Numerical analysis linear viscoelastic 3D concrete specimens: comparison between FE and FFT methods

We investigate the creep behavior of concrete at mesoscale by considering 3D periodic numerical samples composed of a linear viscoelastic matrix ruled by generalized Maxwell models, in which are distributed 872 polyhedral elastic aggregates of various size and shape. Two different numerical methods are applied: the Finite Element (FE) method with various homogeneous stress and strain Boundary Conditions (BC), and Fast Fourier Transform (FFT)-based method. We then analyse the response of the specimens when subjected to creep and relaxation loadings in terms of averaged stresses and strains in the matrix and aggregate phases. The impact of the aggregate shape on both local and macroscopic response is also investigated by generating a meso-structure with flat particles. Overall, FE and FFT methods give very close results when periodic or stress BC are considered for FE, with a much lesser computation time for FFT. (authors)