Assessment of a rolling isolation system using reduced order structural models

Abstract

a b s t r a c tThis paper examines the performances of lightly-and heavily-damped rolling isolation systems (RISs) located within earthquake-excited structures. Six steel structures of varying height and stiffness are selected so as to represent a range of potential RIS installations. Computation models of representative frames from each of the six structures are reduced through dynamic condensation and assembled with models for biaxial isotropic hysteretic behavior within each floor. A novel reduced order modeling approach is presented in this paper. The method combines a dynamic condensation of a linear-elastic frame with the inelastic-push over curve for a detailed elastic-plastic frame model and a novel bi-axial hysteretic model for the net inter-story inelastic behavior. The reduced inelastic model combines stiffness and mass matrices from the reduced linear model with the bi-axial inelastic floor model, and is subsequently fit to push-over curves from the detailed hysteretic model. The resulting reduced order model has three coordinates per floor and provides a much simpler model for simulating the floor responses of inelastic structures. The resulting inelastic structural models are isotropic in plan and uniform along the height. Suites of recorded ground motions representative of near-fault and far-field hazards are scaled and inputted into these hysteretic reduced models. The bidirectional floor responses at varying heights are then applied to experimentally-validated models of lightly-and heavily-damped RISs. Empirical cumulative distribution functions of peak isolator responses (relative displacement and total acceleration) for the two systems are compared, from which installation guidelines are presented.

A Numerical Investigation on Scaling Rolling Friction Effects in Shaking Table Model Tests

“…Harvey and Gavin found that a uniaxial numerical model was unable to predict the chaotic responses of a four-bowl supported system [14]. However, they later found that even a reducedorder numerical model was validated as correct when compared with the test results [15], when all of the initial conditions were fully considered [16]. Ortiz et al also found that the numerical results could be close to the experimental results for a rolling-bearing supported building [17].…”

Influence of the characteristics of isolation and mitigation devices on the response of single‐degree‐of‐freedom vibro‐impact systems with two‐sided bumpers and gaps via shaking table tests

“…The principle of operation is basically the same: The horizontal components of the ground (or floor) movement are mechanically separated from the isolated structure (or equipment) through compatible, sliding, rotating, or rolling interfaces . In rolling isolation systems proposed by Harvey and Gavin, Harvey et al and Harvey and Gavin, the limited rolling of steel spheres encapsulated between convex surfaces is employed in order to confine the displacement of the ball by means of a lip located at the border of every rolling surface. The roll‐n‐cage isolators limit the peak isolator displacements and prevent PADJS under strong seismic excitation by using a self‐braking mechanism, which contains the pounding inside the roll‐n‐cage isolator's frame.…”

Performance-based seismic isolation design using the theory of spatially concave friction distribution

“…Meanwhile, more frictional devices with a long service life have been developed. For example, Harvey and Gavin [7] proposed double rolling isolation systems (RISs). They found that the friction-based isolation devices had perfect seismic isolation performance, long service lives and low cost [2].…”

“…Based on the discussions above, the friction component was better than the viscous damping component, except that the frictional action prevented the structure from moving back to the initial site after earthquakes. After investigating the uniform friction distribution, the convex friction distribution and other variable friction distributions in space [1][2][3][4][5][6][7][8][9], it had a summary that a spatially concave friction distribution, combining with an appropriate spring component, would not prevent the structural restoration [10]. As for the spatially concave friction distribution, the friction coefficient has the smallest value in the contact center, and increases when the structure moves away from the contact center.…”