its residual compressive strength and flexural strength. The test results suggest that, with the increase in heating temperature, the color of the specimen’s surface transitions from dark blue-gray to white, and the quantity of surface cracks on the specimen gradually rises. The mechanical strength gradually decreases as the heating temperature increases. At a consistent heating temperature, the mechanical strength initially rises, and then falls with an increase in fiber content. The maximum compressive strength and flexural strength were achieved at PVA fiber contents of 0.2% and 0.3%, respectively. For different temperatures and fiber contents, the mechanical strength after natural cooling is generally higher than that after immersion cooling. In addition, X-ray polycrystalline diffractometry (XRD) and scanning electron microscopy (SEM) tests were conducted to analyze the compositional alterations and microstructure of the fiber-reinforced HSC following high-temperature exposure, accompanied by an explanation of the factors influencing the alterations in the physical and mechanical properties. Therefore, the findings of this study can serve as a valuable reference for the utilization of HSC in engineering structures and contribute to the advancement of HSC technology.

High-strength concrete (HSC) boasts excellent compressive strength and durability, making it a popular choice in various engineering applications. However, under the impact of high temperatures, HSC tends to crack easily, so it is combined with polyvinyl alcohol fiber (PVA fiber) to explore its engineering application prospect. This paper investigated the physical and mechanical characteristics of HSC reinforced with PVA fibers subjected to different heating temperatures and cooling techniques. The experimental results reveal a correlation between rising temperatures and observable changes in the specimens: a progressively lighter surface hue, an augmented frequency of cracking, and a considerable escalation in the mass loss rate, particularly after the temperature exceeds 400 °C. Regarding mechanical properties, the dynamic elastic modulus and compressive and flexural strength all decrease as the heating temperature increases. As the amount of PVA fiber rises while maintaining a steady temperature, these measurements initially show an increase followed by a decrease. The fiber contents yielding the best compressive and flexural strength are 0.2% and 0.3%, in that order. Considering the influence of cooling methods, water spray cooling has a greater impact on physical and mechanical properties than natural cooling. Furthermore, SEM was employed to scrutinize the microstructure of HSC, enhancing comprehension of the alterations in its physical and mechanical characteristics. The findings of this research offer significant information regarding the high-temperature behavior of HSC, serving as a valuable resource for guiding the design, building, and upkeep of structures that incorporate HSC. Additionally, this study will aid in advancing the progress and utilization of HSC technology.

The performance of reinforced concrete (RC) frame structures will gradually decrease over time, posing a threat to the safety of buildings. Although the performance of some buildings may still meet the safety requirements, they cannot meet new usage requirements. Therefore, this paper proposes a new-type joint to promote the development of research on the reinforcement and renovation of RC frame structures in response to this situation. The RC beams and columns of the joints are connected by embedded horizontal steel plate (a single plate with dimension of 150 mm × 200 mm × 5 mm), and the beams and columns are individually wrapped in steel. Through conducting low cyclic loading tests, this paper analyzes the influence of carrying out wrapped steel treatment and the thickness of wrapped steel of the beam and connector on mechanical performance indicators such as hysteresis curve, skeleton curve, stiffness, ductility, and energy dissipation. The experimental results indicate that the reinforcement using steel plate can significantly improve the dynamic performance of the joint. The effect of changing the thickness of the connector on the dynamic performance of the specimen is not significant, while increasing the thickness of wrapped steel of beam can effectively improve the overall strength of joint. The research results of this paper will help promote the application of reinforcement and renovation technology for existing buildings, and improve the quality of human living.

In the case of engineering structures, the performance of a structure will gradually deteriorate with an increase in the usage time, leading to a decrease in the safety of the structure. In addition, even if the safety of a structure is reliable, its current structure type may no longer meet the latest usage requirements. Therefore, four reinforced concrete specimens were produced in this study: one was a cast-in-place specimen, and three were specimens connected by a T-shaped steel plate with steel cladding reinforcement. This article first introduces the structural form and construction method of the new types of joints, and then it describes the quasi-static testing that was conducted to analyze seismic performance indicators such as the failure characteristics, bearing capacity, ductility, stiffness degradation, and energy dissipation. Finally, combined with a strain analysis of the steel bars and steel plates, the force transmission mechanism of the new types of joints was investigated. The research content of this paper helps to promote the progress of structural retrofitting and strengthening work and the sustainable development of the construction industry.

Fabricated reinforced concrete columns are important components of reinforced concrete structures. During the design reference period, columns are prone to degradation in mechanical and deformation properties, which affects the normal service of the structure. Based on compressive tests of fabricated reinforced concrete columns, this paper uses ABAQUS 2021 finite element analysis software to explore how factors such as column damage and CFRP sheet layout affect the compressive performance of fabricated concrete columns under eccentric compression in order to investigate their mechanical properties and the confinement effect of CFRP sheets on such columns. The results indicate that the change trend of the bearing capacity of the finite element model is largely in agreement with that of the test specimens, and the ultimate bearing capacity error is below 3%, thereby confirming the validity of the finite element model. Compared with strip confinement, full-wrap confinement achieves a greater improvement in ultimate bearing capacity, and two to three layers are recommended as the ideal number of CFRP sheets for strengthening. The maximum increase in ultimate bearing capacity can reach 19.18%. When the strip width is constant, the smaller the spacing, the smaller the concrete strain in the compression zone. When the net spacing is constant, reducing the strip width increases the number of cracks and decreases crack width, but reduces the ultimate bearing capacity of the column accordingly. Strengthening with CFRP sheets can enhance the ultimate bearing capacity, deformability, and ductility of columns with initial damage under both small and large eccentric compression. The maximum increase in ultimate bearing capacity can reach 8.31%. The results obtained in this paper are conducive to promoting the reinforcement and reconstruction of fabricated reinforced concrete columns and reinforced concrete structures.

To enhance the seismic performance of existing reinforced concrete (RC) buildings during retrofitting, the study introduces a new type of joint connected by a T-shaped steel plate. Compared with previous similar strengthening methods, this novel structure incorporating a post-installed beam not only effectively improves the mechanical properties of RC columns, but the connectors also further enhance the integrity of the post-installed beam. Low-cycle reversed loading tests on one cast-in-place specimen (RC) and three T-shaped steel plate connection specimens (TRC1–TRC3) were conducted to evaluate failure modes, hysteresis and skeleton curves, and energy dissipation. Results show that the novel joint failure concentrates at beam-end–column steel jacket weld seams and column-side steel plate cracking, while the core-zone concrete remains intact. Compared with RC, the novel joints TRC1–TRC3 exhibit bearing capacity variations of −1.03%~+15.80% and significantly enhanced energy dissipation. The thickness of the beam’s wrapped steel improves the carrying capacity and energy dissipation, whereas the T-shaped connector thickness has limited influence on bearing capacity. ABAQUS parametric analysis indicates that bolt quantity, concrete strength, and connector thickness have limited influence and serve as secondary design factors. These findings provide a theoretical basis for retrofitting existing buildings.