Abstract

Unlike seismic engineering that attracted the attention of researchers, designers, and code developers for decades, the phenomenon of progressive collapse of structures still needs considerable amount of investigation. The main motivation for this study is to investigate the vulnerability of seismic code designed multistory steel moment resisting frame buildings to progressive collapse, and to propose retrofit solutions for those buildings that show to be prone to progressive collapse.
The studied buildings had 5, 10, and 15 stories (representing low-rise, medium-rise, and high-rise buildings), where each building was designed for three seismic zones (representing low, medium, and high seismicity). All studied buildings have a 3-bays x 6-bays rectangular plan; each bay has a span of 6 meters. Alternate Path Method (APM) recommended by GSA 2003 guidelines is adopted to evaluate the robustness of the buildings against progressive collapse. Three-dimensional models of the buildings are built using the Extreme Loading for Structures (ELS) software, where nonlinear static and nonlinear dynamic time history analysis are conducted for six different column removal scenarios for each building.
The nonlinear dynamic analyses showed that buildings designed for low seismicity do not possess sufficient resistance against column removal cases, thus need to be retrofitted to safeguard against the possibility of their progressive collapse. Consequently, two retrofit methods using top beams grid system and top gravity truss system are proposed for buildings in low seismic zones in order to enhance their robustness against progressive collapse. The nonlinear static and nonlinear dynamic analyses of the retrofitted buildings using the ELS software showed the effectiveness of the proposed retrofit systems in mitigating progressive collapse.