The research objective of this award is provide critical experimental data and assessment tools essential for evaluating the integrity of common steel gravity load resisting systems. A combination of system testing and component testing will be used to assess the behavior of these systems as designed today. These experimental results will then be used to advance models for the analysis of such systems under large deformations and to identify critical details that have a major impact on system performance. Cost-effective details that transform performance will be developed and tested at the component level and then incorporated in system tests. At the component level, steel connections will be tested under combined rotation and tension loading, and important details of the slab on deck system, such as lap splices, beam anchorage, and the tensile behavior of the slabs on metal decks in orthogonal directions will be tested. System tests will involve large-scale push-down tests of gravity frame systems using current practice details and new concepts developed in this research.
The results of this research will directly impact the safety of almost all steel buildings by assessing the integrity of ubiquitous structural components and developing models for engineers to employ. It will also develop transformative solutions for improving the robustness of common gravity frame components and systems. Through close collaboration with the American Institute of Steel Construction, expedient dissemination and rapid implementation will be facilitated. Graduate students will be directly trained through this research as they address the challenges associated with unanticipated structural loadings. Interest and diversity in engineering will be enhanced through partnerships with the Summer Undergraduate Research Fellowship (SURF) program at Purdue, the Summer Research Opportunity Program (SROP) at Illinois and the Seattle Mathematics Engineering Science and Achievement Program (Seattle MESA) at Washington. These programs will provide for undergraduate (SURF and SROP) and high school (MESA) research internships.
In typical steel buildings, gravity framing systems with concrete slabs on steel deck support the majority of the floor area. The rotationally flexible beam-to-column connections in these gravity frames are designed to support the building loads primarily through shear, and the composite steel-concrete floor slabs are designed to support the loads primarily through bending. However, in unforeseen extreme loading, such as a column loss scenario, these components would be required to develop alternative load paths and to resist large deformations (e.g., connection rotations) and the resulting demands through catenary and membrane action. The literature would suggest that gravity framing systems have some inherent structural integrity and robustness, or resistance to disproportionate collapse, with the composite floor slab contributing a significant portion of that resistance. However, little experimental data exists to demonstrate the strength and ductility of the connections, the composite floor slab and its details when subjected to a column loss scenario. This collaborative research project filled gaps in knowledge and provided practical methods for evaluation of the structural integrity of typical, steel gravity load resisting systems. The research integrated large-scale system tests at the University of Illinois, beam-column connection tests at the University of Washington, and composite floor slab component tests at Purdue University. While focusing on the contribution of the composite slab to structural integrity in steel gravity framing systems, the research at Purdue University addressed that contribution from several perspectives. First, relevant literature was studied to identify the state of-the-art in structural integrity research, concentrating on composite slabs. Next, a typical composite slab was developed for use with design of component level specimens. Those specimens corresponded to details and directions of interest (e.g., parallel or perpendicular to the corrugations in the metal deck) with applied loading simulating what would be expected in column loss scenario. Results of tests of those specimens were analyzed and compared to simple behavior calculations, and general qualitative observations were recorded. Finally, the obtained experimental data was implemented into computational studies at several levels of modeling, validating and further developing concepts from previous research. Contemporary approaches for accurately modeling the composite floor slab have been improved through experimentally-validated methods of representing the anchorage of the metal deck to the steel framing (i.e., support fasteners). This outcome has exposed a critical vulnerability in typical composite floor systems, and has also highlighted a key opportunity to implement practical modifications to design and detailing of composite slabs for potentially significant improvements in robustness. Intellectual Merit: Overall, the collaborative research has addressed critical knowledge gaps regarding the behavior of typical steel gravity frames. Integrated component and system tests were used to develop and validate models for evaluation of structural robustness. Specific to Purdue University, the research has produced data for fundamental understanding and improved computational modeling of the behavior of the concrete slab on metal deck and its details under extreme loading. Broader Impacts: The results directly impact the safety of typical steel buildings through assessment of typical details and development of validated models for evaluation of robustness. Dr. Liu serves on the ASCE/SEI Disproportionate Collapse Mitigation Standard committee, ensuring direct dissemination of results and impact on industry practice.
