PI: James Ricles
University: Lehigh University
Collectors are key structural elements in a Seismic Force Resisting System (SFRS), delivering the inertial forces that develop in the floor system to the vertical plane SFRS elements. Yet in contrast to the vertical-plane elements (shear walls, braced frames, moment frames, etc.), which have been studied extensively, including scores of experiments producing terabytes of data, collectors have received almost no treatment. No experimental program, or other research effort has focused specifically on collectors. As a result, current design code provisions for collectors, which recognize their critical role and their poorly understood seismic response, apply special load combinations that include the system overstrength gactor (varying from 2.0 to 3.0), resulting in large design forces for collectors. This stringent prescriptive design approach is an attempt to ensure that critical collector elements remain elastic. Loss of collector elements can be catastrophic, as shown by the collapse of the CTV building in the 2011 Christchurch earthquake, in which 115 lives were lost, or in the collapse of the Northridge Fashion Center parking structure, in which the shear walls were undamaged while the floor system detached and collapsed.
Given that the actual demands on seismic collectors are poorly understood, with essentially no significant research to date, and given the recent insights into the actual nature of inertial forces in building structures during strong earthquakes, now is the time to take a rigorous look at collectors in steel structures. It is an an opportunity to transform the old approach, which attempts to make collectors stronger than the floor diaphragm inertial forces, into a modern approach, which may use collectors to control the floor inertial forces. A similar effort has been undertaken successfully by members of a proposing team for concrete wall structures through the use of special deformable anchorages