Investigation of the effect of cantilever beam on progressive collapse of reinforced concrete structures with dual strength system

The most important issues of passive defense in structures is the issue of progressive collapse. Progressive collapse occurs as a result of events deliberate and administrative, military, terrorist, earthquakes and floods. In progressive collapse, due to the destruction of one member of the structure, the failure is transmitted to other members of the structure and the failure extends in a chain throughout the structure and causes the destruction part of or the entire structure. Determining the key element in the structure and strengthening can prevent progressive collapse, total destruction of the structure and the resulting damage. In this paper, 5, 10, and 15 stories structures with dual system with cantilever beam. To investigate the effect of cantilever beams and the determine key element in reinforced concrete structures with dual system by the sensitivity index method and structural analysis is used by non-linear static analysis of vertical down (Push Down Analysis). The results show that in reinforced concrete structures with dual strength system with cantilever beam, the column failure index with the longest distance from the cantilever beam (23 m) compared to other columns in each three structure 5, 10 and 15 story is 87%, 77%, and 66%, respectively, which is considered as a key element in these structures. According to results, in case of increasing the height of structure with cantilever beam with dual strength system from 20 meters (5 story) to 60 meters (15 story), the failure index of the whole structure will decrease from 87% to 66%.