ABSTRACT
The dynamic behaviour of building structures subjected to seismic action is commonly analyzed using the deterministic approach. The computation model is designed using the finite element method. The time domain response to defined non-stationary ground motion can be computed using direct integration of structure equations of motion. For many reasons, procedures based on structure vibration mode superposition are preferred. The response spectrum method is very frequently applied (ASCE 2000, Braja 1984, Kala et al. 2012). The structure response depends strongly on computed natural frequencies. Due to variances of characteristic model parameters, particularly when soil-structure interaction is considered, high values of variance of computed frequency values could be expected. Hence, possible variation of the natural frequency value in relatively wide range must be respected in the response analysis. Consequently, responses of quite different levels could be obtained (see illustration in Fig. 1).
