Use of Roof Mega-Trusses for Progressive Collapse Retrofit of Existing Buildings

The global concern over the progressive collapse of building structures under abnormal loads has intensified in recent years. Numerous studies in the literature focus on analyzing and designing procedures to enhance progressive collapse resistance and various technological solutions for retrofitting against progressive collapse have been devised. Nevertheless, numerous studies rely on simplistic models, and the generalizability of their research findings to current practical applications remains constrained. In this paper, an alternative retrofit solution is proposed based on an outrigger-belt truss system that is added at the rooftop level of the building. The truss system provides significant vertical stiffness and strength with relatively small sections and limited added mass. Moreover, it is rapid, low-impact, and reversible, does not significantly affect the seismic behavior of the building, and, finally, keeps the building fully operational during the retrofit implementation. A simple design procedure is developed based on simple equilibrium conditions. The effectiveness of the retrofit strategy is estimated by nonlinear static and dynamic analysis of real case studies. Its effects on the existing structural members are finally discussed.