The available methods to model the foundation and underlying soil can be stroked="f" filled="f" path="m@4@5l@4@11@9@11@9@5xe" o:preferrelative="t" o:spt="75" coordsize="21600,21600" ), the slenderness ratio ( ) and the mass ratio ( ) were selected and a comprehensive parametric study was carried out to determine the near-field zone dimensions and dynamic properties. Then, semi-analytical relations were proposed as functions of the dimensionless parameters to calculate the near-field properties. After that, two sets of 3D examples were considered to evaluate the validity and performance of the near-field method. The first set of examples includes applying certain SSI models to an existing building and comparing with actual observed responses. In the second set of examples, a parametric study was performed with evaluating the nonlinear seismic response of five, ten, fifteen and twenty story moment-resisting frame steel buildings. Two site conditions along with different SSI modeling techniques were considered for this part of study. A nonlinear Winkler model developed by El Ganainy and El Naggar was also applied for both sets of examples to compare performance of the near-field method with another new SSI modeling technique. The results show that the near-field method is a simple yet accurate enough approach for analysis of direct SSI problems and can significantly reduce computational cost. Key Words: soil-structure interaction, near-field method, shear modulus, damping
