Quantitative assessment of resistant contributions of two-bay beams with unequal spans

Abstract Following the sudden removal of an internal column from a steel-frame composite-floor system, the two-bay beams connected to the failed column play a key role in the internal force redistribution and rebalancing of the remaining structure. Moreover, the span–depth ratios of the adjacent two-bay beams have a significant influence on the collapse-resistant performance of the structure. To date, studies on structural progressive collapse of beams with unequal spans have been limited. In this study, based on the results of static loading tests on composite beam–column assemblies with cover-plate joints under three different span ratios, the finite element modeling method was validated and numerical models of the beam–column assemblies with three unequal spans were established. The influence of the unequal span of two-bay beams on the internal force development and load-resisting mechanisms of the composite beam–column assemblies were analyzed in detail. To gain deeper insight into the load-resisting mechanisms, the contributions of the flexural and catenary mechanism resistances to the total resistance of two-bay beams were quantitatively separated using the energy equilibrium theory, and it was found that the resistant contributions of the catenary mechanism, in general, account for less than a half of the structure’s resistance capacity. Moreover, theoretical formulas for the different resistant contributions of two-bay beams were proposed as recommendations for structural progressive collapse design and practical engineering applications. The analysis of results demonstrated that the span–depth ratios of two-bay beams determined the resistant contribution coefficients for the flexural mechanism, whereas the span ratios of two-bay beams determined the resistant contribution coefficient for the catenary mechanism, whereas the beam depth had little influence thereon.