Progressive Collapse Simulation Of Multi Story Reinforced Concrete Buildings

This research effort was motivated by the need for additional insight into the mechanics of progressive collapse of reinforced concrete frame buildings resulting from the sudden loss of one or more columns on the lowest story level. Although several studies have investigated disproportionate collapse both experimentally and numerically, there is still a general lack of information not only on modeling and analyses procedures but also on system characteristics such as building height and initiation and sequence of column loss that impact the ability of RC buildings to resist progressive collapse. Nonlinear simulation models of three, six and ten-story reinforced concrete frame buildings using the software platform LS-DYNA (Hallquist 2007) were developed using a reduced-order modeling scheme: line elements with cross-section discretization were employed for beams and columns whereas layered shell elements with smeared reinforcement were used for slabs, and the effectiveness of the modeling was validated with large-scale experimental data. The simulations examined the influence of story height in resisting progressive collapse and the effect of the sequence of column losses in accelerating progressive collapse. Two specific scenarios were considered: column losses that are initiated with the loss of a corner column and in the middle of the building plan at the lowest level of the building. Finally, a methodology based on energy and deformation measures is developed that provides an indirect assessment of structural robustness and can be used to compare the relative robustness of different buildings. Findings from the study indicate that the loss of a corner column on the lowest floor of a reinforced concrete frame building poses a greater threat to progressive collapse than a column loss in the middle of the building. Taller buildings possess greater resilience to progressive collapse than buildings with fewer stories for the same arrangement of vertical elements in the building plan. The vertical drift angle and the change in the axial stress ratio in a column adjacent to a removed column are found to be effective indicators of structural resilience to progressive collapse. This research also provided a basis for comparing the relative robustness of buildings subjected to column losses on the lowest floor. Consequently, findings from the study provide engineers an insight into improving the robustness of a building to resist progressive collapse.