Numerical investigation of the behaviour of bolted and welded top and seat angle connection in progressive collapse of steel structures

After failure of a column in structure by an abnormal loading, undesirable performance and damage of connections of the beams connected to the top of this column, can lead to the local failure of floor and in turn result in progressive collapse in the structure. Accordingly, the best method for rehabilitation of the structure against this incident is the strengthening of the connections. The strength and flexibility of the connections during the large rotations result in spreading the axial forces in beams and forming the catenary action. This action can greatly prevent structural failure due to the column removal. In this paper, the performance of prevalent bolted and welded top and seat angle steel connections is evaluated numerically. All parts of the connections are modeled in finite element software. The modeled structure is analyzed nonlinearly under the vertical displacement in the location of removed column, and its results have been verified with experimental results. In addition, the behavior, failure modes, how the catenary action develops and the effects of different parameters on connection behavior are investigated. The results indicated that bolted connections have better performance than welded connections.Also, in welded connections, increasing the thickness of the angles and increasing the length of the connected angle leg to column, improve the catenary action and the resistance of the connections against progressive collapse. But adding the stiffener plate in the middle of the seat angle does not increase the connection capacity in all cases.