The robustness of typical steel-framed and concrete composite buildings against progressive collapse is commonly assessed under the notion of a column removal scenario. This study sheds light on the response of the gravity floor systems of this type of buildings when the latter are subjected to an interior gravity column loss, focusing particularly on the most vulnerable component of the gravity system: the shear (or gravity) connections. These connections are designed to accommodate mainly shear forces, yet in a column removal scenario they are exposed to additional and significantly high axial demands. Previous work by the authors has identified and semi-analytically described the two most prominent collapse mechanisms of these buildings: the "yielding-type mode" (ductile and desired collapse, initiated by a sequence of gravity connection failures and extensive wire mesh and steel deck yielding, dominant in the upper part of the building column removal scenarios), versus the "loss-of-stability mode" (brittle and undesired collapse, initiated by a column buckling, dominant in the lower part of the building column removal scenarios). This study clearly demonstrates the prevalent role of the gravity connections on the building response, showing that depending on the connection type and geometric characteristics a switch from the yielding-type to the stability mode is possible for a column removal scenario on the same floor. Therefore, this work reveals the necessity to thoroughly investigate the correlation between the adopted gravity connections and potential instability phenomena on the building scale, to further enhance the structural robustness against progressive collapse.
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