RESEARCH ARTICLE Seismic response of rocking frames with top support eccentricity Amitabh Dar 1,2 | Dimitrios Konstantinidis 1 | Wael El‐Dakhakhni 1 1 Department of Civil Engineering, McMaster University, Hamilton, Canada 2 Bruce Power, Tiverton, Canada Correspondence Dimitrios Konstantinidis, Department of Civil Engineering, McMaster University, Hamilton, ON L8S 4L7, Canada. Email: konstant@mcmaster.ca Funding information Natural Sciences and Engineering Research Council of Canada Summary The seismic response of rocking frames that consist of a rigid beam freely sup- ported on rigid freestanding rectangular piers has received recent attention in the literature. Past studies have investigated the special case where, upon pla- nar rocking motion, the beam maintains contact with the piers at their extreme edges. However, in many real scenarios, the beam‐to‐pier contact lies closer to the center of the pier, affecting the overall stability of the system. This paper investigates the seismic response of rocking frames under the more general case which allows the contact edge to reside anywhere in‐between the center of the pier and its extreme edge. The study introduces a rocking block model that is dynamically equivalent to a rocking frame with vertically symmetric piers of any geometry. The impact of top eccentricity (ie, the distance of the contact edge from the pier's vertical axis of symmetry) on the seismic response of rocking frames is investigated under pulse excitations and earthquake records. It is concluded that the stability of a top‐heavy rocking frame is highly influenced by the top eccentricity. For instance, a rocking frame with contacts at the extreme edges of the piers can be more seismically stable than a solitary block that is identical to one of the frame's piers, while a rocking frame with contacts closer to the centers of the piers can be less stable. The concept of crit- ical eccentricity is introduced, beyond which the coefficient of restitution con- tributes to a greater reduction in the response of a frame than of a solitary pier. KEYWORDS critical eccentricity, equivalent rocking block, nuclear facilities, rigid block assemblages, rocking frame, seismic stability 1 | INTRODUCTION Assemblages of unanchored components that can be modeled as rocking frames are observed in various types of structures ranging from ancient Greek temples 1-3 to present day nuclear power plants. 4 The top row of Figure 1 shows examples of typical rocking frames in nuclear power plants, while the bottom row shows schematic representations of various types of rocking frames. Concerns about the seismic stability of such components have arisen during seismic re‐evaluation efforts of nuclear facilities following the Fukushima Daiichi nuclear power plant accident, caused by the 2011 Tohoku earthquake and tsunami. Studies on the seismic response of rocking frames have been scarce, and current relevant nuclear standards offer very limited guidance on solitary rocking components and no guidance on rocking frames. Therefore, the real risk associated with the seismic performance of rocking frames in nuclear facilities remains unknown. Received: 14 January 2018 Revised: 14 June 2018 Accepted: 18 June 2018 DOI: 10.1002/eqe.3096 Earthquake Engng Struct Dyn. 2018;1–23. © 2018 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/eqe 1