Implementation of Fictitious Crack Model Using Contact Finite Element Method for the Crack Propagation in Concrete under Cyclic Load

The mixed freedom finite element method proposed for contact problems was extended to simulate the fracture mechanics of concrete using the fictitious crack model. Pairs of contact points were set along the potential developing path of the crack. The displacement of structure was chosen as the basic variable, and the nodal contact force in contact region under local coordinate system was selected as the iteration variable to confine the nonlinear iteration process in the potential contact surface which is more numerically efficient. The contact forces and the opening of the crack were obtained explicitly enabling the softening constitutive relation for the concrete to be introduced conveniently by the fictitious crack model. According to the states of the load and the crack, the constitutive relation of concrete under cyclic load is characterized by six contact states with each contact state denoting its own displacement-stress relation. In this paper, the basic idea of the mixed freedom finite element method as well as the constitutive relation of concrete under cyclic load is presented. A numerical method was proposed to simulate crack propagation process in concrete. The accuracy and capability of the proposed method were verified by a numerical example against experiment data

Single Spring Joint Element Based on the Mixed Coordinate System

As a FEM for reinforced concrete bond-slip problems, one important feature of the typical double spring joint element method is the selection of the normal stiffness, which may cause the mutual embedding problem and bring challenges to the calculation. In this paper, a novel single spring joint element method based on the mixed coordinate system is proposed to simulate the interaction of two materials. Instead of choosing the normal stiffness arbitrarily, the proposed method makes DOFs of two materials in the normal direction equal to ensure deformation compatibility. And its solid elements for the concrete are solved in global coordinate system, while the beam elements for the steel bar are solved in local coordinate system. In addition, the proposed method can also be applied to RC structures with irregular arrangements of steel bars. Numerical examples demonstrate the validity and accuracy of the proposed approach. Furthermore, the bond model is applied to RC beams with the description of the damage process

Finite element modelling of local scour below a pipeline under steady currents

International audienc