Factors Influencing Catenary Behavior in Ductile Steel-Framed Structures

Abstract

Historical precedent has established progressive collapse as a phenomenon characterized by the potential for extreme structural damage and loss of life. In an attempt to mitigate such behavior in conventional structures, several different approaches for analysis and design have been suggested. These methods include both threat-dependent and threat-independent procedures. Under the latter, a common approach is to subject the structure to a notional column-removal scenario and then check the ability of the structure to bridge over the removed member. The structure’s response under such circumstances can involve the utilization of catenary, or cable-like, behavior to resist the imposed loads once the flexural capacity of the resisting members has been exhausted and sufficient levels of deflection have been attained. In this thesis, an analytical investigation of various factors influencing the response of steel structures during progressive collapse is presented. The investigation consisted of two components: a baseline study and a parametric study. The baseline study considered the collapse-response of a specifically designed, eight-story, six-bay, steel-framed structure during four distinct, first-story column-removal scenarios. The general response of the structure during each scenario, its catenary action demands, and connection ductility demands were recorded, discussed, and compared. Following the baseline study, a parametric study was conducted, which considered the effects of changing selected design parameters on the response of the system during collapse. The investigated parameters included the building location, the number of stories, the number of bays in the lateral load-resisting system, and the building aspect ratio. The Open System for Earthquake Engineering Simulation (OpenSees), an open-source finite-element (FE) software package, was utilized for the FE simulations. The results of the investigation show that each factor can have a significant impact on overall system behavior, and the development of catenary forces in particular.