The high-temperature performance of well cement is critical for the construction of deep geothermal wells and high-temperature energy storage wells, where mechanical integrity and pore structure stability govern wellbore reliability. To address the strength degradation and structural deterioration of conventional cements under high temperature, the G-class cement was modified by ethylene-vinyl acetate (EVA) polymer and polypropylene fibers (PF), and their impact under various temperatures was explored. Results show that at 600 °C, the compressive strength of modified cement remains above 30 MPa. While the cumulative pore area decreases at 500 °C, a significant increase in larger pores and a major restructuring of the pore network occurs at 600 °C, reflecting the dual effects of high temperature on the pore structure. The modified cement retains structural integrity and excellent mechanical performance up to 400 °C with minimal strength loss, uniform strain distribution, and stable pore structure. At 500 °C and above, it still maintains load-bearing capacity and deformation adaptability, meeting the service requirements for geothermal wells and high-temperature energy storage wells. Even at 600 °C, the reinforcing effect of EVA and PF degradation products slow down crack propagation, ensuring durability in extreme conditions. The research findings lay the foundation for the development of well cement for high-temperature service environments.

The outgoing line system in substations is highly susceptible to seismic damage due to the complex dynamic interactions between flexible conductors and interconnected equipment. However, most existing studies model conductors as tension-only elements, neglecting their bending stiffness and geometric slackness, which may lead to inaccurate predictions of seismic response. This study presents an integrated experimental, numerical, and theoretical investigation of the dynamic behavior of flexible conductors and their influence on a typical three-phase multi-span outgoing line system in a 220 kV substation. Quasi-static tests demonstrate that flexible conductors exhibit linear-elastic bending behavior, with stiffness ranging from 1 to 1.7 kNm ² under typical service axial forces. A refined finite element model incorporating conductor bending stiffness is developed, revealing that circuit breakers are the most vulnerable components, with bending moments 1.8 and 4.7 times those of current transformers and disconnectors, respectively. Furthermore, the effect of conductor slackness is systematically evaluated, showing that increasing slackness significantly reduces axial forces and bending moments. A slackness of 10% decreases bending moments on circuit breakers by 8%–13%. Theoretical analysis further explains the slackness-dependent force reduction mechanism. The results demonstrate that incorporating bending stiffness and optimizing slackness are critical for accurately predicting and mitigating seismic responses. A 10% slackness is recommended to improve the seismic resilience of substation outgoing line systems.

The bearing capacity of reinforced concrete (RC) beam will be weakened by fire. It is necessary to strengthen RC beams after fire. The carbon fiber mesh (CFM) can be used to reinforce RC beams. In this paper, RC beams were exposed to varying temperatures, followed by reinforcement with varying layers of CFM. The influence of the heating temperature and the number of CFM layers on the flexural performance of RC beams was investigated. The results indicated that the cracking loads of RC beams were 18.2, 16.4, 16.3, and 15.5 kN when the RC beams were subjected to room temperatures, 150, 350, and 550 °C. Compared to the unreinforced beams at room temperature, the cracking loads of the RC beams were reduced by 9.89%, 10.44%, and 14.84%. As the quantity of CFM reinforcement layers rises, so does the ultimate bearing capacity. For example, when the temperature was 150 °C, the ultimate loads of the beams with one and three layers of CFM were increased by 20% and 31.76% compared to the reference beam. When the temperature was 350 °C, the ultimate loads of the beams with one and three layers of CFM were increased by 19.51% and 28.04% compared to the RC beam without CFM. When the temperature was 550 °C, the ultimate loads of the beams with one and three layers of CFM were increased by 20% and 26.67% compared to the RC beam without CFM. Fire-damaged RC beams can be strengthened by one layer of CFM and mortar if the temperature was below 350 °C. Fire-damaged RC beams can be strengthened by three layers of CFM and mortar if the temperature was below 550 °C. The mechanical properties can be obviously enhanced.

Transmission towers are typically composed of angle steel members connected by ordinary bolts to form spatial truss systems, in which joint slip under axial loading can significantly influence structural performance. In subsidence areas, corrective lifting of tilted towers may cause internal force redistribution, transforming some compression members into tension members and resulting in joints subjected to both compressive and tensile forces. To investigate the slip deformation behavior of angle steel bolted connections under bidirectional axial loading, a series of experiments was conducted on specimens with different angle sizes and bolt numbers, complemented by finite element analysis. The results show that the load–slip relationship exhibits distinct staged characteristics, which can be divided into an initial linear stage, a slip stage, and a hole-bearing stage. The initial slip displacement is generally less than 1 mm, while the slip load and ultimate capacity increase significantly with bolt number, with the ultimate capacity under tension increasing by up to approximately 160% as the number of bolts increases from one to three. Although the slip evolution under compression and tension is generally similar, pronounced differences appear near the ultimate state, indicating a clear directional asymmetry. Based on these findings, a three-stage piecewise mechanical model is established, and a simplified bidirectional slip model is proposed by introducing asymmetric ultimate displacement and capacity parameters. Finite element simulations reproduce the failure modes and load–slip responses with good agreement, confirming the validity of the proposed model. The findings provide a useful reference for the design and performance evaluation of angle steel bolted connections in transmission tower structures.