Progressive collapse resisting capacity of building structures with outrigger trusses

In this paper, the progressive collapse potential of building structures with core and outrigger trusses were evaluated using nonlinear static and dynamic analyses. To this end 36-storey analysis model structures composed of RC core walls and perimeter frames connected by outrigger trusses at the top were prepared. The static pushdown analysis of the structure with mega-columns and outrigger trusses showed that the maximum strength reached only about 20% of the load specified in the US General Services Administration guideline when a mega-column in the first storey was removed. According to dynamic analysis results, the vertical displacement monotonically increased until collapse as a result of buckling of some of outrigger truss members. However the structure with outrigger and belt trusses remained stable after a perimeter column was removed. The stability of the structure with mega-columns and outrigger trusses could be achieved by redesigning it with additional belt trusses or with moment connections in interior or exterior frames. Based on the analysis results it was concluded that the dynamic amplification factor of 2.0 recommended in the guidelines provided reasonably conservative results.