Isogeometric analysis of a multiphase porous media model for concrete

This paper presents isogeometric analysis of a hygro-thermo-chemo-mechanical concrete model at early age and beyond. Balance equations are introduced at the microscale and averaged to obtain balance equations at the macroscale. Constitutive laws are then applied directly at the macroscale. The final balance equations are mass, momentum, and energy based. These are written as a function of five primary variables in two dimensions: gas pressure, capillary pressure, temperature, and displacements. The standard finite-element shape functions are replaced by non-uniform rational B-splines that are used in isogeometric analysis. These basis functions possess a higher degree of continuity and can be used to construct an exact geometry when compared with their finite-element counterparts. Also, local mesh refinement at the mesh boundary is achieved easily with isogeometric basis functions. These properties make the isogeometric basis functions very suitable for describing the many transient processes that occur, especially in concrete at an early age. Isogeometric basis functions are implemented directly into an existing finite-element model. The accuracy of the isogeometric concept is compared and validated against the finiteelement- based approach. The examples show that the isogeometric model is more accurate than the finite-element model on a perdegree- of-freedom basis.