COMPLEX MODULI FOR SEISMIC RESPONSE ANALYSIS OF GROUND

Abstract

Frequency independent stress–strain relationships for the complex moduli used in a seismic response analysis of ground are discussed. In addition, a new complex modulus for the seismic response analysis of ground, named YAS (Yoshida–Adachi–Sorokin) model, is proposed. This model is designed so that the maximum stress and the hysteretic absorption energy agree with those of the cyclic shear test. It is shown that the complex modulus, in which the maximum stress and the damping ratio agree with the test result, is possible only when the damping ratio is less than 0.5. Then, three complex moduli, the Sorokin model used in the original SHAKE, the Lysmer model proposed to improve Sorokin model and used widely in the equivalent linear method, and the YAS model, are compared and discussed. The obtained conclusions are as follows. The Sorokin model overestimates the maximum shear stress. The Lysmer model gives the same maximum stress as the cyclic shear test result, but it underestimates the hysteretic absorption energy. Underestimation of the energy absorption is less than 5% for damping ratio less than 0.3 which is the maximum important damping ratio in practical use.