The near-field method for dynamic analysis of structures on soft soils including inelastic soil–structure interaction

• This research proposes a modified equivalent linear method with a further reduction of the soil shear modulus in the near-field of foundation.
• Three soil types, 6 inelastic building models, and 30 earthquake records are included.
• Regression equations are derived for the reduced equivalent shear modulus of the near-field soil.
• The nonlinear structural responses using the near-field method compares well with those using elastoplastic analysis of soil.

The problem of soil–structure interaction analysis with the direct method is studied. The direct method consists of explicitly modeling the surrounding soil to bedrock and the structure resting on the soil. For the soil medium, usually the traditional equivalent linear method with a reduced shear modulus and an increased damping ratio for the soil is used. However, this method does not work in the vicinity of foundation where the soil behavior is highly nonlinear because of presence of large strains. This research proposes a modified equivalent linear method with a further reduction of the soil shear modulus in the near-field of foundation that results in validity of using the equivalent linear method throughout. For regular short, intermediate and tall structures resting on such soft soils, a series of dynamic time-history analysis is implemented using earthquake records scaled to a sample design spectrum and the nonlinear structural responses are compared for different assumptions of soil behavior including the elasto-plastic Mohr–Coulomb, the traditional equivalent linear, and the proposed modified equivalent linear method. This analysis validates the proposed method.