COLLAPSE BEHAVIOR OF MEGA-FRAME BUILDINGS

A mega-frame structure system, which is composed of super elements to resist both gravity and lateral loads, is considered to be suitable for tall buildings because of its efficiency in resisting lateral load [1]. The mega-frame systems, however, may be vulnerable for progressive collapse caused by sudden loss of a super column because the structural redundancy of a mega-frame is generally limited in comparison with those of conventional buildings. The progressive collapse in buildings refers to the phenomenon that local damage of structural elements caused by abnormal loads results in global collapse of the structure. The analysis method recommended is the alternative path method [2], in which the structure is designed in such a way that if any one component fails, alternate load paths are available and a general collapse does not occur. In most cases design for redundancy requires that a building structure be able to tolerate loss of any one column without collapse. Recently the performances against progressive collapse have been studied for steel structures [3] and for reinforced concrete structures [4,5]. Analysis procedures and program softwares were developed to simulate collapse behavior of structures [6,7]. This study investigates the progressive collapse resisting capacity of mega-frame structures composed of many identical subsystems based on column-loss scenario recommended in the GSA guidelines [2]. To this end nonlinear static analyses of mega-frames composed of various numbers of subsystems and super columns are carried out by removing one of the super columns. Based on the analysis results various modifications and alternative schemes are investigated to enhance the progressive collapse resisting capacity of mega-frame buildings.