Abstract
A structure designed to resist earthquake attack must have a capacity to dissipate kinetic energy induced by the ground motion. In most structures this energy absorption is developed in the vicinity of beam to column connections. Recent research has shown that connections are not reliable when subject to cyclic loading, such as results from earthquake attack. Connections in steel frames deteriorate due to local instabilities in adjacent flanges, and in reinforced concrete frames alternating shear loads produce diagonal tension and bond failures which progressively reduce the strength of the connection.
 Much work in building research and earthquake engineering in laboratories throughout the world is directed toward increasing the reliability and energy absorption capacity of structural connections. In this paper an alternative approach to this problem is described. This approach is to separate the load carrying function of the structure from the energy absorbing function and to ask if special devices could be incorporated into the structure with the sole purpose of absorbing the kinetic energy generated in the structure by earthquake attack.
 To determine whether such devices are feasible a study has been undertaken of three essentially different mechanisms of energy absorption. These mechanisms all utilized the plastic deformation of mild steel. They included the rolling of strips, torsion of square and rectangular bars, and the flexure of short thick beams. These mechanisms were selected for intensive study since they were basic to three different types of device each of which was designed for a separate mode of operation in a structural system.
 The characteristics of these mechanisms which were of primary importance in this study were the load displacement relations, the energy absorption capacity and the fatigue resistance. This information was obtained with a view to the development of devices for specific structural applications.
 This report describes the tests used to explore the basic mechanisms and the data obtained. It also include s a brief description of tests on scale models of a device which was designed to be located in the piers of a reinforced concrete railway bridge.
 It has been shown by the tests that the plastic torsion of mild steel is an extremely efficient mechanism for the absorption of energy. It was found that at plastic strains in the range 3% to 12% it was possible to develop energy dissipation of the order of 2000-7500 lb in/in3 per cycle (14-50 x 106 N/M2 per cycle) with lifetimes within the range of 1000 to 100 cycles. It was also shown that the mode of failure in torsion is an extremely favourable one for use in an energy absorbing device in that it took the form of a gradual decay. The other two mechanisms studied were both less efficient and less reliable than torsion and had capacities of 500-2000 lb in/in3 per cycle (3.5 - 14 x 106 N/M2 per cycle) and life times of around 200 to 20 cycles. Nevertheless they lend themselves to more compact devices than does the torsional mechanism and furthermore the devices may be located in regions in a structure where they are readily accessible for replacement after attack.
Highlights
The attack of an earthquake on a structure is through the interaction of the oscillatory ground acceleration and the inertia of the * On leave from Division of Structural Engineering and Structural Mechanics, Department of Civil Engineering, University of California, Berkeley, California. ** Engineering Seismology Section, Physics and Engineering Laboratory, D.S.I.R., Lower Hutt, N.Z
Structure itself, and as a result the extent of the attack depends on the dynamic response of the structure and the frequency content and duration of the ground motion
Since most highri se structures have natural frequencie s in the same range as the dominant frequencies of the ground motion it is generally agreed ( 1, 2, 3 ) that to resist the attack of a major earthquake it is necessary to accept a degree of plastic action in the structure
Summary
In each case these utilized the plastic deformat ion of mild steel, and included the rolling (with bending) of f1 at strips, torsion of square and re ctangular bars, flexure of beams of rectangular section and combinations of the se. It will be shown in the later sections that the energy absorbing capacity (in terms of energy dissipated per unit volume of material) of mild steel is so large that the se energy absorption requirements can be developed by devices of fairly modest dimensions, 3 .
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