Progressive collapse evaluation of externally mitigated reinforced concrete beams

• Flexural behavior of beams was investigated to demonstrate progressive collapse.
• Control and mitigated beams with catenary action in external rods were studied.
• Proposed mitigating scheme increased substantially the beam durability.
• Proposed mitigating scheme can easily and economically prevent progressive collapse.
• Proposed mitigating scheme can be used in new structures and temporary ones.

One of the factors that lead to potential progressive collapse of structures is removal of a load-bearing element such as a column. In this paper, a technique and a numerical procedure are presented for mitigation and evaluation of potential progressive collapse of reinforced concrete continuous beams following removal of interior columns. The procedure presented for mitigating progressive collapse proposes the use of external unbounded Fiber reinforced plastic (FRP) cables attached to the beam at anchorage locations and deviators/saddle point(s) only, without being posttensioned. The cables will be in effect when excessive vertical displacements and deformations occur in the mitigated beam due to removal of the interior column support of the beam. The proposed numerical model evaluates the progressive collapse of such beams using a push-down analysis to simulate column removal. It assumes that the anchorage and deviator locations of the external cables act as rigid arms that connect the external cables to the beam. Parameters such as beam cross-section shape, location(s) of deviator/saddle point(s), area and profile of the external unbounded FRP cables are considered in the proposed model. The model predicts the strength of beams mitigated by the proposed technique and evaluates the effects of the external cables on the beam ductility. Numerical results of the proposed mitigation technique obtained by the proposed numerical model are compared to those in the literature.