Finite element analysis of moisture migration, creep, shrinkage and cracking

A finite element formulation is presented for the analysis of moisture migra-tion, creep, shrinkage and cracking in cementitious materials. A one-way coupled approach is followed, where the pore humidity, the driving force for shrinkage, is solved for from a diffusion equation. The evolution of the shrinkage strain field is then computed and employed in a subsequent mechanical analysis neglecting stress or cracking influence on the pore humidity. Either a continuous approach is followed, or a discrete approach is followed where the heterogeneity rules out the former, for example in masonry containing large blocks. Cracking is simulated in a smeared way by softening, anisotropic Rankine plasticity. In the second approach cracking is restricted to predefined areas, such as the mortar joints, where interfaces account for debonding and shear-slipping via a combined tension cut-off and Coulomb-friction material law, based on multi-surface plasticity. Bulk creep is modelled with visco-elasticity. Rate dependence of the bond ruptures leading to fracture is accounted for by considering the viscosity of the cracking process. The lat-ter contribution has a regularising effect on the localisation process which accompanies smeared cracking models. The model is able to capture the intricate interaction between creep and cracking, as shown by numerically simulating three-point bending experiments at various loading races, as well as under sustained loading. Subsequently the interaction of moisture migration, creep, shrinkage and cracking is verified in a discrete analysis of drying creep masonry experiments