Progressive Collapse Assessment and Retrofit of a Multistory Steel Braced Office Building

The progressive collapse of the building structures due to abnormal loads has attracted global attention in recent years. Many studies in the literature have been dedicated to the analysis and design procedures for progressive collapse resistance, and several technological solutions have been developed for progressive collapse retrofit. However, many studies are based on simple models and their validity and possibility to generalize the research results to current practice are rather limited. Moreover, there are still not many case studies developed based on full-scale real buildings. The present paper contributes to filling this gap by investigating the robustness of a quite complex real case study, namely a steel braced frame building erected in the early '60 s in Naples-Italy to house the Civil Engineering Authority. To this aim, different column removal scenarios have been considered and both nonlinear static and dynamic analyses have been carried out. The results have highlighted that the simple braced frames are susceptible to progressive collapse due to the weak brace connections. However, joint strengthening is not a viable solution, because it would prevent the full functionality of this strategic building during the implementation of the progressive collapse retrofit. As an alternative, an outrigger-belt truss system has been developed that applies the concept of Vierendeel truss system to redistribute the loads due to the column removal. The effectiveness of the proposed retrofit strategy to improve the progressive collapse resistance of the building has been verified through nonlinear dynamic analyses, proving its feasibility for practical applications.