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.
The robustness, or structural integrity, of structural systems has become an important question for practitioners and researchers. Recent examples of collapse and increased concern over the ability of buildings to withstand malicious attack have motivated researchers to investigate the robustness of various structural systems to unanticipated loads, i.e., to investigate how systems redistribute loads when structural elements are damaged. However, the robustness of steel gravity frame systems, one of the most commonly used structural systems in the United States, had not been thoroughly investigated prior to this research. Steel gravity frame systems are efficient and economical for carrying the weight of buildings materials and occupants to the ground but they have little obvious redundancy and the ability of their components to resist demands other than those that they have been designed for was unclear prior to this research. This research grant has enabled the investigation of steel gravity frame connections under demands consistent with the loss of capacity of a structural column. In such a scenario the beam-to-column connections are subjected to large rotations and large axial forces but have been designed only for the shear force corresponding to the design gravity loads. Tests were conducted on 33 different connections including single-plate shear tab, bolted angle, and top and seat angle connections that are all commonly used in different regions of the country. Test specimen design was aided by close collaboration with an advisory panel consisting of practicing structural engineers, American Institute of Steel Construction representatives, and other researchers to ensure that the specimens would be representative of common practice and the results would be state-of-the-art. A unique connection test frame was constructed to impose the simultaneous rotation and axial load demands on the connections. The experimental results indicated that the modern connections used in steel gravity frames do not have adequate capacity to resist the demands resulting from the change in load path associated with a damaged column. Modern gravity frame connections were able to resist only 10-15% of their design gravity load in this loading state. These results were consistent across connection type and for the wide range of connection design parameters considered. The test results have also been corroborated with the ½ scale system tests conducted in the collaborative part of this project at the University of Illinois. In the system tests the capacity of the steel gravity frame system was limited largely by connection failure and the system was not able to resist the typical loading considered when assessing structural robustness. Some trends in capacity were found to be associated with connection configuration and have been used to develop concepts for improving connection performance. Computational models of these economical solutions were developed and shown to indeed provide enhanced robustness. Recommendations for the design and analysis of steel gravity frame connections for the column damage scenario have been developed and are being disseminated to practicing structural engineers through conference presentations, involvement of the PI in Structural Engineering Institute activities and through archival journal publications. The research should have considerable impact in the design of steel structures for structural robustness. In applications where the structural framing is required to be designed considering the loss of capacity of a column (such as government buildings), the use of common steel gravity frame connections has been found to be inadequate and alternative connections will be required. The research project has also contributed to work force development. One Ph.D. student has completed his dissertation research on this topic. Additionally, one undergraduate participated in the research and has since started a graduate program in structural engineering. Finally, in collaboration with Seattle MESA, six high school interns from underrepresented groups in science and engineering participated. They have all started college and several are considering engineering as a degree path.
