Effects of Structural Bracing on the Progressive Collapse Occurrence

Statistics of human losses and financial casualties induced progressive collapse, as one of the new and modern concepts in the field of civil engineering, have doubled the importance of having knowledge about this phenomenon and strategies to reduce its effect. Progressive collapse starts with a local failure with loss of local load-carrying capacity of a small portion of the structure and spreads throughout the structure from element to element. These consecutive failures may cause the collapse of either the entire structure or a major part of it. This paper studies the effect of adding a bracing system to the steel moment frames designed for seismic loads through a nonlinear dynamic method according to GSA-2003 and UFC-4-023-03 criteria. The study was conducted using computational simulation of building models with two different elevations of three and six floors located in a moderate seismicity region. The simulation results showed higher resistance against the progressive collapse of the structure in the braced steel moment frames and less sensitivity to the removal of the column in the braced spans in comparison to the spans without bracing. The prediction of possible progressive collapse in the UFC-4-023-03 criterion is more conservative than the GSA-2003 criterion. Although, generally there is no significant difference between the analysis results of these two criteria.