With the development of metropolitan areas, the negative influence of ground-borne vibrationsfrom complex transportation systems and human activities on quality of life of occupants andvibration sensitive equipment become more prominent. Current practices include basing theanalysis on either empirical or numerical approaches. While the empirical approach has beenshown to be unreliable, numerical methods are considered overly complex and unsuitable forpractical applications. Therefore, the task was to conduct a sensitivity analysis to determinewhich parameters could be neglected from the latter without affecting the structural responsebeyond accepted tolerance ranges.A simple three-story, single-span steel structure with two rigid foundations was analyzedfor this purpose. The structure is founded on a homogeneous stratum (shear wave velocityof Vs = 225 m/s) with bedrock located at a depth of 11 meters, and it is subjected to a unitharmonic load 10 meters away from the structure. Due to the capability to internally account forSSI effects, the numerical Direct Method was used to retrieve a reference solution. On the otherhand, the Substructure Method was used to replicate the reference solution and subsequentlyconduct a sensitivity analysis to identify negligible parameters.It was determined that, for the analyzed structure, solving the equation of motion using onlythe vertical terms of the impedance matrix and the displacement field vector, while enforcingfixed horizontal and rotational boundary conditions, provides a sufficient approximation tothe reference solution in vertical (dominating) direction. Additionally, the analysis alsorevealed that through-the-soil coupling terms of the impedance matrix directly affect the modalproperties of the structure and are vital for the analysis.Additional sensitivity study was conducted regarding the soil stiffness. It showed that withsofter soil, the number of necessary parameters required for sufficient analysis increases.Finally, the analyzed structure was modified by adding a slab at the foundation level. Sucha configuration is a common practice in structural design. The analysis showed that such acomponent significantly improves the approximation using the suggested impedance matrixand displacement field vector, regardless of the soil stiffness.