Roke et al. 2009
In this paper, analysis results for several SC-CBF configurations are presented. The purposes of SC-CBF are to minimize structural damage under seismic loading and provide significant drift capacity while limiting damage and residual drift. Conventional CBF systems have limited drift capacity before brace buckling and damage leads to deterioration in strength and stiffness. In this paper, system behavior of SC-CBFs is explained, and then the different configurations are considered. Finally, performance based design procedures of the SC-CBF are clarified.
System Concept
The structure at hand is composed of beams, columns, and braces. Column base details permit the columns to uplift. Gravity loads and PT forces resist column uplift and provide a restoring force after uplift. The beams, columns, and braces are intended to behave elastically under the design earthquake while column uplift controls the force levels in the frame.
The fundamental behavior of the SC-CBF system under a lateral load is rocking on its base. This behavior can be observed when the column under tension from overturning moment decompresses and uplifts from its support. The SC-CBF is designed to decompress at the base at a selected level of lateral loading, initiating a rigid-body rotation (rocking) of the frame. Vertically aligned PT bars were used for SC of the system. They resist the uplift and provided a restoring force to return the SC-CBF to the foundation. The frame members are designed to resist the internal member forces that develop at PT yielding, minimizing structural damage before the PT bar yields.
Analytical Study
Drift capacity and self-centering behavior of SC-CBF configurations were obtained from the results of a dynamic analysis. Three different configurations were used. The first one (Frame A) was a typical braced frame with PT steel along each column. The second frame (Frame D) consisted of an SC-CBF placed between two additional columns. The third one (Frame DDIST) was a modification of Frame D: vertical struts are added at the upper stories. The seismic responses of several 6-story SC-CBF systems were obtained from nonlinear time-history analyses by using OPENSEES. Beams, columns and braces were modeled as linear elastic and PT steel was modeled using non-linear truss-bar elements. According to the results, frame configuration has an effect on the dynamic response, and ED elements reduce the dynamic drift demand of the structure. Moreover, the first mode response is effectively limited by the rocking behavior; however, the higher modes contribute to the response during rocking of the SC-CBF.
Reference
Roke, D., Sause R., Ricles J.M., and Gonner N. (2009). “Damage-Free Seismic Resistant Self-Centering Steel Concentrically Braced Frames,” Stessa 2009 – Mazzolani, Ricles & Sause (eds) 2009 Taylor & Francis Group, London, ISBN 978-0-415-56326-0.