AbstractThe performance of an immediate frame span subjected to a falling-debris-impact scenario is of great importance to investigate the spread of initial damage during a progressive collapse event. If the frame span was not able to resist the impact load from possible falling debris, it would become new debris and impact the lower floor with previous debris. After that, progressive collapse might probably happen. However, the impact mechanism considering the contribution of composite slabs of an immediate span remained unclear currently. Therefore, experimental studies on a series of three half-scale composite beam subassemblies were conducted under impact scenarios. The impact loads were applied via a high-performance drop-weight test machine. Various beam–column connections, including welded unreinforced flange-bolted web, fin plate, and reverse channel connections, which represented rigid connection, hinge connection, and semirigid connection, respectively, were investigated. The structural resistances of the specimens were provided by flexural action, compression arch action, and catenary action. Among them, the contribution of compressive arch action was limited and can be ignored. Flexural action always provided the most structural resistance contribution in the whole impact process, and catenary action provided structural resistance under large deformation. The specimen structural resistance increased with increasing deformation before the failure of connections. Good flexural resistance and deformation capacity were the key factors for structures to resist impact load. The reversed channel specimen had the best impact resistance.

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