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Dynamic shear modulus ratios and damping ratios of soil are the parameter of indicating dynamic nonlinearity of soil, and the necessary parameter of seismic site analysis. The 372 pairs of soil samples’ dynamic nonlinear parameters, which were tested by dynamic tri-axial tests in about 40 the seismic safety evaluation reports of ocean oil platforms in the Bohai Sea, were collected and corrected. The dynamic shear modulus ratios and the damping ratios of various soil types with different depth in the Bohai seafloor were calculated and their statistical mean values were obtained. The statistical mean values are reasonable and are the important supplements in case that the tested soil samples are not enough in the Bohai Sea sites.

Differential evolution (DE) algorithm is a heuristic approach that has a great ability to solve complex optimization and converges faster and with more certainty than many other acclaimed global optimization methods. In this paper, DE algorithm is applied to calibrate design seismic response spectra, the basic idea is that design response spectra and calculated response spectra are defined as objective function of characteristic parameters, the first turning point, the second turning point (characteristic period), the platform height and the attenuation index, of design response spectra, and the characteristic parameters are obtained by minimizing the objective function. Three pieces of the calculated response spectra for one real are calibrated as an application example. The obtained results demonstrate the effectiveness and efficiency of the proposed method.

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