Accident tracing of gas explosions in complex frame structures: Numerical simulation of pressure field evolution and structural damage mechanisms

Natural gas explosion accidents in reinforced concrete (RC) frame buildings have distinct propagation and damage characteristics compared to traditional masonry structures. However, the response mechanisms of gas explosions in RC frame structures remain insufficiently understood, and a suitable accident-matching mechanism for frame buildings has not yet been established. This study, focusing on a gas explosion accident in a frame structure in Beijing in 2023, systematically conducted simulation analyses of 54 explosion scenarios and proposed a two-layer matching and reconstruction method for natural gas explosion accidents in RC frame structures, determining the most likely accident scenario. The research found that the progressive failure of lightweight infill walls would trigger a dynamic deflagration process, which alters the flame acceleration characteristics and overpressure distribution patterns within the entire building. The progressive failure of lightweight infill walls produces a dual safety effect: on the one hand, it enlarges the spatial range affected by flame propagation, hot gases, blast waves, and secondary fragments, thereby increasing the potential hazard area; on the other hand, it provides dynamic venting paths that release explosion energy and limit the overpressure acting on the main RC beams and columns, thereby reducing the probability of global structural collapse. Additionally, the study observed that frame building structures would experience a significant negative pressure phase after rapid deflagration, which might lead to the secondary collapse of damaged walls. The research results can provide a scientific basis for the anti-explosion design and safety assessment of cities.