構造物の破壊作用を対象とした地震動の強さの評価

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Authors propose in this paper ascale for evaluating intensity of earthquake motions from the point of view of antiseismic design in which structure is permitted plastic deformation, and from the point of view of earthquake damage to structures. Usually, as this kind of scale, maxmimum magnitude of acceleratien and respones spectrum are used, but there were several cases in which little damage to structures are inconsistent with large values of maximum magnitude of acceleration and response spectrum. For example, maximum magnitude of acceleration of the earthquake motions recorded at Kushiro in 1962 is 513 gal, and its response spectrum shows remarkable peak at T=0.33 second (Fig.1), that is, 2.2g for 5 percent damping and 4.8g for 1 percent damping. But little structures suffered damage. Then they propose to understand these kind of phenomena by means of elasto plastic response of one mass system due to earthquake motions. About the earthquake motions at Kushiro, elastoplastic response for T=0.33 second decreases to one sixth of elastic response (Fig.7), and ductility factor is not so large (Fig.5). Elasto-plastic displacement responses expressed as same as response spectra have linear relation with T (in log scale) for T=0.1-1 second, so the value for T=1 second may be used as a scale for intensity of earthquake motions (Table 1). Elasto-plastic displacement responses are roughly constant for any ultimate strength Q_y within right range. This property mav be used for minimum required ultimate strength to allowable ductility factor of struture Eqs. (2), (3). As the values of Sa' may generally be got from elasto-plastic displacement responses of Q_y=0.3g, 0.4g. This method is good for 2-3 in ductility factor.
1969-06-30

構造物の破壊作用を対象とした地震動の強さの評価

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