Evaluation of period-lengthening ratio (PLR) of single-degree-of-freedom structure via dynamic centrifuge tests

Abstract

Understanding the soil-foundation-structure interaction (SFSI) is crucial for the seismic design. Two important parameters of SFSI, the period-lengthening ratio (PLR) and the foundation-damping ratio (FDR), have been studied by both analytical and experimental methods. However, the present formulas of PLR considering SFSI could not reflect the non-linear characteristics of soil. In this study, to reflect the non-linear characteristics of soil in PLR, shear modulus of soil was back-calculated by using measured PLR from centrifuge test results. The three structure models which have different natural periods and two shallow foundation models which have different mass were used to perform the dynamic centrifuge tests. From the test results, the PLR of the single-degree-of-freedom (SDOF) structure was evaluated by considering the seismic intensity and frequency contents of seismic waves. The reduction coefficient of shear modulus, which can predict the PLR by using present formula, was suggested as a function of peak ground acceleration at surface.