Mechanisms of energy absorption in special devices for use in earthquake resistant structures
DOI:
https://doi.org/10.5459/bnzsee.5.3.63-88Abstract
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.
References
N. M. Newmark, "Current Trends in the Seismic Analysis and Design of High Rise Structures", in Earthquake Engineering, edited by R. L. Weigel, Prentice Hall, 1970.
J. A. Blume, "Structural Dynamics in Earthquake Resistant Design", Trans. A.S.C.E., Vol. 125, pp. 1088-1139, 1960.
G. W. Housner, "Limit Design of Structures to Resist Earthquakes", Procs. 1st World Conference on Earthquake Engineering, Berkeley, California, 1956, pp. 5,1 - 5,13.
E. P. Popov, "Low Cycle Fatigue of Steel Beam to Column Connections", Procs. of the International Symposium on the Effects of Repeated Loadings of Materials and Structures, Vol. VI, RILEM = Inst. Ing., Mexico, 1966.
E. P. Popov and R. B. Pinkney, "Reliability of Steel Beam-to-Column Connections Under Cyclic Loading", Procs. 4th World Conference on Earthquake Engineering, Vol. II, Chile, 1969, PP B-3, 15-30.
B. Bresler and V. Bertero, "Behaviour of Reinforced Concrete Under Repeated Load", Journal of the Structural Division, A.S.C.E., ST 6, 1968. DOI: https://doi.org/10.1061/JSDEAG.0001981
J. A. Blume, "Design of Earthquake- Resistant Poured-in-Place Concrete Structures", in Earthquake Engineering, edited by R. L. Wiegel, Prentice-Hall Inc. 1970.
Kiyoshi Muto, "Earthquake Resistant Design of 36-storied Kasumigaseki Building", Procs. 4th World Conference Earthquake Engineering, Vol. Ill, Chile 1969, PP. J-4s 16-33.
J. L. Beck and R. I. Skinner, "The Seismic Response of a Proposed Reinforced Concrete achieved Railway Viaduct", Tech. Rpt No. 3 6 9 , Physics and Engineering Laboratory, D.S.I.R., 1972.
R. Shepherd and R. E. McConnel, "Seismic Response Predictions of a Bridge Pier", Proceedings A.S.C.E., 98, EM 3, June 1972, 609-627. DOI: https://doi.org/10.1061/JMCEA3.0001613
W. Prager and P. G. Hodge, "The Theory of Perfectly Plastic Solids", John Wiley & Sons Inc., 1956.
J. D. Morrow, "Cyclic Plastic Strain Energy and Fatigue of Metals", in Internal Friction, Damping and Cyclic Plasticity ASTM STP 3178 1965.
A. Nadia, "Theory of Flow and Fracture of Solids", McGraw-Hill, 1950.
R. D. Hanson and W. R. S. Fan, "The Effect of Minimum Cross Bracing on the Inelastic Response of Multi-Storey Buildings", Procs. 4th. World Conference Earthquake Engineering, Chile, 1969 pp. A-4, 15 - 30.
