Robustness of moment steel frames under column loss scenarios

Abstract

To save lives and reduce economic losses, multi-story buildings, like other components of the built infrastructure, should be designed and constructed to withstand extreme natural or human-made hazards without collapse. In order to achieve this essential requirement, the structural systems should be able to absorb the local damage that may be caused by the abnormal event and prevent of collapse. Steel frames are widely used for multi-storey buildings, offering the strength, stiffness, and ductility that are required to resist the effects of the gravity, wind, or seismic loads. Considered to produce robust structures, seismic design philosophy has been seen as appropriate for controlling the collapse of structures subjected to other types of extreme hazards, too. However, there are specific issues that should be considered to forestall the localized failures, particularly of columns. The thesis focuses on the evaluation of the structural response of steel frame buildings following extreme actions that are prone to induce local damages in members or their connections. Extensive experimental and numerical studies were used to identify the critical points and to find the structural issues that are required to contain the damage and to prevent the collapse propagation. Four types of beam-to-column joints, which cover most of the joints used in current practice, have been investigated experimentally, and the data was used to validate advanced numerical models. The findings indicated that catenary action substantially improves the capacity of moment resisting frames to resist column loss, but increases the vulnerability of the connection due to high level of axial force. The results showed that bolted connections could fail without allowing for redistribution of loads if not designed for these special loading conditions. Composite action of the slab increases stiffness, yield capacity, and ultimate force but decreases ductility. Parametric studies were performed to improve the ultimate capacity of joints and implicitly the global performance of steel frame building structures in the event of accidental loss of a column, without affecting the seismic performance and design concepts. Based on validated numerical models, an analysis procedure was developed for evaluating the performance of full-scale structures to different column loss scenarios considering dynamic effects and realistic loading patterns. Moreover, a design procedure was proposed for verification of the capacity of beam-to-column connections to resist progressive collapse, including design recommendations for each connection configuration.