Concrete has been one of the most commonly used modern structural material with quasi-brittle response. Because of its wide usage, numerical prediction of crack path and failure of structural components made of concrete and reinforced concrete has a great importance. To achieve this goal, a wide range of techniques have been introduced by treating fracture differently. In addition, the development of successful element formulations in analysis of 3D structural components has also been an active research topic. Several formulations have been proposed as an alternative to the conventional Lagrangian elements in recent years. In this thesis, localizing implicit gradient damage model and an isogemetric tetrahedral element are combined to investigate failure of 3D quasi-brittle unreinforced structural components. 10 noded B´ezier tetrahedral element is implemented to commercial finite element software Abaqus through user defined element subroutine, UEL. The implementation is validated by using two benchmark problems with nearly incompressible linear elastic and elasto-plastic material behaviors. After validating the implemented element, the formulation is extended such that localizing implicit gradient damage model is embedded within the isogeometric element formulation. Resulting two field formulation is tested on 3D experimental studies that exhibit complex fracture propagation due to combined torsional and bending moments. The sufficiency of the implemented two field formulation is verified by comparing obtained results with the experimental ones in terms of both force versus displacement responses and resulting crack paths.