Floor diaphragm design of steel self-centering moment frames

The self-centering behavior of a Self-Centering Moment-Resisting Frame (SC-MRF) is achieved by post-tensioning the beams with either high strength strands or bars. The behavior of a SC-MRF is characterized by a gap opening and closing at the beam-column interface under earthquake loading. The gap opening behavior causes the SC-MRF to expand, as the distance between the column centerlines increases relative to the original distance in the deformed position. This behavior imposes new requirements on the floor diaphragm design. The objective of this study is to analytically evaluate the effects of the floor diaphragm represented by collector beam elements. The collector beam stiffness, strength and configuration are varied in different prototype buildings, as are the building heights, and these prototype buildings are subjected to hundreds of recorded ground motions. Based on incremental dynamic analysis and reliability assessments, tentative design recommendations are developed for the collector beam designs.