Dynamics of rocking podium structures

Abstract

Summary A rocking podium structure is a class of structures consisting of a superstructure placed on top of a rigid slab supported by free‐standing columns. The free‐standing columns respond to sufficiently strong ground motion excitation by uplifting and rocking. Uplift works as a mechanical fuse that limits the forces transmitted to the superstructure, while rocking enables large lateral displacements. Such ‘soft‐story’ system runs counter to the modern seismic design philosophy but has been used to construct several hundred buildings in countries of the former USSR following Polyakov's rule‐of‐thumb guidelines: (i) that the superstructure behave as a rigid body and (ii) that the maximum lateral displacement of the rocking podium frame be estimated using elastic earthquake displacement response spectra. The objectives of this paper are to present a dynamic model for analysis of the in‐plane seismic response of rocking podium structures and to investigate if Polyakov's rule‐of‐thumb guidelines are adequate for the design of such structures. Examination of the rocking podium structure response to analytical pulse and recorded ground motion excitations shows that the rocking podium structures are stable and that Polyakov's rule‐of‐thumb guidelines produce generally conservative designs. Copyright © 2017 John Wiley & Sons, Ltd.

Rocking amplification and strong‐motion duration

“…Rocking dynamics is of interest to a wide range of structural applications, including historical structures, buildings, and bridges, as well as critical contents such as laboratory equipment and storage casks . Many studies built on Housner classical model and examined analytically the planar and the 3‐dimensional dynamic behavior of rocking structures (eg, Vassiliou et al and Vassiliou and references therein).…”

Rolling and rocking of rigid uplifting structures

“…Such structure consists of rocking columns with curved base extensions placed on the ground floor and capped by a rigid beam that supports a superstructure, the rocking podium structures described by Bachmann et al 55 An assumption that the superstructure behaves as rigid, as used in design of actual buildings in the USSR, 67 has been shown 34,55 to simplify the seismic response analysis of such structures (because the superstructure mass can be lumped in the cap-beam) while maintaining sufficient accuracy. Such structure consists of rocking columns with curved base extensions placed on the ground floor and capped by a rigid beam that supports a superstructure, the rocking podium structures described by Bachmann et al 55 An assumption that the superstructure behaves as rigid, as used in design of actual buildings in the USSR, 67 has been shown 34,55 to simplify the seismic response analysis of such structures (because the superstructure mass can be lumped in the cap-beam) while maintaining sufficient accuracy.…”

“…Since then, a plethora of papers on rocking structures has been published studying these structures theoretically [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and experimentally. This application is usually termed "kinematic isolation" [50][51][52][53][54][55] : The bottom floor comprises rocking concrete rocking columns and is essentially an intentionally designed soft story with large displacement capacity. [44][45][46][47][48][49] What has received less attention in the literature published in English is that rocking has been used in the USSR since 1960s (and is still used in former USSR states) as a seismic response modification technique for buildings.…”

“…[17][18][19][20][21][22] The rocking oscillator has been used in bridge engineering, [23][24][25][26][27][28][29][30][31][32][33][34] as well as to model the behavior of masonry walls, [35][36][37][38][39][40] of ancient temples, [41][42][43] of unanchored equipment, and of museum artifacts. 55 The uplift of the soft story columns acts like a mechanical fuse and limits the seismic forces transmitted to the superstructure. This application is usually termed "kinematic isolation" [50][51][52][53][54][55] : The bottom floor comprises rocking concrete rocking columns and is essentially an intentionally designed soft story with large displacement capacity.…”

Seismic response of a wobbling 3D frame

“…The uplift of rocking columns works as a mechanical fuse and limits the design forces of both the foundation and the superstructure. The idea has been applied in the former Soviet Union to isolate buildings . In the rest of the world, it has been proposed as an isolation method for bridges, where limiting the design forces could be crucial to avoid pile foundations.…”