SUMMARY Base isolation is a well known technology that has been proven to reduce structural response to horizontal ground accelerations. However, vertical response still remains a topic of concern for base‐isolated buildings, perhaps more so than in fixed‐base buildings as isolation is often used when high performance is required. To investigate the effects of vertical response on building contents and nonstructural components, a series of full‐scale shaking table tests were conducted at the E‐Defense facility in Japan. A four‐story base‐isolated reinforced concrete building was outfitted as a medical facility with a wide variety of contents, and the behavior of the contents was observed. The rubber base isolation system was found to significantly amplify vertical accelerations in some cases. However, the damage caused by the vertical ground motions was not detrimental when peak vertical floor accelerations remained below 2 g with three exceptions: (1) small items placed on shelves slid or toppled; (2) objects jumped when placed on nonrigid furniture, which tended to increase the response; and (3) equipment with vertical eccentricities rocked and jumped. In these tests, all equipment and nonstructural components remained functional after shaking. Copyright © 2013 John Wiley & Sons, Ltd.

This paper presents a non-linear, kinematic model for triple friction pendulum isolation bearings. The model, which incorporates coupled plasticity and circular restraining surfaces for all sliding surfaces, is capable of capturing bi-directional behavior and is able to explicitly track the movement of each internal component. The model is general so that no conditions regarding bearing properties, which effect the sequence of sliding stages, are required for the validity of the model. Controlled-displacement and seismicinput experiments were conducted using the shake table at the University of California, Berkeley to assess the fidelity of the proposed model under bi-directional motion. Comparison of the experimental data with the corresponding results of the kinematic model shows good agreement. Additionally, experiments showed that the performance of TFP bearings is reliable over many motions, and the behavior is repeatable even when initial slider offsets are present.A cross-sectional diagram of a TFP bearing with its geometry is shown in Figure 1. The bearing is axisymmetric about the vertical axis. The TFP bearing has four sliding surfaces. In this paper the sliding surfaces are numbered in the following order from 1 to 4: the bottom surface of the inner slider, the top surface of the inner slider, the bottom-most surface and the top-most surface. The nth surface has its own friction coefficient n , radius R n and inner and outer diameter,

Although the behavior of friction sliding bearings is well understood, the failure behavior has not been thoroughly investigated. However, predicting and understanding the failure of bearings is an important key in designing isolated structures to minimize their collapse in extreme events, and thus, this study is critical. Because of its relative simplicity and particular availability in certain markets, the failure of the double friction pendulum (DFP) bearing at its physical displacement limit is investigated. The bearing is modeled with a rigid body model including inertia for each of the bearing components. A nonlinear viscoelastic impact model is included to simulate the impact between bearing components. As isolation systems are particularly vulnerable to long-period excitations, analytical pulses are used as input excitations to investigate the influences of pulse parameters on the failure of DFP. The influences of DFP design parameters are investigated as well. To confirm that the response to the analytical pulses correctly represents the behavior under long-period ground motions, wavelet analysis to is performed on 14 pairs of pulse-type ground motion records to extract their pulses, and the failure prediction made from the extracted analytical pulse is compared with the failure from the real ground motions. It is found that using the extracted pulses provides a good estimation for the failure prediction of the ground motions.

A 2 m by 6 m unidirectional shake table was constructed at the University of California, Berkeley and combined with a real-time hybrid simulation system creating a hybrid shake table. A series of tests were carried out to examine the viability of real-time hybrid simulation techniques to perform experimental simulations of buildings with midlevel seismic isolation. The isolation system and superstructure were physically tested on the table while the portion of the building below the isolation plane was numerically modeled. OpenFresco was used to interface the numerical model with the control system. The isolated superstructure consisted of a two-story steel moment frame on six triple friction pendulum bearings, which exhibit significant nonlinear velocity-dependent behavior, necessitating real-time testing. Shear building models with a range of periods were used to represent the portion of the building below the isolation plane. Increasing the number of degrees of freedom increased the control difficulty as higher modes were excited in the numerical model because of experimental errors caused predominantly by feedback noise and table tracking. Nonetheless, the results illustrate that hybrid shake table tests are indeed an economical and reasonably accurate method to assess the seismic behavior of midlevel isolation systems installed in a range of building configurations. Results showed that midlevel isolation was beneficial for the superstructure and, to a smaller extent, the substructure. However, to achieve maximum benefits, it is recommended that the effective period of the isolation system be sufficiently longer than the period of the substructure.

