عنوان مقاله [English]
In the recent decades designing buildings against progressive collapse has been subjected to growing attention. In progressive collapse, the failure of one single structural member is transmitted to other members resulting in collapse of the entire load-resisting system of the building. Progressive collapse in buildings can be triggered by diverse factors such as accidental gas blast, impact between vehicles and one of the columns, etc. It is, thus, of great importance to design a building to withstand such catastrophic collapse. In this manner, in the design process, the building is subjected to different failure scenarios of single elements, e.g. a column, and investigate whether the failure spread to the remaining parts of the structure. While a substantial effort has been devoted to design earthquake-resilient structures based on the current seismic codes and state-of-the-art researches in earthquake engineering, still further studies are required to investigate the resistance of structures against progressive collapse.
In this research the progressive collapse of dual special steel moment-resisting frames and buckling-restrained braces, as an earthquake-resilient structural system for high-rise buildings, has been numerically investigated considering several failure scenarios. Buckling-restrained braces have been considered to provide appropriate seismic performance due to fair tensile and compressive behavior as well as almost symmetrical hysteresis response. In the performed numerical analyses, progressive collapse in four high-rise residential and commercial 20-story buildings with dual special steel moment-resisting frames and buckling-restrained braces with different configuration, such as (combined V-Inverted V) and (V) located in the corner and edge bays is studied, regarding different failure scenarios. The above-mentioned scenarios include the removal of a corner or edge column in the first or fifteenth floor, as well as the removal of two edge columns of the braced bays in the first or fifteenth floor. The numerical models were verified against existing published experimental and numerical results before being applied to the analytical cases. This is achieved by comparing the results reproduced by the numerical tool to the previously published results regarding both cyclic analysis, at the sub-assembly level, and time-history analysis, at the structural level.
The adopted numerical models were based on Finite Element (FE) simulation of the structures taking into account both material and geometric nonlinearities. The Inelastic force-based plastic hinge frame element type in SeismoStruct software was used to model beam and column elements, while Inelastic force-based frame element type elements was implemented to model the nonlinear behavior along the buckling-restrained braces. Each of the bracing elements consisted of three parts, including: a middle part to simulate the core as well as transition and elastic segments of bracings, and two end parts with large stiffness to simulate the panel zone and gusset plates. Rayleigh damping was also selected to model the damping in time-history analyses of the progressive collapse process. The performance criteria for all the members and connections were selected according to ASCE/SEI 41-17.
Based on the obtained results, the peak vertical deflection of the top node of the removed column was approximated to be as large as 6.5 cm, and collapse was observed in one of the numerical models (commercial building contains X-bracing in the corner bays).
The dual structure with X-bracing in the corner bays represents the weakest performance, while the best performance was related to the case of V-bracing in the edge bays, and the V-bracing in the corner bays and X-bracing in the edge bays have shown similar behaviors. In addition, in all the single column removal scenarios, the peak value of deflection in the cases in which the column removal was not located at the bracing bays was significantly greater, approximately 1.5 to 3 times larger, compared to those of column removals in the bracing bays.