Sause et al. 2010
The paper presents the research and development of the self-centering concentrically braced frame. The SC-CBF is introduced as in option to increase ductility and reduce residual drift of CBFs. The summary of design concepts and seismic performance of the test specimen are discussed.
System Concept
The concept consists of conventionally arranged beams, column, and braces with column base details allow uplift at the foundation. Under low levels of later force, deformation resembles a conventional CBF. At higher levels of lateral force, the overturning moment at the base of the frame becomes large enough for the tension column to decompress and uplift occurs. After uplift, a restoring force is provided by the gravity loads and post-tensioning forces. The PT steel elongates and provides positive stiffness to the later force-later drift behavior.
The configuration chosen for the self-centering concentrically braced frame is placed between two additional columns. Each are attach to the gravity load system of the building. Friction-bearing dampers are designed to allow slip due to relative vertical displacement between the gravity columns and the SC-CBF column. To minimize elongation demand on the PT steel, it was placed at the midbay of the SC-CBF. The vertical distribution strut in the upper story transfers force of the midbay PT steel to the braces over multiple stories.
Analytical Study
A 4-story office building designed for still soil in Van Nuys, California at a 0.6-scale prototype model. OpenSees was used to perform a nonlinear time-history analysis. A suite of 30 scaled DBE-level recorded ground motion and 30 scaled MCE-level recorded ground motions were simulated. The hybrid simulation was applied by hydraulic actuators through a floor diaphragm model.
The design objectives of immediate occupancy under the DBE and collapse preventions under the MCE were both reached. Analytical predictions also relatively matched the experimental results. It was noted under DBE-level ground motions, no significant structural damage occurred, and under MCE-level ground motion only a small loss of pre-stress occurred. Also in all cases, re-centering was accomplished.
Reference
Sause, R., Ricles, J. M., Roke, D.A., Chancellor, N. B., and Gonner, N. P. (2010). “Large-Scale Experimental Studies of Damage-Free Self-Centering Concentrically-Braced Frame under Seismic Loading,” Proceedings of the Structures Congress 2010, Chicago, IL, March 29-31.