Summary While isolation can provide significantly enhanced performance compared to fixed‐base counter parts in design level or even maximum considered level earthquakes, there is still uncertainty over the performance of isolation systems in extreme events. Researchers have looked at component level stability of rubber bearings and on the effect of moat impact on behavior of structures isolated on general bilinear isolators. However, testing of triple friction pendulum (TFP) sliding bearings has not been done dynamically or incorporated into a building system. Here, one‐third scale laboratory tests were conducted to on a 2‐story 2‐bay TFP‐isolated structure. Input motions were increasingly scaled until failure occurred at the isolation level. As the superstructure was designed with a yield force equivalent to the force of the bearing just at their ultimate displacement capacity, there was minimal yielding. A numerical model is presented to simulate the isolated building up to and including bearing failure. Forces transferred to the superstructure in extreme motions are examined using both experimental and numerical data. Additionally, the effect of the hardening stage of the TFP bearing is evaluated using the numerical model, finding slight benefits.

This paper addresses the treatment of the rotation of the internal components of the triple friction pendulum (TFP) isolation bearing in a numerical model previously presented by the authors. The numerical model is based on the kinematic behavior of the individual sliding surfaces and the constitutive relationships between them. The modification suggested in this paper improves the performance of the model so that the results exactly match that of the one‐dimensional piecewise linear behavior previously derived for the TFP bearing for restricted properties. The improved numerical model simulates bidirectional shear response and places no a priori restrictions on the bearing properties. The modification is put in the form of a technical communication so that the notation used and the basis of the correction could be presented with adequate clarity and so that an example of the benefit of the correction could be presented. Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARYFloor isolation is an alternative to base isolation for protecting a specific group of equipment installed on a single floor or room in a fixed‐base structure. The acceleration of the isolated floor should be mitigated to protect the equipment, and the displacement needs to be suppressed, especially under long‐period motions, to save more space for the floor to place equipment. To design floor isolation systems that reduce acceleration and displacement for both short‐period and long‐period motions, semi‐active control with a newly proposed method using the linear quadratic regulator (LQR) control with frequency‐dependent scheduled gain (LQRSG) is adopted. The LQRSG method is developed to account for the frequency characteristics of the input motion. It updates the control gain calculated by the LQR control based on the relationship between the control gain and dominant frequency of the input motion. The dominant frequency is detected in real time using a window method. To verify the effectiveness of the LQRSG method, a series of shake table tests is performed for a semi‐active floor isolation system with rolling pendulum isolators and a magnetic‐rheological damper. The test results show that the LQRSG method is significantly more effective than the LQR control over a range of short‐period and long‐period motions. Copyright © 2013 John Wiley & Sons, Ltd.

Seismic isolation systems are widely recognized as beneficial for protecting both acceleration-and displacement-sensitive nonstructural systems and components. So-called adaptive isolation systems exhibit nonlinear characteristics that enable engineers to achieve various performance goals at different hazard levels. These systems have been implemented to control the horizontal response, but there has been limited research on seismic isolation for controlling the vertical response. Thus, this paper seeks to evaluate the benefit of adaptive vertical isolation systems for components, specifically in nuclear power plants (NPP). To do this, three vertical isolation systems are designed to achieve multiple goals: a linear spring and a linear damper (LSLD), a linear spring and a nonlinear damper (LSND) and a nonlinear spring and a linear damper (NSLD). To investigate the effectiveness of the systems, a stiff piece of equipment is considered at an elevated floor within a NPP. A set of 30 triaxial ground motions is used to investigate the seismic performance of the equipment. The maximum isolation displacement and equipment acceleration are used to assess the effectiveness of the three isolation systems. While all systems significantly reduce the seismic accelerations on the equipment, the relatively simple LSLD and LSND systems exhibit superior performance over multiple hazard levels.