Garlock, Li, and Blaisdell 2006
This paper analytically evaluates the effects of floor diaphragm stiffness, strength, and configuration on the seismic response of a SC-MRF. It is observed that this system exhibits both energy dissipation and self-centering properties. Energy dissipation was provided by supplemental elements that deform due to the gap opening behavior. PT strands were used to provide self-centering.
System Concept
The system is composed of steel frame with PT strands and energy dissipative angles and bars. The beams in the frames were post-tensioned (PT) by either high strength steel strands or steel bars. This system provided a restoring force to the system that resulted in self-centering. Supplemental elements such as top-and-seat angles, steel bars, or friction devices provide energy dissipation. The beam-to-column connections are characterized by a horizontal gap opening which is closed under earthquake loading. The post-tensioned strands compress the beam flanges against the column flange to resist moment, while the friction at the compressed beam-column interface resists beam shear. Moreover, the angles also resist moment and beam shear while dissipating energy under seismic loading.
Analytical Study, Results, and Discussion
The SC-MRF prototypes were modeled in DRAIN-2DX. The prototype building was a 6-story 6-bay steel frame with 30 foot bay widths and 13 foot story heights. The prototype building was subjected to nonlinear time-history analyses with six ground motions. In this study, the floor diaphragm was represented by collector beams and two different collector beam layouts were evaluated. There were a 3 and 15 collector beam layout. According to analytical results, larger collector beam stiffness showed smaller relative displacements between the SC-MRF and the floor system and larger axial forces, moments, and strains in the SC-MRF beams. Moreover, smaller collector beam strength resulted in more collector beams yielding, which in turn caused smaller roof displacements, story drifts, and relative rotations in addition to larger residual drifts. Finally, using a larger number of collector beams improved performance through added redundancy by reducing the percentage of collector beams that yield in the frame.
Reference
Garlock, M.E.M., Li, J., and Blaisdell, M.L. (2006). “Collector Beam Interaction with Steel Self-Centering Moment Frames,” Proceedings of the 4th International Conference on Earthquake Engineering, Taipei, Taiwan, October 12-13.