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Über dieses Buch

Base isolation technology offers a cost-effective and reliable strategy for mitigating seismic damage to structures. The effectiveness of this new technology has been demonstrated not only in laboratory research, but also in the actual response of base-isolated buildings during earthquakes. Increasingly, new and existing buildings in earthquake-prone regions throughout the world are making use of this innovative strategy. In this expanded and updated edition, the design methods and guidelines associated with seismic isolation are detailed. The main focus of the book is on isolation systems that use a damped natural rubber. Topics covered include coupled lateral-torsional response, the behavior of multilayer bearings under compression and bending, and the buckling behavior of elastomeric bearings. Also featured is a section covering the recent changes in building code requirements.

Inhaltsverzeichnis

Frontmatter

1. Seismic Isolation for Earthquake-Resistant Design

Abstract
The idea that buildings can be protected from the damaging effects of earthquakes by using some type of support that uncouples it from the ground is an appealing one, and many mechanisms have been invented over the past century to produce this result. Several of these ideas have proposed using rollers, layers of sand, or similar materials that would allow a building to slide, and some examples have been built. A building in Sevastopol, Ukraine, and a five-story school in Mexico City have been built on rollers, and there is at least one building in P.R. China with a sand layer between the foundation and the building, specifically intended to let it slide in the event of an earthquake.
James M. Kelly

2. Vibration Isolation

Abstract
The theory of seismic isolation has many features in common with the better known theory of vibration isolation. Although there are some distinct differences between them—mainly associated with the degree to which the vibrational disturbance and the amplitude of the displacements in the support system are known—it is valuable to discuss basic vibration isolation theory as a baseline for a development of seismic isolation theory.
James M. Kelly

3. Seismic Isolation

Abstract
Before discussing the dynamics of base-isolated structures, it is useful to review the dynamics of the conventional structure and define some terms that will be used in the subsequent analysis. Consider first a single-degree-of-freedom (1-DOF) model of a structure, as shown in Fig. 3-1, with mass, m, supported on top of a weightless frame with linear stiffness, k, and linear damping constant, c. The absolute displacement of the mass of an inertial frame is denoted by u(t) and that of the ground by u g (t). The rate of change of the absolute momentum of the structure, mü (t), is produced by the negative of the reactive force of the structure
$${R_F} = c\left( {\dot u - {{\dot u}_g}} \right) + k\left( {u - {u_g}} \right)$$
(where the superposed dot denotes differentiation with respect to time).
James M. Kelly

4. Extension of Theory to Buildings

Abstract
The 2-DOF analysis of the simple linear model developed in Chap. 3 can be applied to the case of a multistoried building. Let us represent the structural system of this building by mass matrix, M, damping matrix, C, and stiffness matrix, K. For a conventionally based structure, the relative displacement, u, of each degree of freedom with respect to the ground is given by
$$ {\rm M\ddot u + C\dot u + Ku = - Mr}\mathop {\ddot u}\nolimits_g $$
(4.1)
where r is a vector that couples each degree of freedom to the ground motion.
James M. Kelly

5. Earthquake Regulations for Seismically Isolated Structures

Abstract
The first seismically isolated building in the United States was completed in 1985. Although it was publicized in national engineering magazines and visited by a great many engineers and architects from the United States and around the world, it was several years before the next base-isolated building was begun. The acceptance of isolation in the United States as an anti-seismic design approach for some classes of buildings was clearly hampered by the lack of a code covering base-isolated structures. To address this issue the Structural Engineers Association of Northern California (SEAONC) created a working group to develop design guidelines for isolated buildings.
James M. Kelly

6. Coupled Lateral-Torsional Response of Seismically Isolated Buildings

Abstract
A base-isolated building is unusual in that its frequencies in both horizontal directions are the same or very nearly the same because of the isotropic response of the isolators. The torsional frequency can be close to the horizontal frequencies if the stiffness of an isolator is matched to the load on that isolator, raising the possibility of a coupling between the three lowest modes if there is an imbalance between the center of mass and the center of rigidity.
James M. Kelly

7. Behavior of Multilayered Bearings Under Compression and Bending

Abstract
The vertical frequency of an isolated structure, often an important design criterion, is controlled by the vertical stiffness of the bearings that comprise the system. In order to predict this vertical frequency, the designer need only compute the vertical stiffness of the bearings under a specified dead load, and for this a linear analysis is adequate. The initial response of a bearing under vertical load is very nonlinear and depends on several factors. Normally, bearings have a substantial run-in before the full vertical stiffness is developed. This run-in, which is strongly influenced by the alignment of the reinforcing shims and other aspects of the workmanship in the molding process, cannot be predicted by analysis, but is generally of little importance in predicting the vertical response of a bearing.
James M. Kelly

8. Buckling Behavior of Elastomeric Bearings

Abstract
A multilayered elastomeric bearing can be susceptible to a buckling type of instability similar to that of an ordinary column, but dominated by the low-shear stiffness of a bearing. The previous analysis of the overall deformation of a single pad can be used in a buckling analysis that treats the bearing as a continuous composite system. This analysis considers the bearing to be a beam, and the deformation is assumed to be such that plane sections normal to the undeformed central axis remain plane, but not necessarily normal to the deformed axis.
James M. Kelly

9. Design Process for Multilayered Elastomeric Bearings

Abstract
The preliminary design of a bearing in an isolation system begins with the determination of the vertical load to be carried by the bearing. In most buildings the design load at each column (based on dead load plus live load due to fixed partitions, equipment, furniture, etc.) can vary quite widely. In the interest of designing a cost-effective isolation system, generally the designer minimizes the number of different types of bearings. Once the designer determines how many different bearing types to design, then the design load for each bearing type can be selected to minimize the variation of load on that bearing type.
James M. Kelly

Backmatter

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