The bottom frame masonry structure (BFMS) in a semi-ruined state is vulnerable to secondary collapse under strong aftershocks, posing a significant risk to rescuers during post-earthquake operations. Therefore, investigating the mechanisms and characteristics of secondary collapse of BFMS in a semi-ruined state (BFMS-SR) under aftershocks is critical. This paper proposes a numerical modeling framework for BFMS under mainshock-aftershock conditions, utilizing a combination of the finite element method (FEM) and the finite discrete element method (FDEM). The validation demonstrates that FEM–FDEM can effectively reproduce the transition of BFMS from an intact state to a semi-ruined state, ultimately leading to a secondary collapse state. Subsequently, the mechanisms and structural response characteristics of BFMS-SR under aftershocks are analyzed. The secondary collapse of the BFMS-SR under aftershocks is primarily governed by column hinge development. Furthermore, according to the time-history curve of absolute vertical velocity, the secondary collapse of BFMS-SR exhibits four distinct stages: stabilization, structural response development, secondary collapse, and post-collapse. The end of the stabilization phase is proposed as the early-warning threshold for secondary collapse of BFMS-SR under aftershocks, aiding in post-earthquake rescue operations.

It is a very important task to construct a life-saving passage in building ruins rapidly and scientifically in the process of earthquake rescue. Currently, the virtual scene is built to train rescuers to construct the life-saving passage quickly and scientifically. However, there are problems such as high cost, small quantity, and single form. A new method of constructing building ruins and life-saving passage was proposed based on the combined finite element (FE) and finite-discrete element (F-DE) method and restarted function of LS-DYNA program. First, taking the RC frame structure ruins as research objection, the different types of life-saving passages were constructed. What’s more, a simple and reasonable optimization method of life-saving passage is proposed based on the rescue technologies with the shortest time. Meanwhile, the timing test of four typical rescue technologies was performed considering the influence factors of various rescue situations. Finally, the practicability and validation of the optimization method was verified through comparing with actual earthquake rescue case. The results show that the restart function of ANSYS/LS-DYNA program can construct the life-saving passage rapidly and reasonably, and simultaneously, the optimal method of life-saving passage can give the optimal rescue route intuitively and accurately. The numerical simulation method of construction and optimization of life-saving passages is expected to provide theoretical guidance for rescue drills for on-site earthquake rescue.

It is essential to evaluate the safety of the life-saving passage in building ruins and to ensure the double safety of rescuers and trapped people during the earthquake rescue; however, there are few studies on the safety evaluation method of life-saving passage. In this paper, the vertical displacement of wood shoring is proposed as an evaluation indicator of the saving-life passage considering the characteristics of building ruins and the size of the living space of the trapped. Taking life-saving passage of the pancake-type building ruins as research object, the evaluation of the safety of the life-saving passage was investigated under the action of aftershock. The vertical bearing capacity test of wood shoring is performed in order to obtain the evaluation indicator of saving-life passage. The restart function of ANSYS/LS-DYNA program is used to re-edit the numerical model of the building ruins to construct the life-saving passage, then, the safety evaluation of life-saving passage of the pancake-type building ruins is investigated under the action of aftershock. The results show that the constructed life-saving passage passed the safety evaluation under the actions of different aftershocks. The possibility of the secondary collapse of the life-saving passage increases exponentially with the increase of rescue time within 72-hour gold rescue, and the growth is slow after 72hours when the magnitude of the main earthquake reaches above 7.4; the safety factor K should be increased appropriately if wood shoring is used to construct a life-saving passage when the main earthquakes magnitude is greater than or equal to 7.5. The safety evaluation method of life-saving passage can provide effective reference for earthquake rescue.

Monolithic precast reinforced concrete (RC) frames with cast-in-place joint cores and grouted-sleeve splices are increasingly adopted in seismic regions, yet connection degradation is not carried through to system-level fragility: existing studies take hinge properties from code tables or one test, or stop at the joint. This study closes that gap with a reproducible transfer route in which the degrading, pinched M–θ hysteresis identified from a refined joint model becomes structure-level hinge parameters, with every intermediate quantity reported so that the route can be reproduced elsewhere. The joint model is an explicit finite-element interface-spring/contact strategy with Mohr–Coulomb interface behavior, tension cut-off, local spring failure, and sleeve–grout–rebar bond slip. Incremental dynamic analysis and fragility assessment of a six-story monolithic precast frame and a comparable cast-in-place frame show larger inter-story drift demands in the precast frame. At PGA = 0.40 g, its collapse exceedance probabilities are higher by 0.73 and 0.44 percentage points in X and Y, respectively. Global performance is broadly comparable, but the precast frame shows a consistent, modest unfavorable tendency caused by connection pinching and reduced ultimate rotation. Interface treatment, sleeve grouting quality, and connection-level ductility should therefore be explicitly considered in seismic performance assessment and design.