Avoiding Disproportionate Collapse of Tall Buildings

Accidental circumstances must not result in disproportionate collapse. Strategies for achieving this goal are studied and corresponding design concepts are developed. The focus is on large and slender buildings with a high degree of significance and exposure. The study is based on an examination, one by one, of five general approaches: nonstructural protective measures, specific local resistance, alternative paths, isolation of collapsing sections, and prescriptive design rules. Departing from the specific-local-resistance approach, an arrangement of independent primary and secondary load transfer systems is arrived at where the primary system consists of a compact reinforced-concrete tube forming the vertical spine of the building. Based on the isolation approach, a vertical segmentation accomplished by strengthened floor slabs is suggested where a commencing pancake-type collapse is arrested by dissipating energy in shock-absorbing devices. These two design concepts maximize the tolerable accidental circumstances. The alternative-paths approach can be used for secondary systems or when a set of limited accidental actions is agreed upon.