Abstract: Because of their intrinsic periodicity, three-dimensional frame structures can be analyzed as threedimensional phononic crystals. The wave finite element method can be applied to a model of the three-dimensional unit cell in order to compute the wavenumbers. In this work, frame elements are modeled using spectral elements formulated with the Euler-Bernoulli and Timoshenko beam theories. The forced response of a built-up structure made of the proposed three-dimensional unit frame cell is simulated. The intersections observed in the dispersion diagram of the three-dimensional unit cell are observed as attenuation bands in the forced responses of the built-up structure. The attenuation is investigated considering the imaginary parts of the wavenumbers. Attenuation for all possible propagation directions are analyzed by scanning the irreducible Brillouin zone. Due to imperfect manufacturing, the mechanical properties can vary spatially along each frame element. A methodology for verifying deterministic and stochastic full and complete attenuation bands is proposed. Deterministic results are obtained considering the mean values of the mechanical property probability densities. The stochastic attenuation of the built-up structure agrees with the prediction made using a single cell. Simulation results show that the depth and width of a band gap are not directly related to the robustness against the proposed spatial variability Ver menos