The Multi-Storey Buildinds Steel Frames Progressive Collapse Mechanisms in Fire

An overview of previous studies, dedicated to the vitality of the multi-story building with a steel frame was carried out. Currently, measures are available to increase the multi-story buildings' steel frame vitality in fire, which affects the potential progressive collapse mechanism. The quantitative vitality indicators have been determined earlier. The model used to study a multi-story building steel frame is described. The way of modeling the fire action on steel structures is presented. The criterion for the steel frame elements destruction is determined. The measures of increasing vitality for the multi-story building steel frame model are presented. The sequence of multi-story buildings' steel frames different elements destruction for a various measures of increasing vitality is determined. The collapse duration of each of the considered progressive collapse mechanisms is analyzed. It is established that the initial destruction in the unheated frame element leads to a less projected and more unfavorable progressive collapse mechanism in the event of an accident evacuation. It is determined that to avoid the initial destruction in the unheated frame element, you need to use an attachment of the outriggers to the columns joint with the admission of vertical displacements. It is established that in the case of beam destruction earlier than the column, the progressive collapse mechanism will be longer than in the column's initial destruction case. Earlier internal column destruction leads to a longer progressive collapse mechanism than earlier external column destruction. It is established that the progressive collapse mechanism of the type "beam - the internal column - the external column – progressive collapse" is the longest and the most predictable. The gradation of the progressive collapse mechanisms of steel frames in the role of a qualitative vitality indicator is determined. The gradation presented can be used for the research of frames with a variety of spans and floors.