Investigation of the effect of low-strength steel on 6-story moment frame connections against progressive collapse

Connections have a significant effect on the energy depletion of the structure and its behavior against unusual loads, which often lead to the phenomenon of progressive deterioration.  Therefore, the effect of changing the mechanical and geometric characteristics on the connections in steel moment frames against progressive failure has been studied in this research. In this regard, the variable parameters include the type of beam-to-column connection (reduced beam section connection or RBS, free flange connection FF), the type of steel used at the beam-to-column connection (St37 and Steel LY 160) and the column removal location in different stories (without removing and removing of the columns on the ground, second and fourth stories). Research on a six-story steel frame is performed using ABAQUS finite element software and alternative loads path method. Validation of the finite element method was performed using numerical simulation of a steel frame and a suitable fit was observed. The most important results present that in the frames where low-yielding steel is used at the connection point, the best performance in terms of demand-to-capacity ratio (DCR) of the beams around the removal location belongs to the Free Flange connection frames.