Shake table tests of unattached, asymmetric, dual‐body systems

Abstract

Summary Systems of unattached, or freestanding, structures are highly vulnerable to damage and/or collapse during an earthquake, as evidenced during numerous past events. This class of structural system includes statue–pedestal systems, multidrum columns, radiation shields, unreinforced masonry walls, and other mechanical and electrical equipment. While a number of studies have analyzed the response of the single rocking block, very few have tested the response of multiple block systems subjected to earthquakes. Therefore, this paper details an extensive shake table testing campaign in which the seismic response of a pair of stiff, unattached blocks, herein referred to as a dual‐body system, was evaluated. Experimental variables include the geometry, including asymmetry, of both top (tower) and bottom (pedestal) bodies, input motion, and the coefficient of friction beneath the system. Furthermore, the tower structures were tested both in dual‐body configurations as well as in single‐body configurations allowing an understanding of the effect of the pedestal. The tests indicate that the presence of a pedestal increases the likelihood of collapse and amplitude of rocking demands, in general. However, certain geometric and interface combinations yield a more stable tower in a dual‐body configuration compared to a single‐body configuration, because of the dependence of the pedestal response on the geometry of the tower. Furthermore, a low‐friction interface beneath the pedestal reduces demands on the tower. However, this low‐friction interface may still transfer long‐period contributions of the input motion to the tower, which may be detrimental to its response. Copyright © 2017 John Wiley & Sons, Ltd.

Rocking and Kinematic Approaches for Rigid Block Analysis of Masonry Walls: State of the Art and Recent Developments

“…However, while in the case of free-vibration or harmonic input forces, the response is more controllable, in the case of random motions, such as earthquakes, very large variations are found in the response of similar blocks, both in experimental and in numerical tests [21,24,[52][53][54]. This is due to the combination of different frequency contents, duration and seismic actions parameters.…”

Dynamics of a sliding‐rocking block considering impact with an adjacent wall

“…Dar et al evaluated the ASCE 43‐05 seismic criteria for components vulnerable to overturning in nuclear facilities. There has also been notable interest in the seismic stability of structures consisting of rigid block assemblages, such as vertical block stacks (Allen et al; Psycharis; Spanos et al; Konstantinidis and Makris; Wittich and Hutchinson) and rocking frames (Makris and Vassiliou; DeJong and Dimitrakopoulos; Drosos and Anastasopoulos; Dar et al). The response of freestanding blocks in 3D has also been studied (Konstantinidis and Makris; Chatzis and Smyth; Zulli et al), albeit to a lesser extent than planar rocking becasue of the complexity involved.…”

Seismic response of rocking frames with top support eccentricity

“…DeJong and Dimitrakopoulos demonstrated the dynamic equivalency of various assemblages, including simple rocking frames similar to that in Figure A, to single blocks. Several other types of block assemblages have been studied by Lee, Ikushima and Nakazawa, Allen et al, Psycharis, Spanos et al, Konstantinidis and Makris, Kounadis et al, Minafo et al, and Bachmann et al Wittich and Hutchinson carried out extensive shake table test studies to investigate the seismic response of asymmetric rocking single‐body structures and dual‐body systems …”

“…Several other types of block assemblages have been studied by Lee, 20 Ikushima and Nakazawa, 21 Allen et al, 22 Psycharis, 23 Spanos et al, 24 Konstantinidis and Makris, 25 Kounadis et al, 26 Minafo et al, 27 and Bachmann et al 28 Wittich and Hutchinson carried out extensive shake table test studies to investigate the seismic response of asymmetric rocking single-body structures 29 and dual-body systems. 30 Figure 2A shows the rocking frame investigated by Makris and Vassiliou,3 consisting of rigid unanchored prismatic rectangular piers freely supporting a top rigid beam, having uniformly distributed mass, with sufficient friction at all contact points to prevent sliding. In the undisplaced configuration of such frames, the top surfaces of piers are in full contact with the beam (Figure 2A, dashed outline).…”