DOI: 10.17603/ds2-3wqg-aj61
title: Predetermined Collector Force and Rotation Histories Tests on TFW, in Advancing Knowledge on the Performance of Seismic Collectors in Steel Building Structures

description: Predetermined collector force history tests were conducted on a Top Flange Weld (TFW) collector connection to evaluate its performance under different levels of seismic hazard loading. A test collector specimen with a TFW connection was designed, fabricated, and experimentally evaluated under prescribed seismic collector force and inter-story drift histories, without composite slab or gravity loading. The TFW collector connection demands were obtained from nonlinear time-history analyses of archetype steel buildings. Based on these analyses, representative collector force and story drift demands were selected for the test specimen. Snippets of the loading histories corresponding to different seismic hazard levels were extracted, and each loading history was subdivided as necessary based on force and rotation increments. The selected snippet histories of drift and collector force were applied consecutively. For each loading step, the reaction column was first rotated to the target drift using reaction actuators, followed by application of the corresponding collector force through the loading actuators. This procedure was repeated sequentially until completion of the selected snippet. These tests provide insight into the performance of the TFW collector connection under seismic load demands associated with different earthquake hazard levels.
description: To safely survive an earthquake, and thereby protect its occupants, contents, adjacent property, and passersby, a building structure must transfer the large forces that develop during the earthquake from within the building down to the foundation. Earthquake (lateral) forces are generated by the building weight being accelerated horizontally, and thus most earthquake forces originate in the building's heaviest element, i.e., its floors. A key structural element in the force transfer path to the foundation are collectors, which are either special reinforcement in the floor slab or special beams below the slab, that "collect" the forces in the floor, and transfer them to the primary seismic force-resisting vertical elements (frames, braces, or walls). The loss of collectors or collector connections can be catastrophic, as evidenced by the collapse of the CTV building in the 2011 Christchurch, New Zealand earthquake, which killed 115 people, the largest loss of life in this event, and to some extent the collapse of nine parking garages in the 1994 Northridge, California earthquake. Despite the critical nature of seismic collectors, no research effort, including physical testing, has focused specifically on collectors, and knowledge of their seismic performance is lacking. A challenge in understanding the performance of seismic collectors is the complex nature of the floor system itself, a complicated assemblage of many components of different materials (e.g., steel, metal, and concrete) at different elevations, with multiple purposes and uncertain force paths. Past seismic design methodologies for buildings may have significantly underestimated the collector forces. This lack of knowledge impacts not only new construction but also the assessment and retrofit of existing, especially critical care, facilities in high seismic regions. This condition also applies to older non-seismic compliant steel structures nationwide, where inadequate or non-existent seismic collectors are often a major concern. A better understanding of the performance of steel seismic collectors is needed for safe and economical structures, both in the existing building stock and for new construction. Further, the collector's unique role as the critical link between the floor and the vertical elements provides an opportunity for collectors from trying to "out-strength" the earthquake force to instead serve as an innovative force-limiting element that protects the structure from damage. The goals of this research are to: (1) advance knowledge on the seismic performance, analysis, and design of collectors in steel composite floor systems, and (2) develop new knowledge on the reliable seismic performance and potential benefits of innovative collector concepts that can lead to low-damage structural design. This project will support researchers and graduate students from the University of Arizona, University of California, San Diego, and Lehigh University. The project will benefit from working closely with collaborators who are separately supported, i.e., a researcher and a practitioner in New Zealand and an industry panel of seismic design engineers in the United States. An outreach program will be conducted by the University of Arizona with local K-8 schools identified demographically as possessing student bodies of predominately underrepresented groups. The outreach program will target third, fourth, and eighth grade students to include: (1) slides shows and question and answer sessions on earthquake engineering, (2) career mentoring from graduate and undergraduate students, and (3) hands-on science and math activities.

In this project, an integrated research program will investigate the performance of seismic collectors for steel composite deck structures using the experimental and computational simulation capabilities afforded by the NSF-supported Natural Hazards Engineering Research Infrastructure (NHERI). The research will involve: (1) large-scale testing of collector elements in a steel composite floor system at the NHERI experimental facility at Lehigh University, (2) shake table testing of a 0.4-scale, single-story, steel composite floor system at the NHERI shake table facility at the University of California, San Diego, and (3) nonlinear analysis of steel structure collector elements, details and surrounding regions under seismic effects, and earthquake simulations of steel buildings under strong earthquakes. The planned experiments on steel collectors, with realistic boundary conditions and inertial forces, will be the first of its kind. New data products and calibrated numerical models will be produced from large-scale physical testing. Analytical models will be developed for the collectors and the collector inertial force paths. Transfer of research results into practice will include: (1) new concepts for low-damage structural design, (2) research-based design recommendations, and (3) assessment and retrofit guidelines.