This study deals with structural behavior of reinforced concrete pipes under various loading and support conditions by using nonlinear three-dimensional isoparametric 20-node brick elements. the computer program of three dimensional nonlinear finite element analysis of reinforced concrete structures, written by Al- Shaarbaf is utilized. The behavior of concrete is investigated by using twenty-node brick elements. The reinforcement bars are idealized as axial members embedded within the brick elements with perfect bond between the concrete and the steel curved bars in a brick element were approximated by straight bars parallel to the main coordinate axes. The behavior of concrete in compression is simulated by an (Elastic- Plastic Work Hardening Model) followed by a perfect plastic response, which is terminated at the onest of crushing. In tension, a smeared crack model with fixed orthogonal cracks has been used with the inclusion of models for the retained post-cracking tensile stress and reduced shear transfer modulus. Loading of the pipes and support conditions were properly considered according to the characteristics of the problem.