ABSTRACT
A rocking frame normally appears like a concentrically braced frame, except that the column bases are not bolted directly to the foundation. Instead, a column will lift up from the foundation rather than developing tension in response to lateral loads. Unbonded post-tensioning is sometimes provided to adjust the lateral load that will cause the frame to rock, as well as to provide a positive stiffness during rocking. Supplemental energy dissipation that is activated by the rocking action of the frame is usually also provided in order to limit the peak response. These components result in the hysteretic response that is shown schematically in Figure 1 for a rocking system under
1 INTRODUCTION
As designers shift toward performance-based earthquake engineering, they are moving beyond the traditional objective of ensuring life safety during a design event at a reasonable initial cost. There is an increasing recognition that structures should also be designed to avoid residual drift and damage following design level events. One concept that has been proposed as an economical way of meeting this objective is by controlled rocking. This idea was proposed in the 1970s for concrete bridge piers (Beck & Skinner 1974) and for steel frames (Kelly & Tsztoo 1977, Clough & Huckelbridge 1977). More recently, there has been a renewed interest in rocking steel frames, both in research (Midorikawa et al., 2002, Roke et al., 2006, Wiebe et al., 2007,
a reversed quasi-static lateral load. The response in the negative loading direction is symmetric to the positive response.
