Seismic response of sliding equipment and contents in base‐isolated buildings subjected to broadband ground motions

Abstract

Summary Base isolation has been established as the seismic design approach of choice when it comes to protecting nonstructural contents. However, while this protection technology has been widely shown to reduce seismic demands on attached oscillatory equipment and contents (EC), its effectiveness in controlling the response of freestanding EC that are prone to sliding has not been investigated. This study examines the seismic behavior of sliding EC inside base‐isolated buildings subjected to broadband ground motions. The effect of isolation system properties on the response of sliding EC with various friction coefficients is examined. Two widely used isolation models are considered: viscously damped linear elastic and bilinear. The study finds isolation to be generally effective in reducing seismic demands on sliding EC, but it also exposes certain situations where isolation in fact increases demands on EC, most notably for low friction coefficients and high earthquake intensities. Damping at the isolation level is effective in controlling the EC sliding displacements, although damping over about 20% is found to be superfluous. The study identifies a physically motivated dimensionless intensity measure and engineering demand parameter for sliding equipment in base‐isolated buildings subjected to broadband ground motions. Finally, the paper presents easy‐to‐use design fragility curves and an example that illustrates how to use them. Copyright © 2014 John Wiley & Sons, Ltd.

Building contents sliding demands in elastically responding structures

“…(iii) With a focus on sliding-related failure, no consideration is given on damage caused by rocking of contents. (iv) Previous studies showed both positive and negative influence on sliding demand when considering vertical acceleration [5,13,17,20,27,30,31]. To simplify the problem, the effect of vertical accelerations on frictional bond strength is not considered in this study.…”

“…in Gazetas et al's investigation, the focus was on near-fault motions [30] and friction coefficient was limited to 0.2 for contents sliding on a horizontal plane and subjected to horizontal and vertical motions simultaneously [31]). In based-isolated buildings, numerical studies [20] have shown negligible influence of vertical motion, and even experimental results [5] suggest that vertical motion is not detrimental when the peak vertical acceleration remains below 2 g.…”

“…Different from the above studies which investigated contents behaviour in base-fixed frame structures, Konstantinidis and Nikfar [19,20] focused on the seismic response of sliding equipment and contents in base-isolated buildings. Numerical investigation showed that base-isolated buildings generally are able to reduce seismic demands on sliding objects, though in some circumstances, such as when there is a lower friction coefficient along with higher shaking intensity, isolated structures were found to have larger sliding demands.…”

“…These include investigations into block sliding response to earthquake motions [13][14][15][16][17][18][19][20][21][22][23][24], derivation of formulations and criteria for rigid bodies sliding due to base excitation [21,[25][26][27], and in-field analyses of sliding rock blocks [28][29][30][31][32]. Also, many observations of contents sliding and falling off shelves have been obtained from the 1976 San Fernando, the 1989 Loma Prieta, the 1994 Northridge, and the recent Canterbury earthquakes [33][34][35][36].…”

Assessment of a rolling isolation system using reduced order structural models

“…Seismic isolation reduces the seismic demand on structures and their contents by decoupling the motion of the structure (equipment) from the harsh base (floor) motion [6]. Seismic isolation has been successfully implemented at various scales -from the entire structure [7][8][9][10][11][12], to floors within the structure [13][14][15][16], and down to the component level [17,18].…”