FREQUENCY-DEPENDENT EQUIVALENT LINEAR METHOD FOR SEISMIC SITE RESPONSE CONSIDERING THE COMPATIBILITY OF FREQUENCY PARAMETERS

Based on frequency-dependent soil behavior demonstrated by laboratory tests and equivalent linearization theory, 1D frequency-dependent equivalent linear method for seismic site response is established, considering the parameter compatibility between the frequency Rf for laboratory dynamic tri-axial test or resonant column test and the frequency f(v_s) for shear wave test. Firstly, using the laboratory results given by researchers, the frequency-dependent soil constitute models are proposed through data regression methods, and the formula describing normalized frequency-dependent shear modulus reduction and damp ratio curves with shear strain are deduced. Then, frequency-dependent equivalent linear method is developed by employing frequency-dependent shear modulus and damp ratio in transfer function for the frequency-independent equivalent linear method. Lastly, by using frequency-dependent and frequency-independent methods, linear response for a single-layered site and nonlinear response for another single-layered site under different cases are conducted, and results show that:1) laboratory test frequency Rf has a great impact on site response and shear wave test frequency f(v_s) has a minor effect on site response; 2) if the input parameters of shear modulus and damp ratio are obtained by dynamic tri-axial tests, the results obtained by frequency-dependent methods are slightly lower than that obtained by frequency-independent methods; if the parameters are obtained by resonant column tests, the results obtained by frequency-dependent methods are much higher than that obtained by frequency-independent methods.