With the use of seismic isolation techniques on mega-sub structures, several scholars have carried out research on them. However, little research has been carried out on mega-sub isolated structures under multiaxial earthquakes. There have been instances in actual engineering where the peak vertical acceleration exceeded the horizontal direction, and the vertical seismic component will also amplify the dynamic response of the structure in the horizontal direction, so in practice, it is necessary to consider the influence of the vertical component of the earthquake on the structure. To investigate the dynamic response of mega-sub isolated structures under unidirectional earthquake and coupled earthquake, this paper used numerical methods to analyze the influences of the horizontal and vertical damping ratio of the isolation layer, the horizontal and vertical frequency ratio of the main substructure, and the mass ratio of the main substructure on the acceleration and displacement of the main and substructure. The optimum parameter values are finally achieved by analytical calculations, which provide a basis for further optimization and practical design of the structure. Finally, the collision between the main and sub-structures in the mega-sub isolated structure was simulated, and the influences of the peak ground motion, main and subframe spacing, vertical seismic component, and sub-structure height on the collision force and acceleration were analyzed. It was shown that the conflict of the main and sub-structures generates instantaneous, large collision forces, which also instantaneously amplify the acceleration and base shear force response, which should be avoided in practical engineering.

A structure may be exposed to a range of unexpected loads throughout its full life cycle. Partially precast concrete (PC) beams refer to the process of manufacturing concrete beams in which one part of the component is pre−fabricated in a factory and the other part is completed at the construction site. Through the test, it is possible to better ensure the safety and dependability of the PC composite beams under impact load by examining the reinforcement effect, structural toughness, and damage mode of PC composite beams with bonded steel. Additionally, a scientific basis and practical guidance are provided for the actual project. Their impact resistance can significantly affect the overall safety of a structure when subjected to an impact load. Three of the four PC beams used in this investigation were strengthened with steel plates. Residual flexural bearing capacity tests and drop weight impact tests were then conducted. The impacts of steel plate thickness and U−shaped steel plate hoops on the failure mechanism and dynamic response of the component were investigated. The dynamic responses obtained from the experiments included the displacement–time history curve, impact force, and support reaction force. In order to explore the failure mechanism of the partially precast beam during the impact process, a staged analysis was conducted based on the failure mode and dynamic response characteristic values of each curve. Residual flexural bearing capacity tests were used to examine the residual flexural bearing capacity of PC beams strengthened with bonded steel plates. The results of the research reveal that the failure mechanisms of each test beam are bending–shear failures. With the increase in bonded steel thickness, the peak mid−span displacement reduced by 6.55%, the residual mid−span displacement decreased by 29.53%, and the residual flexural bearing capacity improved by 25.02%. With the adoption of U−shaped steel plate hoops, the residual flexural bearing capacity significantly increased while the peak mid−span and residual mid−span displacements both decreased.

In order to improve the seismic and energy dissipation capacity of the whole structure, a friction-oval section mild steel rod composite damper (FOSRCD) was proposed, and its working principle was clarified. The finite element analysis of FOSRCD was carried out, and the effects of friction, frequency and displacement on the damper performance were studied. Considering the structural characteristics of FOSRCD and the mechanical models of friction dampers and mild steel rod dampers, the restoring force model of the composite dampers was proposed and compared with the numerical simulation results. The results showed that the FOSRCDs had good performance and could provide stable energy dissipation capacities in both directions, with the energy dissipation coefficient exceeding 2.3 and the equivalent damping ratio exceeding 0.37. The theoretical analysis results were in good agreement with the numerical simulation results, which verified the theoretical restoring force model; the FOSRCDs make full use of the friction energy dissipation and the shear and bending energy dissipations of the mild steel rod. It enables the two dampers to work together to achieve the purpose of multi-stage energy dissipation. FOSRCD’s structure allows it to dissipate energy in both the X- and Y-directions. The composite dampers have a variety of restoring force models and can be utilized in a wide range of practical applications.

Lithium-ion batteries (LIBs) electric bicycles are widely used in China, with many accidental fires occurring in parking facilities in high-rise building. Electric bicycle parking areas in high-rise buildings have become fire-prone zones. There are urgent needs to establish fire codes for the parking facilities in high-rise buildings. But only limited research has been conducted on protecting against such fires. There are also uncertainties in the appropriate methods for implementing fire barriers and fire suppression facilities. To better understand the parking facility fires in this area, four fire scenarios were studied in this paper, aiming to seek principles on how to prevent serious fire accidents by isolating E-bicycles parked in parking facilities. These principles include fire barrier design, fire separation distance between the islands and the selection of fire suppression devices. A total of six experiments on LIBs bicycle fires were conducted. Fire spread between the LIBs bicycles and the propagation patterns of smoke generated by electric bicycle fires within parking facilities were studied. The effectiveness of different fire extinguishing methods in suppressing LIBs bicycle fires was discussed. The reasonable fire separation distance for electric bicycles was determined. It was found that LIBs with ternary lithium-ion batteries (such as NCM) are more prone to initiate thermal runaway. A sprinkler system with lower hazard class is proposed to operate under lower water pressure and flow rates. Fire control methods were proposed, such as including fire-resistive eave and fire barrier. The results can be used in setting up fire code and are useful for AI training cases in developing fire models.

Lithium-ion battery-powered (LIB-powered) electric bicycles (E-bicycles) are widely used in China, with many accidental fires occurring in parking facilities in high-rise buildings. E-bicycle parking areas in high-rise buildings have become fire-prone zones. There is an urgent need to establish fire codes for the parking facilities in high-rise buildings. However, only limited research has been conducted on protecting against such fires. Uncertainties also remain about appropriate methods for fire barriers and fire suppression in parking facilities. To better understand parking facility fires in high-rise buildings, four fire scenarios and a total of six experiments on LIB-powered E-bicycle fires were studied in this paper, aiming to seek principles on how to prevent serious fire accidents by isolating E-bicycles parked in parking facilities. Fire spread between the LIB-powered E-bicycles and the propagation patterns of smoke generated by E-bicycle fires within parking facilities were studied. The effectiveness of different fire extinguishing methods in suppressing LIB-powered E-bicycles fires was discussed. The reasonable fire separation distance for E-bicycles was determined. It was found that LIBs with ternary lithium-ion batteries (such as nickel-cobalt-manganese) are more prone to initiate thermal runaway. Setting appropriate separation distances could effectively minimize the spreading of E-bicycle fires in high-rise buildings. A sprinkler system with a lower hazard class is proposed to operate under lower water pressure and flow rates. Fire control methods were proposed, including fire-resistive eave and fire barrier. The results can be used in setting up fire code.