Retrofit of existing steel structures against progressive collapse through roof-truss

The paper presents the results of a comprehensive study on the evaluation of the effectiveness of a retrofit strategy of existing steel buildings against progressive collapse. In this respect, it investigates the performance and the design of a retrofit solution to increase the robustness of steel Moment Resisting Frame buildings. A truss steel system added at the building's rooftop level (i.e., 'roof-truss'), and intended to define an alternative load path, was investigated as a retrofit solution. The numerical model key components, including the plastic hinges and the beam-column connections, were validated against available experimental results. The validated models were then used to study the robustness of the structure under column loss scenarios by means of non-linear static and dynamic analyses performed in OpenSees. The simulations allowed for the identification of possible failure modes and alternative load paths together with the definition of the Dynamic Increase Factor (DIF). In this regard, it is shown that column buckling is critical for the selected case study. Moreover, the outcomes showed how the proposed retrofit solution allows the definition of effective alternative load paths when subjected to column loss scenarios and informs on the critical details that should be checked by employing this retrofit system.